Distribution of Cyanobacteria and Microcystin in Lakes of the US Driven by Combination of Lake, Watershed, and Climate Characteristics
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With increasing concerns about freshwater cyanobacteria blooms, there is a need to identify which waterbodies are at risk for developing these blooms, especially those that produce cyanotoxins. To address this concern, we developed spatial statistical models using the US National Lakes Assessment, a survey with over 3500 spring and summer observations of cyanobacteria abundance and microcystin concentration in lakes across the conterminous US. We combined these observations with other nationally available data to model which lake, watershed, and climate factors best explain the presence of harmful cyanobacterial blooms. We found that both higher cyanobacteria abundance and probability of microcystin detection was associated with higher nitrogen and phosphorus nutrient inputs to the landscape, and lakes with a lower baseflow index, shallower depth, and longer fetch. In both models, nutrient inputs were more strongly associated with blooms in the eastern and central portions of the US compared to the west. Additionally, nitrogen inputs were more strongly associated with higher probability of microcystin in deep lakes compared to shallow lakes. Both models had spatial covariance, indicating there are similarities in lakes that are closer in space beyond that captured by the covariates in the models. Models fit data well with squared correlation coefficient between observed and fitted values for the cyanobacteria abundance of 0.48 and an AUC of 0.92 for the probability of microcystin detection. These models help identify which lakes are more vulnerable to harmful cyanobacteria blooms and can help estimate blooms risk in unobserved locations.