CLIMATE IMPACTS ON NUTRIENT LOADING IN LAKE ERIE

The Maumee River Watershed, the largest of the Great Lakes drainages, is located in NW Ohio, and is comprised of 70% agricultural land. Phosphorous and nitrogen are applied as fertilizer across the watershed. During rain events these nutrients can be mobilized, and travel through the river system, ultimately making their way to Lake Erie. Climate change is expected to increase both average temperature and precipitation events, potentially changing nutrient loading from runoff and impacting harmful algal blooms. Harmful algal blooms (HABs) have been persistent and increasing in recent years as anthropogenic nutrients and water temperatures, both necessary for algal growth, have increased. HABs can contribute a toxin known as microcystin, which can be detrimental to human health if ingested.

Best management practices (BMPs) have been employed to surrounding agricultural fields to help reduce nutrient loading. BMPs and other agricultural practices range from practice and timing of fertilizer application to tilling practices. Previous studies focused on the effects of climate change and BMPs on sediment loading in the Maumee Watershed. This focus on sediment loading also contributed to the growing concern of HABs, showing changes in sediment delivery under different climate scenarios.

We expand on this research, focusing on nutrient loading in addition to sediment loading as phosphorous has been identified as a limiting nutrient to HABs, with the dissolved phase being particularly important. A target of 40% reduction of dissolved reactive phosphorus (DRP) nine years out of ten was established by the Ohio Phosphorus Task force for reduction of HAB occurrences. To investigate how climate change and BMPs interact three climate models, selected from CMIP5, and three BMPs are run in Soil and Water Assessment Tool (SWAT). SWAT is used to model and explain the effects of climate change and land management practices on watershed yields. The climate models incorporate RCP 4.5, RCP 8.5 climate drivers and historical data. BMPs modeled include likely adoption rates of cover crops, fertilizer injection, and buffer strips, along with increased wetlands. Understanding the relationship between climate change and BMPs will aid more effective regulation practices to be considered to help constrain algal growth in the future.