Restoration of an urban lake ecosystem: Water quality, point-source pollution, and non-point source pollution

Nearly 35% of monitored lakes and streams in the United States are too polluted to support fishing and swimming. Urban aquatic ecosystems, important natural resources for city dwellers- particularly the economically disadvantaged- are especially vulnerable to habitat degradation, nonpoint source pollution, and point-source pollution. We are investigating restoration of an urban lake ecosystem adjacent to the Clean Water Plant of The City of Wyoming, Michigan. The lake, altered by extensive gravel mining, is juxtaposed to a railway, interstate highway, and several industrial plants. To support recreational and educational activities, the city seeks to maintain the quality of the watershed, but pollutants might enter through surface runoff (highway and railway) or inlets linked to the Grand River and nearby industrial sites. We investigated patterns between precipitation, linked to surface runoff, and measures of water quality (fecal coliform bacteria, BOD, total suspended solids, phosphorus, nitrates and nitrites, chloride, bromide, sulfate, flouride, temperature, and pH) at six sites within the lake, including sites close to the Grand River and stormwater inlets. Fecal coliform was generally below limits acceptable for full body contact (i.e., swimming). Water quality varied among sampling sites, but was not affected significantly by precipitation the week preceding sampling. Bromide, chloride, nitrates, and sulfates were highest near the stormwater inflow, which drains industrial sites. Bromide and chloride there sometimes reached concentrations toxic to aquatic organisms.We conclude that industrial point-source pollution, rather than non-point source runoff, is the major threat to the water quality of this urban watershed.