GROUNDWATER AND NUTRIENT INFILTRATION IN AN INVERSE ESTUARY: NUECES BAY, TEXAS

Nueces Bay is a sensitive and diverse wetland area near Corpus Christi, Texas on the lower Gulf coast of Texas. As a result of the the arid environment of south Texas Nueces Bay is an inverse or negative estuary meaning the regional evaporation rate typically exceeds the precipitation rate resulting in hypersaline conditions in the waters of the bay. The land use of the surrounding area is primarily industrial and agricultural which makes understanding the pathways and flowrates of water into the estuary valuable in terms of water quality management. In addition, the Nueces River which feeds the estuary is impounded at Lake Corpus Christi and Choke Canyon reservoirs and used as the primary source of municipal water supply for the region. Since the region often experiences water shortages surface freshwater supply to the estuary can be reduced dramatically.

This is a presentation of data collected in 2002 on groundwater inflow rates and bay water nutrient loading. The purpose of this research is to determine the nature, extent, and pattern of groundwater exchange with the waters of the Nueces Bay estuary and to determine if there is any correlation with nutrient distribution. The climate and hydrogeology of the region suggest that the groundwater/estuarine interaction is very dynamic, responding throughout the year to short, intense periods of rain followed by to long periods of drought. In addition to shaping the water chemistry and ecology of the estuary this type of cyclic exchange could have implications for water quality, fishery management, and groundwater usage in the region.

This investigation involved the collection, analysis, and correlation of two types of water samples for radium isotope counting and nutrient analysis. Samples were collected throughout Nueces Bay once during the spring and again in the summer; the first period corresponding to very dry conditions regionally and the second to a period of intense flooding and heavy precipitation. A mass balance approach is used to determine the necessary groundwater input to the bay to maintain the radium activities with respect to the activities of the regional groundwater and the outer coastal waters.