Effects of the St. Louis River Estuary on Water Quality in Lake Superior

The St. Louis River Estuary (SLRE) is a major source of biological and chemical materials to Lake Superior. The SLRE spans a wide range of biochemical properties and has a long history of impacts from anthropogenic activities. Despite the unique setting of the SLRE and its significant contribution of material to Lake Superior, little is known about the contributions of the estuary or their effects on water quality in the nearshore of Lake Superior. This work characterizes biochemical gradients in the estuary using a 10-year record of water quality data and characterizes differences along a spatial gradient. Preliminary data show significant increasing trends in water temperature and chlorophyll a over time, and a decrease in ammonium, nitrite, and nitrate. Nearly all parameters demonstrate seasonality, which also has important implications for downstream water quality. These findings highlight the importance of considering watershed and lake interactions for lake water quality.