Publication Date


Document Type


Committee Members

Silvia E. Newell, Ph.D. (Advisor); Stephen J. Jacquemin, Ph.D. (Committee Member); Mark J. McCarthy, Ph.D. (Committee Member)

Degree Name

Master of Science (MS)


Grand Lake St. Marys is the largest (52 km2) inland lake in Ohio, USA, and receives high nutrient loadings (90th percentile for total nitrogen (N) and phosphorus (P) concentrations in the USA) from a watershed dominated by agricultural row-crops and livestock production. Eutrophication has led to cyanobacterial harmful algal blooms, dominated by non-N2 fixing Planktothrix, that persist year-round, including in winter months. In summer 2020 and 2021, multiple treatments using P-binding agents within a 3.5 ha swimming enclosure were conducted to remove excess dissolved P from the water column. The objective of this study was to examine pre-and-post treatment biogeochemical and physicochemical conditions in contrast to the surrounding lake, in addition to evaluating anomalous conditions that led to removal of the lake's no-contact advisory for the first time in 12 years. In four out of five treatments across both years, total P and chlorophyll-a (chl-a) values were higher three weeks post-treatment within the treated area, indicating failures of the treatments to reduce biomass long-term. The harsh winter of 2020-2021, along with a dry Spring 2021, led to large, temporary reductions in algal biomass and toxicity and sediment oxygen demand, and allowed for denitrifying bacteria to remove excess N from the water column. However, chl-a levels returned to > 300 µg L-1 by July 2021. This study, along with previous studies regarding failures of treatments using P-binding agents to reduce algal biomass and toxicity long-term, provide further evidence that reducing watershed N and P loads is likely the only long-term solution to mitigating eutrophication and cyanobacteria blooms in GLSM.

Page Count


Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded