Lamisa Malik, Kimberly J. Van Meter, Nandita B. Basu (2022). Legacy Phosphorus and Eutrophication in the Lake Erie Basin. Proceedings of the GWF Annual Open Science Meeting, May 16-18, 2022.

Phosphorus (P) is one of the key nutrients required for crop and food production. However, excess P loading from anthropogenic activity has contributed to algal blooms and eutrophication in freshwater systems across the world. Fertilizer application, livestock manure, and human waste production accumulate P in the soil and in the stream network – which we call legacy phosphorus. Accumulation of legacy P from decades of agricultural activity has been attributed to the persistence of algal bloom. Much work remains to understand how P usage in a watershed leads to the buildup of legacy stores and how these legacy stores contribute to stream P fluxes even when watershed P inputs have been reduced.
To address this knowledge gap, we first developed temporal trajectories of P input and output across multiple watersheds in the Lake Erie Basin. We used a mass balance approach to quantify P surplus across these watersheds over 87 years (1930-2016). These decadal input trajectories were then compared with the total P and soluble P trajectories in the streams draining these watersheds to determine time lags in water quality response. We found response patterns to vary significantly across the Lake Erie basins, with watersheds dominated by point source inputs documenting shorter lag times than those dominated by non-point sources. As Lake Erie continues to be impacted by algal blooms, our work provides a path forward for designing more targeted approaches to water quality management and will help guide decision-makers to set realistic targets for reducing phosphorus loading.

AOSM2022 Lake Futures First Author: Lamisa Malik Additional Authors: Kimberly J. Van Meter(Department of Geography, Pennsylvania State University, PA, USA); Nandita B. Basu (Department of Earth and Environmental Sciences, University of Waterloo, ON, Canada)