Water Quality
ESI
insoluble
Stream Water
Suspended solids or
sediment
Particles settle out
soluble
Total Dissolved Solids
(TDS)
Mostly salts - ions
Mass after collecting by
filtration
Evaporate water after
filtering, determine mass of
residue
Cause of turbidity or
cloudiness of stream water
TDS by conductivity since
common solids are ions
Suspended Sediment
Does suspended sediment vary with stream discharge?
Susquehanna River at Conowingo Dam, MD
6/95 - 12/00
1400
Suspended
Sediment, mg/L
1200
1000
800
mean
600
400
200
0
0
150000
300000
450000
600000
Discharge, cfs
Data from http://va.water.usgs.gov/chesbay/RIMP/conc.html
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
Suspended Sediment
Depth of Visibility (inches)
Wades in until
70
his feet
60
disappear!
Bernie Fowler Sneaker Index for Patuxent River
goal
50
40
30
20
10
0
Late 1980’s
s
s
8
9
0
0' 60' 98
9 8 19 9
5
1
1
19
19
19
91
19
92
19
93
19
95 996 997 998 999 000 001 002
19
1
1
1
1
2
2
2
Year
94
Late 1990’s
The GOAL
Source: www.mdp.state.md.us/info/patux.htm
Turbidity and Light Penetration
What is the biological importance
of light penetration to submerged
aquatic vegetation (SAV)?
As turbidity increases, light penetration decreases.
SAV
How has the area of SAV’s in the Bay region varied?
Recovery of bay grasses has occurred!
http://www.dnr.state.md.us/bay/sav/past_present.html
The importance of bay grasses
Disperse wave energy, decrease turbidity and erosion
Provide food and shelter for many organisms
Produce O2 by photosynthesis
Absorb nutrients from the water
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
drinking water
rivers
seawater
<10 mg/L
<500 mg/L
100 – 2000 mg/L
35,000 mg/L
Water Temperature
How does temperature vary over a year?
2000
Temperature (deg C)
30
2001
2002
25
20
15
10
5
0
0
3
6
9
12
15
18
21
24
27
30
33
Time in months
http://www.dnr.state.md.us/bay/conditions/le11.html
36
Dissolved oxygen (DO)
anoxic
0
1
mg O2/L water
2
3
4
hypoxic
Severely
stressful
or
lethal
5
6
7
8
oxic
Stressful
Healthy
Required by higher organisms!
9
10
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)
Solubility, mg/L
How does the solubility change when temperature increases?
Is this your prediction?
Temperature, oC
Now consider both the dissolved oxygen and
temperature data over an annual cycle.
Shephardstown on Potomac River
30
15
25
12
20
9
15
6
10
5
3
0
0
0
1
2
3
4
5
6
7
8
9
10
11
12
Dissolved Oxygen
Temperature
How does the solubility change when temperature increases?
13
Time in months
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
14
Dissolved Oxygen
12
10
8
6
4
2
0
0
5
10
15
20
25
30
Temperature
DO is an indirect function of temperature.
Dissolved Oxygen in the
Chesapeake Bay
Monthly for 1998
mg O2/L
August levels for
1984 to 1998
Images from http://noaa.chesapeakebay.net/data/interp1.htm
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.
acid rain (NOx, SOx)
pH of 4.2 - 4.4 in
Washington DC area
pH
0-14 scale for the chemists
2
3
4
5
acidic
(H+) > (OH-)
normal rain (CO2)
pH = 5.3 – 5.7
6
7
8
neutral @ 25oC
(H+) = (OH-)
distilled water
fish populations
drop off pH < 6
and to zero pH < 5
9
10
11
basic or alkaline
(H+) < (OH-)
natural
waters pH =
6.5 - 8.5
12
Nutrients
• nitrate (NO3-) – very soluble
• phosphate (PO4-3) – soluble at low levels
• part of TDS
• cause excessive biological growth, which
consumes DO
Nutrient Sources in the Environment
phosphorus/phosphates
nitrogen/nitrates
Banned in Bay
watershed
fertilizers
acid rain
detergents
animal feedlots
wastewater
phosphate rock
Not found in
Bay watershed
sources of both nutrients
Judging Water Quality Using
Macroinvertebrate Organisms
Organism Tolerance
to Environmental Stress
in Bottom Sediments
POOR
high
medium
low
FAIR
GOOD
Wide-range tolerance
Intermediate tolerance
Clean water
only
Water quality
Increasing species diversity