Influence of upstream impoundment prevalence on downstream harmful algal concentrations and microcystin toxin levels

Abstract:

In recent years, an abundance of cyanobacterial harmful algal blooms worldwide can be attributed to a variety of factors including rising water temperatures and higher nutrient levels, often from human waste or agricultural runoff. Although not all cyanobacteria are harmful, certain kinds produce dangerous toxins, such as microcystin, which are harmful to humans, animals, and other aquatic organisms. Predicting the location within a watershed where these blooms may occur has often focused on lakes or other slow moving impounded waters, with less research in faster flowing in-stream waters where blooms historically been less abundant. In recent years, blooms in flowing water have also begun to be observed locally in Hudson Valley watersheds, and improved abilities to predict which locations within the free flowing watersheds may be most at-risk is needed. In this study, we aim to help improve this predictive ability by testing the hypothesis that cyanobacteria and toxin levels increase as the number of upstream water impoundments also increases. We theorize these upstream water impoundments serve as “nurseries” needed for “seeding” downstream waterways, and may have a stronger ability to predict the locations of elevated in-stream cyanobacteria and toxin levels in flowing watershed systems – more than other common in-stream drivers, such as: water temperature, nutrient concentrations (e.g., nitrate), flow velocity, or turbidity. To do this, water samples from varying locations in the Wallkill watershed were analyzed for cyanobacteria concentrations and microcystin levels via spectral fluorometry and microcystin-focused ADDA Elisa tests. GIS analysis of aerial imagery and data from in-stream water quality and flow measurements provided the ability to assess how these cyanobacteria and toxin concentrations changed as the number of upstream impoundments and other common drivers varied throughout the watershed.