Managing Total Phosphorus Dynamic in a Small Rural/Urban Watershed using Geochemical Inference

Watershed fingerprinting or geochemical tracing of hydrologic pathways and processes involves the strategic spatial and temporal collection of water samples for chemical indicators. We used the stable isotopes of hydrogen and oxygen and major cations and anions found in fresh water systems to infer total phosphorus (TP) movement and storage in a small Midwestern rural/urban watershed. Typically in Minnesota, water chemistry is dominated by calcium and magnesium charge balanced by bicarbonate alkalinity unless altered by human activity. Ion concentrations will vary in a landscape depending on the relative amounts of new precipitation added to the sampled water. Pre-event water found in lakes, wetlands and groundwater are influenced by biotic and abiotic factors such as organic carbon and soil/rock mineralogy. Results of this study suggested that historically high concentrations of TP from years of wastewater treatment plant discharge were trapped in a down gradient wetland system. We inferred that new cleaner wastewater discharge may drive a change in equilibrium phosphorus concentration between sediment stored TP and event-based flow. Redirecting flow around TP wetland sinks will help prevent long-term down river water quality impairment