Less agricultural phosphorus applied in 2019 led to less dissolved phosphorus transported to Lake Erie

Authors: GUO, TIAN - Purdue University; JOHNSON, LAURA - Heidelberg University, Ohio; LEBARGE, GREG - The Ohio State University; Penn, Chad; STUMPF, RICHARD - National Oceanic & Atmospheric Administration (NOAA); BAKER, DAVID - National Oceanic & Atmospheric Administration (NOAA); SHAO, GANG - Purdue University

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2020
Publication Date: 12/7/2020
Citation: Guo, T., Johnson, L., Lebarge, G., Penn, C.J., Stumpf, R., Baker, D., Shao, G. 2020. Less agricultural phosphorus applied in 2019 led to less dissolved phosphorus transported to Lake Erie. Journal of Environmental Science and Technology. 55(1):283-291. https://doi.org/10.1021/acs.est.0c03495.
DOI: https://doi.org/10.1021/acs.est.0c03495

Interpretive Summary: Excess dissolved phosphorus (P) transported to the western Lake Erie Basin via Maumee River is considered responsible for the re-eutrophication and harmful algal blooms of Lake Erie. Knowledge of the relative contribution of the P source, i.e. soil P or recently applied fertilizer/manure P ("incidental P") would allow policy makers to focus on certain types of best management practices (BMPs) that can more efficiently target each source. 2019 was a unique growing season that could provide insight into the relative contribution of these two P sources to the Maumee river. Due to excessive rainfall, a record area was un-planted, and therefore only 54% of fertilizer was applied. Even though the Maumee river discharge was high from the excess rainfall, which is normally well correlated to dissolved P loads transported, the actual measured dissolved P loads were only 29% of that expected based on discharge. Evidence strongly suggested that the reduced P load was a direct result of the reduced P applications, allowing for an estimate of around 50% of the dissolved P load coming from recently applied incidental losses of fertilizer and manure. Therefore, a large percentage of the Maumee river dissolved P load can be somewhat easily reduced by using BMPs that target fertilizer/manure application timing and techniques.

Technical Abstract: Extreme precipitation events affect water quantity and quality in various regions of the world. Heavy precipitation in 2019 resulted in a record high area of un-planted agricultural fields in the U.S. and especially in the Maumee River Watershed (MRW). March–July phosphorus (P) loads from the MRW drive harmful algal bloom (HAB) severity in Lake Erie; hence changes in management that influence P export can ultimately affect HAB severity. In this study, we found that the 2019 dissolved reactive P (DRP) load from March–July was 29% lower than the prediction while particulate P (PP) load was similar to the predicted value. Furthermore, the reduced DRP load resulted in a less severe HAB than predicted based on discharge volume. This reduction appears to be linked to decreased P fertilizer and manure applications in fall 2018 and spring 2019. Other possible contributing factors to this reduced load include lower precipitation intensity, altered tillage practices, and effects of fallow soils, but more data is needed to assess their importance. Based on the results of this study, it is estimated that approximately 29-48% of the DRP in the MRW is from incidental loss of applied manure and fertilizer, transported prior to equilibration with soil. This suggests that conservation practices targeted towards fertilizer management such as rate, timing, and application method, can have an immediate and appreciable impact on water quality in the MRW.