Cyanobacterial harmful algal blooms (cyanoHABs) are increasing in frequency worldwide. CyanoHABs can produce toxins (e.g., microcystin), which can be a contaminant in recreational and drinking water reservoirs. Reservoirs have been increasing worldwide, highlighting the importance of understanding their biogeochemical processes. Dissolved organic matter (DOM) is a reactive and readily available source of nitrogen (N) and carbon (C) for microbes in aquatic systems, however, the relationships between DOM and cyanoHABs remain relatively unexplored in agricultural reservoirs. Our primary objective is to determine if an increase in allochthonous DOM leads to an increase in autochthonous DOM during a summer cyanobacterial bloom event in a warm monomictic agricultural reservoir. Water samples were collected two to three times per week from June 21st until October 5th, 2018 and analyzed for algal biomass and community composition, DOM quality and quantity. A variety of spectral parameters were used to determine DOM quality. One cyanobacterial bloom event was detected on July 16th. Maximum microcystin concentration for the sampling period was 0.68 [mu]gL-1 which is well under the EPA recommended recreational limit (8 [mu]gL-1). Dissolved organic carbon (DOC) concentrations were positively correlated with high amounts of terrestrial DOM. DOC concentrations and a350 also correlated positively with microcystin concentrations. Specific UV absorbance at 254nm (SUVA254) correlated positively with Chl-a (r=0.37, p=0.033). Our findings indicate that high DOM quantity has a significant relationship to microcystin concentration, which has negative implications for recreation and drinking water quality.Kyra M. Flora, Ruchi Bhattacharya, and Rebecca L. North (School of Natural Resources, University of Missouri, Columbia
