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Eutrophic conditions in lakes and reservoirs in agricultural regions often drive summer blooms of toxic cyanobacteria. Aluminum sulfate (alum) applications are commonly used to control cyanobacteria blooms and restore water quality in eutrophic lakes. However, studies of alum treatments often lack true replication, comparison to reference lakes, or comparison to other restoration techniques, such as an alum and biomanipulation combined or “dual” treatments. Without these comparisons, the variation of treatment response between replicate lakes and restoration techniques remains uncertain. Therefore, I sought to assess how water quality is affected by multiple restoration techniques among geographically proximate (1.4 km2) lakes. I hypothesized that: 1) alum restoration would uniformly improve water quality in replicate lakes via nutrient limitation, and 2) dual treatment restoration would out-perform alum treatment alone due to added top-down mechanisms amplifying the alum-only improvements. Regardless of lake or restoration technique, the phytoplankton community was dominated by cyanobacteria pre- and post-treatment in each lake. Treatment success was highly variable among replicate lakes. I found that trends for overall restoration success were not always representative of average lake condition post-treatment, but were often dominated by extreme response in a few lakes. Fully understanding how similar ecosystems are affected by alum will help determine if lake alum treatments alone can consistently combat algal toxins and other symptoms of eutrophication. Overall, the alum treatment effectively controlled nutrient levels, however, if restoration goals are more biological, adding biomanipulation as a dual treatment may enhance lake restoration success.
Advisor: Amy Burgin