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Stream Chemistry and Ecology:

Stream-chemistry studies were designed to measure how natural factors and human activities affect water quality. Eight drainage basins representing the dominant hydrologic and land-use settings in the study unit were selected for the stream-chemistry network (basic and intensive sites). Seasonal variations in stream chemistry were measured for a range of streamflows; intensive sites were sampled more frequently than basic sites. Samples were collected at 30 sites in the northwestern part of the study unit after heavy spring rains to determine concentrations of agrichemicals in runoff . During summer low-flow conditions, streamwater quality was assessed at 30 sites representing a gradient of agricultural to urban land use . Treated and untreated drinking water samples were collected to assess pesticide concentrations in a water-supply reservoir (East Fork Lake).

Fish tissue and bed sediment was analyzed for environmental contaminants at each stream-chemistry site. Surveys of fish, benthic invertebrates, algae, and stream habitat were done one to four times to assess aquatic community status. Multiple-reach surveys were done at two sites; reaches ranged 200 to 500 meters. Periphyton, phytoplankton, chlorophyll, and streambed sediment samples were collected to compare concentrations of nutrients, algae, and various hydrophobic contaminants along a gradient of agricultural to urban land use. Water, streambed sediment, and sportfish fillet samples were analyzed for mercury and methylmercury at eight stream-chemistry sites.

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