Geological controls on submarine groundwater discharge into an upper bay estuary-Copano Bay

2010-2013 - $266,898

Timothy Dellapenna
Department of Marine Sciences
Texas A&M University at Galveston

Egon Weber
Department of Physical and Environmental Sciences
Texas A&M University-Corpus Christi

James Garrison
Department of Marine Sciences
Texas A&M University at Galveston

Abstract

Submarine Groundwater Discharge (SGD) to estuaries and the ocean has long been recognized as an important component of the estuarine and coastal hydrological cycle, but has more recently been recognized as an important pathway for nutrients, contaminants, and dissolved organic matter from the regional and local aquifers to the estuaries and the ocean. The purpose of this study is to determine both the mechanisms and the relative importance of SGD in the delivery of nutrients, dissolved organic matter, and dissolved contaminants to the estuaries of the central Texas coast by using Copano Bay as an example. This bay is a relatively undisturbed and natural system, is typical of the upper-bay systems of Texas, and the rivers flowing into Copano Bay, including the Aransas River, Mission River and Copano Creek, are natural rivers with no significant impoundments. During the summer of 2007 the Coastal Geology Lab at Texas A&M University-Galveston (TAMUG) mapped all of Copano Bay with side scan sonar, single beam bathymetry and CHIRP high resolution seismics, running lines every 150 m for the entire bay, providing the most comprehensive subsurface data set for any bay in Texas. In addition, a series of cores were collected for additional subsurface control. As a result, there is a tremendous data set to draw from when designing and conducting this study.

This study will test three hypotheses: (1) significant freshwater SGD is from aquifers consisting of Holocene filled incised channels; (2) fringing marshes are a source of brackish SGD with high ammonia and phosphate; (3) oyster reefs act as conduits, or are co-located within conduits.

These hypotheses will be tested using towed marine resistivity arrays, seismic CHIRP profiling, coring, groundwater sampling, and chemical analyses. Groundwater models will be used to verify the conceptual models of the flow rates, patterns, and pathways.