Water Quality of Nagawicka Lake in Response to Hydrologic and Phosphorus Loading
Project Number: 9KB35
Project Chief: Herbert S. Garn
Project Topics:
Cooperators: City of Delafield, Lake Welfare Committee
Period of Project: October 2002–September 2007
Problem
The trophic state of Nagawicka Lake is mesotrophic-borderline eutrophic, and quantified information on actual phosphorus loading sources and rates are not available to accurately evaluate the potential changes in lake condition under increased or decreased loading. Critical information to the City of Delafield, Lake Welfare Committee necessary for the management of Nagawicka Lake is needed to address identified nonpoint-pollution sources and stormwater management. Potential changes in the water quality of Nagawicka Lake due to human activities and development in the watershed, and operation of lake outlet structures to maintain water levels and reduce flooding were identified as issues in the lake-management plan. The effects of increasing development in the watershed and possible resulting increased stormwater runoff and nutrient loading are a concern to residents, the City, and other entities. In order to establish realistic water-quality goals for Nagawicka Lake, accurate nutrient loading estimates are needed to enable water-quality models to be calibrated and used to simulate future response of the lake. With a calibrated model, the lake’s response to incremental increases or decreases in phosphorus loading can be evaluated and used to refine the lake-management plan.
Objectives
This study will quantify the actual phosphorus and sediment loads entering and leaving Nagawicka Lake from the Bark River watershed, and will determine how incoming loads affect lake water quality. The objectives of the proposed project are to:
• quantify the flows, phosphorus and sediment loads entering and leaving Nagawicka Lake;
• determine measured water and phosphorus budgets for Nagawicka Lake, thereby providing a better understanding of the problems and sources of nutrients for developing future lake management actions;
• relate the measured water and contaminant loads to observed and modeled water-quality responses within the Lake; and
• model the response of the Lake to future phosphorus- loading scenarios and to specific management actions aimed at reducing phosphorus loads to Nagawicka Lake.
A better understanding of the hydrologic and phosphorus inputs and potential response of the lake to various management scenarios will enhance the management of Nagawicka Lake.
Approach
The study will consist of gage installation and two years of data collection followed by data analysis and report preparation. Water quality will be sampled six times per year in Nagawicka Lake and water levels will be recorded continuously at a lake gage. To estimate the nutrient loading at the Bark River inlet and outlet, daily streamflow will be measured and samples will be collected by automatic water sampler at the inlet and manually at the outlet. To estimate nutrient loading from other direct tributaries, three miscellaneous sites will also be sampled manually and with siphon samplers. Phosphorus load data at the stream sites will be used to estimate unit-area loads for unmonitored portions of the basin. These measured data, along with other estimates, will be used to develop complete hydrologic and phosphorus budgets for the lake. Concurrent water and phosphorus budgets for the lake and in-lake water-quality data will be used to calibrate WiLMS (Wisconsin Lake Modeling Suite) and used to estimate the response of the lake to various phosphorus-loading scenarios.
Publications and Reports
Garn, H. S., Robertson, D. M., Rose, W. J., Goddard, G. L., and Horwatich, J. A., 2006, Water quality, hydrology, and response to changes in phosphorus loading of Nagawicka Lake, a calcareous lake in Waukesha County, Wisconsin: U.S. Geological Survey Scientific Investigations Report 2006-5273, 41 p.
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