U.S. Department of the Interior U.S. Geological Survey Hydrology and Water Quality of Geneva Lake, Walworth County, Wisconsin Water-Resources Investigations Report 02-4039 Prepared in cooperation with the Geneva Lake Environmental Agency Wisconsin Department of Natural Resources science for a chanoina world Hydrology and Water Quality of Geneva Lake, Walworth County, Wisconsin By Dale M. Robertson, Gerald L. Goddard, Elizabeth A, Mergener, William J. Rose, and Paul J. Garrison U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 02-4039 Prepared in cooperation with the Geneva Lake Environmental Agency and the Wisconsin Department of Natural Resources Middleton, Wisconsin 2002 uses science for a changing world Cover photo: Geneva Lake Area Chamber of Commerce U.S. DEPARTMENT OF THE INTERIOR Gale A. Norton, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Government. For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 8505 Research Way Box 25286 Middleton, Wl 53562-3586 Denver, CO 80225-0286 CONTENTS Abstract.........................................................................................................................................................^ 1 Introduction.........................................................................................._^ 1 Geneva Lake and its watershed............................................................................................................................................. 3 Methods................................................................................................................................................................................. 4 Lake samph'ng..................................................................................................................^ 4 Tributary sampling...................................................................................................................................................... 5 Lake-sediment sampling............................................................................................................................................. 6 Surficial sediments............................................................................................................................................ 6 Sediment-core analyses..................................................................................................................................... 6 Design of a long-term sampling strategy.............................................................................................................................. 7 Climatic conditions during the study period......................................................................................................................... 11 Water quality of Geneva Lake............................................................................................................................................... 11 Water temperature and ice cover................................................................................................................................. 13 Dissolved oxygen........................................................................................................................................................ 17 Water clarity................................................................................................................................................................ 17 Nutrient concentrations............................................................................................................................................... 17 Chlorophylls concentrations...................................................................................................................................... 19 Trophic State Indices................................................................................................................................................... 19 Plankton ....................................................................................................................................................^ 21 Phytoplankton................................................................................................................................................... 21 Zooplankton...................................................................................................................................................... 23 Chemical composition of the surficial sediment................................................................................................................... 24 Water quality of and loading from tributaries to Geneva Lake............................................................................................. 24 Hydrologic budget................................................................................................................................................................. 32 Change in storage........................................................................................................................................................ 32 Precipitation................................................................................................................................................................ 32 Surface-water inflow................................................................................................................................................... 33 Base flow........................................................................................................................................................... 33 Surface runoff.................................................................................................................................................... 38 Surface-water outflow................................................................................................................................................. 38 Evaporation and ground-water inflow and outflow .................................................................................................... 38 Summary of hydrologic budget................................................................................................................................... 42 Phosphorus budget................................................................................................................................................................ 42 Precipitation................................................................................................................................................................ 42 Surface-water inflow................................................................................................................................................... 44 Buttons Bay Creek............................................................................................................................................ 44 Base-flow contributions from unmonitored areas............................................................................................. 44 Surface runoff.................................................................................................................................................... 46 Total tributary loading....................................................................................................................................... 46 Allocation of tributary loading.......................................................................................................................... 47 Ground water............................................................................................................................................................... 47 Septic systems............................................................................................................................................................. 47 Waterfowl.................................................................................................................................................................... 49 Internal release from hypolimnetic sediments ............................................................................................................ 49 Summary of phosphorus budget................................................................................................................................. 50 Nutrient-reduction scenarios................................................................................................................................................. 51 Historical changes in ice cover and water quality................................................................................................................. 53 Ice cover...................................................................................................................................................................... 53 Measured changes in water quality............................................................................................................................. 55 Water temperature............................................................................................................................................. 55 Dissolved oxygen.............................................................................................................................................