Of Small Streams and Great Lakes: Integrating Tributaries to Understand the Ecology and Biogeochemistry of Lake Superior

Lake Superior receives inputs from approximately 2,800 tributaries that provide nutrients and dissolved organic matter (DOM) to the nearshore zone of this oligotrophic lake. Here, we review the magnitude and timing of tributary export and plume formation in Lake Superior, how these patterns and interactions may shift with global change, and how emerging technologies can be used to better characterize tributary-lake linkages. Peak tributary export occurs during snowmelt-driven spring freshets, with additional pulses during rain-driven storms. Instream processing and transformation of nitrogen, phosphorus, and dissolved organic carbon (DOC) can be rapid but varies seasonally in magnitude. Tributary plumes with elevated DOC concentration, higher turbidity, and distinct DOM character can be detected in the nearshore during times of high runoff, but plumes can be quickly transported and diluted by in-lake currents and mixing. Understanding the variability in size and load of these tributary plumes, how they are transported within the lake, and how long they persist may be best addressed with environmental sensors and remote sensing using autonomous and unmanned vehicles. The connections between Lake Superior and its tributaries are vulnerable to climate change, and understanding and predicting future changes to these valuable freshwater resources will require a nuanced and detailed consideration of tributary inputs and interactions in time and space.