Year Established: 2017 Start Date: 2017-03-01 End Date: 2018-02-28
Total Federal Funds: $29,087 Total Non-Federal Funds: $31,001
Principal Investigators: Audrey Sawyer
Abstract: Nutrients are a primary contaminant of concern for the Great Lakes, especially Lake Erie. Nutrient contamination has driven persistent eutrophication coupled to harmful algal blooms in recent decades. As a consequence, lake derived drinking water sources are commonly compromised and threaten the health of humans and the aquatic ecosystem. In an effort to understand and improve Lake Erie water quality, most research and best management practices have targeted nutrients in runoff, especially phosphorus. Yet dissolved phosphorus reductions have not met expectations. Additionally, growing concerns have been raised for nitrogen, which can be dissolved in direct groundwater discharge in high concentrations. In light of these concerns, a clear need exists to understand not only surface water but also groundwater sources of nutrients to Lake Erie and the other Great Lakes. Groundwater-borne nutrient loads depend on the rate of direct groundwater discharge and nutrient concentrations. Both these factors are highly heterogeneous and can vary over the scale of meters. Direct groundwater discharge is particularly difficult to quantify along large lakes because it is diffuse (unlike river discharge, which is focused in easily measured locations along the coast). The overarching goal of this study is to quantify direct discharge rates to Lake Erie and the other Great Lakes at high spatial resolution (< 1 km) and identify areas that are vulnerable to large nutrient contributions from groundwater. We will accomplish this objective using a water budget approach that integrates freely available hydrographic and hydroclimatological datasets. A key product will be a map of direct groundwater discharge along more than half of the Lake Erie coast. We will use this map with freely available land cover data to identify coastal areas that are vulnerable to high groundwater-borne nutrient loads. Vulnerable areas will be designated where the recharge zones, or contributing areas, for direct groundwater discharge are largely developed or agricultural. However, vulnerability estimates are qualitative and only indicate the potential for high groundwater-borne nutrient loads. Field measurements are needed to understand whether groundwater discharge rates and land use are good qualitative indicators of the “hidden” nutrient loads in groundwater. Therefore, a second objective of the proposal is to measure groundwater-borne nitrogen and phosphorus loads to the Lake Erie coast at two new sites. We will use seepage meters and collect lakebed pore water samples in order to measure fluxes of water, dissolved inorganic nitrogen, and dissolved phosphorus to the coast. Existing measurements from a third site at Cedar Point Wildlife Refuge in the Western Lake Erie Basin suggest that direct groundwater discharge may be responsible for a surprisingly high phosphorus load sourced from shallow lakebed sediments. We will use measurements from the three sites to evaluate strengths and limitations of our vulnerability maps. We will make all map products from the proposed project freely available through online data repositories.