An investigation of the relationships between phytoplankton community composition, cyanotoxins, and water quality parameters in Missouri reservoirs
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Cyanotoxins are potent toxins that are produced by specific cyanobacteria. They have become a significant concern for the water quality and human health in freshwater ecosystems, including reservoirs. In Missouri, where aquatic ecosystems encounter the dual challenge of agricultural nutrient runoff and climate change, the variability of cyanotoxins presents a major problem. Previous studies have investigated the relationship between phytoplankton and cyanotoxins in Missouri reservoirs but found no significant relationships. Microcystin (MIC) and cylindrospermopsin (CYL) are the most studied toxins, while very few studies are available on anatoxin (ANA) and saxitoxin (SAX). As a result, the objective of this study was to investigate the relationship between phytoplankton community composition, cyanotoxins, and water quality parameters in Missouri reservoirs. Specifically, we seek to determine if the abundance of potentially toxigenic (PTOX) cyanobacteria correlates with cyanotoxins and if the same factors influencing cyanobacterial abundance and MIC concentrations can predict other cyanotoxins such as CYL, ANA, and SAX. The research questions were: (1) Are there any significant correlations between PTOX cyanobacteria and cyanotoxins in Missouri reservoirs? (2) Does this relationship differ by type of toxin (i.e., MIC, CYL, ANA, and SAX)? (3) What are the main drivers of cyanotoxins in Missouri reservoirs? The data for this study were collected for 6 years (2017 - 2022) from 16 reservoirs selected across a trophic gradient. We found significantly higher levels of CYL in oligotrophic reservoirs compared to more eutrophied reservoirs. We also observe significant relationships between cyanotoxins and PTOX cyanobacteria, but the relationship varies depending on the toxin type (i.e., MIC, CYL, ANA, SAX). Chlorophyll-a (Chl-a) has a significantly positive relationship with MIC, ANA, and SAX whereas its relationship with CYL is significantly negative. Phytoplankton abundance is negatively related to CYL and positively related to SAX, and both MIC and SAX are positively correlated with phytoplankton biovolume. There are variations in cyanotoxin types across trophic gradients. This study represents a significant step forward in understanding cyanotoxin drivers in Midwest US reservoirs.
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M.S.