In this project, we use paleolimnological techniques to reconstruct the trophic and sedimentation history of Horse and Lotus Lakes (Polk County, WI). Both lakes currently have marginal to poor water quality and are the subject of local and state concerns to develop management plans that include an understanding of presettlement conditions, management targets, and historical lake response to landuse and past management. Piston and overlapping Livingston cores were collected fi·om each lake; cores were lead-21 0 dated, and sediments were analyzed for changes in magneticsusceptibility, loss-on-ignition, and diatom community composition. Cores from both lakes show an increase in sedimentation rate beginning in the early 1900s, with a more rapid rate of increase in the most recent 10 to 20 years. In both lakes, samples that date prior to European settlement have a higher percentage of benthic diatoms, indicating higher water clarity. The more recent core sections in each lake show a shift to an increased abundance of planktonic diatoms, indicating more turbid and eutrophic conditions in modern times. Both cores also show increases in diatom-inferred TP values at the time of European settlement. However, quantitative TP reconstructions in shallow lakes dominated by small Fragilaria species can be problematic.

The Polk County Land and Water Resources Department is continuing a comprehensive study of Lotus Lake. Phases 3 and 4 for Lotus Lake coordinate with similar projects for Horse Lake (LPL-1117/1118-07). These phases utilize various public education elements, including results-sharing, newsletter mailings, presentations, and report publication and will provide management recommendations. Phase 3 project activities include: water quality monitoring (mid-lake, inflow, outflow, and turnover); tributary flow monitoring; groundwater monitoring; algal community assessment and toxin analyses; zooplankton community assessment; macrophyte mapping; macroinvertebrate assessment; and coarse woody habitat inventory. Phase 4 project activities include: paleolimnological core collection and full-core analysis. Land use history will be compared with trophic reconstructions inferred from the sediment core to determine the impact and timing of watershed disturbances on water quality. This information will assist with determination of stable ecosystem state and development of water quality goals. The final deliverables for this project will be a compilation of results from the various studies and a comprehensive report with management recommendations.