Benthic Cyanobacteria Production and Abundance in the Tidal Occoquan River



Mohney, Samantha

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The freshwater Tidal Potomac River has an extensive history of eutrophication and planktonic cyanobacterial harmful algal bloom (cHAB) occurrence. Improvements and upgrades to local sewage treatment facilities have helped to stem nutrient loading from wastewater effluent released into the river. Today, planktonic cHAB occurrence has dramatically decreased due to reduced nutrient concentrations, resulting in increased water transparency. Anecdotal evidence suggests the improved transparency has aided in the appearance and proliferation of the toxic benthic cyanobacteria species, Lyngbya wollei, within the Potomac River and its tributaries. Limited resources and available information on benthic cHABs, coupled with increased concern regarding their environmental and public health impacts, necessitates an in-depth study of the seasonality, magnitude, and growth dynamics of benthic algae production. This thesis investigates the seasonal progression of L. wollei biomass, variation between measured parameters, and the relationship between submerged aquatic vegetation (SAV) and benthic mats within the Tidal Occoquan River, a tributary of the Tidal Potomac River. Analysis of L. wollei samples, collected from July through October 2020, show a significant upward trend for chlorophyll a and SAV measurements, indicating an upsurge in biomass and growth. Chlorophyll a and SAV demonstrate a strong correlation (p = 0.003), suggesting that the presence of Vallisneria americana, with its vertical growth form actually promotes the growth of L. wollei in contrast to results from other SAV species. Results provide a framework for future research, while highlighting the significant relationship between L. wollei and SAV presence, in addition to emphasizing the need for subsequent studies.



Benthic, Cyanobacteria, Lyngbya wollei, Harmful algal bloom