Informing Lake Erie Agriculture Nutrient Management via Scenario Evaluation

ABSTRACT Harmful algal blooms (HABs) have been increasing in extent and intensity in the western basin of Lake Erie. The cyanobacteria Microcystis produces toxins that pose serious threats to animal and human health, resulting in beach closures and impaired water supplies, and have even forced a “do not drink” advisory for the City of Toledo water system for several days in the summer of 2014. The main driver of Lake Erie HABs is elevated phosphorus loading from watersheds draining to the western basin, particularly from the Maumee River watershed (Obenour et al. 2014). Through the 2012 Great Lakes Water Quality Agreement (GLWQA), the U.S. and Canadian governments agreed to revise Lake Erie phosphorus loading targets to decrease HAB severity below levels representing a hazard to ecosystem and human health. New targets limit March-July loadings from the Maumee River to 186 metric tonnes of dissolved reactive phosphorus (DRP) and 860 metric tonnes of total phosphorus (TP) – a 40% reduction from 2008 loads (GLWQA 2016). The Great Lakes region must now determine what policy options are most effective and feasible for meeting those targets. While all sources are important, our focus is on agriculture because it overwhelms other sources. In a conservative ballpark estimate we found that 85% of the Maumee River’s load to Lake Erie comes from farm fertilizers and manures, even though this is only 10% of farmland fertilizer applications (Figure 1). Load targets will not be met without reductions from agriculture. Therefore, the overall goal of this study was to identify potential options for agricultural management to reduce phosphorus loads and lessen future HABs in Lake Erie. We applied multiple watershed models to test the ability of a series of land management scenarios, developed in consultation with agricultural and environmental stakeholders, to reach the proposed targets.This project was supported by an Fred A. and Barbara M. Erb Family Foundation grant (Grant #856), a NSF Watershed Sustainability Climate grant (Grant # 1313897), a Joyce Foundation grant (Grant # 15-36415), and a NOAA Coastal and Oceanic Climate Applications grant (Grant #NA13OAR4310142) to the University of Michigan; an NSF Coupled Human and Natural Systems grant (GRT00022685) and a NOAA/Ohio Sea Grant to Ohio State University; U.S. Army Corps of Engineers – Buffalo District task orders, a Great Lakes Protection Fund grant (Project No. 936.01), and an International Plant Nutrition Institute grant through the 4R Nutrient Stewardship Research Fund (Agreement # 58-3604-4-005) to LimnoTech; a 4R-Research Project sub-award from USDA Agricultural Research Service (Agreement # 59-3604-4-001) with the prime grant from the International Plant Nutrition Institute made to the USDA-ARS (Agreement #58-3604-4-005) to Heidelberg University; and USDA support to the Blackand Research & Extension Center, Texas A&M University. The authors would also like to thank Jeff Arnold and Mike White for their thoughtful insights and advice throughout the project. The authors would also like to thank the environmental and agricultural communities for helping to shape the questions we asked of the models, and Elizabeth Cisar of the Joyce Foundation, David Saad of USGS, and Tom Bruulsema of IPNI for reviewing this report