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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