Archived: July 29, 2004


Background

Ecosystemsalong the south Texas coast are subject to a multitude of environmental problems which are directly related to land-sea coupling. At the global level, there are strong indications that sea level is rising. If this occurs, coastlines will retreat, and terrestrial ecosystems will shrink in size. In some places, the topography will lead to a smooth transition as water replaces marsh which migrates to areas that are currently upland. In many areas, however, topography and efforts to protect property from inundation will constrain development of coastal marsh habitats. Because productivity of coastal waters is higher when associated with a marsh ecosystem, reduction of marsh area could reduce marine food production. With regard to environmental processes, low relief coastal watersheds are prone to flooding from both uplands and from the sea; they are regions of active topographic change resulting from sediment deposition near river mouths and dynamic beach morphology along coastal margins, and they serve as storage areas for contaminants sorbed to sediments stored in flood plains and channel deposits.

While sea level rise combined with global climate change will significantly change the dynamics of Texas coastal ecosystems, as well as patterns of land use, fresh water inflow is even more critical to maintaining Texas estuarine ecosystems. Adequate freshwater inflow is important for maintaining biological productivity in bays and estuaries. The diversion of fresh water from natural systems for industrial, municipal, and agricultural purposes has had a profound effect on the living resources of the nation's bays and estuaries. This is especially true in semiarid areas such as the south Texas coast where fresh water is scarce. The changes in these estuaries resulting from poor water management strategies are striking and can include: high or hyper-salinity, groundwater or water table changes, low biological productivity, sediment trapping, and habitat losses. Finally, the artificial waterways dredged through the barrier islands modify natural exchange of water and affect species migration. An appropriate resource management plan for the South Texas coastal region would maintain critical wetland habitats and produce high levels of species diversity with desirable community structure and high yields of living marine resources. Unfortunately, Very little is known about the influence of landscape morphology on estuarine ecological processes. This is an critical area for collaborative research.

Overview of Proposed Research

The South Texas coast, and in particular, the San Antonio - Nueces watersheds provide an ideal laboratory for a collaborative multi-university, State of Texas, NASA research effort to study a range of complex issues including

Extensive research is already underway in each of these areas by individual groups which, if integrated, could provide the foundation for developing a meaningful collaboration model as well as the basis for ongoing research of these critical issues. These efforts are summarized in the following section, and a preliminary plan for initiating ongoing research is outlined.

High altitude color infrared aerial photography was acquired over the eastern half of Texas in 1995. The Texas Natural Resource Conservation Commission (TNRCC) funded the development of the State's first DOQQ's over the San Antonio - Nueces watersheds. Additionally, TNRCC supported a study at the University of Texas at Austin to develop a preliminary GIS based hydrologic model of the basin which included topography from the original USGS DEM, digital line graphs of the stream network obtained from 1:100,000 scale maps, streamflow, rainfall, and point source pollution measurements. While the model is a useful prototype, the original DEM and stream maps were found to be inadequate for developing this model, particularly near the coast where relief is very low. Improved landcover maps are also needed to improve the rainfall/streamflow relationships. A higher spatial resolution network of stream gauges and improved spatial and temporal resolution measurements of rainfall are also required.

In addition to the TNRCC effort, the Texas General Land Office has supported development of vegetation and land cover maps from Landsat TM data. Rice University and Texas Parks and Wildlife Department participated in development of these maps and has a long term research program in characterization of coastal plant communities. The UT Marine Science Institute also has ongoing research on in the estuaries of the south Texas Coast, including Compano and Corpus Christi Bay, on a range of topics including response of organisms to nutrient influx and habitat maintenance for nurseries. The University of Texas at Austin is conducting research in sea level rise in Galveston Bay and is studying circulation in the Gulf of Mexico at a mesoscale level. These research efforts as well as other efforts at the University of Houston, UT Brownsville, and Corpus Christi State Universities provide an ideal base for the first Texas Collaborative Environmental Change project.

The focus of the initial research will be to improve topography and land cover maps for the purpose of hydrologic modeling in the San Antonio - Nueces watersheds through the use of remotely sensed data with a focus on characterizing the wetland vegetation in two specific areas of the watershed. However, other parallel efforts may evolve, particularly related to improved atmospheric and oceanographic data acquisition in the area.

The University of Texas at Austin is acquiring and processing real time AVHRR data over the entire U.S. This imagery, in conjunction with the CIR photography, CAMS imagery, and available recent Landsat data, will be used initially to provide a spatially and temporally improved vegetation signature over the watershed. NASA will be acquiring airborne AIRSAR/TOPSAR data in June 1996 for another project in Galveston and has scheduled an acquisition of TOPSAR over the San Antonio-Nueces watershed which will be funded by the University of Texas Center for Space Research. Three TOPSAR flight lines will be acquired over the three primary streams flowing into Compano Bay. In addition, two fully polarimetric AIRSAR flight lines at C, L, and P bands will be acquired over the St. Charles inlet and Rincon Bayou, two wetland areas - one pristine and the other in a more urban area. We also hope to acquire additional near simultaneous multispectral data from the airborne CAMS system developed and flown by NASA Stennis over the wetland areas. These acquisitions would be supported by a limited field campaign conducted by multiple universities, for which limited funding for fieldwork has been made available by Texas Space Grant Consortium.

All data will be processed and input to a commonly georeferenced database for analysis. Initially, the capability of the polarimetric AIRSAR radar data in conjunction with optical data will be investigated for distinguishing and characterizing wetland habitats. In addition, the TOPSAR flight lines will provide both digital elevation models along a flight line and high resolution long wavelength data which can be investigated for improved mapping of vegetation covered streams. The new topographic information will be compared to that obtained from both the USGS DEM's and the DOQQ's. Methodology for integration of the multiple topographic maps and adaptively updating topographic information in the DEM will need to be developed as a long term goal. The updated DEM and landcover maps will be utilized in conjunction with the hydrologic model to compute updated streamflows and pollutant loadiings. Finally, a study to investigate the effect of landscape morphology on various estuarine ecological processes will be initiated.


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