Load, not loading: External nutrient loading impact on cyanobacteria and cyanotoxins

Abstract

Eutrophication is the process in which excessive nutrients enter a body of water resulting in a rapid growth in population and density of phytoplankton. One type of phytoplankton made more concentrated during eutrophication is cyanobacteria. Some cyanobacteria can produce cyanotoxins. Cyanotoxins have many negative impacts on both aquatic ecosystems and human health. The objective of this research is to determine the effects chronic and episodic nutrient loading have on cyanobacteria and the resultant cyanotoxin concentrations. We simulated chronic loading by adding small amounts of nitrogen (N) and phosphorus (P) over a six-day period in a nutrient simulation experiment. Episodic loading was simulated by adding a large spike of nutrients to lake water on only the first day of the nine-day experiment. At the end of the experiment, we analyzed sample water for pH, microcystin and cylindrospermopsin concentrations, chlorophyll-a and phycocyanin as proxies for phytoplankton and cyanobacteria respectively, N and P concentrations, and suspended solids. Our experiment showed that there was no significant differences found between treatments testing episodic and chronic loading in the production of cyanobacteria or cyanotoxins for any of the test sites. Additions of N and P increased the nutrient load causing cyanobacteria and cyanotoxin production, however the form of nutrient loading was not significant. This research is relevant to better understand how cyanobacteria respond to different nutrient loading mechanisms and the possible effects climate change and the associated increases in episodic nutrient loading could have on bodies of freshwater.