Report to TasWater - EPA Tasmania · of the EPA Development Permit, issued in December 2008). This report presents the results of water quality monitoring since 2007. The infauna

Report to TasWater

Blackmans Bay Outfall

Water Quality Monitoring Program

December 2015

Consulting Environmental Engineers

Water Quality Monitoring at Blackmans Bay Outfall – December 2015 i



Water Quality Monitoring

Table of Contents

1 Background ......................................................................................................... 1

2 Environmental Context ....................................................................................... 1

3 Sampling Sites and Methods ............................................................................. 2

4 Water Quality Sampling – December 2015 ........................................................ 4

4.1 Salinity ............................................................................................................ 4

4.2 Temperature ................................................................................................... 8

4.3 Calculation of Position of Submerged Effluent Field ..................................... 10

4.4 Dissolved Oxygen......................................................................................... 12

4.5 pH ................................................................................................................. 13

4.6 Nutrients ....................................................................................................... 14

4.7 Ammonia ...................................................................................................... 19

4.8 Total Nitrogen ............................................................................................... 22

4.9 Total Phosphorus ......................................................................................... 24

4.10 Chlorophyll-a ............................................................................................. 26

5 Conclusions ...................................................................................................... 29

6 References ......................................................................................................... 30

7 Appendix A: Salinity Profiles: 2009 to 2014 .................................................... 31

8 Appendix B – Temperature Profiles: 2009 to 2014 ......................................... 35

9 Appendix C – Dissolved Oxygen Profiles: 2009 to 2014 ................................ 38

10 Appendix D – pH Profiles: 2013 to 2014 ..................................................... 41

Tables

Table 3-1 Locations of water quality profile sites ....................................................... 2

Table 3-2 Location of Samples Collected for Nutrient Analysis ................................. 2

Table 4-1 Effluent Plume Depth and Estuary Conditions– 2010 to 2015 ................... 6

Table 4-2. Water Quality Monitoring Results – Ammonia – 2009 to 2015 ................ 15

Table 4-3. Water Quality Monitoring Results – Total Nitrogen – 2009 to 2015 ......... 16

Table 4-4 Water Quality Monitoring Results – Total Phosphorus – 2009 to 2015 ... 17

Version Prepared by Date Reviewed by

00 Ian Wallis 15 June 2016 P Crockett

Water Quality Monitoring at Blackmans Bay Outfall – December 2015 ii


Figures

Figure 1 Location of Blackmans Bay Outfall .............................................................. 1

Figure 2 Location of Water Quality Monitoring Sites .................................................. 3

Figure 3 Salinity Profiles – December 2015............................................................... 4

Figure 4 Salinity Profiles – December 2015............................................................... 5

Figure 5 Monthly Salinity Profiles Offshore of Blackmans Bay 2004 ......................... 7

Figure 6 Temperature Profiles at Blackmans Bay – December 2015 ........................ 8

Figure 7 Temperature Profiles Offshore from Blackmans Bay – 2004 ....................... 9

Figure 8 Density (Sigma-T) over the water column – December 2015 .................... 10

Figure 9 Calculated Seawater Density Profile and Plume Density Profile ............... 10

Figure 10 Dissolved Oxygen Profiles – December 2015 ......................................... 12

Figure 11 pH profiles – December 2014 .................................................................. 13

Figure 12 Total Ammonia (NH3) Concentration – 2009 to 2014 .............................. 19

Figure 13 Ammonia Concentration Offshore from Blackmans Bay .......................... 20

Figure 14 Ammonia Concentration in Derwent Estuary ........................................... 21

Figure 15 Total Nitrogen Concentrations – 2009 to 2015 ........................................ 22

Figure 16 Total Nitrogen Concentration in Derwent Estuary.................................... 23

Figure 17 Total Phosphorus Concentration – 2009 to 2014 ..................................... 24

Figure 18 Total Phosphorus Concentration in Derwent Estuary ............................... 25

Figure 19 Chlorophyll a Measurements – June 2013 to December 2015 ................. 26

Figure 20 Chlorophyll a profiles – September 2009 .................................................. 27

Figure 21 Chlorophyll-a Concentration in Derwent Estuary ...................................... 28

Figure 22 Salinity Profiles – December 2014........................................................... 31

Figure 23 Salinity Profiles – July 2014 ..................................................................... 31

Figure 24 Salinity Profiles – November 2013 – ebb tide .......................................... 32

Figure 25 Salinity Profiles – June 2013 – flood tide ................................................. 32

Figure 26 Salinity Profiles – March 2011 ................................................................. 33

Figure 27 Salinity Profiles – August 2010, flood tide ............................................... 33

Figure 28 Salinity Profiles – August 2010 – ebb tide ............................................... 34

Figure 29 Salinity Profiles – September 2009 – Slack tide ...................................... 34

Figure 30 Temperature Profiles – December 2014 .................................................. 35

Figure 31 Temperature Profiles – July 2014 ............................................................ 35

Figure 32 Temperature Profiles – November 2013 .................................................. 36

Figure 33 Temperature Profiles – June 2013 ........................................................... 36

Figure 34 Temperature Profiles – March 2011 ......................................................... 37

Figure 35 Temperature Profiles – September 2009 .................................................. 37

Figure 36 Dissolved Oxygen profiles – December 2014 .......................................... 38

Figure 37 Dissolved Oxygen profiles – July 2014 .................................................... 38

Figure 38 Dissolved Oxygen Profiles – November 2013 ......................................... 39

Figure 39 Dissolved Oxygen Profiles – June 2013 .................................................. 39

Figure 40 Dissolved Oxygen Profiles – March 2011 ................................................ 40

Figure 41 Dissolved Oxygen Profiles – September 2009 ........................................ 40

Figure 42 pH profiles – December 2014 .................................................................. 41

Figure 43 pH profiles – July 2014 ............................................................................ 41

Figure 44 Measured pH Profiles – November 2013 ................................................. 42

Figure 45 Measured pH Profiles – June 2013 ......................................................... 42

Water Quality Monitoring at Blackmans Bay Outfall – December 2015 iii


Summary of Findings – December 2015 Survey Blackmans Bay Outfall Water Quality Monitoring Program

This report provides the results and assessment of the December 2015 monitoring survey of water quality at the Blackmans Bay outfall. There were two baseline surveys before the outfall was commissioned - in December 2007 and July 2009. The seven surveys with the outfall in operation have been in December 2010, March 2011, May 2013, November 2013, June 2014, December 2014 and December 2015. The conclusions from the December 2015 water quality monitoring are as follows:

There was weak natural stratification in salinity and temperature at the outfall and adjacent sites in December 2015 which produced a submerged effluent field at about 1 to 4 m below the surface.

The measured dissolved oxygen levels ranged from 100 to 104 per cent saturation. There was no detectible effect of the effluent plume on dissolved oxygen profiles around the outfall.

In the submerged plume at and adjacent to the outfall, measured ammonia levels were 0.005 to 0.033 mg/L, whereas background was 0.005 mg/L. There was a significant signature of ammonia in one sample near the outfall, corresponding to a dilution of 850:1. The dilution based on ammonia data from all surveys is 185:1.

It is noted that the highest ammonia level was well under the ANZECC trigger level for ammonia (0.7 mg/L at a pH of 8.1). All measured ammonia levels are within the range of natural variation in the estuary and well below the ANZECC trigger limit for toxicity effects.

The peak total nitrogen level was 0.28 mg/L which is just under the ANZECC trigger limit of 0.30 mg/L. Total nitrogen levels in the estuary are generally elevated and often naturally above the trigger level. The dilution calculated from the total nitrogen measurements is 600:1, but there is a large range around this estimate as the concentration increase is small relative to the high ambient total nitrogen levels.

In December 2015, the highest phosphorus level near the outfall was 0.04 mg/L which is the same as the measured background level. Because of the high natural background, the outfall discharge only occasionally causes a small and localized increase in total phosphorus.

Measured chlorophyll-a levels at and near the outfall were the same as natural levels, within the range of natural variation and below the ANZECC trigger limit.

The local increase in nutrient concentrations in December 2014 was very small and confined to ‘patches’ in the submerged effluent field within about 50 m from the outfall. The changes in nutrient concentrations in this survey correspond to a dilution in the range of 600:1 or more. The combined water quality data indicate the initial dilution is consistently around 200:1.

In summary, the high dilution achieved by the outfall means that the concentrations of nutrients are close to background concentrations, and there is only a small variation in water quality within the mixing zone.

It is recommended that water quality surveys continue annually. The sampling procedure with multiple water quality samples over vertical profiles at 10 m and 50 m north and south of the outfall achieves better sampling of the submerged plume.

1


Blackmans Bay Outfall Water Quality Monitoring

December 2015

1 BACKGROUND

The Blackmans Bay Sewage Treatment Plant (STP) treats wastewater from the Kingborough area to secondary standard with the effluent being discharged to the lower Derwent Estuary via a long outfall. The outfall was installed in 2010 with a multi-port diffuser located 600 m offshore in 13 m water depth. Figure 1 shows the location of the Blackmans Bay STP, the location of the diffuser of the long outfall and also the location of the previous shoreline outlet (before the outfall was extended).

Figure 1 Location of Blackmans Bay Outfall

A requirement of the environmental approval for the outfall is that water quality and infauna monitoring take place prior to and after outfall commissioning (Condition M5 of the EPA Development Permit, issued in December 2008). This report presents the results of water quality monitoring since 2007. The infauna monitoring results are presented in a separate report: This report provides the results and assessment of the December 2015 survey of water quality at the Blackmans Bay outfall. There were two baseline surveys before the outfall was commissioned - in December 2007 and July 2009. The seven surveys with the outfall in operation have been in December 2010, March 2011, May 2013, November 2013, June 2014, December 2014 and December 2015.

Water Quality Monitoring at Blackmans Bay Outfall – December 2015 1


2 ENVIRONMENTAL CONTEXT

Blackmans Bay is located in the lower Derwent Estuary, approximately 15 km south of Hobart. The outfall is located to the south of Blackmans Bay about 600 m south from Soldiers Rocks. The Derwent River is the major source of fresh water to the estuary, with an annual average discharge rate of 90 m3/s. Other tributaries contribute about 1 m3/s on average. The discharge from the Blackmans Bay plant (currently 4.1 ML/d) is only 0.05 per cent of the total fresh water entering the estuary. The multi-port diffuser on the extended outfall at Blackmans Bay produces a high initial dilution and minimises adverse effects of the freshwater input from the discharge. Baseline marine biological conditions were assessed as part of the Marine Environmental Risk Assessment and the DPEMP for the Blackmans Bay outfall extension. The ongoing monitoring program seeks to identify any effects of the effluent discharge on water quality and the marine environment. In August 2010, shortly after the outfall was commissioned, a dye dispersion study was carried out. Dye was released with the effluent to confirm the position and direction of dispersal of the plume; divers verified the correct function of the ports on the outfall diffuser and documented the position and extent of plume dispersal using underwater video. Water quality profiles were measured in, at the edge of and beyond the 15 m mixing zone. Water samples were collected for laboratory analysis at the same time as the profiles were measured to establish initial dilution and the extent of a significant increase in concentrations above background. The observations of the dye in the effluent plumes showed that the rising plumes from the ports did not reach the surface, but reach neutral equilibrium at a depth of 6 m to 8 m below the surface due to natural stratification. Analysis of the water quality samples in August 2010 showed that the initial dilution was 200:1 at 15 m from the diffuser. The dilution calculated by the CEE computer model for a submerged effluent field at the time of the field measurements predicted a dilution of 150:1 at the edge of the mixing zone, 15 m from the diffuser. This is somewhat lower than the measured initial dilution of 200:1 because the additional dispersion due to shear in the stratified waters and tidal currents is not included in the model. In the 2011 water quality monitoring report, the initial dilution produced by the diffuser was calculated from the measured peak concentrations of ammonia, total nitrogen and total phosphorus, the background levels in the estuary and the concentrations of these nutrients in the effluent. The calculated dilutions on this basis were 170:1, 400:1 and 500:1. From the measurements in May 2013, the calculated dilutions from the measured peak concentrations were 240:1, 290:1 and 500:1. In the November 2013 survey a dilution of about 500:1 was found. In the July 2014 survey, a dilution of 800:1 was found and in the December 2014 survey the dilution was 230:1 to 280:1.



In the most recent December 2015 survey, dilution was high owing to the weak density stratification present (meaning the plume rose to within 1.8 m of the surface). The weak stratification is due to two factors: below average rainfall across the Derwent River catchment in spring 2015 (leading to low river flows) and the reduction in the rate of intrusion of oceanic waters into the estuary from the Southern Ocean. Overall the average dilution is high and is considered satisfactory to safeguard estuarine water quality.

3 SAMPLING SITES AND METHODS

For the monitoring on 14 December 2015, water samples were collected from several depths in the water column at stations near the outfall to increase the likelihood of obtaining a sample in the centre of the submerged effluent field. The modified sampling regime was designed to better detect the effluent plume, as recommended by the EPA and consistent with condition M5 of the EPA development permit. Profiles of seawater salinity, temperature, dissolved oxygen and pH were recorded at 14 sites (Table 3-1). The salinity and temperature data are used to ascertain the density stratification of the water column and to determine the depth at which the submerged effluent plume is likely to be encountered on the day of sampling.

Table 3-1 Locations of water quality profile sites

North of outfall Outfall South of outfall East of outfall

10 m Outfall 10 m 25 m 25 m

100 m 100 m 500 m 500 m 500 m

1000 m 1000 m

In the field survey on 14 December 2015 no thermocline or halocline was detected; rather there was a linear change in temperature and salinity with depth. Calculations undertaken on the boat indicated that the plume would be submerged at depths between 1.8 m and 3.8 m, and the sampling strategy was undertaken on this basis. When a strong thermocline or halocline is present, the plume is typically found just below it. Samples for nutrient analysis were collected at 1.8 m, 2.8 m and 3.8 m depths using a Niskin bottle according to the sampling pattern shown in Table 3-2. Water samples were collected from multiple depths at 10 m and 50 m north and south of the outfall, and from 6 m depth at 1000 m north and south, as outlined below in Table 3-2. A sample was also collected at 2.8 m depth 500 m east (offshore) from the outfall.

Table 3-2 Location of Samples Collected for Nutrient Analysis

Position Depth North

Ou

tfa

ll South

1000 m 50 m 10 m 10 m 50 m 1000 m

Top of plume 1.8 m

Middle of plume 2.8 m

Bottom of plume 4.0 m



Tides and Wind Conditions Water profiles were collected between 0840 and 1155 near high tide (at 10:14 am on 14 December 2015 for Hobart). Weather conditions were clear with a light breeze from the east-southeast.

Figure 2 Location of Water Quality Monitoring Sites



4 WATER QUALITY SAMPLING – DECEMBER 2015

4.1 Salinity

Salinity profiles recorded north and south of the outfall on 14 December 2015 are shown in Figure 3 and 4). The figures show slight salinity stratification – less than 1 psu between the seabed and surface. There was minor halocline at 5 m below the surface at most sites, and below this salinity increased linearly with depth. The plume was not apparent in salinity profiles recorded 10 m north or south of the outfall.

Figure 3 Salinity Profiles – December 2015

De

pth

(m

)

De

pth

(m

)

De

pth

(m

)

Salinity (PSU)

0

5

10

15

33.5 34 34.5 35

25 m N0

5

10

15

33.5 34 34.5 35

10 m N

0

5

10

15

33.5 34 34.5 35

1000 m N0

5

10

15

33.5 34 34.5 35

500 m N0

5

10

15

33.5 34 34.5 35

100 m N0

5

10

15

33.5 34 34.5 35

50 m N

0

5

10

15

33.5 34 34.5 35

Outfall0

5

10

15

33.5 34 34.5 35

10 m S0

5

10

15

33.5 34 34.5 35

25 m S

0

5

10

15

33.5 34 34.5 35

50 m S0

5

10

15

33.5 34 34.5 35

100 m S0

5

10

15

33.5 34 34.5 35

500 m S0

5

10

15

33.5 34 34.5 35

1000 m S0

5

10

15

33.5 34 34.5 35

500 m E

The salinity profiles in Figure 4 show that higher salinity water from mid-depth and deeper layers has been carried up with the rising effluent plume to about 2 m below the surface. There also is a longitudinal gradient in salinity with all salinity values at 1000 m south being larger than the salinity values at 100 m (at the same depths).




Salinity profiles recorded between September 2009 and December 2014 are shown in Appendix A: Salinity profiles: 2009 to 2014. The amount of stratification in December 2015 (less than 1 psu) was low compared to other surveys; stratification was greater in November 2013 (5 psu) following a period of high rainfall. Stratification of the water column affects the height of rise and thus the dilution of the effluent plume and how easily it can be detected by salinity measurements. Monthly salinity profiles were measured over several years approximately 1 km offshore from Blackmans Bay outfall in the Derwent Estuary study. The monthly profiles for 2004, which reflect seasonal variations over a year, are shown in Figure 5. Salinity is typically highest and stratification lowest in summer and autumn months. Salinity is lowest and stratification highest in spring while winter months are intermediate. The December 2015 data (summer) are consistent with annual patterns in salinity in the lower Derwent Estuary.



Table 4-1 summarizes findings on the effluent plume depth and extent in the operational surveys to date. The table shows that the plume generally cannot be distinguished from background salinity, due to high dilution. The depth of the top of the plume is used to determine the depth for nutrient sampling and is calculated from the temperature and salinity profiles measured in the field: generally the plume will be trapped below the halocline where present. Monthly salinity profiles were measured over several years approximately 1 km offshore from Blackmans Bay outfall in the Derwent Estuary study. The monthly profiles for 2004, which reflect seasonal variations over a year, are shown in Figure 5. Salinity is typically highest and stratification lowest in summer and autumn months. Salinity is lowest and stratification highest in spring while winter months are intermediate. The December 2015 data (summer) are consistent with annual patterns in salinity in the lower Derwent Estuary.



