Cyanobacteria overgrowth can lead to cyanobacterial harmful algal blooms (cyanoHABs), which are expected to increase in frequency and intensity in midwest reservoirs on account of the worsening effects of climate change and nutrient pollution. CyanoHABs can lead to many detrimental ecological effects, in addition to harmful public health effects from the production of cyanotoxins. Many studies suggest that high nutrient influxes and warm temperatures promote cyanobacterial growth in the summer months, however, less is known regarding biologic activity and factors that promote growth in winter months. This study aims to investigate how varying environmental conditions affect microcystin production in the hypereutrophic Ohio reservoir, Grand Lake Saint Marys. This study uses a 2x2x2 factorial study design where temperature (ambient, elevated by + 3°C), nutrients (ambient, +N+P nutrient addition), and light (low light, high light) are manipulated over the months of February and March. Our results indicate that cyanobacterial taxa are indeed biologically active in the winter months and are capable of toxin production. Additionally, the results indicate that light, temperature, and nutrient variations are influential in toxin production in Grand Lake Saint Marys but the effects vary by month.

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