Trends in Anatoxin-a and Microcystin Concentrations in Two Eutrophic Lakes: The Role of Habitat and Season

Abstract

As an undergraduate student participating in the LAKES REU, an interdisciplinary research experience for undergraduates funded by the National Science Foundation (NSF), I got to develop my own research question and work on addressing it over the course of the summer. As an interdisciplinary group, the LAKES team bridges sustainability, psychology, political science, and environmental science to better understand degradation of lake waters and brainstorm solutions to this challenging problem. Lake Menomin, a part of the Red Cedar Watershed that gives the town of Menominee, Wisconsin, its beautiful lakefront, is a great example of how the degradation of lakes impacts the entire community. The lake, covered in ice and adorned with ice fisherman during the cold months of the winter, turns brilliantly green during the summer months, often dissuading recreators and sometimes emitting an odor that can be smelled throughout Menomonie.

An overabundance of blue-green cyanobacteria during the summer months is mostly what you see when faced with this dramatic seasonal color change on Menomonie’s waterfront. For context, cyanobacteria are single-celled organisms that use sunlight to carry out photosynthesis. Cyanobacteria can produce chemicals that are dangerous to humans, including microcystin and anatoxin. Microcystin can cause liver failure at high concentrations, while other impacts continue to be researched. Anatoxin can cause neurological and gastrointestinal symptoms at high concentrations. One difference between the two toxins is that, for microcystin, symptoms typically occur over an extended period. For anatoxin, however, symptoms could be present within minutes of exposure. The presence of cyanobacteria in the water does not necessarily indicate that the water is toxic. The Environmental Protection Agency (EPA) has set limits for microcystin in drinking water and similar recommendations for anatoxin have been made by the World Health Organization (WHO).

With the assistance of my mentor, Nicole Hayes, and the rest of the LAKES team, I eventually decided that I wanted to know more about how lake habitat influences the presence of microcystin and anatoxin. I hypothesized that cyanobacteria that live towards the bottom of the lake which produce anatoxin would be more abundant earlier in the season. I also predicted that cyanobacteria that produce microcystin would be more abundant near the surface of the lake and later in the season. In June and July I went out on the boat to collect data near the lake surface and near lake sediment for Lake Menomin and Lake Tainter. At each site I collected water that we would take back to the lab to determine the amount of cyanobacteria and toxins. All of this was done with lots of help from other students and my faculty mentor.

After the data was analyzed, I found that microcystin levels were above safe drinking water levels at nearly all of the sampling sites in July. However, none of the sites were above recommended microcystin or anatoxin levels in June. Anatoxin was found less frequently in Lake Menomin and Lake Tainter but was detected at several sites near the lake's surface and towards the bottom. One site in Lake Menomin had concerning levels of anatoxin above the limit of detection. Overall, we saw an increase in cyanobacteria at the lake surface later in the summer and higher microcystin levels. I did not find evidence for my hypothesis that anatoxin would be present more in the spring and near the bottom of the lake.

The detection of high levels of microcystin and anatoxin should encourage further monitoring of toxins in the lake. Caution should be exercised when interacting with these lakes. Although the EPA recreational microcystin limit is higher than levels detected during sampling, there is potential for microcystin levels to be above EPA recreational limits. The relationship between habitat and toxin levels in both west-central Wisconsin lakes was not as simple as was predicted at the beginning of the study. Further research on lake habitat and cyanobacteria community is needed to better understand and predict toxin presence.