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Region 6 Texas Coast Project Information
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.
1.0 INTRODUCTION
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:
- Collect additional data to characterize the extent and severity of potential waterbody-specific problems identified by EMAP-E.
- Obtain the scientific information that environmental managers need to identify toxic pollutants of most importance in specific geographic areas.
- Evaluate the usefulness of coupling the EMAP regional approach as a screening tool with the R-EMAP approach of obtaining refined measurements in specific waterbodies.
- Design and implement procedures that link an EMAP and a R-EMAP project and that maximize data comparability between the projects.
- Test whether the EMAP approach (statistical design and indicators) is appropriate for addressing waterbody-specific questions.
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.
2.0 ACTIVITIES
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.
2.1 GALVESTON BAY SEDIMENTS
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:
- The extent of sediment in the Galveston Bay estuary with TBT concentrations exceeding 1 ppb and 5 ppb.
- Whether high concentrations of TBT and other contaminants in sediment are correlated with degraded fauna conditions.
- How TBT concentrations in the water column are related to TBT concentrations in the underlying sediment.
2.2 BIOLOGICAL IMPAIRMENT IN THE EAST BAY BAYOU OF GALVESTON BAY
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:
- Whether there is, in fact, a significant difference between the fis pathology rate found in the East Bay Bayou and that found across the Louisianian Province.
- Which specific areas in the East Bay Bayou have the highest fish pathology rates.
- What the contaminant levels are in fish and sediment in the East Bay Bayou.
- Whether the sediments in the East Bay Bayou are toxic to sediment organisms in laboratory tests.
- Whether the sites with the highest contaminant levels correspond to the sites where the greatest biological impairment if found.
2.3 TOXIC CONTAMINATION IN TIDAL REACHES OF THE ARROYO COLORADO RIVER
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.
2.4 TOXIC CONTAMINATION IN TIDAL REACHES OF THE RIO GRANDE RIVER
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.
3.0 TECHNICAL APPROACH
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.
3.1 SAMPLING DESIGN
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).
3.2 INDICATORS
REMAP-TX is measuring the following indicators to assess the environmental status of the estuaries under study:
- Fish pathology
- Species richness in benthic communities
- Levels of contaminants in fish tissue
- Levels of TBT and other contaminants in sediments
- Sediment toxicity
3.3 HYPOTHESIS TESTING
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:
- What is the frequency of pathologies in the East Bay Bayou?
- What are some of the potential sources for these observed pathologies?
- The incidence rate of pathologies observed at the East Bay Bayou does not differ from the rates found across the Louisianian Province.
- The incidence rate of pathologies observed at specific East Bay Bayou sites does not differ from the rate of pathologies found overall in the East Bay Bayou.
- (If the high rates of pathology found by EMAP-E are confirmed, managers will need to consider follow-up investigations of potential sources. The R-EMAP-TX results will help managers focus on areas where biological impairment is greatest.)
- Are the anoxia (lack of oxygen) and high concentrations of agriculture-related contaminants found by EMAP-E in the Arroyo Colorado of deep south Texas indicative of conditions throughout the tidal portion of the river? Do similar contamination problems exist in the tidal reaches of the Rio Grande River?
- Tissue levels of chlorinated hydrocarbons in the tidal rivers of south Texas do not exceed human health criteria.
- What is the extent and distribution of high TBT levels in Galveston Bay sediments?
- Do TBT concentrations in the sediments correspond to the condition of the bottom fauna?
- Less than 20 percent of Galveston Bay sediments contain greater than 1 ppb TBT.
- Less than 20 percent of Galveston Bay sediments contain greater than 5 ppb TBT.
- (If either of these hypotheses is rejected, environmental managers will be alerted to the need for additional controls on TBT releases to Galveston Bay.)
- There is no positive association between species richness and concentrations of TBT and other contaminants found in Galveston Bay sediments.
(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.)
4.0 CONTACTS
FOR MORE INFORMATION, CONTACT:
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