The relationship between aerators and microcystin : a comparison between two ponds

Abstract

Increasing concentrations of nutrients in aquatic ecosystems are resulting more instances of cyanobacterial harmful algal blooms (cyanoHABs). Agricultural and nutrient runoff has contributed greatly to this phenomenon. Nitrogen (N) and phosphorus (P) are the two main nutrients that fertilize algae, leading to increased algal biomass. Microcystin is a common toxin produced by cyanobacteria, which is known to have adverse effects on humans and wildlife. Aeration has been used as a tool to control cyanoHABs, primarily by increasing dissolved oxygen (DO) content throughout the water column to prevent sediment release containing various elements ((P), Iron (Fe), Ammonium (NH4+)) and creating hydrology conditions that are unfavorable to cyanobacteria. The use and effects of aerators have been studied to see how effective they are in controlling HABs and often, there are conflicting results. The objective of this work is to shed more light on the impact aeration can have on influencing microcystin production. To test this, nutrient addition experiments were conducted in Missouri at Crow Pond, a non-aerated pond, and Stephen's Lake, an aerated pond. Nutrient amendments of nitrate (NO3-), P, NH4+, urea and an addition containing all the treatments were added to the lake water. P was added to all the samples excluding the control to ensure P would not be a limiting nutrient. Lake water was collected into one L cubitainers and was incubated for nine days to allow for the growth of phytoplankton. Along with microcystin and chlorophyll-a, the concentrations of the nutrient additions were analyzed. Analytics suggest there is positive relationship between chl-a and microcystin. Microcystin values got as high as 30 [mu]g L-1 for Crow Pond, but did not exceed 1 [mu]g L-1 in Stephens Lake. Aeration appeared to have a positive effect in decreasing microcystin. This experiment will add more insights and perspectives to the role aerators play in alternating water chemistry that may either perpetuate or alleviate the effects of cyanoHABs.