Table 4-1 Effluent Plume Depth and Estuary Conditions– 2010 to 2015

Survey Plume depth

(inferred)

Background salinity

stratification

Halocline depth

Tide phase

Dec-10 Observed by dye and

diver at 6 to 7 m 0.9 psu 3.5 m Ebb/Flood

Mar-11 Inferred at 5 m 3.0 psu 5 m Ebb

May-13 Inferred at 3 m 0.5 psu 3 m Flood

Nov-13 Inferred at 3 m 5.0 psu 4 m Ebb

Jul-14 6 to 7 m 0.9 psu 4 m Flood

Dec-14 Inferred at 5 to 7 m 2.0 psu No halocline Flood

Dec-15 Inferred at 1.8 to 3.8 m <1 psu No halocline High

Figure 5 Monthly Salinity Profiles Offshore of Blackmans Bay 2004



4.2 Temperature

The temperatures recorded in December 2015 are shown in Figure 6 and range from 14.6 to 16°C, with a 1.4°C temperature increase from the seabed to the surface. There was a minor thermocline at 2-3 m depth at most sites, above which a temperature increase of 0.5-1°C was observed. The effluent plume was not apparent in the temperature profiles.

Figure 6 Temperature Profiles at Blackmans Bay – December 2015

De

pth

(m

)

De

pth

(m

)

De

pth

(m

)

Temperature (deg C)

0

5

10

15

14.5 15 15.5 16 16.5

25 m N0

5

10

15

14.5 15.5 16.5

10 m N

0

5

10

15

14.5 15.5 16.5

1000 m N0

5

10

15

14.5 15.5 16.5

500 m N0

5

10

15

14.5 15.5 16.5

100 m N0

5

10

15

14.5 15.5 16.5

50 m N

0

5

10

15

14.5 15.5 16.5

Outfall0

5

10

15

14.5 15.5 16.5

10 m S0

5

10

15

14.5 15.5 16.5

25 m S

0

5

10

15

14.5 15.5 16.5

50 m S0

5

10

15

14.5 15.5 16.5

100 m S0

5

10

15

14.5 15.5 16.5

500 m S0

5

10

15

14.5 15.5 16.5

1000 m S0

5

10

15

14.5 15.5 16.5

500 m E

Temperature profiles were measured monthly through the water column approximately 1 km offshore from Blackmans Bay outfall in the Derwent Estuary study. The monthly profiles made in 2004 are shown in Figure 6. The temperatures recorded in December 2015 were similar to those seen in November/December 2004. The profiles show that water temperature in the estuary varies seasonally due to freshwater flows, oceanic water intrusion, solar heating and vertical mixing. The profiles in Figure 7 demonstrate that:

Waters are warmest in December, January and February with a peak water temperature of 17 C and some thermal stratification. In the summer, waters are warmest near the surface and coolest near the seabed

Waters were coldest in July and August, with a minimum water temperature of 10 C and some vertical stratification due to lower density, but cooler, freshwater layers. In winter, waters are coolest near the surface and warmest near the seabed



Figure 7 Temperature Profiles Offshore from Blackmans Bay – 2004

For comparison, the temperature profiles recorded in previous surveys are shown in Appendix B – Temperature Profiles: 2009 to 2014. The December 2014 profiles showed a 2°C difference between the cooler waters near the seabed and warmer waters near the surface with a linear increase in temperature with depth (no thermocline). The July 2014 temperatures showed less than 1°C stratification but there was a distinct thermocline and temperature inversion – the highest temperatures were seen near the seabed, the lowest temperatures were seen at around 5 m depth, and temperature increased between 5 m depth and the surface. Warm water temperatures were recorded in the March 2011 survey, ranging from 16.3 to 16.5 degrees Celsius with little variation in temperature over the depth. The temperatures recorded in the September 2011 survey were lower and also showed little thermal stratification.



4.3 Calculation of Position of Submerged Effluent Field

Figure 8 shows profiles of seawater density at each site calculated from the temperature and salinity data. Density is given as Sigma-t, the difference between the measured density and that of pure water (1000 kg/m3). There was no density stratification over the water column, with a gradual 1.5 kg/m3 decrease in Sigma-t from the seabed (just under 26 kg/m3) to the surface (around 24.5 kg/m3).

Figure 8 Density (Sigma-T) over the water column – December 2015

De

pth

(m

)

De

pth

(m

)

De

pth

(m

)

Sigma-T (kg/m3)

0

5

10

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22 24 26 28

25 m N0

5

10

15

22 24 26 28

10 m N

0

5

10

15

22 24 26 28

1000 m N0

5

10

15

22 24 26 28

500 m N0

5

10

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22 24 26 28

100 m N0

5

10

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22 24 26 28

50 m N

0

5

10

15

22 24 26 28

Outfall0

5

10

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22 24 26 28

10 m S0

5

10

15

22 24 26 28

25 m S

0

5

10

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22 24 26 28

50 m S0

5

10

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22 24 26 28

100 m S0

5

10

15

22 24 26 28

500 m S0

5

10

15

22 24 26 28

1000 m S0

5

10

15

22 24 26 28

500 m E

The position of the effluent field in the water column, and thus the depths for collecting water quality samples, are calculated in the field from the temperature and salinity profiles measured at the outfall site. The ambient seawater density is calculated from the temperature and salinity readings at 2 m intervals in the vertical profile. The resulting seawater density profile is shown as the blue line in Figure 9. Then the plume density profile is calculated, using predictions of the rate of dilution in each 1 m deep layer as the plume rises from the outfall ports towards the surface. The resulting plume density profile is shown as the pink line in Figure 9. The plume density equals the seawater density at a depth of 3.8 m (see Figure 9) and this depth is therefore the base of the submerged effluent field. However, the plume continues to rise due to the upward momentum at this depth, until a level where the negative pressure gradient matches the upward momentum of the plume at the base of the field. Generally this corresponds to a negative density difference of 0.3 to 0.4 kg/m3. At this depth (which is about 1 m below the surface), the plume stops rising and this is the top of the submerged effluent field.



Figure 9 Calculated Seawater Density Profile and Plume Density Profile

-14

-12

-10

-8

-6

-4

-2

0

20 21 22 23 24 25 26

Density, sigma-t in kg/m3D

ep

th, m

Ambient Density Plume Density

Thus for the conditions measured on 14 December 2015, a submerged effluent field forms at 1 to 4 m below the surface. Based on this calculation, water quality samples were collected at 1.4 m, 2.8 m and 3.8 m depth, as follows:

At 1.8 m depth from 50 m N, 10 m N, 10 m S, 50 m S and 500 m offshore;

At 2.8 m depth from 1000 m N, 50 m N, 10 m N, 10 m S, 50 m S, 1000 m S and 500 m offshore;

At 3.8 m depth from 10 m N and 10 m S. This sampling strategy was selected to ensure that water samples would be collected from within the submerged plume with (relatively) high concentrations of effluent. It should be noted that the CEE plume dilution model predicted a minimum initial dilution of 165:1 in this submerged effluent field. Because the stratification is weak, the position of the plume can vary on the water column by 2 m over a period of several minutes. Thus the plume can be as high at 1 to 3 m below the surface, and as low as 3 to 5 m below the surface a few minutes later, depending on current speed and the action of internal waves. Interfacial waves move the submerged effluent field up and down over a period of several minutes.



4.4 Dissolved Oxygen

The dissolved oxygen (DO) profiles from the December 2015 survey are shown in Figure 10. The profiles show a nearly linear decrease in DO with depth. The decrease is relatively small, with a surface DO of around 104 per cent saturation and a seabed DO concentration of around 100 per cent. Estuary waters were fully saturated with oxygen throughout their depth.

Figure 10 Dissolved Oxygen Profiles – December 2015

De

pth

(m

)

De

pth

(m

)

De

pth

(m

)

Dissolved Oxygen (% Saturation)

0

5

10

15

95 100 105 110

25 m N0

5

10

15

95 100 105 110

10 m N

0

5

10

15

95 100 105 110

1000 m N0

5

10

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95 100 105 110

500 m N0

5

10

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95 100 105 110

100 m N0

5

10

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95 100 105 110

50 m N

0

5

10

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95 100 105 110

Outfall0

5

10

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95 100 105 110

10 m S0

5

10

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95 100 105 110

25 m S

0

5

10

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95 100 105 110

50 m S0

5

10

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95 100 105 110

100 m S0

5

10

15

95 100 105 110

500 m S0

5

10

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95 100 105 110

1000 m S0

5

10

15

95 100 105 110

500 m E

The ANZECC (2000) guideline limit for dissolved oxygen in marine waters is > 80 per cent saturation and < 110 per cent saturation. The measured dissolved oxygen levels in all surveys at all sites are within this range. There has been no detectible effect of the effluent plume on DO profiles around the outfall in any survey. For comparison the DO profiles from previous surveys are shown in Appendix C – Dissolved Oxygen Profiles: 2009 to 2014. A similar pattern in DO stratification was seen in December 2014, June 2013, March 2013 and September 2011. In November 2013 and July 2014 DO saturation decreased increased with depth before increasing again towards the seabed. The combined results of all surveys show that the outfall has minimal effect on dissolved oxygen levels in the estuary.



4.5 pH

The results of pH profiles measured in December 2015 are shown in Figure 11. There was no appreciable difference in pH through the water column at any site, the maximum range of pH at any site was 0.02 units.

Figure 11 pH profiles – December 2014

De

pth

(m

)

De

pth

(m

)

De

pth

(m

)

pH

0

5

10

15

7 8 9

25 m N

0

5

10

15

7 8 9

10 m N

0

5

10

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7 8 9

1000 m N

0

5

10

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7 8 9

500 m N

0

5

10

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7 8 9

100 m N

0

5

10

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7 8 9

50 m N

0

5

10

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7 8 9

Outfall

0

5

10

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7 8 9

10 m S

0

5

10

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7 8 9

25 m S

0

5

10

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7 8 9

50 m S

0

5

10

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7 8 9

100 m S

0

5

10

15

7 8 9

500 m S

0

5

10

15

7 8 9

1000 m S

0

5

10

15

7 8 9

500 m E

According to Table 8-3-7 of the ANZECC (2000) guidelines, the marine trigger value for total ammonia varies with the pH level. At a pH of 8.0 the ammonia trigger concentration is 0.91 mg/L. The trigger level for ammonia decreases as the pH increases, so the ammonia trigger concentration is 0.62 mg/L at pH of 8.2, 0.42 mg/L at pH of 8.4, 0.29 mg/L at pH of 8.6 and 0.22 mg/L at pH of 8.75 (although this elevated pH level is unlikely in estuarine or marine waters). Profiles of pH recorded in July 2014 and June and November 2013 are presented in Appendix D – pH Profiles: 2013 to 2014. The results from previous surveys also show only a small pH variation over time, ranging between 8.05 and 8.12. The combined results of all surveys show that the outfall has minimal effect on pH levels in the estuary.



4.6 Nutrients

Based on the vertical profiles of salinity and temperature, it was concluded that the diluted effluent plume on 14 December 2015 was submerged at 1.8 to 3.8 m below the water surface. The weak stratification meant the plume was dispersed over the upper water column, resulting in a high dilution and very small perturbations in water quality. Water samples for nutrient analysis were collected from three depths – at 1.8 m, 2.8 m, and 3.8 m depth. This sampling strategy aims to increase the likelihood that samples are collected from within the middle of the plume. The results from laboratory testing of water quality samples collected in each survey since 2009 are shown below in Table 4-2 to Table 4-4. The laboratory tests include results for nutrient concentrations (ammonia, total nitrogen and total phosphorus) and chlorophyll-a. Phenol concentrations at all sites were below detection limits for the 2009 and 2011 surveys and were therefore not continued in subsequent surveys. The results for the various parameters in the latest survey are shown in the bottom rows of each table, in bold font. Sample values that were elevated above those seen at reference sites (500 m and 1000 m away) are highlighted in yellow. Nutrient concentrations were elevated in two samples collected in December 2015 – ammonia was slightly elevated in the sample taken at the bottom of the plume 10 m north of the outfall, and ammonia and total nitrogen was slightly elevated at the bottom of the plume 50 m south of the outfall. A discussion of ammonia, total nitrogen, total phosphorus and chlorophyll-a levels across the study area from 2009 to 2015 follows.



Table 4-2. Water Quality Monitoring Results – Ammonia – 2009 to 2015

Survey details North

Outfall South

1000 m 500 m 100 m 50 m 10 m 10 m 50 m 100 m 500 m (*East)

1000 m

Survey Date Depth Total ammonia (mg/L)

Baseline Sep-09 0.011 0.009 0.011 0.011 0.017 0.013 0.009 0.01 0.009 0.013

Dispersion Study Aug-14 7 m 0.028 0.125 0.057 0.090 0.070 0.043 0.098

Operational 2 Mar-11 5 m 0.007 0.006 0.006 0.008 0.075 0.086 0.011 0.008 0.007 0.011 0.012

Operational 3 Jun-13 3 m 0.016 0.016 0.017 0.018 0.025 0.137 0.124 0.086 0.098 0.019 0.014

Operational 4 Nov-13 4 m 0.009 0.009 0.011 0.011 0.008 0.007 0.012 0.008 0.01 0.01 0.009

Operational 5 Jul-14 6 m 0.008 0.008 0.005 0.093 0.005 0.021 0.009 0.011 0.008 0.008 0.006

Operational 6 Dec-14 5 m 0.097 0.010 0.054 0.006 0.009*

6 m 0.007 0.007 0.037 0.005 <0.005 0.007* 0.006

7 m 0.008 0.005

Operational 7 Dec-15 1.8 m <0.005 0.006 <0.005 0.006

2.8 m 0.005 0.006 <0.005 <0.005 0.033 0.006* 0.008

3.8 m 0.009 <0.005

Values in yellow are elevated relative to reference samples

* Results for samples collected 500 m offshore (east) of the outfall in

December 2014 and December 2015 are listed at 500 m distance south of the outfall.



Table 4-3. Water Quality Monitoring Results – Total Nitrogen – 2009 to 2015

Survey details North Outfall South

1000 m 500 m 100 m 50 m 10 m 100 m 10 m 50 m 100 m 500 m (*East)

1000 m

Survey Date Depth Total nitrogen (mg/L)

Baseline Sep-09 0.4 0.39 0.4 0.39 0.49 0.44 0.38 0.38 0.38 0.41







6 m 0.27 0.24 0.26 0.22 0.24* 0.24

7 m 0.23 0.23 0.26

Operational 7 Dec-15 1.8 m 0.22 0.25 0.22 0.25

2.8 m 0.25 0.24 0.21 0.20 0.28 0.23* 0.23

3.8 m 0.25 0.24






Table 4-4 Water Quality Monitoring Results – Total Phosphorus – 2009 to 2015


Outfall South

1000 m 500 m 100 m 50 m 10 m 10 m 50 m 100 m 500 m (*East)

1000 m

Survey Date Depth Total phosphorus (mg/L)

Baseline Sep-09 0.036 0.038 0.036 0.034 0.036 0.036 0.034 0.037 0.036 0.035







6 m 0.02 0.02 0.02 0.02 0.02* 0.02

7 m 0.02 0.02


2.8 m 0.04 0.03 0.04 0.03 0.04 0.04* 0.04

3.8 m 0.04 0.04






Table 4-5 Water Quality Monitoring Results – Chlorophyll-a – 2009 to 2015


Outfall South

1000 m 500 m 100 m 50 m 10 m 10 m 50 m 100 m 500 m (*East)

1000 m

Survey Date Depth Chlorophyll a (µg/L)





6 m 0.9 1.1 1.2 1.0 1.2 1.2* 0.9

7 m 1.1 1.1


2.8 m 0.7 1.0 1.2 0.6 0.8 0.8* 0.8

3.8 m 0.8 1.0


* The results for samples collected 500 m offshore (east) of the outfall in




4.7 Ammonia

The survey in December 2015 found ammonia concentrations ranging from 0.005 mg/L and 0.033 mg/L. Most samples had background ammonia concentrations between 0.005 and 0.008 mg/L. The highest measurement of 0.033 mg/L was at 50 m S of the outfall. All other samples appeared to be at or close to background. All ammonia values recorded in December 2015 were well below the ~0.7 mg/L trigger value for the recorded pH range of 8.1-8.2 (ANZECC 2000, Table 8.3.7, p 8.3-161). Figure 12 shows the ammonia concentration at study sites since September 2009. The baseline 2009 survey found consistently low levels of ammonia. The 2010 dispersion study found elevated ammonia to 50 m north and 100 m south of the outfall. The March 2011 survey found elevated ammonia at and just south of the outfall. The June 2013 survey found higher concentrations of ammonia up to 100 m south of the outfall. The November 2013 survey found consistently low levels of ammonia at all sites. The July 2014 survey found elevated ammonia levels at 50 m south of the outfall – as did the December 2014 survey. The December 2015 survey found slightly elevated ammonia in one sample.

Figure 12 Total Ammonia (NH3) Concentration – 2009 to 2014

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0.180

0.200

-1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200

Co

nce

ntr

atio

n, m

g/L

(North) metres to outfall (South)

Sep-09 (Baseline) Aug-10 (Dispersion study) Mar-11 (Operational)June 13 (Operational) Nov-13 (Operational) Jul-14 (Operational)Dec-14 (5 m) Dec-2014 (6 m) Dec-14 (7 m)Dec-15 (1.8 m) Dec-15 (2.8 m) Dec-15 (4 m)

ANZECC 2000 trigger value: ~0.7 mg/L (pH 8.1-8.2)

The combined results of the surveys show that all measured ammonia levels are well below the ANZECC trigger limit for toxicity effects of about 0.7 mg/L (trigger level depends on pH as described above).



