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Region 6 Texas Coast Project Information

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Text reproduced from the publication, USEPA 1993. Regional Environmental Monitoring and Assessment Program. EPA/625/R-93/012. September 1993. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC.

Figures and tables not reproduced here. The complete publication may be ordered from the U.S. Environmental Protection Agency, Center for Environmental Research Information, Cincinnati, OH 45268. The publication request desk may be reached by phone at 513-569-7562.


Since 1991, a full-scale EMAP study has been under way in the Louisianian Province, encompassing the Gulf Coast from northern Florida through Texas. This study, known as EMAP-Estuaries or EMAP-E, has generated concerns about contaminants in fish and sediments in several estuaries along the Texas coast. The Region VI R-EMAP project, R-EMAP-TX, is using the EMAP sampling design to address waterbody-specific questions arising from the 1991 EMAP-E study. R-EMAP-TX is focusing on potential problems in several estuarine systems: contaminated sediments in the Galveston Bay estuary, biological impairment (fish pathology and sediment toxicity) in the East Bay Bayou of Galveston Bay, and contamination in tidal reaches of the Arroyo Colorado River and the Rio Grande River. The goals of R-EMAP-TX are to:

Planning for R-EMAP-TX is provided by an interagency team representing the Environmental Services and Water Quality Management Divisions of Region VI, the Texas Water Commission, and EPA's Office of Research and Development (ORD). To ensure that the data from R-EMAP-TX are comparable to the data from EMAP-E, R-EMAP-TX is employing the EMAP-E protocols, personnel, equipment, and laboratories. Texas A&M University in College Station, Texas, will conduct the field activities. The laboratories for R-EMAP-TX are the EPA/ORD Environmental Research Laboratory in Gulf Breeze, Florida; the Gulf Coast Research Laboratory in Biloxi, Mississippi; and Texas A&M University.

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Table 6-1 presents the milestones and schedule for R-EMAP-TX. The activities of R-EMAP-TX in each of the four study areas are described below.


The results of the 1991 EMAP-E study found tributyltin (TBT), a substance highly toxic to aquatic life, in 11 of 12 EMAP sediment samples collected from Galveston Bay and its associated tributaries and embayments. Five of the samples had concentrations higher than 5 parts per billion (ppb). In contrast, only 13.3 percent of the 183 sites sampled in the Louisianian Province taken in that year's EMAP study had TBT sediment levels higher than 1 ppb. REMAP-TX will attempt to confirm these preliminary findings and further document the extent of contamination and the severity of effects on aquatic life resulting from contamination by TBT and other pollutants. Further sampling in Galveston Bay will be conducted to determine:


In the 1991 EMAP-E study, the East Bay Bayou, a small tidal river of Galveston Bay, exhibited a high fish pathology rate (45 percent for Atlantic croaker and 65 percent for sand seatrout). The background pathology rate for the whole Louisianian Province was less than 1 percent. In addition, the toxicity tests of the sediment from this area showed significantly high mortality rates for benthic invertebrates. R-EMAP-TX will conduct more intensive sampling in the East Bay Bayou to determine:


Measurements taken during the 1991 EMAP-E study from one site in the tidal portion of the Arroyo Colorado River showed high fish tissue concentrations of agriculture-related contaminants, particularly toxaphene. REMAP-TX will take additional measurements to determine whether the results from the one site are indicative of conditions throughout the tidal portion of the river. This part of REMAP-TX will focus on the levels of chlorinated hydrocarbons in fish tissue, chemical and toxicity tests of sediments, and benthic community analyses.


REMAP-TX is also sampling the tidal reaches of the Rio Grande, another major tributary in southern Texas. During the EMAP-E survey, investigators were not able to sample the Rio Grande. To determine whether or not the Rio Grande has problems similar to those in the Arroyo Colorado, REMAP-TX is performing the same tests in the Rio Grande as in the Arroyo Colorado. In addition, REMAP-TX will take water column samples to complement a separate toxics study being conducted by EPA and Texas on the nontidal reaches of the Rio Grande.

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REMAP-TX is designed to obtain unbiased statistical estimates of the ecological condition of the four estuarine systems under study. R-EMAP-TX will collect field samples during August and September 1993 to coincide with the field sampling season used by EMAP-E. Sampling is limited to a time period in which environmental stress is expected to be most severe. A second sampling season is planned for September 1994. This will allow investigators to further assess problems confirmed by the 1993 sampling, to expand sampling to additional estuaries, and to address any unusual climatic conditions (such as hurricanes or high freshwater runoff) that could bias the results during a single sampling season.


The areas to be sampled by R-EMAP-TX are Galveston Bay and its adjacent embayments and tributaries, with the exception of the Houston Ship Channel; the East Bay Bayou; the Arroyo Colorado River from the mouth to Port Harlingen, TX; and the estuarine portion of the Rio Grande from the mouth to a point 5 kilometers inland. To obtain data that provide unbiased estimates of the status of these estuaries, R-EMAP-TX is randomly selecting sample sites using an extension of the EMAP-E sampling design. In Galveston Bay, sample site selection is based on a randomly placed hexagonal grid. The sampling scale for this project calls for a grid of 31 hexagons of 70 square kilometers each (four times the density of the sampling conducted in the 1991 EMAP-E survey). Sampling sites are chosen randomly within each hexagon. Figure 6-1 shows the sampling sites for the Galveston Bay estuary. For the three small tidal riversþthe East Bay Bayou, the Arroyo Colorado, and the Rio Grandeþa systematic linear grid is used to select sampling sites. The linear grid defines the spine of the rivers, starting at the mouth and extending upstream to designated points. Sampling segments are placed every 2.5 km along the spine (four times the density used in the 1991 EMAP-E project). Sampling sites are chosen randomly within each segment. The sampling design results in 6 segments in the East Bay Bayou (Figure 6-1), 10 in the Arroyo Colorado (Figure 6-2), and 3 in the Rio Grande (Figure 6-2).


REMAP-TX is measuring the following indicators to assess the environmental status of the estuaries under study:


To address questions of concern to environmental managers, R-EMAP-TX will test several hypotheses. Some of the questions to be addressed and hypotheses to be tested are listed below. East Bay Bayou Questions of Interest:

Hypotheses: Tidal Reaches of the Arroyo Colorado and Rio Grande Rivers Question of Interest: Hypothesis: (If this hypothesis is rejected, further studies of the potential sources, fate, and transport of agriculture-related contaminants in these rivers would be warranted. The Texas Department of Health would also be advised to consider fish advisories or fish bans in these areas.) Galveston Bay Sediments Questions of Interest: Hypotheses:

(If this hypothesis is rejected, precautions regarding TBT use and/or further studies on the biological effects of TBT and other contaminants would be warranted.)



Charlie Howell
Environmental Services Division
Region VI
U.S. Environmental Protection Agency
First Interstate Bank Tower
at Fountain Place
1445 Ross Avenue
12th Floor, Suite 1200
Dallas, TX 75202-2733

(214) 655-8354

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