William J. Rose

Long‐Term Hydrologic and Biogeoehemieal Responses of a Soft Water Seepage Lake in North Central Wisconsin

Hydrologic and chemical budgets were determined for the period October 1980 through September 1988 for Vandercook Lake, a 43-ha soft water seepage lake located in predominantly sandy outwash in northern Wisconsin. The 1951–1980 mean annual precipitation for the lake, based on nearby National Weather Service (NWS) stations, was 825 mm; volume-weighted pH of bulk atmospheric deposition during the 8-year study averaged 4.7. From October 1980 through September 1983, annual precipitation was 108% of the 30-year NWS average, annual recharge was 144% of the 8-year study period average, and annual groundwater inflow to the lake ranged from 5 to 9% of the total inflow. From October 1986 through September 1988, annual precipitation was 90% of the NWS average, annual recharge was 30% of the study period average, and the lake received no groundwater inflow. During the study, the lake changed from a system whose buffering mechanism was significantly influenced by mineral weathering in inflowing groundwater to one dominated by in-lake sulfate reduction. The functional differences exhibited by this lake during the 8 years of study demonstrate the tenuousness with which conclusions based on shorter-term studies of similar systems must be considered.

Response of calcareous Nagawicka Lake, Wisconsin, to changes in phosphorus loading

Abstract Nagawicka Lake is a 400-ha, phosphorus (P)-limited, calcareous lake (hardness of 300 mg/L CaCO3) in Wisconsin. Because of concern over potential degradation in water quality associated with urban development in the watershed, a study was conducted to determine the effects of past and future changes in P loading on the lakes water quality through the use of empirical eutrophication models. Six existing empirical P models consistently overestimated total P (TP) concentrations in the lake by a factor of about 2 over a range in external P loading because the models do not account for the unique properties of calcareous lakes: co-precipitation of P with calcite and negligible release of P from the deep sediments. Confirmation of the calcite mechanism was proven by analysis of sediment cores. Once the results were adjusted for the consistent biases, other conventional empirical models fairly accurately predicted the measured chlorophyll a concentrations (CHL) and Secchi depths in the lake. The models, adjusted for the consistent overestimation of TP, were then used to predict the effects of increases and decreases in P loading. Total P and CHL were predicted to decrease or increase by a % similar to the % change in P loading to the lake; however, these relations may become very nonlinear with increases in P loading >100%. Because the natural buffering capacity resists eutrophication caused by P loading, roughly twice the P loading can be permitted in oligotrophic calcareous lakes than in noncalcareous lakes before eutrophication thresholds are exceeded.

Water Quality, Hydrology, and Simulated Response to Changes in Phosphorus Loading of Butternut Lake, Price and Ashland Counties, Wisconsin, with Special Emphasis on the Effects of Internal Phosphorus Loading in a Polymictic Lake

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