Monitoring of ammonia at 1 km offshore of Blackmans Bay shows substantial variation in ammonia between the surface and near the seabed (see Figure 13). There is a general pattern of higher ammonia concentrations during winter and lower ammonia concentrations during summer. This is a combination of intrusion of oceanic, nutrient-rich waters from the Southern Ocean in winter and the influence of lower nutrient waters in summer.

Figure 13 Ammonia Concentration Offshore from Blackmans Bay

In December 2015, the highest ammonia level near the outfall was 0.033 mg/L which is 0.027 mg/L above the background level of 0.006 mg/L. The ammonia concentration in the discharged effluent averages 24 mg/L (range of 20 to 30 mg/L). Thus the calculated dilution corresponding to the measured average ammonia concentration is 850:1. This appears to be rather high. Taking ammonia data from all surveys (see Figure 12), the calculated dilution corresponding to the highest concentration is 185:1.



Figure 14 shows the longitudinal profile of ammonia concentration in the Derwent Estuary for monitoring between 2003 and 2008. At Site C, which is 1 km offshore from Blackmans Bay, the measured ammonia levels are mostly below the ANZECC trigger level for biological stimulation of 0.020 mg/L (or 20 ug/L), but with occasional exceedances up to 0.030 mg/L. Some of the peak ammonia levels measured near the outfall are above the range of natural variation (surface concentrations), indicating elevated ammonia in the vicinity of the outfall.

Figure 14 Ammonia Concentration in Derwent Estuary



4.8 Total Nitrogen

Total nitrogen includes all nitrogen containing compounds – it is the sum of organic nitrogen, ammonia and oxidized nitrogen. Figure 15 shows the total nitrogen concentration at monitoring sites since 2009. In December 2015 total nitrogen concentrations showed only a small variation across the study area because of the elevated natural background levels of total nitrogen in the Derwent Estuary. The highest total nitrogen concentrations in 2015 were seen at 2.8 m depth within 50 m of the outfall. All total nitrogen values in 2015 were below the ANZECC 2000 trigger value of 0.30 mg/L.

Figure 15 Total Nitrogen Concentrations – 2009 to 2015

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

-1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200

Co

nce

ntr

atio

n, m

g/L


Sep-09 (Baseline) Aug-10 (Dispersion study) Mar-11 (Operational)June 13 (Operational) Nov-13 (Operational) Jul-14 (Operational)Dec-14 (5 m) Dec-14 (6 m) Dec-14 (7 m)Dec-15 (1.8 m) Dec-15 (2.8 m) Dec-15 (4 m)

ANZECC 2000 trigger value: 0.300 mg/L

The data from December 2015 showed similar total nitrogen concentrations as those in previous surveys with little variation across the study area. In December 2015 all measured values were below the ANZECC 2000 trigger value. In July 2014 total nitrogen showed little variation across the study area and values were below the ANZECC 2000 trigger value of 0.30 mg/L at all sites except directly above the outfall. In November 2013 the total nitrogen concentration was between 0.28 and 0.38 mg/L with an average of 0.32 mg/L. Total nitrogen concentration was relatively constant across sites with the highest concentration recorded 1,000 m north of the outfall, and no peak observed at the outfall. The June 2013 results show higher concentrations of total nitrogen between 0.34 and 0.63 mg/L, with peak concentrations at the outfall and to the south. The 2011 results show much lower total nitrogen concentrations of 0.01 to 0.08 mg/L, with an average of 0.02 mg/L. The August 2010 results showed some elevated total nitrogen at sites up to 100 m north and south of the outfall.



The September 2009 baseline survey documented some of the highest total nitrogen values over the period, including a peak around the outfall (but this was prior to the outfall being commissioned). Presumably organic detritus from the string kelp was adding significantly to total nitrogen levels in Blackmans Bay. Figure 16 shows the longitudinal profile of total nitrogen concentration in the Derwent estuary for monitoring between 2003 and 2008. At Site C, which is 1 km offshore from Blackmans Bay, the measured total nitrogen levels extend over a wide range, with the median just below the ANZECC trigger level of 300 ug/L (or 0.3 mg/L). The levels measured at the outfall between 2009 and 2015 (see Figure 15) are within the range measured in earlier years.

Figure 16 Total Nitrogen Concentration in Derwent Estuary

In December 2015, the highest total nitrogen level was 0.28 mg/L which is just 0.04 mg/L above the background level of 0.24 mg/L. The total nitrogen concentration in the discharged effluent averages 30 mg/L. Thus the dilution corresponding to the measured total nitrogen concentration is 600:1. Because of the high natural background, the outfall discharge causes only a small and localized increase in total nitrogen. Only one sample from near the outfall exhibited a total nitrogen concentration above background levels – 50 m south at 2.8 m depth. Taking total nitrogen data from all surveys (see Figure 15), the calculated dilution corresponding to the highest concentration is 150:1.



4.9 Total Phosphorus

Figure 17 shows the total phosphorus concentration in surveys since September 2009. In December 2015 total phosphorus concentrations ranged between 0.03 and 0.04 mg/L. Concentrations of 0.04 mg/L were seen in samples from the two reference sites 1000 m north and south of the outfall and in samples between 10 and 50 m south of the outfall. All other sites, including those within 50 m of the outfall had total phosphorus concentrations equal to the ANZECC 2000 trigger value of 0.03 mg/L.

Figure 17 Total Phosphorus Concentration – 2009 to 2014

In December 2014, total phosphorus concentrations were elevated in the sample taken at 5 m depth 50 m south of the outfall. All other concentrations were 0.02 mg/L, below the trigger value of 0.03 mg/L. In July 2014 there was a peak in total phosphorus (0.05 mg/L) 50 m north of the outfall, with a smaller peak at the outfall itself. Total phosphorus was similarly higher at 1000 m south (a reference site). The survey in November 2013 found the total phosphorus concentration averaged 0.03 mg/L, with a peak concentration of 0.035 mg/L at 500 m north. There was no observable peak above the outfall. The June 2013 survey had an average total phosphorus concentration of 0.045 mg/L, with a peak of 0.056 mg/L at the outfall and at 10 m north, and a background concentration around 0.04 mg/L. In 2011, the total phosphorous concentrations were very similar with an average of 0.035 mg/L. In 2009, all the total phosphorous readings were between 0.03 and 0.04 mg/L, with an average of 0.036 mg/L. Total phosphorus concentrations have mostly been above the ANZECC 2000 trigger value of 0.030 mg/L at all sites in all surveys.



Data for surface concentrations of total phosphorus between 2003 and 2007 at a site offshore from Blackmans Bay is shown in Figure 18 (from Derwent Estuary Study). The results show the concentrations at this site are consistent with those recorded during monitoring of the Blackmans Bay outfall (ie. mostly above the ANZECC trigger value of 0.030 mg/L).

Figure 18 Total Phosphorus Concentration in Derwent Estuary

In December 2015, the highest phosphorus level near the outfall was 0.04 mg/L which is the same as the measured background level. Taking total phosphorus data from all surveys (see Figure 15), the calculated dilution corresponding to the highest concentration is 390:1. Because of the high natural background, the outfall discharge only occasionally causes a small and localized increase in total phosphorus.



4.10 Chlorophyll-a

Chlorophyll-a concentration is a measure of micro-algal abundance. The chlorophyll-a values recorded in December 2015 were between 0.6 and 1.4 µg/L. The highest chlorophyll-a values recorded in December 2015 were from samples within 50 m of the outfall, however they were mostly only 0.2-0.4 ug/L higher than those seen at reference sites. Concentrations were generally lower than those seen in previous years and well below the ANZECC 2000 trigger value of 4.0 ug/L for the Derwent Estuary. Figure 19 shows the chlorophyll-a measurements taken since June 2013. The average concentration in June 2013 was 1.4 µg/L, in November 2013 it was 1.7 µg/L, slightly higher than the June 2013 average. In July 2014 lower values were recorded – on average 1.2 µg/L. Average values in December 2014 were 1.1 ug/L and in December 2015 they were <1.0 ug/L. All Chlorophyll-a levels have been well below the ANZECC trigger value of 4.0 µg/L.

Figure 19 Chlorophyll a Measurements – June 2013 to December 2015

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

-1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200

Co

nce

ntr

atio

n, µ

g/L


June 13 (Operational) Nov-13 (Operational) Jul-14 (Operational)

Dec-14 (5 m) Dec-14 (6 m) Dec-14 (7 m)

Dec-15 (1.8 m) Dec-15 (2.8 m) Dec-15 (4 m)

ANZECC 2000 trigger value: 4.0 µg/L



Figure 20 shows the baseline profiles for chlorophyll-a measured in September 2009. Surface chlorophyll-a concentrations were around 1.5 µg/L (much the same as in 2015) and decreased to around 0.5 µg/L at 15 m depth.

Figure 20 Chlorophyll a profiles – September 2009



Figure 21 shows the longitudinal profile of chlorophyll-a in the Derwent estuary for monitoring between 2003 and 2008. At Site C, which is 1 km offshore from Blackmans Bay, the measured levels are mostly between 0.5 and 2.5 ug/L. Generally chlorophyll at Site C is below the ANZECC trigger level of 4 ug/L.

Figure 21 Chlorophyll-a Concentration in Derwent Estuary



5 CONCLUSIONS

The conclusions from the December 2015 water quality monitoring are as follows:

There was weak natural stratification in salinity and temperature at the outfall and adjacent sites in December 2015 which produced a submerged effluent field at about 1 to 4 m below the surface.

The measured dissolved oxygen levels ranged from 100 to 104 per cent saturation. There was no detectible effect of the effluent plume on dissolved oxygen profiles around the outfall.

In the submerged plume at and adjacent to the outfall, measured ammonia levels were 0.005 to 0.033 mg/L, whereas background was 0.005 mg/L. There was a significant signature of ammonia in one sample near the outfall, corresponding to a dilution of 850:1. The dilution based on ammonia data from all surveys is 185:1.

It is noted that the highest ammonia level was well under the ANZECC trigger level for ammonia (0.7 mg/L at a pH of 8.1). All measured ammonia levels are within the range of natural variation in the estuary and well below the ANZECC trigger limit for toxicity effects.

The peak total nitrogen level was 0.28 mg/L which is just under the ANZECC trigger limit of 0.30 mg/L. Total nitrogen levels in the estuary are generally elevated and often naturally above the trigger level. The dilution calculated from the total nitrogen measurements is 600:1, but there is a large range around this estimate as the concentration increase is small relative to the high ambient total nitrogen levels.

In December 2015, the highest phosphorus level near the outfall was 0.04 mg/L which is the same as the measured background level. Because of the high natural background, the outfall discharge only occasionally causes a small and localized increase in total phosphorus.

Measured chlorophyll-a levels at and near the outfall were the same as natural levels, within the range of natural variation and below the ANZECC trigger limit.

The local increase in nutrient concentrations in December 2014 was very small and confined to ‘patches’ in the submerged effluent field within about 50 m from the outfall. The changes in nutrient concentrations in this survey correspond to a dilution in the range of 600:1 or more. The combined water quality data indicate the initial dilution is consistently around 200:1.

In summary, the high dilution achieved by the outfall means that the concentrations of nutrients are close to background concentrations, and there is only a small variation in water quality within the mixing zone.

It is recommended that water quality surveys continue annually. The sampling procedure whereby multiple water quality samples are collected over vertical profiles at 50 m and 10 m north and south of the outfall, achieved better sampling of the submerged plume and should continue to be used as it records conditions in a submerged and patchy effluent field with high dilution.



6 REFERENCES

ANZECC/ARMCANZ (2000a) Australian and New Zealand Guidelines for Fresh and Marine Water Quality. Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand.

ANZECC/ARMCANZ (2000b) Australian Guidelines for Water Quality Monitoring and

Reporting. Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand.

Coughanowr C, Whitehead S, Einoder, L, and Taylor U, 2010. State of the Derwent

Estuary 2015: a review of pollution sources, loads and environmental quality data from 2009 – 2014. Derwent Estuary Program, DPIPWE, Tasmania.

Whitehead S, Coughanowr C, Agius J, Chrispin J, Taylor U, Wells F, 2015. State of

the Derwent Estuary 2009: a review of pollution sources, loads and environmental quality data from 2003 – 2009. Derwent Estuary Program, DPIPWE, Tasmania.



7 APPENDIX A: SALINITY PROFILES: 2009 TO 2014


Figure 23 Salinity Profiles – July 2014



Figure 24 Salinity Profiles – November 2013 – ebb tide

Figure 25 Salinity Profiles – June 2013 – flood tide



Figure 26 Salinity Profiles – March 2011

Figure 27 Salinity Profiles – August 2010, flood tide



Figure 28 Salinity Profiles – August 2010 – ebb tide

Figure 29 Salinity Profiles – September 2009 – Slack tide



8 APPENDIX B – TEMPERATURE PROFILES: 2009 TO 2014

Figure 30 Temperature Profiles – December 2014

Figure 31 Temperature Profiles – July 2014

July 2014

1000 m N 500 m N 100 m N 50 m N 25 m N

0

5

10

15

20

De

pth

(m)

10 m N Outfall 10 m S 25 m S 50 m S

10 11 12

Temperature (deg C)

0

5

10

15

20

De

pth

(m)

100 m S

10 11 12

Temperature (deg C)

500 m S

10 11 12

Temperature (deg C)

1000 m S (a)

10 11 12

Temperature (deg C)

1000 m S (b)

10 11 12

Temperature (deg C)

0

5

10

15

20

De

pth

(m)



Figure 32 Temperature Profiles – November 2013

November 2013

0

5

10

15

20

Depth

(m)

0

5

10

15

20

Depth

(m)

13 14 15 16 17

Temp (deg C)

13 14 15 16 17

Temp (deg C)

13 14 15 16 17

Temp (deg C)

13 14 15 16 17

Temp (deg C)

13 14 15 16 17

Temp (deg C)

0

5

10

15

20

Depth

(m)

1000 m North 500 m North 100 m north 50 m North 25 m North

10 m North Outfall 10 m South 25 m South 50 m South

100 m South 500 m South 1000 m South 300 m West 500 m East

Figure 33 Temperature Profiles – June 2013



Figure 34 Temperature Profiles – March 2011

Figure 35 Temperature Profiles – September 2009



9 APPENDIX C – DISSOLVED OXYGEN PROFILES: 2009 TO 2014

Figure 36 Dissolved Oxygen profiles – December 2014

Figure 37 Dissolved Oxygen profiles – July 2014



Figure 38 Dissolved Oxygen Profiles – November 2013

Figure 39 Dissolved Oxygen Profiles – June 2013



Figure 40 Dissolved Oxygen Profiles – March 2011

Figure 41 Dissolved Oxygen Profiles – September 2009



10 APPENDIX D – PH PROFILES: 2013 TO 2014

Figure 42 pH profiles – December 2014

Figure 43 pH profiles – July 2014



Figure 44 Measured pH Profiles – November 2013

Figure 45 Measured pH Profiles – June 2013

Report to: TasWater


Marine Ecological Monitoring Program

Infauna Community and Giant Kelp

Sixth Operational Survey

December 2015


Marine Ecological Monitoring Program Infauna Community

Sixth Operational Survey – December 2015

Contents 1 Background ........................................................................................................... 1

2 Environmental Context .......................................................................................... 3

3 Potential Effects of Effluent Discharges on Marine Infauna Communities............. 5

4 Sediments ............................................................................................................. 7

5 Gazameda gunnii .................................................................................................. 8

6 Infauna Methods ................................................................................................... 9

7 Infauna Sampling Sites ......................................................................................... 9

8 Giant Kelp methods............................................................................................. 10

9 Results ................................................................................................................ 12

9.1 Assessment of effects ................................................................................. 12

9.2 Infauna Taxa, 2007 to 2015 ........................................................................ 15

9.3 Total infauna abundance, 2007 to 2015 ...................................................... 16

9.4 Key Infauna Groups – 2007 to 2015............................................................ 17

9.4.1 Polychaete worms ................................................................................ 19

9.4.2 Crustaceans ......................................................................................... 23

9.4.3 Molluscs ............................................................................................... 30

9.5 Summary of Infauna community analysis ....................................................... 32

9.6 Giant Kelp (Macrocystis pyrifera) .................................................................... 38

10 Conclusion: Possible Effects of Outfall Discharge on Marine Ecosystem ....... 39

11 Appendix 1 ...................................................................................................... 40

12 Appendix 2 ...................................................................................................... 44

Report to Report by

TasWater PO Box 1060 Glenorchy TAS 7010

Peter Crockett, Sam Ibbott, Ian Wallis, Scott Chidgey and Lynda Avery Consulting Environmental Engineers Unit 4, 150 Chesterville Rd, Cheltenham, VIC, 3192

Cover Image: Images of key infauna groups at Blackmans Bay in December 2015. Clockwise from top left: Phoxocephalidae,

Corophiidae, Capitellidae and Polygordiidae.

