LINKING SEASONAL VARIATION OF SUBMARINE GROUNDWATER DISCHARGE TO HYPOXIA IN CORPUS CHRISTI BAY

The South Texas Gulf Coast is comprised of an extensive network of intracoastal waterways and bay systems. These systems, being shielded by Padre Island, provide a unique habitat for a variety of marine species. Annual formations of hypoxia and brown tide in the Corpus Christi Bay (CCB) system have become a focus of concern. These formations have cyclically surfaced during the late spring through the fall months in CCB. Due to the semi-arid climate of the South Texas Gulf Coast, these seasons experience limited precipitation and annual lows of surface freshwater inflows, which in turn would point to non-riverine sources such as groundwater, which has a tendency to accumulate high concentrations of nutrients and organic matter. Research efforts are underway to evaluate the influence of groundwater as a nutrient source to the CCB. Water samples and resistivity soundings are collected seasonally along five transects and 29 stations within CCB and the upper Laguna Madre.

Preliminary analysis of field parameters and major elements (i.e. sodium, calcium, potassium, magnesium, manganese and iron) data collected during January and July shows increasing stratification of salinity levels, which is customary, a strong chemical variance between the water column and porewater parameters. An initial principal components analysis (PCA) shows strong correlations between depth and pH during the winter and summer sampling events. In addition, resistivity images from Shamrock Island, located along the southeast corner of CCB, show pockets of very fresh water as well as groundwater and surface water interactions. Furthermore, buried old channels at the mouth of Laguna Madre prove to be conduits for surface water and groundwater interaction. Submarine groundwater discharge of nutrient to CCB and the relationship to hypoxia will be quantified using geochemical tracers coupled with resistivity time-lapse images.