MICROCYSTIN DYNAMICS IN LAKE ERIE LINKED TO NITRATE CONCENTRATIONS
Microcystin toxicity has been a primary concern related to harmful algal blooms in Lake Erie. Considering the previously described links between nitrogen status and microcystin gene regulation, I hypothesized that the nitrogen form and concentration in Lake Erie might determine microcystin toxicity. Using data collected by the Ohio Environmental Protection Agency at 25 sites in Western Lake Erie between 2011 and 2015, microcystin concentrations were compared with nutrient concentrations to explore possible relationships. This data set, which contains nearly 350 observations, confirmed a basic relationship between algal biomass (as Chlorophyll a) and microcystin concentration (Pearson’s r = 0.67, p < 0.001). When examining nitrogen form and concentration, microcystin was only present when ammonium was below analytical detection levels, except in a very small subset of samples. The highest microcystin concentrations were observed when ammonium was absent and nitrate was still detectable. In examining temporal trends at several sites in Lake Erie a repeatable pattern emerged. A brief window between the drawdown of ammonium concentrations to undetectable levels and in the presence of detectable levels of nitrate generated the highest concentrations of microcystin. While microcystin could still be found after nitrate was reduced to below detection, it was generally decreasing in concentration after the disappearance of nitrate. The maximum nitrate concentration at a site explained 55% of the variation in the maximum microcystin concentration. This relationship remained significant when controlling for soluble reactive phosphorus.
Bade, D. L., Kent State University, USA, email@example.com
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