Phytoplankton response to water quality threats in Midwest reservoirs

Abstract

Harmful cyanobacterial blooms and invasive species threaten water quality. These threats are expected to worsen in the future, emphasizing the need for creative management solutions and a thorough understanding of their impacts. The objective of this dissertation is to investigate the influence of light on biomass and community composition of phytoplankton with the hypothesis that light will have an impact, regardless of nutrients and grazing. We investigate a novel geoengineering approach designed to control cyanobacteria by reducing light. We demonstrate that daily application of glacial rock flour, a fine particulate that floats on the water's surface, reduces light by half and results in up to a 78 percent decrease in cyanobacterial biovolume. We also look at the accumulation of microcystin in the tissues of bluegill and largemouth bass. Microcystin is higher in bluegill, likely because they feed from lower trophic levels. It is also higher in spring and decreases throughout the year, suggesting that time of the year might be an important consideration for microcystin fish consumption advisories. We also find that invasive zebra mussels are not causing an increase in water clarity in MO reservoirs like they are in natural, northern latitude lakes. This could be because reservoir conditions are suboptimal for zebra mussels, thus preventing them from reaching high densities. Understanding how aquatic resources have responded to stressors in the past enables us to predict how they will respond to changes in the future.