Hydrologic and biogeochemical controls on phosphorus export from western Lake Erie tributaries

Authors: Williams, Mark; King, Kevin; BAKER, DAVID - Heidelberg University, Ohio; JOHNSON, LAURA - Heidelberg University, Ohio; Smith, Douglas; Fausey, Norman

Submitted to: Journal of Great Lakes Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2016
Publication Date: 11/25/2016
Publication URL: http://handle.nal.usda.gov/10113/5801830
Citation: Williams, M.R., King, K.W., Baker, D., Johnson, L., Smith, D.R., Fausey, N.R. 2016. Hydrologic and biogeochemical controls on phosphorus export from western Lake Erie tributaries. Journal of Great Lakes Research. 42:1403-1411.

Interpretive Summary: Water quality in Lake Erie has made national and international headlines in recent years due to the extent and severity of harmful algal blooms. In this study, we examine discharge and nutrient concentration data (1975-2014) from two of Lake Erie tributaries, the Maumee and Sandusky rivers, which have experienced substantial shifts in phosphorus concentration and loading over the past 40 years. Our objective was to use these long-term data sets to identify the dominant processes influencing past phosphorus loading patterns and inform predictions of future watershed response. Results suggest that watershed discharge was the primary control on phosphorus loadings in the Maumee and Sandusky rivers, but biological and chemical processes were also important for determining phosphorus availability. Findings from this study not only have implications for nutrient management in the environmentally relevant study watersheds, but also in other intensively managed watersheds across the world.

Technical Abstract: Understanding the processes controlling phosphorus (P) export from agricultural watersheds is essential for predicting and mitigating adverse environmental impacts. In this study, discharge, dissolved reactive phosphorus load, and total phosphorus load time series data (1975-2014) from two Lake Erie tributaries, the Maumee and Sandusky Rivers, were evaluated to identify the dominant processes responsible for observed patterns in P export. Findings indicate that hydrologic processes in these watersheds controlled P loading patterns, as P export was transport-limited (i.e., P loading was strongly correlated to watershed discharge) and P concentrations exhibited chemostatic behavior (i.e., low variability in concentration relative to discharge). The nature and behavior of observed P transport likely stems from a large, ubiquitous source of P present within each watershed as results were similar to those reported for geogenic constituents. Over the 40-year record, analyses showed that the magnitude of the P source has remained relatively unchanged indicating that biogeochemical processes also play a key role in determining P availability. Future P loading in the Maumee and Sandusky watersheds should be expected to continue to be proportional to water flux and current P management strategies may need to be reevaluated to better balance agricultural P requirements and watershed P loadings.