Feb 17, 2017

Effect of Daphnia biomass on total phosphorus levels: A microcosm study

Tanner Swenson '17

There was a significant difference in Square Lake (Washington County, MN) in the total amounts of phosphorus during a three-year moratorium on stocking trout (Hembre, 2016). This was supported by research to be directly altering to the abundance of a large-bodied zooplankton Daphnia, which are heavily preyed on by the size-selective rainbow trout. Daphnia maintain lower nitrogen to phosphorus ratio than other zooplankton (e.g., copepods) and will not excrete the phosphorus, recycling it back into the environment. We looked to study the effect of Daphnia on total phosphorus (TP) levels and expected the TP to diminish as the biomass of the Daphnia increased. To test our hypothesis we put varying densities of Daphnia pulicaria in 4-liter tanks with algae and filtered lake water, maintaining the zooplankton at low, medium and high densities, with controls of just lake water and lake water with algae. We found that after 14 days of running our experiment the treatments began to differentiate in biomass totals, but we did not see any significant differences in phosphorus levels between treatments, except for our water-only control. Our algae with water control showed a similar decline in the TP to the trials with Daphnia, which we can most likely attribute to the algae binding together and becoming hard to keep suspended, minimizing the amount of phosphorus we could evaluate.

Health Risk Evaluation for Microcystin Biomagnification in Aquatic Food Webs

Julia Albrecht '17

Increased occurrence of toxic phytoplankton blooms fueled by anthropogenic pollution of aquatic environments presents significant global health risks. Consequently, cyanobacteria are the most notable phytoplankton organisms associated with eutrophication of freshwater systems. Cyanobacteria have the ability to form toxic metabolites known as cyanotoxins. The most commonly occurring cyanotoxin in most aquatic systems, including those in Minnesota, is microcystin (MC). These toxins are highly stable in water and resistant to boiling, thereby posing a major threat to water and food if not monitored properly. As a result of contaminated waters, bioaccumulation of MC through aquatic food webs poses potential risks for species at higher trophic levels, including piscivorous fish. The ability of various invertebrates to accumulate MC can cause a transfer of harmful toxins through the food web to more sensitive species. Moreover, MC may have the ability to indirectly transfer to individuals consuming freshwater fish in larger quantities. Until now, more attention has been focused towards human uptake of MC through drinking water than to bioaccumulation in aquatic organisms. Fish can represent a significant and sometimes dominant source of MC to consumers, particularly where individuals are consuming fish species from freshwater lakes containing elevated MC concentrations. In a nation that spends roughly 42 billion dollars a year on recreational fishing, the need for such data is crucial. This presentation will focus on research from Joan Hardy, Art Johnson, Kathy Hamel and Ellen Preece on Cyanotoxin bioaccumulation in freshwater fish, Washington State, USA. As the environment continues to be impacted, it is important to identify bioaccumulation patterns of MC at varying trophic states to understand the impact of exposure on human health from cyanotoxins through fish consumption.