PS 1-16
Reducing algal blooms in Dream Lake: Algal and zooplankton seasonal dynamics indicate response to food web manipulation
Many freshwater ecosystems are experiencing increased algal bloom formation due to cultural eutrophication, or increased nutrient inputs from the surrounding watershed. Dream Lake, a small water body located in Brown Co, WI, has frequent algal blooms and decreased recreational and aesthetic value. Starting in 2012 and continuing through 2014, we are implementing a combined top-down trophic cascade by adding piscivores; i.e. largemouth bass (Micropterus salmoides) and bottom-up reduction of fertilizer inputs approach to reduce algal blooms. We hypothesize that by combining both top-down and bottom-up remediation techniques, algal bloom frequency will decline, recreational and aesthetic value will increase and sport fishing will be enhanced. Baseline pre-manipulation data were collected from May - September 2012, 106 fingerling largemouth bass were stocked in October 2012, and post-manipulation data were collected from May-September 2013. Secchi depth and zooplankton were obtained weekly. Zooplankton samples were counted, measured, and identified to species.
Results/Conclusions
Percent change in water transparency during the warm-water period from 2012-2013 was 11.23% ± 10.95 (N = 15). Chlorophyll a did not differ significantly during the entire warm-water period between years (p = 0.237), but weekly chlorophyll levels differed significantly between August of 2012-2013 (p < 0.05). Zooplankton biomass was dominated by small bodied species in both years. Total zooplankton biomass did not differ between 2012 and 2013 (p = 0.074), but biomass of Bosmina longirostris and Leptodiaptomus minutus was significantly greater in 2013 (p = 0.016, p = 0.028, respectively) and Diaphanosoma birgei biomass was significantly lower (p = 0.008) in 2013. Average length of Bosmina longirostris and Leptodiaptomus minutus was significantly greater in 2013 (p < 0.001, p = 0.001, respectively), and length of Diaphanosoma birgei was significantly lower in 2013 (p = 0.047). Change in August algal biomass post-manipulation, and an increase in the biomass and length of the two dominant zooplanktors indicate that Dream Lake may be beginning to respond to the top-down manipulation.