Factors Affecting Water Quality Chapter 6 Introduction Many
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Factors Affecting Water Quality Chapter 6
Introduction Ø Many types of pollutants and many factors affecting the toxic effect of those pollutants Ø Factors include l l l physicochemical properties Mode and time of exposure Environmental factors Interactions among toxicants in a mixture Biological factors Nutritional factors
Chemical Characterization of Water I. Structure • Chemical Structure 1. limited in freshwater Inorganic Cations Anions Ca++ Mg++ Na++ (K+) HCO-3 SO 4 - Cl- PO 4 - NO 3 bicarbonate Normal environmental concentrations mg/L 15 8 6 23 120 12 8 v. low (<1) limited in oceans Note: because NO 3 - is not limited in freshwater casual about disposal (i. e. Spring River)
2. Organic Carbonate-bicarbonate equilibrium Normal range p. H is the master variable but p. H of aquatic system is intricately linked to the relative abundance of carbonate, bicarbonate and carbon dioxide.
Hardness Degree of difficulty in precipitating soap Ø Based on combined concentrations of calcium, magnesium and other cations Ø Can have great effect of toxicity (increasing hard = decreasing toxicity) Ø l l Units – Ca. CO 32 - mg/L (accounts for all metals which are +2) Typical values (as Ca. CO 32 -) • • • l <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
Alkalinity Ø Measurement of the capacity to accept protons (esp. H+) called buffering capacity l l l Units also expressed as Ca. CO 32 Really measures Ca. CO 32 - (bicarbonate) Alkalinity directly correlated with hardness in many systems • Soft water = low alkalinity • Hard water = high “ (but exceptions AMD) l l Measured by titrating with H 2 SO 4 drives bicarbonate to CO 2 Rule of thumb water of low hardness, low alkalinity (headwaters) = higher effect of toxicants (especially true of metals, acid)
Alkalinity (con’t) l 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
Oxygen Ø 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 O 2 is is usually in very short supply in water
Physical structure B. Stream order – rough numerical sequence that allows characterization of a stream 1. springs headwaters 1 1 2 Mid-reach 2 Note: streams of same order have to come together to form next order 3 1 3 Lower reach 4 6 -12 = river 6 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
II. Function - function always based on structure can infer function from structure A. Rivers 1. River Continuum Concept - RCC based on two concepts a. b. 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
Upper reaches -------- mid-reach ----------- lower reach (headwater to 3 rd 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!!
B. Lakes l l l 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
C. Groundwater Pollutants usually introduced as leachate from contaminated soils Ø Dependent on physical/chemical properties of soils in addition to water Ø
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