Hydrology and water quality of Whitewater and Rice lakes in southeastern Wisconsin, 1990-91

The hydrology and water quality of Whitewater and Rice Lakes was studied by the U.S. Geological Survey during November 15, 1990November 14, 1991, in cooperation with the Whitewater-Rice Lakes Management District, Walworth County, Wis. Whitewater and Rice Lakes are small, shallow lakes; surface areas are 697 and 162 acres and mean depths are 8.4 feet and 5.8 feet, respectively. Although both lakes have surface outlets, water levels were below the dam crests during the study, and no water left the lake through the outlets. The drainage basin of Whitewater Lake is 10.9 square miles and that of Rice Lake is 11.8 square miles; but, because of large amounts of depressional areas, only 1.4 square miles and 0.2 square mile, respectively, contribute surface runoff to the lakes. Whitewater Lake is an artificial lake created in 1947 by the damming of three smaller lakes. Rice Lake is an artificial lake created in 1954 by the damming of Whitewater Creek, which drains Whitewater Lake. Maintaining the lake levels at the elevations of their dam crests has been difficult since the lakes were created. For most years, water levels were below the lakes' dam crests.

Ground water, precipitation, and evaporation are important components in the hydrologic budgets of the lakes. For Whitewater Lake, ground water was the dominant source of water, accounting for 57 percent of the inflow budget; precipitation accounted for 26 percent. Ground water also dominated the outflow, accounting for 81 percent of the outflow budget. The remaining 19 percent of the outflow budget was evaporation. For Rice Lake, precipitation was the dominant source of water, accounting for 88 percent of the inflow budget; ground water accounted for 8 percent. Evaporation dominated the outflow budget, at 70 percent, whereas ground water accounted for 30 percent.

The external phosphorus budget for Whitewater Lake showed that shoreline drainage was the largest source of phosphorus to the lake42 percent of the total input of 558 pounds. Other sources of phosphorus were septic systems, 19 percent of the total; precipitation, 18 percent; a spring inlet at base flow, 13 percent; and ground water, 8 percent. The external phosphorus budget for Rice Lake showed that shoreline drainage also was the largest source of phosphorus to the lake-59 percent of the total input of 63 pounds; other sources were precipitation, 38 percent of the total; and ground water, 3 percent. Application of Vollenweider's phosphorus loading model fairly accurately predicted the lakes' spring turnover phosphorus concentrations and suggested that the external loading of phosphorus would result in mesotrophic to eutrophic conditions for Whitewater Lake and mesotrophic conditions for Rice Lake. Dillon and Rigler's model further suggested additional phosphorus from internal recycling was required to result in the high chlorophyll-a concentrations experienced in both systems during summer. Internal recycling of phosphorus in addition to external loading seems to also cause waterquality problems in both lakes. The amount of phosphorus recycled from the lake sediments was estimated from a mass-balance approach for April 1-November 14, 1991. For Whitewater Lake, the internal load of 582 pounds was slightly greater than the annual external load of 558 pounds. For Rice Lake, the internal load of 295 pounds far exceeded the annual external load of 63 pounds.