Characterization of Water Quality, Nutrients, and Algae Under Ice in the St. Louis River Estuary 2013 - 2018

This data package includes physical, chemical, and biological measurements characterizing under-ice and early open-water conditions in the St. Louis River Estuary—a freshwater estuary located at the western tip of Lake Superior. Data were collected annually during February and March from 2013 to 2018, with additional sampling in May and June 2018. Sampling sites were distributed across the estuary to assess spatial variability and investigate potential hypoxia. Field data include in situ water quality measurements (e.g., temperature, dissolved oxygen, conductivity, pH), light penetration, and snow and ice thickness. Laboratory analyses were conducted on collected samples to quantify nutrients, suspended sediment, and chlorophyll-a concentrations. Phytoplankton samples were collected using plankton nets and preserved in Lugol’s solution for taxonomic identification. Sampling and analysis followed EPA and USGS Standard Methods where applicable to ensure compatibility with other environmental datasets. This dataset fills a critical gap in winter limnology by providing rare observations of under-ice estuarine conditions. It supports ecological research, environmental monitoring, and comparative studies of seasonal dynamics, nutrient cycling, and primary producer communities in Great Lakes coastal wetlands and other northern freshwater systems. The dataset is complete and not ongoing, although data acquired through the System-wide Monitoring Program at the Lake Superior National Estuarine Research Reserve is complementary and ongoing.