Blackmans Bay Outfall Ecological (Infauna) Monitoring Program, Dec-2015 iii

CEE Consultants Pty Ltd

Figures

Figure 1. Location of Blackmans Bay Outfall ............................................................... 1

Figure 2. Spatial Variation in Sediment Composition – 2007 Video Survey ................ 3

Figure 3 Median sediment grain size – 2007 to 2014 .................................................. 7

Figure 4 Volume of sediment > 1 mm in infauna samples – 2007 to 2014 .................. 8

Figure 5 Six-spine leatherjacket (Meuschenia freycineti) in Giant Kelp ..................... 10

Figure 6. Location of Blackmans Bay Outfall ............................................................. 11

Figure 7. Images of the 10 most abundant infauna in 2015 ....................................... 14

Figure 8. Average Number of Infauna Taxa per Sample – 2007 to 2015 .................. 15

Figure 9. Average number of infauna per square metre 2007-2014 .......................... 16

Figure 10 Polychaete worm abundance, 2007 to 2015 ............................................. 19

Figure 11 Abundance of Onuphidae, 2007 to 2015 ................................................... 20

Figure 12 Abundance of Spionidae, 2007 to 2015 ..................................................... 21

Figure 13 Abundance of Polygordiidae, 2007 to 2015 ............................................... 22

Figure 14 Crustacean abundance, 2007 to 2015 ....................................................... 23

Figure 15 Abundance of Corophiidae, 2007 to 2015 ................................................. 24

Figure 16 Abundance of Phoxocephalidae, 2007 to 2015 ......................................... 25

Figure 17 Abundance of Ostrocoda, 2007 to 2015 .................................................... 26

Figure 18 Abundance of Ampheliscidae, 2007 to 2015 ............................................ 27

Figure 19 Abundance of Urohaustoriidae, 2007 to 2015 ........................................... 28

Figure 20 Abundance of Gynodiastylidae, 2007 – 2015 ............................................ 29

Figure 21 Abundance of Molluscs, 2007 to 2015 ....................................................... 30

Figure 22 Abundance of Veneridae, 2007 to 2015 .................................................... 31

Figure 23 Time series data for infauna families and total infauna abundance ........... 35

Figure 24 Time series data for Polychaete worms and Crustaceans ......................... 36

Figure 25 Time series data for Onuphidae and Corophiidae ..................................... 37

Figure 26 Giant Kelp canopy density in 2014 and 2015 ............................................ 38

Figure 27 Giant Kelp stipe density in 2014 and 2015 ................................................ 38

Figure 28 Total infauna per sample versus sediment and distance ........................... 44

Figure 29 Number of families per sample versus sediment > 1 mm and distance ..... 45

Figure 30 Polychaetes per sample versus sediment >1 mm and distance ................ 45

Figure 31 Crustaceans per sample versus sediment >1 mm and distance ............... 46

Figure 32 Molluscs per sample versus sediment >1 mm and distance ..................... 46

Figure 33 Corophiidae per sample versus sediment > 1 mm and distance ............... 47

Figure 34 Onuphidae per sample versus sediment > 1 mm and distance ................. 47

Figure 35 Phoxocephalidae per sample versus sediment > 1 mm and distance ....... 48

Figure 36 Ostracoda per sample versus sediment > 1 mm and distance .................. 48

Figure 37 Veneridae per sample versus sediment > 1 mm and distance .................. 49

Figure 38 Spionidae per sample versus sediment > 1 mm and distance................... 49

Figure 39 Ampheliscidae per sample versus sediment >1 mm and distance ............ 50

Figure 40 Urohaustoriidae per sample versus sediment > 1 mm and distance ......... 50

Figure 41 Polygordiidae per sample versus sediment > 1 mm and distance ............. 51

Figure 42 Gynodiastylidae per sample versus sediment > 1 mm and distance ......... 51

Blackmans Bay Outfall Ecological (Infauna) Monitoring Program, Dec-2015 iv


Tables

Table 1 Details of infauna surveys at Blackmans Bay Outfall ...................................... 2

Table 3. Infauna Sampling Sites for the Infauna Surveys ............................................ 9

Table 2 Giant Kelp survey sites ................................................................................. 10

Table 4. Summary of Infauna Statistics – 2007 to 2014 ............................................ 13

Table 5. Abundance of the Ten Most Common Infauna Families, December 2015 ... 17

Table 6 Summary of graphical analysis of infauna data ............................................ 32

Table 7 Summary of correlation analysis – December 2015 ..................................... 33

Table 8 Results of statistical tests on infauna data – Dec-10 to Dec-15 .................... 34

Table 9 Infauna data for December 2007 (baseline) ................................................. 40

Table 10 Infauna data for July 2009 (baseline) .......................................................... 40

Table 11 Infauna data for December 2010 (operational) ........................................... 41

Table 12 Infauna data for May 2013 (operational) ..................................................... 41

Table 13 Infauna data for November 2013 (operational) ........................................... 42

Table 14 Infauna data for July 2014 .......................................................................... 42

Table 15 Infauna data for November 2014 ................................................................ 43

Blackmans Bay Outfall Ecological (Infauna) Monitoring Program, Dec-2015 v


Foreword to Report on Sixth Operational Survey

Blackmans Bay Outfall Infauna Monitoring Program

This report provides the results and assessment of the eighth survey of infauna communities near the Blackmans Bay offshore outfall. There were two baseline surveys in December 2007 and July 2009, before the outfall was constructed and commissioned in 2010. There have been six post-operational surveys, in December 2010, May 2013, November 2013, June 2014, November 2014 and December 2015. Each survey has sampled infauna (small animals that live in the sediments) and sediment grain size at sites between 1 km north and 1 km south of the outfall. The data from all eight surveys are presented in this report in the same format, to assist in comparison of results between surveys, as requested in the EPA letter dated 6 June 2014. The key question addressed by the monitoring program is whether or not there are any impacts on the infauna community relating to effluent exposure. Water quality modelling and monitoring suggests that measurable effluent exposure is confined to areas within 50 m of the outfall, but infauna integrate effects over long time scales. Therefore small scale differences in key infauna community parameters relating to effluent exposure are tested for statistical significance. Patterns of the infauna community are also examined in relation to distance from the diffuser (in case of broad-scale impacts) and sediment composition. The results show no evidence of broad-scale impacts on the infauna community as a whole or on individual infauna families. However, infauna monitoring between 2010 and 2015 has documented a small-scale impact on two infauna families which is consistent with the minor, small-scale impacts documented on water quality. Onuphidae polychaete worms are generally more abundant at sites ≤ 10 m from the outfall (n=6, df=10, p=0.02) and Corophiidae amphipod crustaceans are less abundant at sites ≥ 10 m from the outfall (n=6, df=10, p=0.07). The small scale changes in the infauna community are consistent with the small-scale, low-level nutrient and organic enrichment documented by water quality monitoring. While there are changes in the infauna community immediately adjacent to the outfall, the monitoring program has not documented any ‘typical’ impacts on infauna known from studies on wastewater discharges, such as reduced species richness, increased overall infauna abundance/productivity due to organic enrichment. The Giant Kelp (Macrocystis pyrifera) in Blackmans Bay was again surveyed in December 2015. The area where Giant Kelp occurs in Blackmans Bay has not changed appreciably since the offshore outfall was commissioned. The density of the canopy and kelp stipes in 2015 was comparable to that seen in 2014. Giant kelp grows profusely on and immediately adjacent to the outfall pipeline and the ports installed to supply the kelp bed with nutrients. Based on these results, it is recommended that infauna surveys continue at 12 month intervals, with a survey of the Giant Kelp community at 2 year intervals.


Marine Ecological Monitoring Program

Infauna Community

Sixth Operational Survey – December 2015

1 Background

The Blackmans Bay Sewage Treatment Plant (STP) treats wastewater from the Kingborough area to secondary standard prior to the effluent being discharged to the lower Derwent Estuary via a long outfall. Effluent from the treatment plant was previously discharged at the shoreline and there were concerns about the potential impacts on the health of swimmers, surfers and the near-shore environment. Consequently a new long outfall with a multi-port diffuser was commissioned on 30 June 2010. The new diffuser is located 600 m offshore in 13 m water depth. Figure 1 shows the location of the Blackmans Bay STP, the previous shoreline discharge and also the location of the diffuser of the long outfall.

Figure 1 Location of Blackmans Bay Outfall

Blackmans Bay Outfall Ecological (Infauna) Monitoring Program, Dec-2015 2


The extended outfall was installed to protect nearshore public health and environmental values. However, the discharge from the outfall has the potential to interact with components of the marine environment exposed to the diluted effluent. The subtidal soft seabed (infauna) community adjacent to the outfall may be affected due to its exposure to dispersing effluent. The environmental approval for the upgrade required that infauna be monitored prior to outfall commissioning, at 6 months post-commissioning and at regular intervals thereafter. Eight infauna community surveys have been conducted including two baseline and six operational surveys (Table 1).

Table 1 Details of infauna surveys at Blackmans Bay Outfall

Date Survey number Time since commissioning

December 2007 First baseline survey 2.5 years prior to commissioning

July 2009 Second baseline survey 1 year prior to commissioning

June 2010 No survey New offshore outfall and diffuser commissioned

December 2010 First operational survey 6 months post commissioning

May 2013 Second operational survey 3 years post commissioning

November 2013 Third operational survey 3.5 years post commissioning

June 2014 Fourth operational survey 4 years post commissioning

November 2014 Fifth operational survey 4.5 years post commissioning

December 2015 Sixth operational survey 5.5 years post commissioning

This report provides the results of the most recent post-commissioning survey including comparison with data from the previous 7 surveys and comments on spatial and temporal patterns in the infauna community.



2 Environmental Context

Blackmans Bay is located in the lower Derwent Estuary, approximately 15 km south of Hobart. The outfall is located south of Blackmans Bay, near Soldiers Rocks. The extended outfall discharges 600 m offshore through an 80 m long multi-port diffuser at 13 m depth. The seabed at the diffuser is mobile soft sediment. The seabed to the north and south of the outfall is undulating soft sediment that varies from fine sandy sediments to coarser shell and gravel sediments. The mobile sediments are reworked by tidal currents and ocean swells entering the estuary. The sediments vary in coarseness spatially on the scale of meters to tens of meters. Interestingly, there are often distinct boundaries between sediments of different coarseness (see Figure 2). Approximately 400 m inshore of the diffuser (between the shoreline and 200 m offshore), there is an area of reef which is home to the last remaining stand of Macrocystis pyrifera (Giant Kelp) in the Derwent Estuary (CEE, 2002). The extended outfall pipeline includes three adjustable ports within the kelp forest to supply nutrients. Scientific evidence suggests that Macrocystis responds positively to the nutrients and the Blackmans Bay outfall can contribute to having a healthy forest of Macrocystis in Blackmans Bay. This marine ecological monitoring program focuses on the infauna community living in the sediments at the same depth as the diffuser because they are the most likely marine community to exhibit a measurable response to effluent discharge. The infauna is subject to the greatest exposure to the dispersing effluent and comprises polychaete worms, crustaceans (amphipods, isopods, ostracods, shrimp), molluscs and some echinoderms and cnidarians.

Figure 2 Spatial Variation in Sediment Composition – 2007 Video Survey

Shows fine sand to the top left and coarse, shelly sand to the bottom right



The composition of the infauna community is influenced by a range of environmental factors on different spatial and temporal scales. Variations in the physical environment are major factors. Sediment is constantly reworked by waves, especially at times of storms. Water temperature, salinity and nutrient levels are affected by both upstream and downstream factors. High nutrient, low salinity river flows vary with rainfall and hydroelectricity releases. The intrusion of cold, high salinity, nutrient rich Southern Ocean waters into the lower Derwent Estuary varies on a seasonal and inter-annual basis. Biological or ecological events are also a major factor. Many biological factors affect recruitment of new individuals to infauna species populations including the reproductive strategy of the species (broadcast spawning or brooding), the presence or not of a planktonic stage in the life cycle, the biological or environmental cues for larval settlement and environmental factors such as currents that disperse spawn or larvae, and water temperature. Infauna typically have short life spans of months to one or two years. Most of the infauna have either a planktonic stage in their life cycle or are broadcast spawners. This means that each year a new cohort of animals is recruited into the community. The overall result of these ecological processes is that a species that is present one year may not necessarily be present in the same area the next year or may be present in very different abundances. Thus there are often significant changes in infauna characteristics over time periods of months and years. The effect of effluent exposure may vary between infauna species. Consequently, the extent of effect may vary according to the species present in the vicinity of a discharge from year to year. Long periods of monitoring are therefore required to define the range of effluent discharge impacts on infauna communities.



3 Potential Effects of Effluent Discharges on Marine Infauna

Communities

Effluent contains a range of constituents including ammonia, other nutrients and fine organic matter, and has a much lower salinity than seawater. Effluent constituents can affect different species in different ways. The type of response of organisms to effluent depends on their physiology, biology, habit and habitat and interactions with other organisms. Dilution from a deep-water outfall is achieved initially by the buoyant rise of the effluent through the water column (fresh water is less dense than seawater) and then from subsequent mixing by waves and currents. Exposure is determined by the concentration (dilution), frequency and duration of effluent contact. Exposure decreases with distance from the outfall due to (1) increasing dilution of effluent with ambient seawater, (2) the dispersing effluent plume less frequently reaching a particular position and (3) the shorter duration in which diluted effluent is present. At Blackmans Bay, effluent is discharged at a rate of around 4 ML per day. The diffuser is designed to produce a minimum initial dilution of 150:1 (dilution calculated by CEE model; the measured dilutions have been higher than this, see CEE (2014) water quality report). The diluted effluent is dispersed by ambient currents. The 2014 suspended solids concentration in the effluent averaged 22 mg/L which corresponds to a discharge load of 89 kg/d of organic solids. The load of nitrogen averaged 166 kg/d and the load of phosphorus averaged 28 kg/d. The frequency and duration of the presence of a dispersing effluent plume at a site is determined by the water currents around the outfall. Tidal currents change direction depending on the phase of the tide; wind driven currents can be more persistent due to prevailing winds but vary in strength and direction with the wind. The habit and habitat of organisms is also a key determinant of their exposure. Planktonic and pelagic organisms are likely to only be present in the vicinity of an outfall plume for a short period. Demersal and benthic organisms either move within a small home range or are attached to the seabed. These organisms typically have higher exposure close to the outfall, especially sessile or sedentary organisms which cannot move to avoid direct contact with the effluent plume. The biology and physiology of an organism determines the nature of their response. Responses may be direct (responding to the elevated ammonia, nutrients and freshwater) or indirect (responding to the changed abundance of other organisms). Organisms which are able to take advantage of the modified conditions around an outfall are likely to exhibit a positive response to it and increase in abundance or size. Direct positive responses are often seen in certain types of algae that can take advantage of higher nutrient levels and in filter and deposit feeders that can take up residual organic matter in the effluent. Other organisms may in turn increase in abundance as they feed on the algae or deposit/filter feeders or shelter within the habitat provided by them.



Some organisms may be disadvantaged by the modified conditions, either through an inability to live in the modified conditions (adverse responses to freshwater or ammonia) or due to interactions (such as competition or predation) with other organisms that are better suited to the modified conditions. Likewise some organisms may be advantaged by the reduced abundance of other organisms, even if they do not respond directly to the effluent discharge. As a result, a range of direct and indirect effects determine the changes which may occur in an ecosystem as a result of effluent discharge.

The response of the ecosystem will reflect the gradient in exposure to effluent with distance from the outfall. Responses are likely to be strongest nearest the outfall, and become smaller and less noticeable further from the outfall. This is because exposure to effluent is highest closest to the outfall and decreases exponentially with distance. Effluent dispersion modelling for the Blackmans Bay offshore outfall showed that initial dilution of effluent with seawater would be in the order of 150:1. Water quality monitoring has consistently shown that measured dilutions are consistently above 200:1 – therefore the modelling is conservative. Based on water quality monitoring results, measurable effluent exposure is confined to areas within 50 m of the outfall.



4 Sediments

The sediments in the region of the Blackmans Bay outfall comprise predominantly fine sand (median grain size of 0.2 mm) with patches that have a large amount of coarse sand/shell grit (median grain size 0.5-1 mm). The composition of sediments at particular sites changes over time. The patches of coarse sand appear to be quite mobile, with sediments at many sites varying between having a small or large proportion of shell grit on a number of occasions during the monitoring program. This is illustrated in Figure 3 and Figure 4. The data shown in Figure 3 is from sediment samples collected at each site during each survey (one sample per site). Median grain size is determined through size fractionation. Sieves of standard mesh size (4 mm, 2 mm, 1 mm, 0.05 mm, 0.025 mm, 0.0125 mm, 0.0063 mm) are used to determine the proportion of sediment in each sediment grain size class. From the data the size distribution of each sediment sample is established. The median grain size is interpolated from plots of grain size versus cumulative sediment percentage (by volume). All sites between 100 m north and 100 m south of the outfall have had coarse sediment from time to time. The only site that has had consistently coarser sediment since installation of the outfall is the outfall site itself. The disturbance of prevailing currents due to the outfall pipeline may be creating conditions suitable for shell grit accumulation (just as a rock pool may accumulate shells or pebbles). However, it is unlikely that any effect of the outfall structure extends beyond the immediate vicinity of the outfall. Broader scale coastal processes (such as underlying bathymetry and hydrodynamics) are responsible for the coarse sand seen between 100 m north and 100 m south, not the presence of the outfall.

Figure 3 Median sediment grain size – 2007 to 2014

*In December 2007 samples were collected at the proposed diffuser location, and at 200 m north and south.



In addition to size fractionation of sediment samples, the volume of material over 1 mm in size in infauna samples is measured when they are sorted to provide a rough indication of sediment composition. These data are used to test whether patterns of the infauna community relate to sediment coarseness. The data for volume of sediment over 1 mm diameter recorded in infauna samples between 2007 and 2014 are shown below in Figure 4. There has typically been a small volume of material over 1 mm at most sites and times. Some sites have occasionally shown a larger volume of material > 1mm – particularly at the outfall site, 100 m north, 10 m south, 50 m south and 100 m south. The patterns shown in Figure 4 are similar to those in Figure 3, in that the only sites showing large volumes of coarse material are those between 100 m north and 100 m south of the outfall, with the outfall the only site with persistently coarse sediment (according these data, also during the baseline period).

Figure 4 Volume of sediment > 1 mm in infauna samples – 2007 to 2014

5 Gazameda gunnii

Gazameda gunnii sampling has been conducted according to standard protocols and requirements of DPIPWE at the time of each survey. A new protocol was introduced in 2010 and has been used since. No Gazameda gunnii have been found at any survey site in any survey.



