Revitalization of a northcentral Texas river, as indicated by benthic macroinvertebrate communities

Macrobenthic communities were surveyed in 1987-88 as part of a comprehensive study of fish kills and water quality in the upper Trinity River. The purpose was to characterize macrobenthic integrity in relation to ambient and storm-associated water quality and other environmental factors. No physical habitat features were found to be substantially limiting to aquatic life. Water and sediment quality generally were good, and macrobenthic communities typically were healthy. Ecological conditions were vastly improved compared to the recent past, attributable mainly to decreased contaminant loading from wastewater treatment plants and reduced incidence of raw sewage bypassing. Nonetheless, some impact was evident in certain reaches. Deleterious effects at Beach St. evidently resulted from pesticides derived from urban runoff. Slight impacts by dissolved metals were suggested for Grand Prairie and Continental Ave.; possible sources included urban runoff and wastewater treatment plant effluents. Moderate impacts at S. Loop 12 were attributed to low-flow toxicity induced by a wastewater treatment plant discharge; ammonia and chlorine were considered primarily responsible, with metals and pesticides possibly involved. Macrobenthic communities were somewhat degraded from Trinidad to US 79, due to storm-related stresses by DO depression, pesticides, and metallic oxides. Overall impacts were relatively slight on a long-term basis, however, and a high aquatic life use was attained at most sites. The degree of macrobenthic integrity was considered remarkable for an effluent-dominated system with such extensive urbanization in the watershed