Water QualityWater Quality

ESIESI

Stream Water

Mass after collecting by filtration

Evaporate water after filtering, determine mass of residue

TDS by conductivity since common solids are ions

solubleinsoluble

Cause of turbidity or cloudiness of stream water

Suspended solids orsediment

Total Dissolved Solids(TDS)

Mostly salts - ions

Particles settle out

Suspended SedimentDoes suspended sediment vary with stream discharge?

Susquehanna River at Conowingo Dam, MD6/ 95 - 12/ 00

0

200

400

600

800

1000

1200

1400

0 150000 300000 450000 600000

Discharge, cf s

Sus

pend

ed

Sed

imen

t, m

g/L

Data from http://va.water.usgs.gov/chesbay/RIMP/conc.html

mean

Mean discharge 60,000 cfs based on 34 years of data

How can we control suspended sediment?

• Use of silt fence at construction sites

• Settling ponds for stormwater runoff

• Riparian Forest buffers along streams and rivers

• No till/contour plowing agriculture

Bernie Fowler Sneaker I ndex f or Patuxent River

0

10

20

30

40

50

60

70

Year

Dep

th o

f V

isib

ility

(in

ches

)goal

Suspended SedimentWades in until his feet disappear!

Source: www.mdp.state.md.us/info/patux.htm

Late 1980’s

Late 1990’s

The GOAL

Turbidity and Light Penetration

What is the biological importance of light penetration to submerged aquatic vegetation (SAV)?

As turbidity increases, light penetration decreases.

SAV

http://www.dnr.state.md.us/bay/sav/past_present.html

Recovery of bay grasses has occurred!

How has the area of SAV’s in the Bay region varied?

The importance of bay grasses

Produce O2 by photosynthesis

Disperse wave energy, decrease turbidity and erosion

Absorb nutrients from the water

Provide food and shelter for many organisms

http://www.dnr.state.md.us/bay/sav/importance.html

Total Dissolved Solids (TDS)

• Mostly dissolved mineral salts as ions (cause of conductivity)

Na+ Cl- Ca++ SO4-2

• Organic compounds

Examples: rain <10 mg/Ldrinking water <500 mg/Lrivers 100 – 2000 mg/Lseawater 35,000 mg/L

Water Temperature How does temperature vary over a year?

0

5

10

15

20

25

30

0 3 6 9 12 15 18 21 24 27 30 33 36

Time in months

Tem

pera

ture

(deg

C)

200220012000

http://www.dnr.state.md.us/bay/conditions/le11.html

Dissolved oxygen (DO)

0 1 2 3 4 5 6 7 8 9 10

mg O2/L water

oxichypoxic

anoxic

StressfulSeverely stressful

orlethal

Healthy

Required by higher organisms!

What is the source of dissolved oxygen in stream water?

• Oxygen, O2, from air (79%N2/20%O2) dissolves in water – added by turbulence in stream flow

• Produced by photosynthesis by organisms such as algae

CO2 + H2O (CH2O)x + O2

Solubility of oxygen gas (O2)

How does the solubility change when temperature increases?

Temperature, oC

Solu

bili

ty,

mg/L

Is this your prediction?

Shephardstown on Potomac River

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Time in months

Tem

pera

ture

0

3

6

9

12

15

Dissolved O

xygen

Now consider both the dissolved oxygen and temperature data over an annual cycle.

Mean values from http://www.dnr.state.md.us/bay/conditions/pot1830.html

How does the solubility change when temperature increases?

Dissolved oxygen as a function of temperature

0

2

4

6

8

10

12

14

0 5 10 15 20 25 30

Temperature

Dis

solv

ed O

xyg

en

How does the solubility change when temperature increases?

DO is an indirect function of temperature.

Dissolved Oxygen in the Chesapeake Bay

Monthly for 1998

August levels for 1984 to 1998

Images from http://noaa.chesapeakebay.net/data/interp1.htm

mg O2/L

Oxygen Demand

• Substances that use oxygen in reactions:organic compounds + O2 products

• STELLA dissolved oxygen model

• Lower the dissolved oxygen of streams.

• Once reaction is over, DO levels can recover.

pH

2 3 4 5 6 7 8 9 10 11 12

neutral @ 25oC(H+) = (OH-)

distilled water

acidic(H+) > (OH-)

basic or alkaline(H+) < (OH-)

natural waters pH = 6.5 - 8.5

normal rain (CO2)pH = 5.3 – 5.7

acid rain (NOx, SOx)pH of 4.2 - 4.4 in Washington DC area

0-14 scale for the chemists

fish populationsdrop off pH < 6 and to zero pH < 5

Nutrients

• nitrate (NO3-) – very soluble

• phosphate (PO4-3) – soluble at low

levels

• part of TDS

• cause excessive biological growth, which consumes DO

phosphorus/phosphatesnitrogen/nitrates

fertilizers

acid rain

wastewater

animal feedlots

detergents

phosphate rock

Nutrient Sources in the Environment

Banned in Bay watershed

Not found in Bay watershed

sources of both nutrients

Judging Water Quality Using

Macroinvertebrate Organismsin Bottom Sediments

high

medium

low

Water qualityIncreasing species diversity

POOR FAIR GOOD

Org

an

ism

Tole

ran

ceto

En

vir

onm

en

tal S

tress

Wide-range tolerance

Intermediate tolerance

Clean wateronly