6 Infauna Methods

Sampling in the first survey (December 2007) followed the method used by TAFI in their study on the ecological status of the Derwent Estuary (Macleod and Helidoniotis 2005). A Van-Veen grab, which samples a seabed surface area of 0.0675 m2, was used to collect three samples at each site and samples were combined. Samples were sieved through 1 mm mesh and fixed in formalin/seawater solution. A sub sample of one-third the volume of sediment was separated for laboratory analysis. Infauna were sorted to family level and counted in the laboratory. The volume of sediment over 1 mm in size was measured. Sampling in all subsequent surveys (from July 2009) followed methods tested by TAFI for assessing the impacts of salmon farms on seabed ecology in Tasmania (Crawford et al 2002). Divers collected three samples at each site using hand-corers. Each sample consisted of a single sediment core 150 mm in diameter (0.018 m2) and 100 mm deep. Each sample was sieved underwater through 1 mm mesh bags and fixed in formalin/seawater solution. The infauna in the samples from each site were sorted to family taxonomic level and counted. The volume of sediment over 1 mm size was also established. In November 2014 five large samples were subsampled to ½ their total volume. In December 2015 seven large samples were subsampled to ½ their total volume. Infauna data from the analysed cores were standardised to average number of infauna/m2 at each site to enable comparison between surveys. Infauna data from split samples was multiplied by two before being standardized to infauna/m2.

7 Infauna Sampling Sites

Figure 6 shows the location of the outfall diffuser and the sampling sites north and south of the diffuser. Table 2 lists the sites where infauna samples were collected in each survey. The sites are north and south of the diffuser on the 13 m depth contour.

Table 2. Infauna Sampling Sites for the Infauna Surveys

Dec-2007 Jul-2009 Dec-2010 May-2013 Nov-2013 Jun-2014 Nov-2014 Dec-2015

1000 m N 1000 m N 1000 m N 1000 m N 1000 m N 1000 m N 1000 m N 1000 m N 500 m N 500 m N 500 m N 500 m N 500 m N 500 m N 500 m N 200 m N 100 m N 100 m N 100 m N 100 m N 100 m N 100 m N 100 m N 50 m N 50 m N 50 m N 50 m N 50 m N 50 m N 50 m N 10 m N 10 m N 10 m N 10 m N 10 m N 10 m N 10 m N Outfall Outfall Outfall Outfall Outfall Outfall 10 m S 10 m S 10 m S 10 m S 10 m S 10 m S 10 m S 50 m S 50 m S 50 m S 50 m S 50 m S 50 m S 50 m S 200 m S 100 m S 100 m S 100 m S 100 m S 100 m S 100 m S 100 m S 500 m S 500 m S 500 m S 500 m S 500 m S 500 m S 500 m S 1000 m S 1000 m S 1000 m S 1000 m S 1000 m S 1000 m S 1000 m S 1000 m S Tafi Reference*

WGS 84, Zone 55G Easting Northing

Offshore end of diffuser 527,398 5,237,380 Middle of diffuser 527,258 5,237,380

* Reference site is Derwent Estuary Site 25 in Macleod & Helidoniotis 2005



8 Giant Kelp methods

Giant kelp monitoring is conducted using standardised methods that have been applied throughout Tasmania. The stipe density, canopy extent and condition are assessed by divers along transects laid along the seabed. When surveying the transect, the divers record the following information in 5 m sections of the transect:

• Number of stipes counted within 1 m to one side of the transect, 1 m above the seabed, along every other 5 m section of transect.

• Extent of the canopy to the nearest 25 %, estimated every 5 m along the transect

• Amount of epiphytes (algae and invertebrates that grow on the kelp, a measure of condition), estimated every 5 m along the transect and ranked from 0 (no epiphytes) to 3 (heavy epiphyte growth)

The data from each transect was averaged over each 50 m of transect. The table below shows where transects were surveyed in 2014 and 2015:

Table 3 Giant Kelp survey sites

Survey North of outfall South of outfall

300-400 m 100-200 m 0-100 m 0-100 m 100-200 m 300-400 m Oct-2014 � � � � � � Dec-2015 � � �

Figure 5 Six-spine leatherjacket (Meuschenia freycineti) in Giant Kelp



Figure 6 Location of Blackmans Bay Outfall Sampling Sites



9 Results

Summary statistics for each survey are shown in Table 4. The table shows that infauna numbers in the region increased steadily between 2007 and May 2013. This increase was not consistent with organic enrichment by the discharge; such changes typically involve a continuous growth in the numbers of a small group of species. Between May and November 2013 there was a 50 % reduction in infauna numbers from 4,421 per m2 to 1,832 per m2. There was a further 45 % decrease between November 2013 and June 2014, and a 43 % decrease between June 2014 and November 2014 (784 per m2 - the lowest infauna numbers recorded to date). In December 2015 infauna numbers had increased to an average of 2092 per m2. The temporarily lower infauna numbers between November 2013 and November 2014 was consistent across all the monitoring sites: it was not related to the presence of the outfall. Likewise, the higher average infauna in December 2015 does not show any patterns relating to the outfall. The average number of taxa collected at each site in December 2015 was 36 (range of 29 - 43), and a total of 65 families were collected. The increase in the number of infauna families collected in December 2015 is consistent with the increase in total infauna numbers. Surveys with low infauna numbers tend to have a low number of infauna families (as in November 2014) and surveys that have higher numbers of infauna tend to have higher numbers of families. A feature of the summary data is that the ten most abundant infauna taxa in each of the surveys are very similar. Three taxa are common to all eight surveys (Corophiidae, Spionidae, Phoxocephalidae). Two are common to six surveys (Onuphidae and Tanaidacea), two are common to five surveys (Magelonidae, Syllidae) and two are common to four surveys (Polygordiidae, Ostrocoda).

9.1 Assessment of effects

The patterns in key infauna community parameters (taxonomic richness, abundance of key groups) are assessed below for patterns relating to effluent exposure. An effluent exposure effect entails a positive or negative effect on infauna community parameters:

• A positive effect is represented by consistently high values close to the diffuser relative to reference sites; or an increase in values between sites along the north/south effluent dispersion gradient.

• A negative effect is represented by consistently low values close to the diffuser relative to reference sites; or a decrease in values between sites along the north/south effluent dispersion gradient.

Analysis of the available data on infauna abundance is presented below, it includes graphical analysis of infauna abundance, tests for correlations between infauna abundance and distance from the outfall and sediment coarseness (a test for broad-scale ecological patterns), and, statistical tests for differences in infauna abundance at sites ≤10 m from the outfall or ≥50 m from the outfall (a test for small-scale patterns).


Table 4 Summary of Infauna Statistics – 2007 to 2014

Survey Baseline Operational

December 2007

July 2009

December 2010

May 2013

November 2013

June 2014

November 2014

December 2015

Average infauna (per m

-2)

2729 3156 4316 4521 1832 1041 784 2092

Average families (per site)

24 37 51 53 26 27 20 36

Major Groups (per cent abundance)

Annelida (A) 12 58 54 28 32 40 43 26

Crustacea (C) 78 39 40 61 52 50 46 62

Mollusca (M) 9 2 5 9 11 8 9 10

Top ten families (by abundance)

Rank

1 Corophiidae Magelonidae Magelonidae Tanaidacea Tanacidacea Corophiidae Spionidae Corophiidae

2 Tanaidacea Spionidae Corophiidae Corophiidae Corophiidae Spionidae Onuphidae Onuphidae

3 Cypridinidae Corophiidae Spionidae Magelonidae Ostrocoda sp Onuphidae Corophiidae Phoxocephalidae

4 Philomedidae Tanaidacea Phoxocephalidae Phoxocephalidae Spionidae Ostrocoda sp Phoxocephalidae Ostrocoda sp.

5 Ampeliscidae Phoxocephalidae Syllidae Ostrocoda sp Magelonidae Phoxocephalidae Polygordiidae Veneridae

6 Phoxocephalidae Ampeliscidae Ampeliscidae Onuphidae Phoxocephalidae Paraonidae Syllidae Spionidae

7 Veneridae Orbiniidae Tanaidacea Spionidae Polygordiidae Magelonidae Ostrocoda sp. Ampheliscidae

8 Syllidae Syllidae Sabellidae Ampeliscidae Syllidae Glyceridae Paraonidae Urohaustoriidae

9 Spionidae Sabellidae Orbiniidae Sabellidae Onuphidae Polygordiidae Urohaustoriidae Polygordiidae

10 Diastylidae Onuphidae Gynodiastylidae Urohaustoriidae Lumbrineridae Lumbrineridae Tanaidacea Gynodiastylidae

Draft Blackmans Bay Outfall Ecological (Infauna) Monitoring Program, Dec-2015 14

Images of the 10 most abundant taxa in December 2015 are shown in Figure 7.

Figure 7 Images of the 10 most abundant infauna in 2015

A) Corophiidae B) Onuphidae C) Phoxocephalidae D) Ostracoda E) Veneridae F) Spionidae G) Ampheliscidae H) Urohaustoriidae I) Polygordiidae J) Gynodiastylidae



9.2 Infauna Taxa, 2007 to 2015

Figure 8 shows the average number of infauna taxa (families) per sample at each site between December 2007 and December 2015 (columns show mean +/- standard deviation).

The figure shows that the variation over time in the number of taxa (taxonomic richness) at reference sites (500 m and 1000 m either side of the outfall) is similar in magnitude to the variation in the number of taxa at the sites close to the outfall before and after commissioning of the outfall. Taxonomic richness was highest in December 2007, December 2010 and May 2013. The lowest taxonomic richness was seen in November 2014 (when record low infauna numbers occurred). Over the course of the monitoring program taxonomic richness has averaged around 10-12 taxa per sample. The outfall and other nearby sites have had a comparable number of taxa to other monitoring sites in most surveys.

Figure 8 Average Number of Infauna Taxa per Sample – 2007 to 2015

Appendix 2 (Figure 29) shows a plot of the number of infauna families per sample versus the volume of sediment > 1 mm and distance from the outfall. The plot shows that there is no correlation between the number of infauna families and coarse sediment (Dec-07 to Dec-15, n=220, r2<0.01) or between the number of infauna families and distance from the outfall (Dec-10 to Dec-15, n=184, r2=0.03). There is no evidence of an effect of effluent discharge on infauna taxonomic richness.



9.3 Total infauna abundance, 2007 to 2015

Figure 9 shows the average abundance of infauna per square metre at each site in the December 2007 to December 2015 surveys. Large interannual fluctuations in infauna numbers have been seen right across the study area. Between 2009 and May 2013, infauna numbers were fairly consistent across the study area. In November 2013, infauna numbers at most sites were substantially lower than previous years. Numbers were lower again in June and November 2014. The largest declines in infauna numbers between May 2013 and November 2014 were seen at the outfall and 10 m south and 1000 m south (around 50 %) and 500 m south (around 80 %). The decline in in infauna numbers was a regional trend: it was apparent across the entire study area. In December 2015, infauna numbers had again increased to be intermediate between the high numbers seen in 2009-2013 and the low numbers in 2014. In December 2015, similar numbers of infauna were seen at all sites, though slightly more were seen at the outfall and 500 m south.

Figure 9 Average number of infauna per square metre 2007-2014

Appendix 2 (Figure 28) shows a plot of the number of infauna per sample versus the volume of sediment > 1 mm and distance from the outfall. The plot shows that there is no correlation between total infauna numbers per sample and coarse sediment (Dec-07 to Nov-14, n=220, r2<0.01) or between total infauna numbers per sample and distance from the outfall (Dec-10 to Nov-14, n=184, r2<0.01). Samples with the highest volume of coarse sediments tend to be associated with low infauna numbers however. There is no evidence of an effect of effluent discharge on total infauna numbers.



9.4 Key Infauna Groups – 2007 to 2015

This section discusses the spatial distribution of the ten most common infauna taxa at the monitoring sites in December 2015, with comparison to past years. A summary of infauna data in December 2015 survey is shown in Table 5. Data for previous surveys are provided in Appendix 1. Table 5 shows that in December 2015 the infauna community was dominated by crustaceans; they accounted for 6 of the top ten families, 29 of the 71 families and 62 per cent of total infauna abundance. The next most abundant group were the annelids (worms); they accounted for three of the top ten families, 24 of the 71 families and 26 per cent of total infauna abundance. Molluscs were a minor component of the community with just one family in the top-ten, 10 of the 71 families and comprised just 10 per cent of the infauna community. A small number of other infauna families were also found including four Echinoderm families, and one Nemertean, Nematode, Cnidarian and Hemichordate family. Table 5 Abundance of the Ten Most Common Infauna Families, December 2015

Data North South

1000 500 100 50 10 Outfall 10 50 100 500 1000 Av.

Average infauna per m-2 1811 1490 1886 1811 1056 2773 1905 2283 2358 3547 2094 2092 Total infauna families 42 34 39 29 35 31 32 43 40 37 29 36

Major groups Average abundances (per m-2) Annelida 302 132 905 208 340 2018 679 792 264 189 170 545 Crustacea 1415 1000 755 1434 509 453 1056 1264 1792 3188 1679 1322 Mollusca 57 321 170 75 170 245 170 208 283 113 226 185

Major groups Per cent abundances

Annelida 17 9 48 11 32 73 36 35 11 5 8 26 Crustacea 78 67 40 79 48 16 55 55 76 90 80 62 Mollusca 3 22 9 4 16 9 9 9 12 3 11 10

Top ten families Per cent abundances

Corophiidae (C) 41 48 15 50 18 5 21 10 50 60 62 35 Onuphidae (A) 1 1 0 1 7 46 18 8 0 2 0 8 Phoxocephalidae (C) 6 4 2 20 11 1 5 2 6 7 4 6 Ostracoda sp. (C) 7 4 0 1 5 3 14 15 6 4 1 5 Veneridae (M) 1 9 0 2 7 6 6 7 6 2 8 5 Spionidae (A) 2 0 3 0 7 8 8 13 6 1 2 5 Ampheliscidae (C) 4 1 6 1 2 5 6 6 5 1 1 3 Urohaustoriidae (C) 5 5 2 3 0 0 1 1 2 5 5 3 Polygordiidae (A) 1 0 8 6 2 4 0 3 0 0 1 2 Gynodiastylidae (C) 1 1 2 2 0 0 1 0 1 9 1 2

(C) Crustacean, (P) Polychaete, (M) Mollusc

The ten most common families represented 73 per cent of all infauna collected during the December 2015 survey. There was a large gap in abundance between the most abundant taxon, Corophiidae (35 per cent), and the next most abundant, Onuphidae (8 per cent). The only site where Corophiidae did not have the highest per cent abundance was the outfall site. Corophiidae numbers were low here, while Onuphidae (polychaete worms) were abundant (46 per cent of infauna).



The uneven spread of infauna numbers between families is not unusual; in many infauna communities it is common for the two most abundant families to comprise over 50 per cent of the infauna in the community. However, the evenness of the infauna community varies from year to year, in November 2014 the combined abundance of the top three infauna families was 34 per cent (compared to just one family, Corophiidae, accounting for 35 per cent of the infauna in December 2015). Examination of the infauna database shows that the majority of the remaining 61 families were distributed over all sites with no obvious relationship to distance from the outfall. One family with generally very low total abundance was in higher abundance near the outfall in June and November 2014: higher numbers of Hesionidae worms were found in the samples from the outfall and 10 m south than elsewhere in June 2014, higher numbers were found at the outfall and 10 m north in November 2014. Hesionidae were only seen at two sites in December 2015 – 10 m north and south of the outfall. Low numbers of this family were found throughout the area in November 2013, but it has otherwise not been documented in previous surveys. The sections below discuss the abundance of the major infauna groups (Polychaete worms, Crustaceans, Molluscs) and top-ten families in December 2015, such as their spatial distribution and changes over time. Data from surveys since 2007 is included.



9.4.1 Polychaete worms

Some polychaete worm species are known indicators of organic enrichment and are associated with wastewater discharges. They are otherwise generally common and abundant components of any infauna community. Three of the ten most abundant infauna taxa in December 2015 were polychaete worms. A plot of polychaete worm abundance at each site in the baseline period (points) and operational period (box and whisker) is shown below in Figure 10. Polychaetes are distributed throughout the study area. Some large differences in their abundance are seen between surveys, though differences between sites are typically smaller. Polychaete worm abundance has been higher at the outfall than at adjacent sites in four of the six post-commissioning surveys: November 2013, June 2014, November 2014 and December 2015. Note that particularly high polychaete numbers were seen throughout the study area in July 2009 (prior to commissioning).

Figure 10 Polychaete worm abundance, 2007 to 2015

Appendix 2 (Figure 30) shows the number of Polychaetes in samples does not correlate with the volume of material > 1 mm (Dec-07 to Dec-15, n=220, r2 <0.01). Nor do Polychaete numbers per sample correlate with distance from the outfall (Dec-10 to Dec-15, n=184, r2=0.01). Though higher numbers of polychaetes have tended to be found at the outfall since commissioning, this pattern is small in magnitude and spatial scale. Baseline surveys and reference site data show wide background variation in polychaete abundance.



Onuphidae

Onuphidae polychaete worms are deposit feeders and have been amongst the 10 most abundant families in six of the eight surveys. They are one of the larger infauna found around the outfall (Figure 7-B). They were the second most abundant taxon in December 2015 (and November 2014). Figure 11 shows that Onuphidae have tended to be more abundant (and variable) at the outfall and adjacent sites since the outfall was commissioned. In December 2015 there was a gradient ranging from high numbers at the outfall, moderate numbers at 50 m south of the outfall and no Onuphidae at 100 m south. There were some Onuphidae 10 m north of the outfall but few were seen at sites from 50 m north and 1000 m north of the outfall. The highest numbers of Onuphidae in the study area have occurred at the outfall on three occasions since commissioning – May 2013, November 2014 and December 2015.

