Impact of Extreme Rain Events on Lake Superior’s Biogeochemistry

Abstract:

The frequency and intensity of extreme weather events is increasing as a result of climate change. This includes the Great Lakes region, which contains 20% of the world’s available freshwater resources. Lake Superior is the world’s largest freshwater lake by surface area, containing 10% of the world’s surface freshwater and is a highly oligotrophic ecosystem. Two “500 year” events have occurred in the lake’s watershed within the past 4 years. Each raised the level of the world’s largest lake by a measurable amount (e.g. 10 cm for the 2012 event) and resulted in plumes of runoff visible for weeks in satellite images. Previous research indicates that large concentrations of nutrients are present in plume-impacted waters but that the effect of nutrients delivered to the lake in extreme runoff events are complex. They appear sensitive to relative amounts and locations of CDOM, suspended sediment and nutrient peaks in the runoff plume. In this project we are investigating the relative area of the lake impacted by these extreme-event plumes and relating this data to in-situ water column data collected just after each of these extreme events. Our goal is to understand how these plumes affect nutrient dynamics in the lake. We use the combination of satellite and wet chemical data to estimate nutrient (N and P) inputs from each event and in situ chlorophyll data as a measure of ecosystem response to these inputs.