Changes in water quality of Michigan streams near urban areas, 1973-84

Monthly water-quality monitoring of streams was begun by Michigan Department of Natural Resources in 1973 to (1) determine temporal and spatial variability, (2) detect long-term trends, and (3) describe changes in water quality near urban areas. This report provides a statistical analysis and summary of data collected from 1973 through 1984. Concentrations and discharges of nine commonly measured water-quality constituents and specific conductance are examined. Twenty-three sites on inland streams (streams draining basins wholly within Michigan) and 20 sites on Detroit River are discussed. The changes in water quality in 9 rivers near 12 urban areas in Michigan's southern Lower Peninsula and the relation between streamflow and selected waterquality characteristics, including phosphorus, chloride, sulfate, nitrogen, specific conductance, and solid residues are described.

Results show that the median dissolved-solids concentration in Clinton River downstream from Pontiac exceed Michigan's 1986 stream water-quality standard. Among inland streams, constituent concentrations and discharges generally were greatest in Saginaw River and least in Grand River upstream from Jackson. Upstream from Detroit, constituent concentrations in Detroit River did not differ appreciably across the Windmill Point Transect; downstream from Detroit, at the Fermi Transect across Detroit River, most constituent concentrations were higher near the American and Canadian shorelines. Among urban areas, greatest changes in constituent concentrations occurred in the Grand River near Jackson, in the Clinton River near Pontiac, and in the Tittabawassee River near Midland; the least changes in constituent concentrations occurred in the Saginaw River near Saginaw, in Detroit River near Detroit and the Kalamazoo River near Battle Creek. Greatest changes in constituent discharges occurred in the Detroit River near the Detroit area; the least occurred in the Chippewa River near Mount Pleasant.

Of the 230 regressions between streamflow and constituent concentrations in inland streams, about 73 percent were significant at the 5-percent level. The degree of the correlation and nature of the relation varied among sites and constituents. Generally, higher streamflows were associated with lower concentrations. Changes in streamflow and changes in constituent concentrations near urban areas were correlated in 57 percent of the 120 analyses. Generally, higher changes in streamflow were associated with lower changes in concentrations.