State Water Resources Research Institute Program (WRRI)

Details for Project ID 2012AL143G, 2012

Submarine Groundwater Discharge (SGD) Dynamics at the Gulf Shores of Alabama: Characterization of Nutrient Loading and Saltwater Intrusion using Numerical Modeling Constrained by Geophysical Field Data

Institute: Alabama
USGS Grant Number:
Start Date: 2012-09-01 End Date: 2013-09-01
Total Federal Funds: $35,885 Total Non-Federal Funds: $35,893

Principal Investigators: Geoffrey Tick, Natasha Dimova

Abstract: In recent years, increased agricultural land-use, urban, and residential expansion have been observed for the coastal areas along the Gulf of Mexico. The contamination of groundwater resources of southern Baldwin County, Alabama and nutrient loading to the Gulf of Mexico has been a major concern for the area. The aquifer system is dominantly comprised of a single inter-connected hydrological system in direct connection with coastal waters of the Gulf of Mexico. While previous studies have demonstrated the degradation of the local aquifers in the area as a result of saltwater intrusion and nitrate contamination, there is a lack of knowledge of the fate of these contaminants, elucidation of submarine groundwater discharge, and nutrient/contaminant mass flux in the coastal zone. Over the last decade, areas along the Alabama coastline have experienced significant outbreaks of harmful algal blooms (HABs) causing extensive dead zones whereby oxygen levels in the water are depleted. Coastal studies in other parts of the world have clearly demonstrated that nutrient loadings from submarine groundwater discharge (SGD) are often responsible for initiating and sustaining HABs. Our limited knowledge in the pathways of SGD to the coastal areas of Baldwin County, Alabama indeed suggests that nutrients and contaminants conveyed by submarine groundwater discharge could be accountable for the HABs in the area. Very recent studies also showed that, in addition, because of extensive groundwater withdrawals the Alabama coastline is experiencing already effects of seawater intrusion. These not only contaminate local drinking water supplies but also deteriorate the quality of fresh coastal aquifers and aid in leaching trace metals and contaminants to coastal zones. However, although much is done in assessing SGD fluxes to coastal areas, very little is known about the actual pathways of SGD in the area. Knowledge of the hydrogeological characteristics of the aquifers and actual groundwater flow paths are critical in further understanding the fate of the contaminants and their impact to the places of discharge. In this study we propose to apply numerical modeling approaches, constrained by subsurface electrical resistivity field data and geochemical sampling/analyses, to examine the groundwater discharge pathways and extent of saltwater intrusion at the Gulf Shores region of Alabama. Previous flow and transport modeling studies have only focused on regional dynamics or have been limited to describing processes along single flow paths. The development of a local high-resolution three-dimensional groundwater flow and transport numerical model will allow for the quantification of submarine groundwater discharge rates and nutrient mass flux to the Gulf of Mexico along the entire coastline of the study area. This will allow for the identification of target discharge and source zones of contaminant mass along the coast so that management or remediation strategies can focus on specific areas/points that are primarily contributing to mass loading to the Gulf of Mexico. This tool will be critical for developing cost-effective aquifer management plans to ensure sustainable freshwater supplies and preserve the health of the regional ecosystem along the coast of Alabama and the Gulf of Mexico.