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2 Conceptual Foundations for Water Quality Management
Pages 22-31

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From page 22...
... The goal of an ambient water quality management program is to measure the condition of a waterbody and then determine whether that waterbody is meeting water quality standards. By definition, this process is dependent on the setting of appropriate water quality standards.
From page 23...
... Waterbodies vary greatly in size for example, from a small area such as a mixing zone below a point source discharge on a river to an estuary formed by a major river discharge. Water quality standards themselves consist of two parts: a specific desired use appropriate to the waterbody, termed a designated use, and a criterion that can be measured to establish whether the designated use is being achieved.
From page 24...
... For example, a reproducing trout fishery in downtown Washington, D.C., may be desired, but may not be attainable because of the development history of the area or the altered hydrologic regime of the waterbody. Similarly, designating an area near the outfall of a sewage treatment plant for shellfish harvesting may be desired, but health considerations would designate it as a restricted shellfish harvest water.
From page 25...
... Square 2 includes measures of a water quality parameter such as dissolved oxygen (DO) , pH, nitrogen concentration, suspended sediment, or temperature.
From page 26...
... measure of the biological community as a whole, or a measure of contaminant concentration in fish tissue. In square 1, where the criterion is farther from the designated use, are measures of the pollutant discharge from a treatment plant (e.g., biological oxygen demand, NH3, pathogens, suspended sediments)
From page 27...
... Thus, an ambient nutrient criterion may be set in a small headwater stream to secure a designated use in a downstream estuary, even if there are no localized effects of the nutrients in the small headwater stream. Conversely, a higher fecal coliform criterion that supports only secondary contact recreation may be warranted for a waterbody with little likelihood of being a recreational resource if the fecal load dissipates before the flow reaches an area designated for primary contact recreation.
From page 28...
... to responses similar to models used in hazardous waste risk assessment and many other fields. Stressors include human activities likely to cause impairment, such as the presence of impervious surfaces in a watershed, cultivation of fields too close to the stream, over-irrigation of crops with resulting polluted return flows, the discharge of domestic and industrial effluent into waterbodies, dams and other channelization, introduction of nonindigenous taxa, and overharvesting of fishes.
From page 29...
... Sometimes, models are simple conceptual depictions of the relationships among important variables and indicators of those variables, such as the statement "human activities in a watershed affect water quality including the condition of the river biota." More complicated models can be used to make predictions about the assimilative capacity of a waterbody, the movement of a pollutant from various point and nonpoint sources through a watershed, or the effectiveness of certain best management practices. There are two significant sources of uncertainty in any water quality management program: epistemic and aleatory uncertainty (Stewart, 2000~.
From page 30...
... Although the purpose of water quality modeling will change depending on how close to the designated use the criterion is positioned, the importance of modeling and the inevitable uncertainties of model results remain. CONCLUSIONS AND RECOMMENDATIONS The two major themes of this chapter represent areas in water quality management where science and public policy intersect.
From page 31...
... 3. Expectations for the contribution of "science" to water quality management need to be tempered by an understanding that uncertainty cannot be eliminated.


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