Measurable microcystin in Ozark streams was rare during summer 2018 baseflow conditions

Accelerated eutrophication due to human activity has been linked to an increase in the occurrence of cyanobacteria in freshwater systems. The purpose of this study was to document the occurrence of microcystin, a common cyanotoxin, within northwest Arkansas streams. Twenty streams were sampled from May through October 2018, and water and periphyton samples were analyzed for microcystin and chlorophyll-a (CHL-a). Mean microcystin concentrations in water samples were low across sites, ranging from < 0.10 to 0.21 μg L⁻¹. Mean microcystin in the periphyton across sites ranged from 2.6 to 9.9 μg m⁻² and were within values observed in the literature. All microcystin concentrations measured in these Ozark streams were well below the current USEPA recreational guidelines of 8.0 μg L⁻¹ and the drinking water guidelines of 0.3 μg L⁻¹ for infants and 1.6 μg L⁻¹ for adults.