Water Quality and Ecological Survey of the Trinity River


It is the purpose of this report to summarize the results of a water quality and ecological study of the Trinity River jointly conducted by the Institute of Applied Sciences at the University of North Texas and by the Graduate Program in Environmental Sciences at the University of Texas at Dallas. The study, funded by the City of Dallas Water Utilities, started in June 1987 and concluded in December 1988. The purpose of the study was to develop a contemporary understanding of the chemical, physical and, perhaps most importantly, the biological water quality in strategic reaches above, in and below the Dallas-Fort Worth Metroplex. Specific objectives were to: document the spatial and temporal distribution of fish and benthic macroinvertebrates in the Trinity River; physically, chemically and biologically characterize sediments in the Trinity River; assess toxicity of water and sediments in the Trinity River; develop a data base which can be used to better understand relationships between point and nonpoint loadings to the Trinity River and fish kills which have occurred. Twelve stations were established and sampled every three months for the duration of the project. Water and sediment samples were analyzed for presence of contaminants. The toxicity of Trinity River water and sediment samples during each quarterly survey was determined by conducting acute and chronic toxicity tests using fish and invertebrates. Concomitant with chemical, physical and toxicological evaluations, field studies were conducted to assess the status of the fish and benthic macroinvertebrate communities in the Trinity River. Results of the study clearly document that the Trinity River in may reaches supports diverse fish and macroinvertebrate communities. However, reaches of the river immediately downstream of wastewater treatment plants have depauperate fish and macroinvertebrate faunas. Toxicity tests of ambient waters in these reaches documented the presence of acute and chronic toxicity particularly under lower discharge conditions. However, Trinity River sediments were not found to be consistently acutely or chronically toxic via the assay methods used. Deposits if highly organic sediments were not present in the Trinity River during the study. Chemical analyses of water and sediments showed that concentrations for some metals and pesticides occasionally exceeded site specific water quality criteria and or screening/action levels. No distinct spatial pattern of exceedences was evident. Whether or not these exceedences of water quality criteria or screening/action levels contributed to the observed toxicity in the river can not be determined since the duration of exposure is not known. While the results of the study identify some continuing water quality problems in the Trinity River in the Metroplex, they also document significant overall improvements in chemical and biological water quality from conditions that previously existed in the river. The study demonstrates that the Trinity River has the potential to support reasonably diverse and viable communities of aquatic life. However, for it to achieve this potential will require additional efforts to improve the quality of point source discharges while minimizing nonpoint source loadings.


2 volumes; Volume I - Report - 339 pages; Volume II - Appendix - 300 pages


Trinity River, toxicity levels, fish population, biological communities, water quality