Figure 11 Abundance of Onuphidae, 2007 to 2015

*In December 2007 the 100 m sites were actually 200 m north and south of the outfall,

they are shown as 100 m for consistency with subsequent surveys

Appendix 2 (Figure 34) shows there is no correlation in Onuphidae number per sample with either volume of sediment >1 mm in samples (Dec-10 to Dec-15, n=220, r2=0.07) or distance from the outfall (Dec-10 to Dec-15, n=152, r2=0.04). The results show that there is no evidence of a gradient in Onuphidae numbers relating to the outfall. The monitoring data show that the increase in Onuphidae is small in scale, that is, it is confined to the immediate vicinity of the outfall. The increase or positive effect also varies in size from year to year, indicating abundance of the species also is subject to natural environmental influences (there has been little change in discharge characteristics over the period).



Spionidae

Spionid Polychaete worms (Figure 7-F) are deposit feeders and the group includes species that are known indicators of organic enrichment (such as Boccardia proboscidea). Spionidae have been listed in the 10 most abundant infauna families in all surveys and were the sixth most abundant family in December 2015. Figure 12 shows that spionid worms are dispersed across all sites. Particularly high numbers were documented 1000 m south of the outfall in July 2009 (baseline) and December 2010 (just after commissioning). In November 2013 and June 2014 higher numbers of Spionidae were detected at the outfall and up to 50 m south. In December 2015 the highest numbers of Spionidae were seen at 50 m south, outfall and 100 m south; numbers were moderate in comparison to past years. Numbers have occasionally been elevated at or around the outfall compared to other sites, but there is no consistent pattern or gradient in their numbers relating to the outfall. Background and interannual variation in Spionidae numbers is moderate.

Figure 12 Abundance of Spionidae, 2007 to 2015



Appendix 2 (Figure 38) shows there is no correlation in Spionidae numbers per sample with distance from the outfall (Dec-10 to Dec-2015, n=184, r2=0.03) or volume of sediment >1 mm in samples (Dec-07 to Dec-2015, n=220, r2=0.01). These results suggest that other sources of natural variability determine Spionidae abundance in this part of the Derwent Estuary.



Polygordiidae

Polygordiidae polychaete worms (see Figure 7-I) have been amongst the 10 most abundant taxa in the last four surveys. They have been present sporadically, patchily and in variable numbers over the monitoring period. Polygordiidae were numerous at the outfall site in December 2007 (baseline) and in November 2013. In December 2015 they were present at most sites but in relatively low numbers compared to other polychaete worms. The highest numbers were seen 100 m north, 50 m north, at the outfall site and 50 m south. There is no consistent pattern in their numbers relating to the position of the outfall.

Figure 13 Abundance of Polygordiidae, 2007 to 2015



Appendix 2 (Figure 41) shows a plot of the number of Polygordiidae per sample versus the volume of sediment > 1 mm and distance from the outfall. The plot shows some relationship between Polygordiidae numbers and the volume of coarse sediment > 1 mm (Dec-07 to Dec-2015, n=220, r2=0.17), but none between Polygordiidae numbers and distance from the outfall (Dec-10 to Dec-15, n=184, r2=0.01).

There is no evidence of an effect of effluent discharge on Polygordiidae numbers.



9.4.2 Crustaceans

Six of the ten most abundant infauna groups in December 2015 were crustaceans and they typically comprise around 30 to 70 % of infauna in the area. Numbers of crustaceans are typically similar at all sites in the study area (Figure 14), though there are differences in abundance between years. In December 2007 and May 2013, some sites showed substantially higher crustacean abundances than others. In December 2015, Crustacean abundance was around 50 % lower at the outfall and 10 m North than at adjacent sites. Other than the pattern seen in 2015, there is no consistent pattern in crustacean numbers relating to distance from the outfall.

Figure 14 Crustacean abundance, 2007 to 2015

Appendix 2 (Figure 31) shows the number of Crustaceans in samples does not correlate with the volume of material > 1 mm (Dec-07 to December 2015, n=220, r2 = <0.01). Nor do Crustacean numbers per sample correlate with distance from the outfall (Dec-10 to Dec-15, n=184, r2 = <0.01). The abundance of the six crustacean families in the ten most abundant infauna taxa in December 2015 is discussed below.



Corophiidae

Corophiidae are amphipod crustaceans (beach hoppers, Figure 7-A) and have been amongst the top three most abundant families in all surveys since 2007 (Table 4), Corophiidae were the most abundant infauna taxon in December 2015. The plot of Corophiidae abundance in Figure 15 shows that corophiids are typically distributed unevenly across the sites. Numbers of Corophiidae are consistently highest at sites from 50 to 1000 m north and 50 to 1000 m south. Numbers are lower at sites to 10 metres either side of the outfall, and they have been absent from this zone in two recent surveys. In December 2015 low numbers of Corophiidae were seen between 10 m north and 50 m south of the outfall and the highest numbers were seen between 100 m and 1000 m south.

Figure 15 Abundance of Corophiidae, 2007 to 2015



Comparing Corophiidae numbers with the plots of sediments in Figure 4 shows higher numbers of Corophiidae tend to be associated with finer sediments (and sites within 100 m of the outfall have tended to have coarser sediment over the course of the monitoring program). However, Appendix 2 (Figure 33) shows the number of Corophiidae in samples does not correlate with the volume of material > 1 mm (Dec-07 to Dec-15, n=220, r2 = 0.02). Likewise, while Corophiidae numbers appear lower in the vicinity of the outfall, the statistical results in Figure 33 show only a low correlation with distance (Dec-10 to Dec-15, n=184, r2 = 0.1). Overall, there is a tendency for a reduction in numbers within 10 m of the outfall.



Phoxocephalide

Phoxocephalidae are also amphipod crustaceans (beach hoppers, Figure 7-C) and have also been amongst the 10 most abundant infauna families in every survey. The plot of Phoxocephalidae abundance in Figure 16 shows that these crustaceans are distributed across all sites in all surveys. The variation in Phoxocephalidae numbers between surveys is lower than for many other taxa. Numbers at the outfall have typically been lower than those at sites further away and December 2015 was no exception (when the lowest Phoxocephalidae numbers were seen at the outfall). Otherwise there is no clear gradient in Phoxocephalidae numbers relating to distance from the outfall.

Figure 16 Abundance of Phoxocephalidae, 2007 to 2015



Appendix 2 (Figure 35) shows a plot of the number of Phoxocephalidae per sample versus the volume of sediment > 1mm and distance from the outfall. The plot does not show that there is any correlation between total infauna numbers per sample and coarse sediment (Dec-07 to Dec-15, n=220, r2<0.01) or distance from the outfall (Dec-10 to Dec-07, n=184, r2<0.02). There is no evidence of an effect of effluent discharge on numbers of Phoxocephalidae.



Ostracoda

Ostracod crustaceans (seed shrimp, Figure 7-D) are a common component of infauna communities and may include predators, deposit feeders and filter feeders. Due to difficulty distinguishing families in some years, data for the whole order (Ostracoda) is shown below. The Ostracoda have been amongst the ten most abundant taxa in five of the eight surveys. Figure 17 shows the abundance of Ostracoda from 2007 to 2015. High numbers of Ostracoda were seen in December 2007 while numbers were lower in July 2009, December 2010 and June and November 2014. Numbers in December 2015 were comparable to those seen in past surveys. While numbers of Ostracoda are occasionally higher at the outfall and 10 m south compared to reference sites, there is no consistent pattern in Ostracod numbers relating to the outfall.

Figure 17 Abundance of Ostrocoda, 2007 to 2015



Appendix 2 (Figure 36) shows a plot of the number of Ostracoda per sample versus the volume of sediment > 1mm and distance from the outfall. The plot does not show that there is any correlation between numbers of Ostracoda per sample and coarse sediment (Dec-07 to Dec-15, n=220, r2<0.01) or distance from the outfall (Dec-10 to Dec-15, n=184, r2<0.01).

While, there is a tendency for a reduction in numbers within 10 m of the outfall, there is no statistical evidence of any effect of effluent discharge on numbers of Ostracoda.



Ampheliscidae

Ampheliscidae crustaceans are another group of amphipods (Figure 7-G) and have been amongst the ten most abundant taxa in 5 of the 8 surveys. Their numbers are typically quite low but vary substantially between surveys and sites (Figure 18). There is no pattern in ampheliscidae numbers relating to the outfall – numbers at and near the outfall are typically comparable to those at reference sites.

Figure 18 Abundance of Ampheliscidae, 2007 to 2015



Appendix 2 (Figure 39) shows a plot of the number of Ampheliscidae per sample versus the volume of sediment > 1mm and distance from the outfall. The plot does not show that there is any correlation between numbers of Ampheliscidae per sample and coarse sediment (Dec-07 to Dec-15, n=220, r2=0.04) or distance from the outfall (Dec-10 to Dec-15, n=184, r2=0.04).

There is no evidence of any effect of effluent discharge on numbers of Ampheliscidae.



Urohaustoriidae

Urohaustoriidae crustaceans are another group of amphipods (Figure 7-H) and have been amongst the 10 most abundant taxa on three occasions – May 2013, November 2014 and December 2015. They have been distributed patchily across the study area in each survey, but have not been seen at the outfall since the December 2007 survey (Figure 19). However, Urohaustoriidae are often absent from other sites, sometimes for two or more surveys in a row. There is no consistent pattern in their distribution to but it appears that conditions in the immediate vicinity of the outfall are unsuitable for this group.

Figure 19 Abundance of Urohaustoriidae, 2007 to 2015



Appendix 2 (Figure 40) shows a plot of Urohaustoriidae numbers per sample versus the volume of sediment > 1 mm and distance from the outfall. The plot does not show that there is any correlation between Urohaustoriidae numbers and distance from the outfall (Dec-10 to Dec-15, n=184, r2<0.01). Nor does the plot show a relationship between Urohaustoriidae numbers and volume of sediment > 1 mm (Dec-07 to Dec-15, n=220, r2<0.03). These results provide no evidence of an effect of effluent discharge on Urohaustoriidae numbers.



Gynodiastylidae

Gynodiastylidae are cumaceans (hooded shrimp, Figure 7-J) have been amongst the ten most abundant families just twice in the eight surveys (December 2010 and 2015). Their numbers show a large amount of variation from survey to survey and from site to site (Figure 20). In December 2015 their abundance was mostly accounted for by the high numbers seen 500 m south of the outfall. There is no pattern in Gynodiastylidae numbers relating to the outfall.

Figure 20 Abundance of Gynodiastylidae, 2007 – 2015



There is no correlation between Gynodiastylidae numbers and sediment coarseness (Dec-07 to Dec-15, n=220, r2<0.01) or distance from the outfall (Dec-10 to Dec-15, n=184, r2=0.02), as shown by Figure 42.



9.4.3 Molluscs

Just one of the ten most abundant infauna groups in December 2015 was a mollusc family (Veneridae). Molluscs typically comprise less than 10 % of infauna in the area. Numbers of Molluscs are typically similar at all sites across the study area but there is some variation in abundance between years. There are no consistent patterns in mollusc numbers relating to the outfall (Figure 21). Mollusc numbers were lower at the outfall than the other sites in May 2013 and November 2013 but in all other years numbers have been comparable with the other sites.

Figure 21 Abundance of Molluscs, 2007 to 2015



Appendix 2 (Figure 32) shows the number of Molluscs in samples does not correlate with the volume of material > 1 mm (Dec-07 to December 2015, n=220, r2 = <0.01). Nor do Crustacean numbers per sample correlate with distance from the outfall (Dec-10 to Dec-15, n=184, r2 = 0.06). The abundance of the Veneridae, the only mollusc family within the top ten infauna families in December 2015 is discussed below.



Veneridae

The Veneridae (bivalve molluscs, Figure 7-E) have been amongst the top ten infauna families just twice in the eight surveys. Their abundance is typically low right across the study area but occasionally moderate numbers are seen at some sites (Figure 22). Numbers in 2015 were higher than in most previous years, but there was no pattern in their abundance relating to the outfall.

Figure 22 Abundance of Veneridae, 2007 to 2015



There is no correlation between Veneridae numbers and sediment coarseness (Dec-07 to Dec-15, n=220, r2<0.01) or distance from the outfall (Dec-10 to Dec-15, n=184, r2<0.01), as shown by Figure 37.



9.5 Summary of Infauna community analysis

A summary of the graphical analysis of key infauna data parameters is presented in Table 6. The table classifies patterns based on whether the parameter (ie. Polychaete abundance) was found to be higher or lower at sites around the outfall. Where an obvious pattern is apparent in the graphical analysis, the pattern at each site is colour coded blue (positive impact, increase) or orange (negative impact, decrease). Where a pattern is seen to be weak or uncertain, lighter shades are used. The table shows that there are no changes in overall infauna abundance or number of infauna families relating to the outfall. Polychaetes, as a group, show a weak positive impact (increased abundance) at the outfall and there is an uncertain pattern up to 50 m either side of the outfall. An uncertain negative impact on crustacean abundance (decreased abundance) is seen at the outfall. Molluscs show no pattern. Two individual infauna families show patterns relating to the outfall. Corophiidae abundance is low at the outfall, and this pattern appears to extend up to 50 m north and south of the outfall. Onuphidae numbers are high at the outfall and 10 m either side, with above-average numbers seen 50 m south of the outfall in December 2015. The Phoxocephalidae, Spionidae and Urohaustoridae showed uncertain negative or positive impacts.

Table 6 Summary of graphical analysis of infauna data

Parameter North Outfall South

1000 500 100 50 10 10 50 100 500 1000

Total infauna

Infauna families

Polychaetes

Crustaceans

Molluscs

Corophiidae

Onuphidae

Phoxocephalidae

Ostracoda

Veneridae

Spionidae

Ampheliscidae

Urohaustoriidae

Polygordiidae

Gynodiastylidae

KEY Positive pattern Negative pattern

Weak positive pattern Weak Negative pattern

Uncertain positive pattern Uncertain negative pattern



To test for broad-scale effects on the outfall on infauna communities, correlations of key infauna community parameters versus distance from the outfall were plotted. These are discussed in the sections above and shown in Appendix 2. Correlations of sediment coarseness versus infauna abundance were also plotted to check for physical environmental effects on infauna abundance. Table 7 summarises correlation coefficients for correlations between key infauna community parameters, distance from the outfall and sediment coarseness. Correlation coefficients greater than 0.3 indicate a reasonably strong relationship between two variables. Just one of the top ten infauna families in December 2015, Polygordiidae, showed a weak positive correlation of their abundance to the volume of sediment > 1 mm in samples (highlighted in Table 4). Polygordiidae is generally present in smaller numbers. Two other infauna families that have shown high abundance in the past also show positive correlation with sediment coarseness: Lumbrineridae (n=220, r2=0.17) and Paraonidae (n=220, r2= 0.35). The table shows that no parameters have a strong correlation with distance from the outfall in December 2015. Other infauna families that have shown high abundance in the past have likewise not shown any relationship with distance from the outfall. The correlation data are consistent with the graphical analysis discussed above. That is, where observed, impacts are very limited in their spatial scale, rather than being broad in scale. Water quality data shows that impacts on water quality only extend 10-50 m north and south of the outfall, so any effects on the infauna community should be confined to this zone.

Table 7 Summary of correlation analysis – December 2015

Correlations Correlation coefficient (r

2)

Sediment > 1mm Distance to outfall

Total infauna <0.01 <0.01

Infauna families <0.01 0.03

Polychaetes <0.01 0.01

Crustaceans <0.01 <0.01

Molluscs <0.01 0.06

Corophiidae 0.02 0.1

Onuphidae 0.07 0.04

Phoxocephalidae <0.01 0.01

Ostracoda 0.01 <0.01

Veneridae <0.01 <0.01

Spionidae 0.01 0.03

Ampheliscidae <0.01 <0.01

Urohaustoriidae 0.03 <0.01

Polygordiidae 0.17 0.01

Gynodiastylidae <0.01 0.02



To test for the significance of the small scale effects of the outfall, the average abundance of the ten most abundant infauna families (infauna per square metre) over the 2010 to 2015 period was compared between sites close to the outfall and those further away. Two-sample t-tests (pooled variance) were conducted on data for the ten most abundant families during the six surveys conducted in the operational period (December 2010 to December 2015). Data were grouped based on their exposure to effluent: so data were classified into sites ≤ 10 m and ≥ 50 m from the outfall, and the average for each survey calculated. Due to the skewed distribution of raw data, data were log transformed and verified for normality and homogeneity of variance using boxplots. Only one family, the Onuphidae, have statistically different (higher) abundance in the near vicinity of the outfall, compared to sites further away. This result is consistent with the graphical analysis presented and discussed in Section 9.4.1. Conditions at the outfall appear to be favourable for this taxon. One family, the Corophiidae, has consistently shown lower abundance within 50 m of the outfall, with the statistical test result close to significant in 2015 (0.07). Graphs presented above suggest that conditions near the outfall are unsuitable for this family.

Table 8 Results of statistical tests on infauna data – Dec-10 to Dec-15

Family Means (log10) Standard Deviation p-value <50 m >50 m <50 m >50 m df=10 Magelonidae 1.22 1.96 1.54 0.85 0.33 Corophiidae 1.71 2.61 0.99 0.39 0.07 Tanaidacea 1.14 1.88 1.37 0.68 0.27

Spionidae 2.13 2.1 0.36 0.27 0.82 Phoxocephalidae 2.05 2.02 0.26 0.28 0.84 Onuphidae 2.24 1.70 0.47 0.17 0.02 Ampheliscidae 1.36 1.65 0.79 0.54 0.48 Ostrocoda sp.* 1.72 1.62 0.94 0.82 0.85 Syllidae 1.67 1.65 0.40 0.40 0.94

Veneridae 1.68 1.55 0.27 0.48 0.58 *outliers in dataset



The charts below in Figure 23 and Figure 24 summarise changes in key infauna community parameters over time at the grouped reference sites (500 and 1000 m north and south of the outfall) compared to the grouped sites at the outfall (10 m north, outfall and 10 m south). The first two surveys were before the diffuser was installed and operating, the next six surveys reflect conditions with the diffuser in operation. Figure 23 shows that changes over time in infauna families per site and total infauna abundance have been very similar at both reference and outfall sites. There was a general increase in infauna numbers and families between July 2009 and May 2013, followed by a decline to 2007 levels by 2014. The high number of infauna (mostly crustaceans) found at the (proposed) outfall site in 2007 was anomolous, these data relate to a single sample (Van-veen grab) from a single site. Infauna numbers reached a low point in November 2014, but rose again in December 2015.

