Comparison of flow and chemical data collected at the principal inlet and at the outlets of Lake Ellynman urban lake in the Chicago metropolitan are--shows that detention storage alters the discharge and the quality of urban runoff. Peak water discharge and variation in the concentration of constituents transported by the runoff are usually reduced. Mass-balance relations based on comparison of measured constituent loads at the inlet and the outlets show that the lake is very efficient in trapping suspended solids, suspended sediment, and sediment-associated metals. Calculated trap efficiencies for many dissolved constituents were negative. However, negative efficiencies appear to be influenced mostly by insufficient sampling in winter. Trap efficiencies for nitrogen and phosphorus are intermediate to those determined for other constituents.
Solids accumulate on the lake bottom as organic-rich muds that reduce lake storage and cover potential habitat for aquatic organisms. Lake sediments, particularly fine-grained sediments, have elevated concentrations of metals associated with them. Several organic compounds, not detected in inlet- or outlet-water samples, were detected in a lake-sediment sample collected near the inlet.
Concentrations of many constituents dissolved in lake water are seasonally cyclic, with annual concentration peaks occurring during the winter. Establishment and maintenance of desirable benthic invertebrate and fish populations appear to be inhibited by sediment deposition.
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USGS Numbered Series
Relations between quality of urban runoff and quality of Lake Ellyn at Glen Ellyn, Illinois