Relationship of nonpoint-source discharges, streamflow, and water quality in the Galena River basin, Wisconsin

Four small tributaries of the Galena River Madden Branch tributary, Pats Creek, Apple River, and Madden Branch that drain nonpoint agricultural sources and that receive no significant point-source discharges were monitored from October 1980 through September 1982 to determine water quality.

Streamflow in the tributaries during the 1981 water year was about 25 percent below normal and, during the 1982 water year, about 38 percent above normal. Precipitation in the basin was near the 30-year normal during the 2-year study period.

The yields of suspended solids, volatile solids, total phosphorus, and ammonia plus organic nitrogen during the 1982 water year were at least twice the yields of the 1981 water year. The greatest suspended-solids yield was 740 tons per square mile from Madden Branch tributary. The greatest yields of volatile solids (70.8 tons per square mile), total phosphorus (2,289 pounds per square mile), and ammonia plus organic nitrogen (8,529 pounds per square mile), were from Madden Branch. The lowest annual yields of suspended solids, volatile solids, total phosphorus, and ammonia plus organic nitrogen for both years were from the Apple River.

Concentrations of many constituents were very high during runoff periods. The highest concentration of ammonia nitrogen 12 mg/L (milligrams per liter) measured during the study period was in Pats Creek during spring runoff, February 21, 1982. The highest concentration of total phosphorus, 17 mg/L, was measured in Madden Branch tributary during a storm on July 10, 1982. The storm of July 10 exceeded a 100-year recurrence interval of a 1-hour storm intensity for the area.

Dissolved-oxygen concentration sags were noted at three of the monitoring stations during surface runoff. Although not all observed sags caused instream dissolved oxygen to fall to critical levels, one such decline was associated with a fishkill at Pats Creek. In that instance, highly oxidizable material with a biochemical-oxygen demand of 27 milligrams per liter was sampled at peak discharge; 16 hours later, the dissolved oxygen had dropped to 1.2 milligrams per liter.

Concentrations of many constituents exceeded State and Federal water-quality standards. Dissolved-oxygen concentrations were lower than the minimum State standard on numerous occasions at all sites except Madden Branch tributary. Most phosphorus concentrations during periods of surface runoff at all sites exceeded U.S. Environmental Protection Agency standards. Concentrations of ammonia nitrogen potentially exceeded the Wisconsin State standard only once at Pats Creek.