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A Brief History of Time…in Severn Sound
• Severn Sound was Area of Concern – Eutrophication was major factor
• Remedial Action Plan implemented – Emphasis on phosphorus load reductions
• Delisting achieved in 2003 – Under condition that monitoring continue to
prevent regressing
• Severn Sound Environmental Association continues to monitor water quality in open waters and tributaries – New challenges: impacts of climate change,
invasive species, continued landscape changes
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Severn Sound
Watershed
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Toronto ~2 hrs
/PV
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Key Map
Sampling Program
• Biweekly sampling during ice free period (May-Oct)
• Temperature, conductivity, dissolved oxygen and pH profiles - 1m depth intervals (now higher res.)
• Secchi depth - measure of water clarity
• Integrated water samples analyzed for trophic status indicators: nutrients (TP, TNO3, TNH3, TKN), chlorophyll a and algal community (biovolume)
• Also analyzed for metals, ions, basic chemistry
• Zooplankton collected for community analysis (density, biomass, length)
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Trends in Trophic Status - TP RAP targets
- Significant trend based on Mann-Kendall trend test (p<0.05)
t= -0.70 t= -0.72
t= -0.60 t= -0.71
t= -0.77
t= -0.65
t= -0.61
t= -0.54
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Seasonality - TP
7 of 23 Biweek Dates: 9 Apr22-May5 11 May20-Jun2 13 Jun17-Jun30
15 Jul15-Jul28 17 Aug12-Aug25 19 Sep9-Sep22 21 Oct7-Oct20
Trends in Trophic Status – TNH3
- Significant trend based on Mann-Kendall trend test (p<0.05)
t= -0.30
t=0.39
t=0.46
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Trends in Trophic Status – TNO3
- Significant trend based on Mann-Kendall trend test (p<0.05)
t=0.49 t=0.46 t=0.43 t=0.39
t=0.42 t= -0.49 t=0.32 t= -0.31
t= -0.39
t= -0.44 t= -0.50
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Seasonality – TNO3
10 of 23 Biweek Dates: 9 Apr22-May5 11 May20-Jun2 13 Jun17-Jun30
15 Jul15-Jul28 17 Aug12-Aug25 19 Sep9-Sep22 21 Oct7-Oct20
Trends in Trophic Status - TKN
- Significant trend based on Mann-Kendall trend test (p<0.05)
t= -0.57 t= -0.67 t= -0.56 t= -0.33
t= -0.44
t= -0.31
t= -0.32
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Trends in Trophic Status – Chl a RAP targets
- Significant trend based on Mann-Kendall trend test (p<0.05)
t= -0.43 t= -0.58 t= -0.52 t= -0.44
t= -0.41 t= -0.50
t= -0.46 t= -0.27 t= -0.67
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Trends in Trophic Status – Tot Ann Biovol
- Significant trend based on Mann-Kendall trend test (p<0.05)
t= -0.64 t= -0.56 t= -0.46 t= -0.56
t= -0.53
t= -0.48 t= -0.46 t= 0.40
t= -0.54
t= 0.35
t= 0.61 t= 0.42, p=0.06 t= 0.58
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Trends in Trophic Status – Algae Community
Microcystis Dolichospermum
• Significant reductions in overall biovolume
• Genus-specific shifts – e.g. Microcystis vs
Dolichospermum
• Decreases in most eutrophic indicator taxa – e.g. Ceratium, Stephanodiscus,
Tabellaria, Aulacoseira, Cryptomonas
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Trends in Trophic Status - SDV RAP targets
- Significant trend based on Mann-Kendall trend test (p<0.05)
t=0.37 t=0.40 t=0.34
t=0.47 t=0.21 t= -0.35
t= -0.39
t=0.27
t= -0.72 t= -0.72
t=0.20, p=0.06
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Driving Factors – Trends & Station
Differences
• Invasive species (dreissenid mussels – regime shift in 1994/5)
• Phosphorus load reductions (WWTPs, other P control strategies)
• Seasonality (effect on within-year variability)
• Changes in lab methods (esp. TP, chl a)
• Station depth and location (prox. to Severn R.), urban influence
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Life “Post-Dreissenids” • Clarity is most obvious marker of filter feeding
effect from dreissenids
– Step trend analysis pinpointed 1994/1995 as time period for regime shift
• Analyzing “Post” trends (1994/5-2017):
– TP no change almost everywhere; ↓ at P1
– NO3 ↓ almost everywhere but conc. higher than “Pre”; no change at P1-3, PS, NB
– TKN no change almost everywhere; ↓ at P1-3
– Chla ↓ almost everywhere; no change at M5, PM1, HH sites (data limitation)
– Biovolume no change in west, ↑ in east, HH sites
– Clarity ↓ almost everywhere; no change at P1-3, M5, BS, PS, NB
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Phosphorus Load Reductions • Many strategies implemented
during RAP years
• P control activities now fall under
different programs (DWSP, muni.)
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Total STP loading to Penetanguishene
Bay vs Biovolume at Pen Bay Stations
Changes in Lab Methods
• 1969-2005, samples sent to MOECC Rexdale – +/− 6.8 μg/L (0–20 μg/L range)
– +/− 10.2 μg/L (21–40 μg/L range)
• In mid-2000 on, samples sent to MOECC Dorset
• Provide low level analysis, duplicates – +/−0.7 μg/L
• Overlap – 2000-2005; lots of scatter around 1:1 line
• Confidence intervals around annual mean decreased since samples sent to DESC – some of year to year change was due to analytical variability
t = 0.51
p << 0.001
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Influence of Depth on Trophic
Status
Deep 14-20 m Moderate 5-13 m Shallow 0-4.5 m
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Station Location – West to East
Urban influence
GBay Severn R GBay Severn R
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Summary • Trophic indicators show an improvement in overall conditions
since ’73 – Parts of Severn Sound were eutrophic, now meso- to
oligotrophic
• Important driving factors include dreissenids, P loads, change in lab methods, depth, location, urban influence
• Trends since dreissenids show we’re in a period of higher nitrate (although declining), generally decreasing water clarity despite decreasing algae
• Mostly meeting RAP targets post-dreissenids except in some years for: – SDV at HH, NB, PM1, PM2, SB, BS (plants)
– CHLA at NB, SB
– TP at SB, P1, PM1, BS
• Future focus needed on – Refining monitoring program for efficiency/new areas
– Investigating conditions in shallow nearshore (0-2 m)
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Acknowledgements • Funding support from our member municipalities
• COA funding (federal/provincial partnership)
• MOECC (lab analysis, use of historical data, technical
advice)
• Fabulous staff (past and present) at SSEA
@SSEA_SSRAP
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