Figure 23 Time series data for infauna families and total infauna abundance



Figure 24 shows the time series of changes in Polychaete and Crustacean numbers. The figure shows that polychaete worms have consistently been more abundant at sites within 10 m of the outfall (including during the baseline period). In recent surveys there has been up to two or three times more polychaetes within 10 m of the outfall, though in November 2013 and November 2014 there was little or no difference. Crustacean numbers have been similar at reference and outfall sites in most surveys. The exceptions were December 2007 (prior to the outfall being built, infauna numbers were anomalously high at the time of this survey) and December 2015 (when crustacean numbers at the outfall were around 50 % lower than those at reference sites).

Figure 24 Time series data for Polychaete worms and Crustaceans



Figure 25 shows time series data for the two families that show significant (Onuphidae), or nearly significant (Corophiidae) differences in their numbers between sites near the outfall and reference sites. The chart of Onuphidae abundance over time shows that their numbers at reference sites have been relatively stable over the eight surveys – generally between 20 and 100 individuals per square metre. At outfall sites, however, their numbers have been noticeably higher in the five surveys since May 2013 with the largest differences seen in May 2013 and December 2015. The chart of Corophiidae abundance over time shows that their numbers have been highly variable at reference sites, ranging from 100 per square metre (November 2014) to 1300 per square metre (December 2015). At outfall sites their numbers have been lower than at reference sites in every survey since July 2009 (prior to outfall commissioning).

Figure 25 Time series data for Onuphidae and Corophiidae



9.6 Giant Kelp (Macrocystis pyrifera) The 2015 survey documented extensive and healthy stands of Giant Kelp either side of the outfall pipeline. Giant Kelp grows profusely on the pipeline itself, which includes three ports designed to maintain a nutrient supply into the kelp forest. Epiphyte scores in 2015 were mostly around 1 (low epiphyte cover). The kelp canopy to the north of the outfall pipeline was comparable to that seen in October 2014, ranging between 5 per cent to 20 per cent cover. The kelp canopy to the south of the outfall pipeline was denser than in October 2014, at around 15-25 per cent cover. The kelp canopy 300-400 m south of the outfall was also estimated to be somewhat denser than in 2014, at 15-30 per cent cover.

Figure 26 Giant Kelp canopy density in 2014 and 2015

Stipe density was comparable to that seen in October 2014 to 100 m north and south of the outfall. Stipe density was higher along the transect 300-400 m south of the outfall.

Figure 27 Giant Kelp stipe density in 2014 and 2015



10 Conclusion: Possible Effects of Outfall Discharge on Marine Ecosystem

The monitoring program has not documented any ‘typical’ impacts known from studies on wastewater discharges, such as:

• Reduced taxonomic richness

• Increased total infauna numbers due to organic enrichment

• Dominance of the infauna community by high numbers of one or a few taxa (usually polychaete worms).

The sections above discuss infauna community parameters (total infauna numbers, taxonomic richness, major infauna taxa) in terms of patterns relating to proximity to the outfall. The monitoring program has documented some small scale impacts on the infauna community, namely higher Onuphidae abundance at sites ≤10 m from the outfall (n=6, df=10, p=0.02). Localised enrichment by the nutrients and organic matter in the effluent may be benefitting Onuphidae, which are detritus feeders. There is also lower Corophiidae abundance at sites ≤ 10 m from the outfall (n=6, df=10, p=0.07) – Corphiidae may have a variety of feeding modes including deposit and suspension feeding. Corphiidae appear to be responding negatively to conditions at the outfall. Other patterns in the infauna community can be summarised as follows:

• There are no broad-scale patterns in the infauna community relating to the outfall, as evidenced by lack of correlation between distance from the outfall and total infauna abundance; infauna taxonomic richness; or, abundance of any of the top-ten infauna families in December 2015.

• There are several families which show a positive correlation between their abundance and the coarseness of sediments over the 2007-2015 period (Appendix 2), these include the Polygordiidae, Paraonidae and Lumbrineridae. All three taxa are polychaete worms.

Sediment composition varies at a broad spatial scale and over time. Sediments in the region are mostly fine sands, however mobile patches or coarse sand (shell grit) are present throughout the area. Coarse sediment patches have occurred between 100 m north and 100 m south of the outfall since outfall commissioning. The outfall diffuser structure may affect hydrodynamics in its immediate vicinity (and affect sediment composition). However, the wide distribution of coarse sediments suggests the cause of the observed pattern is due to broad scale natural hydrodynamic features (bathymetry and currents), rather than the outfall structure. The Giant Kelp forest in Blackmans Bay was surveyed in December 2015 and found to be in good condition. The density of stipes and the canopy was similar to or slightly higher than the conditions seen in 2015. In summary, the infauna monitoring studies have documented small-scale modification of the infauna community within less than 50 m from the outfall consistent with the small-scale, low-level nutrient and organic enrichment, consistent with the results of the water quality monitoring.



11 Appendix 1

Infauna data from previous surveys is shown below. Data includes average infauna numbers (per square metre), total infauna families (per site), average abundance for the three major infauna groups (Annelida, Crustacea, Mollusca, per square metre) and per cent abundance of the ten most abundant families in each survey.

Table 9 Infauna data for December 2007 (baseline)

Direction North Proposed South

Average Distance to OF 1000 200 Outfall 200 1000

Infauna per m-2

2607 2459 5363 2770 444 2729

Total families 30 26 26 23 13 24

Major groups Abundance per m-2

Average

Annelida 119 59 1274 193 104 350

Crustacea 2237 2222 3985 1956 311 2142

Mollusca 178 178 15 622 30 204

Top ten families Per cent abundances Total

Corophiidae 45 49 16 26 7 30

Tanacidacea 1 0 28 0 0 11

Cypridinidae 13 11 13 4 0 9

Philomedidae 8 8 2 10 0 5

Ampheliscidae 3 1 4 8 43 5

Phoxocephalidae 0 6 2 11 7 5

Vereridae 3 3 0 14 0 4

Syllidae 1 1 6 1 7 3

Spionidae 1 1 6 1 0 3

Diastylidae 0 4 4 2 0 2

Table 10 Infauna data for July 2009 (baseline)

Direction North South

Average Distance to OF 1000 500 100 50 10 10 50 100 500 1000

Infauna per m-2

1905 2981 5150 1962 4565 1698 4924 1868 2018 4490 3156

Total families 39 35 42 34 52 33 29 35 28 43 37


Average

Annelida 755 1717 3452 1226 3339 604 4056 453 1415 3264 2028

Crustacea 1113 1226 1660 679 1151 1038 773 1302 509 1094 1055

Mollusca 19 19 19 57 75 57 94 75 75 75 57


Magelonidae 25 43 45 29 57 2 74 0 34 21 40

Spionidae 6 4 4 5 2 7 1 1 25 44 10

Corophiidae 28 15 16 4 7 3 5 1 7 11 10

Tanacidacea 7 1 2 3 3 46 2 59 1 2 8

Phoxocephalidae 5 6 5 12 2 2 6 2 7 4 5

Ampheliscidae 4 12 3 1 1 6 0 2 8 3 4

Orbiniidae 1 3 6 3 4 3 4 1 3 2 3

Syllidae 0 3 6 2 3 7 2 6 2 3 3

Sabellidae 5 4 6 1 4 4 1 2 3 1 3

Onuphidae 0 0 0 18 1 2 1 1 4 0 2



Table 11 Infauna data for December 2010 (operational)

Direction North South

Distance to OF 1000 500 100 50 10 10 50 100 500 1000 Average

Iinfauna per m-2

5584 3509 5263 4018 5037 5018 5225 2075 2188 5244 4316

Total families 65 48 55 49 52 51 45 36 49 62 51


Average

Annelida 2830 1509 3056 2622 3867 3339 3679 302 943 2886 2503

Crustacea 2434 1868 2018 1151 849 1490 1339 1566 1019 1943 1568

Mollusca 264 94 132 226 245 189 132 170 132 377 196


Magelonidae 37 28 45 58 68 58 58 0 15 5 41

Corophiidae 21 35 22 6 2 9 8 3 20 20 14

Spionidae 3 5 1 1 1 1 1 2 8 32 6

Phoxocephalidae 1 3 4 6 4 5 5 1 3 3 4

Syllidae 1 3 3 0 1 2 3 2 5 12 3

Ampheliscidae 6 4 3 2 0 2 3 6 6 3 3

Tanacidacea 3 1 0 0 0 0 0 54 0 1 3

Sabellidae 6 3 4 1 1 0 1 0 9 4 3

Orbiniidae 1 0 3 2 3 4 5 3 0 0 2

Gynodiastylidae 3 2 3 3 1 3 1 2 6 2 2

Table 12 Infauna data for May 2013 (operational)

Direction North Outfall

South

Distance to OF 1000 500 100 50 10 10 50 100 500 1000 Av.

Infauna per m-2

3980 4697 5905 6037 3433 5395 2660 2943 7923 2886 3867 4521

Total families 63 53 43 54 60 60 40 37 50 57 61 53


Av.

Annelida 1453 1226 660 2471 1490 1679 811 811 887 698 868 1187

Crustacea 2169 2905 4716 3226 1660 3565 1509 1849 6772 1849 1566 2890

Mollusca 321 396 453 245 151 132 302 283 189 226 1377 370


Tanacidacea 1 0 64 0 2 35 0 0 65 3 0 23

Corophiidae 31 32 2 17 12 3 23 13 15 34 17 16

Magelonidae 18 1 1 32 23 1 27 13 0 0 0 10

Phoxocephalidae 1 1 3 10 10 2 11 15 1 6 5 5

Ostrocoda sp 7 6 1 4 9 10 2 8 0 5 4 5

Onuphidae 3 4 3 0 5 21 0 1 1 2 1 4

Spionidae 6 10 3 2 2 3 0 0 2 8 9 4

Ampheliscidae 4 5 4 5 1 2 5 11 1 5 3 4

Sabellidae 4 3 1 6 7 1 1 8 2 3 3 3

Urohaustoriidae 2 10 0 4 4 0 10 12 0 3 0 3



Table 13 Infauna data for November 2013 (operational)

Direction North Outfall South

Distance to OF 1000 500 100 50 10 10 50 100 500 1000 Av.

Infauna per m-2 2292 905 1217 1160 792 3820 2999 1585 934 2886 1556 1832

Total families 30 22 17 27 19 37 40 21 16 30 25 26


Av.

Annelida 1217 170 340 226 311 1528 934 283 141 1641 424 656

Crustacea 707 368 764 594 283 1952 1726 1160 651 1075 934 929

Mollusca 311 198 57 255 113 28 255 113 113 113 113 152


Tanacidacea 0 0 49 0 4 24 21 0 0 1 2 11

Corophiidae 0 16 2 15 0 0 2 34 33 26 24 11

Ostrocoda sp1 1 9 0 10 18 6 21 13 12 0 5 8

Magelonidae 15 0 0 2 0 0 0 2 6 36 0 8

Spionidae 12 6 12 2 7 9 7 7 0 6 13 7

Phoxocephalidae 9 6 0 17 11 1 3 14 12 4 15 6

Polygordiidae 0 0 5 0 11 21 2 0 0 0 0 6

Syllidae 6 3 2 2 11 6 1 2 0 5 7 4

Onuphidae 7 3 0 2 4 1 10 0 0 2 5 4

Lumbrineridae 9 0 0 2 4 2 6 0 0 0 0 3

Table 14 Infauna data for July 2014


South

Distance 1000 500 100 50 10 10 50 100 500 1000 Average

Infauna per m2 1000 887 585 1302 189 1962 1339 1471 849 509 1358 1041

Total taxa 30 25 23 34 9 31 32 35 31 15 27 27

Major Groups Abundance per m-2

Average

Polychaeta (P) 321 170 170 151 38 1679 943 1019 377 189 283 485

Crustacea (C) 585 604 302 830 151 245 245 340 415 302 849 442

Mollusca (M) 75 57 57 226 0 38 132 113 57 19 189 87

Top 10 families Per cent abundance Total

Corophiidae (C) 23 40 13 35 0 0 0 1 11 30 54 18

Spionidae (A) 8 4 3 3 10 53 8 17 4 4 6 15

Onuphidae (A) 2 0 10 3 0 10 17 23 18 7 1 9

Ostrocoda sp (C) 15 11 6 10 10 3 4 6 13 4 3 7

Phoxocephalidae (C) 6 2 3 9 20 6 13 6 2 0 3 6

Paraonidae (A) 0 0 3 1 0 7 14 8 4 0 0 4

Magelonidae (A) 13 0 0 0 0 0 0 0 9 11 1 2

Glyceridae (A) 0 0 0 0 0 2 10 6 0 0 0 2

Polygordiidae (A) 0 0 3 0 0 0 7 5 2 0 4 2

Lumbrineridae (A) 0 0 0 0 10 4 4 5 2 0 0 2



Table 15 Infauna data for November 2014


South

Av. Distance to OF 1000 500 100 50 10 10 50 100 500 1000

Average infauna per m-2

981 509 302 132 1717 1358 245 358 1132 792 1094 784

Total infauna families 36 17 5 6 30 21 11 14 23 22 32 20

Major groups Average abundances (per m-2)

Annelida 434 94 19 19 1377 1038 113 132 660 434 415 430

Crustacea 453 321 245 113 151 245 94 170 396 302 509 273

Mollusca 75 57 38 0 113 75 38 38 75 57 151 65

Major groups Per cent abundances

Annelida 44 19 6 14 80 76 46 37 58 55 38 43

Crustacea 46 63 81 86 9 18 38 47 35 38 47 46

Mollusca 8 11 13 0 7 6 15 11 7 7 14 9

Top ten families Per cent abundances

Spionidae (P) 0 11 0 0 14 0 0 17 29 12 17 12

Onuphidae (P) 8 0 0 0 14 0 11 8 0 12 33 12

Corophiidae (C) 17 22 50 29 0 23 26 0 0 19 4 10

Phoxocephalidae (C) 6 11 0 29 3 0 0 7 14 7 11 7

Polygordiidae (P) 4 0 0 0 18 8 0 3 17 0 0 6

Syllidae (P) 2 4 0 0 11 8 0 7 2 7 7 6

Ostrocoda sp. (P) 4 4 31 29 3 0 16 5 0 3 3 5

Paraonidae (P) 0 0 0 0 12 0 0 5 0 0 7 4

Urohaustoriidae (C) 2 15 0 0 0 0 0 0 12 3 0 3

Tanacidacea (C) 0 0 0 0 0 0 0 17 2 0 0 2



12 Appendix 2

Correlations between infauna numbers, sediment coarseness and distance from the outfall for total infauna numbers (Figure 28), total infauna families (Figure 29) and the 10 most abundant families in December 2015 (Figure 33 to Figure 42) are shown below. Data are for individual samples. Data for the full monitoring period (2007 to 2015) are used to plot infauna numbers versus the volume of sediment > 1 mm. Data for the operational monitoring period (2010 to 2015) are used to plot infauna numbers versus distance from the outfall.

Figure 28 Total infauna per sample versus sediment and distance



Figure 29 Number of families per sample versus sediment > 1 mm and distance

Figure 30 Polychaetes per sample versus sediment >1 mm and distance



Figure 31 Crustaceans per sample versus sediment >1 mm and distance

Figure 32 Molluscs per sample versus sediment >1 mm and distance



Figure 33 Corophiidae per sample versus sediment > 1 mm and distance

Figure 34 Onuphidae per sample versus sediment > 1 mm and distance



Figure 35 Phoxocephalidae per sample versus sediment > 1 mm and distance

Figure 36 Ostracoda per sample versus sediment > 1 mm and distance



Figure 37 Veneridae per sample versus sediment > 1 mm and distance

Figure 38 Spionidae per sample versus sediment > 1 mm and distance



Figure 39 Ampheliscidae per sample versus sediment >1 mm and distance

Figure 40 Urohaustoriidae per sample versus sediment > 1 mm and distance



Figure 41 Polygordiidae per sample versus sediment > 1 mm and distance

Figure 42 Gynodiastylidae per sample versus sediment > 1 mm and distance

January 2015

CEE Giant Kelp – EPBC Act referral assessment

Internal Memo Blackmans Bay STP Upgrade – Assessment of effects on Giant Kelp and North West Bay ecosystem, January 2015

Executive Summary

The nearshore area between Flowerpot Point and south of the Blackmans Bay outfall has boulder-reef habitat between 1 m and 8 m depth. This area supports a diverse macroalgae community, including the Giant Kelp, Macrocystis pyrifera. A monitoring program has been in place since 2008 and Macrocystis pyrifera has been a constant presence between 400 m north and south of the outfall, though the extent of the surface canopy it forms varies. The most recent monitoring survey in December 2014 documented patchy M. pyrifera extending along the coastline from Blackmans Bay south to Tinderbox Marine Reserve. Relatively high nutrient availability (particularly nitrate) is important for the maintenance of giant kelp. When the outfall was upgraded, it was recognized that nutrients from the Blackmans Bay outfall (treatment of sewage produces substantial quantities of nitrate) may benefit Giant Kelp near the outfall. In light of this, the nearshore section of the outfall pipeline includes three adjustable discharge ports to maintain some extra nutrient input for the kelp. The Giant Kelp at Blackmans Bay has been monitored since 2008. Since installation of the new outfall no change in its extent or condition has been observed, indeed Macrocystis pyrifera rapidly colonized the new outfall structure. “Giant Kelp Forests of South East Australia” were listed as a threatened ecological community under the EPBC Act in 2012. The Macrocystis pyrifera community near the Blackman’s Bay outfall does not fulfill all the requirements to be considered a “Giant Kelp Marine Forest”. The upgrade of the Blackmans Bay STP does not entail any recognized threatening process. On this basis, it was decided that the presence of Giant Kelp is not a reason to refer the upgrade project for consideration under the EPBC Act. Under this proposal the two sewage discharges in North West Bay at Electrona and Margate will be closed. North West Bay is a sheltered embayment that extends to the west of the D’Entrecasteaux Channel, South of Hobart. While much of the shoreline of the bay is undeveloped, the townships of Electrona, Margate, Snug and Howden occupy parts of the shoreline. North West bay has a large range of uses including marine industries, recreational activities, tourism and marine farming (Jordan et al, 2002). Two fish farm leases near the entrance to North West Bay are currently in use (Tinderbox and Shepherds Point). North West bay is used for recreational purposes including sailing, fishing and swimming and it retains a number of natural values (such as seagrass beds) and areas of historical and ecological importance. The proposal will reduce nutrient loads discharged to the head of North West Bay and may lead to localized improvements water quality there.

