1. Factors Affecting Water Quality
Chapter 6

2. Introduction
Many types of pollutants and many factors affecting the toxic effect of those pollutants
Factors include
physicochemical properties
Mode and time of exposure
Environmental factors
Interactions among toxicants in a mixture
Biological factors
Nutritional factors

3. Chemical Characterization of Water
I. Structure
Chemical Structure
Inorganic
Cations Anions
Ca++ Mg++ Na (K+) HCO-3 SO Cl- PO NO3-
bicarbonate
Normal environmental concentrations
mg/L v. low (<1)
Note: because NO3- is not limited in freshwater  casual about disposal (i.e. Spring River)
limited in freshwater
limited in oceans

4. Carbonate-bicarbonate equilibrium
Organic
Carbonate-bicarbonate equilibrium
Normal range
pH is the master variable but pH of aquatic system is intricately linked to the relative abundance of carbonate, bicarbonate and carbon dioxide. 

5. Hardness Degree of difficulty in precipitating soap
Based on combined concentrations of calcium, magnesium and other cations
Can have great effect of toxicity (increasing hard = decreasing toxicity)
Units – CaCO32- mg/L (accounts for all metals which are +2)
Typical values (as CaCO32-)
< mg/L soft
mg/L moderately hard
> “ hard
Carbonate vs. Non-carbonate hardness
Note: heat can change hardness -> forms scale on boilers, coffee pots

6. Alkalinity
Measurement of the capacity to accept protons (esp. H+)  called buffering capacity
Units also expressed as CaCO32-
Really measures CaCO32- (bicarbonate)
Alkalinity directly correlated with hardness in many systems
Soft water = low alkalinity
Hard water = high “ (but exceptions  AMD)
Measured by titrating with H2SO4  drives bicarbonate to CO2
Rule of thumb  water of low hardness, low alkalinity (headwaters) = higher effect of toxicants (especially true of metals, acid)

7. Headwaters of the Hudson River
Alkalinity (con’t)
Rule of thumb: water of low hardness, low alkalinity (headwaters) = higher effect of toxicants (especially true of metals, acid)
Photo by R. Grippo
Headwaters of the Hudson River

8. Oxygen
Amount of oxygen that can be dissolved in water (solubility) is highly dependent on temperature
Note: atmosphere = 210,000 mg/L but ~10 mg/L in most water so O2 is is usually in very short supply in water

9. Note: streams of same order have to come together to form next order
Physical structure
Stream order – rough numerical sequence that allows characterization of a stream 1
springs 2 3 4 6
headwaters
Mid-reach
6-12 = river
Lower reach
Note: streams of same order have to come together to form next order
Note: headwaters generally straight, starts to wander (form bends = sinuosity) as hit order Sinuosity is a function of slope, hardness of substrate (mud<silt<gravel)
Hard substrate = low sinuosity
Soft substrate = high sinuosity

10. II. Function
- function always based on structure  can infer function from structure
Rivers
River Continuum Concept
- RCC based on two concepts
From headwaters to mouth = continuous change (gradient) in physical conditions within a stream system
Gradient produces a continuous and predictable change in the make-up of the assemblages of organisms within a stream system

11. Upper reaches ---------------- mid-reach --------------------- lower reach
(headwater to 3rd order) (order 4 to 6) (>6)
Continuous and predictable changes in biotic assemblages
Use bioassessment (sample, enumerate organisms)  if do not find what is predicted  problem!!

12. B. Lakes systems are dynamic but slow
Pollution stays put (reason why sewage treatment plants are built on rivers, not lakes
More likely to
Serve a pollution sinks (bioremediation slow if lake is deep (e.g. Great Lakes)
Can be highly influenced by aerial deposition

13. C. Groundwater Pollutants usually introduced as leachate from
contaminated soils
Dependent on
physical/chemical
properties of soils
in addition to water