Identification and Characterization of Phosphorus Composition in Lake Superior and St. Louis River Estuary Sediments Using Phosphorus Nuclear Magnetic Resonance Spectroscopy

Phosphorus has been a contaminant of concern for many freshwater lakes for decades. Excessive bioavailable phosphorus often leads to the eutrophication of a particular body of water. Information on the specific chemical composition of phosphorus in sediment is fundamental to understanding its bioavailability and eutrophication potential to a lake ecosystem. A single-step sodium hydroxide-ethylenediaminetetraacetic acid (NaOH-EDTA) extraction and a phosphorus nuclear magnetic resonance (31P NMR) spectroscopy protocol were developed and subsequently performed on St. Louis River Estuary (SLRE) and Chequamegon Bay (CB) sediment samples. Results show the presence of phosphorus-containing compounds comparable to other oligotrophic waterbodies, and compounds typically detected in sediment samples from eutrophic lakes were not detected in any sample. For the CB samples, as the water depth increased, so did the number of peaks identified. Similarly, as the number of peaks increased, there was an increase in relative abundance of different phosphorus. For the SLRE samples, it was observed that the phosphorus composition in the sediment mirrored the phosphorus sediment composition from the Chequamegon Bay samples, suggesting there are similar hydrological conditions between the two sites.