Giant Kelp ‘Marine Forest’ at Blackman’s Bay The marine outfall associated with the Blackmans Bay STP discharges 600 m offshore from the shore in 13 m water depth, around 1 km south of Flowerpot Point. The nearshore area between Flowerpot Point and south of the outfall has boulder-reef habitat between 1 m and 8 m depth. This area supports a diverse macroalgae community, including the Giant Kelp, Macrocystis pyrifera. This stand of M. pyrifera is the last giant kelp ‘forest’ in the Derwent Estuary (Figure 1).

Figure 1 Giant Kelp habitat in the southern Derwent Estuary Relatively high nutrient availability (particularly nitrate) is important for the maintenance of giant kelp. When the outfall was upgraded, it was recognized that nutrients from the Blackmans Bay outfall (treatment of sewage produces substantial quantities of nitrate) may indeed be the reason Giant Kelp persists near the outfall. In light of this, nearshore section of the outfall pipeline includes three adjustable discharge ports to maintain some extra nutrient input for the kelp (Figure 2). TasWater, who manage the Blackmans Bay STP, are planning to increase the capacity and upgrade the treatment process at the plant. This will result in a higher volume of wastewater being discharged via the outfall but a lower load of nitrogen (owing to upgraded treatment).

Figure 2 Blackmans Bay STP outfall and nearby giant kelp habitat

In August 2012, Giant Kelp ‘Marine Forests’ in south-east Australia were listed as a threatened ecological community under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). Due to the planned changes to the Blackmans Bay outfall discharge (effluent volume and nutrient loads) it is appropriate to consider whether the plant upgrade requires federal environmental approval. Determining whether changes to the discharge require federal environmental approval requires answering two questions:

1. Does the Macrocystis pyrifera community near the Blackman’s Bay outfall constitute a protected “Giant Kelp Marine Forest”?

2. If so, will the changes to the Blackmans Bay outfall discharge have a “significant detrimental impact on the ecological community”?

Question 1: Does the Macrocystis pyrifera community near the Blackman’s Bay outfall constitute a protected “Giant Kelp Marine Forest”? The defining attributes of Giant Kelp Marine Forests were outlined in Conservation Advice provided to the Minister in August 2012 (s266B, EPBC Act 1999): The key defining attributes of the ecological community are:

• Macrocystis pyrifera plants which form a forest with either a closed or semi-closed surface or sub-surface canopy;

• Macrocystis pyrifera plants growing at a depth generally greater than eight metres below sea level;

• A rocky substrate for Macrocystis pyrifera plants to attach to; • A diversity of marine species on the seafloor, in the understory and

throughout the water column; • Cold water with mean sea surface temperature between 5C and 20C; • Moderate wave exposure; and • Distribution restricted to waters off the coast of Tasmania particularly in the

Bruny, Freycinet and Davey bioregions, but also the Boags and Franklin, Flinders and Otway bioregions….[details of Victorian and South Australian distribution left out].

Does Macrocystis pyrifera form a forest with either a closed or semi-closed surface or sub-surface canopy? The simple answer to this question is that M. pyrifera ‘forms a forest with either a closed or semi-closed surface or subsurface canopy’ from time to time in the area. As part of monitoring for the previous shoreline discharge, and upgraded offshore discharge, CEE has undertaken several surveys of the M. pyrifera habitat at Blackman’s Bay. CEE surveys have documented M. pyrifera cover on the seabed. This measure provides a better indication of the persistent density of the forest – as the canopy is subject to large seasonal variations. M. pyrifera cover of the seabed is determined by the area covered by the kelp’s holdfasts. In 2008 transects spanning the 4 m depth contour to the north and south of the outfall, and from the old shoreline discharge to 300 m offshore were examined. Macrocystis was present along the 4 m depth contour to at least 400 m north and 400 m south of the outfall (Figure 3). In areas where it covered more than 20% of the seabed, a canopy was formed (indicated by the green ovals). The densest part of the forest in 2008 was between 100 m and 280 m south of the outfall (then a shoreline discharge).

Figure 3 Macrocystis pyrifera distribution along the 4 m depth contour - 2008

Macrocystis

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Distance from outfall, m

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South North

The survey of the transect perpendicular to shore spanned the depths 2.5 to 11.5 m (Figure 4). Boulder reef was present from 2.5 m depth to around 9 m depth. Boulders became sparse 200 m from the outfall (at 8 m depth) and the seabed was entirely sand beyond 240 m from the outfall (10.5 m depth). Macrocystis was present from around 30 m from the old outfall out to around 200 m from the old outfall. The densest area of Macrocystis, and the area in which it formed a forest, was between 90 m and 150 m offshore the old shoreline discharge (5 m to 6 m depth). Beyond this plants were only sparsely distributed (as boulder substrate became sparser), and other macroalgae, such as Caulerpa and red algae species were dominant.

Figure 4 Macrocystis pyrifera distribution from shoreline discharge to offshore - 2008

Satelite images provide a record of the dynamics of the Giant Kelp forest at Blackman’s Bay (Google Earth). The table below describes whether or not a surface canopy was apparent, and its extent, immediately offshore from the Blackmans Bay STP. Table 1 Visibility and extent of M. pyrifera surface canopy, 2005-2014

Date of imagery Surface Canopy ExtentApril 2005 Present 250 m N-S, 200 m E-W

November 2005 Present 250 m N-S, separate small patch to the south May 2011 Present Up to 500 m N-S, patches further north and south

October 2011 Present Up to 500 m N-S, patches further north and southSeptember 2012 Present Unclear November 2012 Present Unclear

February 2013 Present Around 200 m N-S, 200 m E-W April 2013 Not visible

August 2013 Present Around 200 m N-S, 200 m E-W October 2013 Present Unclear

February 2014 Not visible July 2014 Not visible

The table shows that over the past 10 years or so, a surface canopy of M. pyrifera has been a persistent feature of the area off the Blackmans Bay STP. The canopy has varied in its extent, but has been most persistently present immediately offshore from the STP. From time to time, the surface canopy has disappeared, most likely due to natural seasonal variations in giant kelp growth. Kelps grow most from spring through to summer, and usually die back in late summer. Autumn and Winter storms can remove both intact and senescent fronds. A survey conducted in August 2012 quantified the distribution of Macrocystis pyrifera along the same transect alignments used in 2008 (CEE, 2013, Ecological Risk Assessment for the Blackmans Bay outfall). The survey found giant kelp was present along the transects in a similar distribution to the 2008 survey, including on inshore section of the new outfall structure, although abundance was slightly lower than 2008. A further survey was conducted on 30 October 2014, a time when Macrocystis abundance is often high following winter and spring growth. Transects were surveyed either side of the outfall (200 m north and 200 m south) and at reference sites to (300-400 m north and 300-400 m south). All transects were layed at depths between 6 and 7 m.The number of M. pyrifera stipes (stems) and the percent cover of the canopy was estimated along sections of each transect. Figure 5 shows the results of the survey. As in 2008 the densest area of M. pyrifera is seen to the north of the outfall, particularly between 50-150 m north, and near Flower Pot Point between 300-400 m north of the outfall. To the south M. pyrifera is more patchy, but was present in all areas surveyed except 150-200 m south of the outfall. It is important to note that M. pyrifera is most abundant in the areas to 200 m either side of the outfall.

Figure 5 Macrocystis pyrifera abundance – October 2014

Do Macrocystis pyrifera plants grow at depths generally greater than 8 m? The discussion above shows that at Blackmans Bay the majority of M. pyrifera, and all the ‘canopy forming’ kelp, grows between approximately 3 and 6 m depth. Plants become sparse at 7 m depth and a lack of rocky substrate means they are absent beyond this depth. Therefore, the answer to this question is no, the plants do not grow at a depth generally greater than 8 m below sea level. Is there a rocky substrate for Macrocystis pyrifera plants to attach to? At Blackmans Bay, there is rocky substrate consisting of boulders between the shoreline and approximately 7-8 m depth. Is there a diversity of marine species on the seafloor, in the understorey and throughout the water column? Surveys by CEE have noted the other marine species on the seafloor and in the water column beneath the M. pyrifera forest at Blackmans Bay. The 2008 survey noted a diverse benthic macroalgae assemblage beneath the M. pyrifera canopy including kelp and other brown algae (Ecklonia radiata, Carpoglossum confluens, Acrocarpia paniculata), green algae (Ulva sp., Caulerpa trifaria and other Caulerpa spp.), and red algae (encrusting coralline algae, encrusting Feldmania sp, Gloiosaccion brownii, Plocamium spp. Phacelocarpus sp., Ballia sp). The giant kelp canopy and diverse macroalgae understory provides habitat for a wide range of invertebrates, though these are generally not visible beneath the dense algae cover. Fish regularly observed under and around the area of kelp forest include the ubiquitous Blue Throat Wrasse (Notolabrus tetricus), Senator Wrasse (Pictilabrus laticlavius), Hulafish (Trachinops caudimaculatus ), Leatherjackets (including Acanthaluteres vittiger), and Bastard Trumpeter (Latridopsis forsteri). The October 2014 survey again documented a diverse range of seaweed, invertebrate and fish species within and adjacent to areas of M. pyrifera (Table 2).

Table 2 Species observed in October 2014 Brown Algae Green Algae Invertebrates

Halopteris glutinosa Bryopsis gemellipara Plagusia chabrus (Red bait crab)

Acrocarpia paniculata Ulva sp. Jasus edwardsii (Spiny rock-lobster) Ecklonia radiata Caulerpa longifolia Turbo undulates (Turban shell) Carpoglossum confluens C. simpliciuscula Haliotis rubra (Black-lip abalone) Undaria pinnatifida C. trifaria Heliocidaris erythrogramma (sea-urchin)

Zonaria spp. Chaetomorpha coliformis Patiriella calcar (Seastar)

Perithalia caudata Holothurians (Sea-cucumber) Macrocystis pyrifera Fish Sargassum spp. Aracana ornate (Ornate cowfish) Red Algae Latridopsis forsteri (Bastard trumpeter) Plocamium sp. Notolabrus tetricus (Blue throat wrasse)

Corallina officinalis Cephaloscyllilum laticeps (Draughtboard shark)

Delisea sp. Urolophus cruciatus (Banded stingaree) Encrusting coralline Trachinops caudimaculatus (Hulafish) Unknown sp. (felt-like) Pictilabrus laticlavius (Senator Wrasse)

?Hemineura frondosa Dotalabrus aurantiacus (Castelnau's Wrasse)

cf. Thuretia sp There is a diversity of marine species on the seafloor, understorey and throughout the water column. Is there cold water with mean sea surface temperature between 5°C and 20°C? Records of sea surface temperatures at a site offshore from Blackmans Bay (Site C in State of the Derwent Estuary report 2009, Figure 6.4) show that temperatures in the area range between 9°C and 19.5°C. There area is therefore suitable for growth of M. pyrifera. Incidentally, bottom temperatures for the same site range between 10°C and just over 17°C. Does the site have moderate wave exposure? Ocean swells sometimes penetrate up the Derwent Estuary as far as Backmans Bay, surfing is popular at Blackmans Bay beach to the north of the site. The site is otherwise sheltered. Is the site in the right region? Blackmans Bay is within the Bruny bioregion – which forms part of the south-eastern Australian range for M. pyrifera. Summary While the M. pyrifera forest offshore from the Blackmans Bay STP meets most of the criteria for it to constitute a ‘Giant Kelp Marine Forest’, its shallow depth means it cannot properly be considered part of the threatened ecological community. The forest is restricted to waters less than 8 m deep (due to restricted habitat availability and light availability).

Question 2: Will the changes to the Blackmans Bay wastewater discharge have a detrimental impact on the M. pyrifera forest at Blackmans Bay? To answer this question it is important to place the current proposal in context. There has been a sewage discharge associated with the Blackmans Bay STP for decades. Prior to 2010 sewage was discharged just below low tide mark at the shoreline. This discharge performed poorly with regard to effluent dilution, caused some alteration to marine ecological communities near the shoreline and posed a risk to bathing water quality. However, it was recognized that nutrients from the discharge were likely a factor in the persistence of Macroscystis pyrifera near the outfall. The previous discharge did not appear to have any deleterious impact on the giant kelp. In 2010 a new outfall was installed 600 m offshore in 13 m water depth, incorporating a multiport diffuser to achieve effluent dilutions in excess of 100:1 and to remove the risk posed to bathing water quality. The new outfall included three ports within the existing M. pyrifera forest to maintain a supply of nutrients into the kelp bed. While flow from the ports is adjustable, since commissioning the ports have been operating at full capacity. A dye-study conducted to evaluate performance of the outfall in 2010 showed the ports providing a steady flow of nutrient-rich effluent into the kelp bed (Figure 6). Observations and satellite images (Table 1) show that the kelp bed has remained intact since installation of the new outfall, though there have been seasonal and interannual variations in its density. It was most recently visible in aerial images in October 2013, three years after commissioning of the new outfall. A survey in October 2014 found substantial abundance of giant kelp to both the north and south of the outfall. Since commissioning of the offshore outfall in 2010, large numbers of giant kelp plants have colonized the outfall pipeline between around 1 m and 6 m depth.

Figure 6 Fluorosceine dye dispersing through the Macrocystis pyrifera canopy - 2010

Implications of the project for Giant Kelp The upgrade to the Blackmans Bay STP will involve an increase to volumes treated at the plant (wastewater currently treated at Margate and Electrona will be diverted to Blackmans Bay). The treatment plant upgrade will significantly improve nutrient removal. As a result the nutrient loads released to the Derwent Estuary, and into the giant kelp forest, will be less than half the present loads. The current arrangement does not appear to be having any deleterious impacts on the giant kelp bed. Increased nutrient availability due to the sewage discharge is an accepted factor in Macrocystis persistence at the site. Increases to the flow of effluent from the outfall will not be detrimental to the Macrocystis. The current outfall diffuser achieves a high dilution whereby salinity or nutrient changes caused by the outfall cannot be detected beyond 15 m from the diffuser. Increased flow may mean this area of reduced salinity extends to 20 m from the diffuser – still several hundred metres offshore from the Macrocystis forest. The

ports that discharge into the Macrocystis forest may cause some localized salinity reduction, but no detrimental impacts have been documented at current flow rates. Warming seawater temperatures and decreased nutrient availability associated with warming ocean temperatures and reduced frequency of ingress of sub-Antarctic waters onto the south east Australian coast are seen as the key threats to persistence of Giant Kelp Marine Forests. These threats are regional by their nature. Intrusion of cold water from the ocean into the Derwent Estuary is an important driver of ecosystem productivity in the region – intrusion of oceanic waters is the major source of nitrogen for the lower Derwent Estuary (State of the Derwent Estuary - 2009). While point source pollution (such as wastewater) is also recognized as a threat, sewage effluent is also recognized as containing nutrients that can sustain kelp forests. The main threat from wastewater discharge is reduction of light availability through introduction of suspended solids. This threat is not considered relevant to the Blackmans Bay situation: Giant Kelp in the region is limited by habitat availability to water less than 8 m deep and the effluent is low in suspended solids. Ambient water quality may also be important – there may not be sufficient water clarity for algae like Giant Kelp beyond 8 m depth. Nevertheless, it is important that suspended solids loads are maintained at their currently low levels. The discussion above shows that the proposed changes to the volume of wastewater discharged at Blackmans Bay will not have a detrimental impact on M. pyrifera. A reduction in nutrient load is unlikely to be detrimental to M. pyrifera as their main nutrient source is intrusion of oceanic waters. Nevertheless the supply of nutrients into the kelp forest may be managed by adjusting flow from the ‘fertiliser’ ports. Conclusion Based on the analysis in this report, the Macrocystis pyrifera community near the Blackman’s Bay outfall does not constitute a protected “Giant Kelp Marine Forest”. Nitrogen discharges are to decrease, but the outfall includes three ports that can be adjusted as desired to manage the nutrient input to the kelp forest at Blackmans Bay. Thus it is concluded that the proposed upgrade of the Blackmans Bay STP will not have a “significant detrimental impact on the ecological community”? On this basis, it was decided that the string kelp is not a reason to refer the upgrade project for consideration under the EPBC Act.

Documents

Report to TasWater - EPA Tasmania · of the EPA Development Permit, issued in December 2008). This report presents the results of water quality monitoring since 2007. The infauna