INFLUENCE OF PRECIPITATION ON THE SPATIAL DEVELOPMENT OF ALGAE IN A LARGE EUTROPHIC LAKE

The upper Midwestern U.S. is experiencing more intense rain events, leading to greater runoff events, and potentially increasing the risk of eutrophication in lakes. Despite advancements provided by buoys, they do not capture spatial variability of algal blooms. Algal blooms on lake surfaces are notoriously heterogenous and can be underestimated or missed if monitoring efforts occur at a single location. We conducted a comprehensive study in Lake Mendota, WI, a eutrophic lake, to investigate the influence of precipitation events on nutrient inputs, and chlorophyll a concentration. We compared chlorophyll fluorescence collected through time at a centralized buoy and spatially across the entire lake surface using a mobile sampling boat on 45 occasions in 2016 and 2022. While precipitation events were hypothesized to enhance nutrient influx and stimulate algal growth, we observed increases, decreases, and no changes in chlorophyll a concentrations, following different rain events. Notably, the two major inlets exhibited little or no positive correlation in N:P ratios or algal concentrations, highlighting effects of different land uses on nutrient dynamics. Moreover, the buoy failed to capture the full range of chlorophyll concentrations in the lake during two relatively low production years. This counterintuitive result underscores the complexity of lake ecosystems and emphasizes the need for spatially comprehensive monitoring approaches, especially given ongoing changes in precipitation trends increasing the risk of eutrophication and the heterogeneity of bloom development.

Primary Presenter: David Ortiz, University of Wisconsin - Madison (dortiz4@wisc.edu)

Authors:

Emily Stanley, Center for Limnology  (ehstanley@wisc.edu)

Luke Loken, USGS  (lloken@usgs.gov)

Steve Carpenter, Center for Limnology  (steve.carpenter@wisc.edu)

Sean Bertalot, University of Wyoming  (sbertalo@uwyo.edu)

Ally Kundinger, Center for Limnology  (akundinger@wisc.edu)