MULTIDISCIPLINARY METHODOLOGY TO CHARACTERIZE SUBMARINE GROUNDWATER DISCHARGE, WEEKS BAY, ALABAMA

Much recent research has focused on the influx of dissolved, agriculturally derived nutrients to ecologically sensitive coastal environments via submarine groundwater discharge. These chemicals have been implicated as causes of eutrophication and associated biodiversity changes and benthic hypoxia/anoxia. Assessments of submarine groundwater discharge frequently entail the use of point-of-discharge detection methods, such as seepage meters that directly measure the volume of groundwater influx over time at a certain point, and shallow offshore piezometers that measure the local vertical hydraulic gradient between surface water and groundwater. A problem with these tools is that they do not characterize hydrogeological and chemical variations along terrestrial and offshore groundwater flow paths, which are important contaminant fate and transport considerations. This study combines an offshore seepage meter and shallow piezometer network with contamination assessment tools, such as nested monitoring wells, continuous soil/sediment borings, aquifer tests, and downhole geophysical logs, to quantify and chemically characterize effluent groundwater in Weeks Bay, a shallow subestuary of Mobile Bay, located along the Alabama portion of the U.S. Gulf Coast. Land use around Weeks Bay is predominantly agricultural, and local synthetic fertilizer usage rates have historically been among the highest in the nation. These facts, combined with natural climatological and geological conditions, render local aquifers particularly susceptible to surface derived nitrate contamination. This research is the first quantification and water quality investigation of groundwater discharge to Weeks Bay.