Quantifying Direct Groundwater Discharge to Lake Erie and Vulnerability to Hidden Nutrient Loads

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Nutrients from human activities discharge to coastal waters through streams, rivers, surface run off and direct groundwater discharge, contributing to the formation of harmful algal blooms. The nutrient concentrations coming directly from streams and rivers are easier to measure. However, groundwater, which seeps from the lakebed over broad areas, also contains dissolved nutrients and is a more difficult source to measure. With Ohio WRC funding, Dr. Audrey Sawyer and her team aimed to quantify the threat and identify coastal areas that are particularly vulnerable to groundwater seepage. Dr. Sawyer used a combination of geospatial analysis and field testing to estimate direct groundwater discharge in the United States portion of the Great Lakes.

Locations for direct groundwater discharge measurement were selected using NHDPlus program, which was also used to estimate the geometry and size of wedge-shaped recharge areas outside stream catchments where water flows directly to the coast. Using the findings from the geospatial analysis, Sawyer and her team conducted a detailed field study of an at-risk location. The principle findings of this study show that 43% of the United States Great Lake Coast is vulnerable to ground water nutrient seepage, and that Lake Erie has the highest percentage of at-risk coastal groundwater seepage (31%). The key findings of this project led to the creation of a freely available map that may help tailor strategies aimed towards reduced nutrient loading in Lake Erie and other lake systems.

If you'd like to find out more about other Ohio WRC research projects, visit: https://wrc.osu.edu/past 

Researcher Profile

Dr. Audrey Sawyer is an Assistant Professor in the School of Earth Sciences at Ohio State University. She reveiced her Ph.D. from the University of Texas-Austin, and has expertise in Hydrogeology, Surface Water-Groundwater Interactions, and Coastal Hydrology. Sawyer's research group focuses on two research themes:

  • Understanding interactions between surface water and groundwater in streams, rivers, estuaries, and coasts
  • Determining hydrologic controls on the movement of nutrients, contaminants, and heat in watersheds

Sawyer's group pursues these themes by combining laboratory and field observations with mathematical modelling. Sawyer maintains a computational hydrodynamics laboratory with hydrogeologic field instrumentation, experimental tanks, and high-performance computing.