Factors Affecting Water Quality

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 CationsAnions Ca++ Mg++ Na++ (K+) HCO-3 SO4- Cl- PO4- NO3- bicarbonate Normal environmental concentrations mg/L 15 8 6 23 120 12 8 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. 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-) • <5- - 100 mg/L soft • 100 - 200 mg/L moderately hard • >200 “ 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. 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. springs headwaters 1 1 Mid-reach 2 2 3 1 3 Lower reach 6-12 = river 4 6 • Physical structure • Stream order – rough numerical sequence that allows characterization of a stream 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 4-6. 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