By Will Bartsch
Today is the beginning of a twelve day effort to thoroughly characterize the benthic community of Lake Superior’s Chequamegon Bay. The benthic zone is the lowest level of a body of water, including sediment at the bottom of a lake or ocean. The invertebrate organisms that live on the bottom of lakes and oceans form an important part of the lake’s food web. Because they all have varying degrees of sensitivity to environmental degradation, the presence or absence of certain species can help us determine the condition of the entire aquatic system.
At 8:00 am this morning, the Research Vessel Lake Explorer II cruised out of the Duluth Superior harbor on its way to the Chequamegon Bay. The Lake Explorer II is a 90′ long EPA vessel that is based in Duluth, MN. It can accommodate up to eleven people. The six crew members and scientists aboard will reach their destination after approximately six hours of cruising.
By the time the Lake Explorer II arrives at the Chequamegon Bay, three other scientists in the 26’ Research Vessel Praire Sounder will have already started collecting Ponar samples of the sediment. A Ponar is a heavy, metal sampling device that is lowered from the boat into the soft sediment below. Its jaws automatically close upon retrieval and a sample is brought to the surface. During this survey we will take close to 300 Ponar samples and an additional dozen benthic sled samples (I’ll tell you more about the sled in a later post; stay tuned).
On this twelve day sampling journey, we will travel all around the Chequamegon Bay to get samples that will give us an accurate characterization of the entire benthic community. To choose these sampling locations – or sample points – we used a method called Generalized Random Tessellation Stratified (GRTS). This method uses a spatially-balanced, random selection technique to ensure good areal coverage of the study location and minimize the chance of bias that can come from oversampling particular habitat types.
Throughout this project, my colleague Julie Barker and I will be chronicling our efforts in the field and writing a blog post every few days. We hope that you enjoy the posts and learn more about the methods used to characterize aquatic environments.
About the Author: Will Bartsch is an ORISE fellow with EPA’s Midcontinent Ecology Division, which is part of the Agency’s Office of Research and Development. He primarily analyzes data collected as part of the National Coastal Condition Assessment survey, and he works on early detection methods for invasive species in Great Lakes coastal embayments.