By KATERI SALK
I’ve had the privilege this year to study the largest freshwater body in the world, the Laurentian Great Lakes. Together, the five lakes make up nearly 20% of the Earth’s fresh water and supply 40 million people with drinking water. Being so large and depended on by so many people, the Great Lakes have unique ecology and environmental issues that are fascinating for aquatic scientists to study. The research I conducted this summer has, in many ways, explored two extremes within the Great Lakes. The projects I worked on took me to Lake Superior (the clearest, deepest, and most surrounded by wilderness) and Lake Erie (the shallowest, most populous, and most impacted by algae blooms).
What ties these dissimilar environments together is a common question: how is the biology of the system interacting with a key element for life, nitrogen? Which organisms are using nitrogen, and what happens to it after organisms take it in or transform it chemically? In Sandusky Bay in Lake Erie, a great deal of nitrogen runoff flows from the Sandusky River into the bay. Much of this nitrogen is lost from the water before it reaches the main part of Lake Erie, so we want to know which organisms are responsible for this reduction and how it might be impacting the species of toxic algae that grow in Sandusky Bay vs. the main part of the lake. In collaboration with a team from Bowling Green State University, I’ve been tracking the microbes that remove dissolved nitrogen from the water and release it to the atmosphere. We hope to be able to make connections between toxic algae growth and the trends in nutrients, including nitrogen, in Lake Erie.
While Lake Erie struggles with pea-green water that’s packed with algae, Lake Superior is crystal clear, mainly because of a lack of phosphorus, a nutrient that supports algal growth. Sandusky Bay displays boom-and-bust trends in nitrogen concentrations, whereas Lake Superior has a more constant, moderate amount of nitrogen that is left behind in the water because algal growth is limited by phosphorus. One possible commonality between the two environments is that microbial communities could be converting dissolved nitrogen to a chemical form called nitrous oxide, a greenhouse gas that contributes to climate change. For both projects, I am investigating which communities of microbes are producing nitrous oxide and how much of it is released to the atmosphere.
As different as these two projects were in terms of the environment, scientific operations were quite different as well. In Sandusky Bay, the depth of the water is just a few meters deep. This means that research can be done from a motorboat, and water can be collected directly into a bottle from the side of the boat. Even sediment can be gathered by means of a long tube, a gasket that pulls suction, and a little muscle.
Lake Superior science is a different beast. This research was done aboard a research ship, the R/V Blue Heron (its sister ship is the one from The Perfect Storm, to give you an idea of its size and the high seas it can handle). Scientists work and live on the ship for several days on end, and there is a full-time crew that runs the ship while research goes on. Water and sediment collections must be done with heavy equipment that is deployed by motorized winches, and hard hats are worn on deck.
This research campaign was part of a training program run by the Large Lakes Observatory at the University of Minnesota. In addition to the research I conducted on board the ship, I also was trained on how to lead scientific operations aboard a research vessel. This meant that I got to experience the wide variety of the capabilities of the ship: collecting water and sediment, deploying large nets to collect tiny swimming animals (zooplankton), using remotely operated vehicles to explore beneath the surface, and setting off in a small boat to collect samples in shallow water.
Just as the school kids are back in class, it’s time for me to shift out of summer mode. I plan to spend my fall semester in the laboratory, analyzing the samples that have been collected from the Great Lakes over the summertime. Many thanks to the Rose Fellowship in Water Research, the MSU College of Natural Science, and the MSU Department of Integrative Biology for supporting this research.
Kateri Salk is a Ph.D. student in Integrative Biology and Environmental Science and Policy. She is the first recipient of the Joan Rose Fellowship in Water Research.