A toxicological study was initiated because of concerns about allegations that the Texas Water Commission that effluent from the Dallas Central Wastewater Treatment Plant, which discharges into the Trinity River, was affecting downstream water quality. Monthly, flow-weighted composite effluent samples were collected. Grab samples were also collected upstream and downstream from the effluent from April 1989 to August 1991. Toxicity tests were conducted on these samples using Ceriodaphnia dubia as the test organism. Samples were collected four times during this study in which rainfall occurred prior to sampling. In every instance, this "first flush" of the watershed during a rising hydrograph was toxic to C. dubia upstream. Analyzing toxicity by season resulted in a statistically significantly lower neonate production in the effluent than in the river samples during the months of June, July, and August. This impact on neonate production was suspected of being caused by organic pesticides which are used for insect control on lawns. The effluent was never acutely toxic to C. dubia. Primarily, toxic occurrences in either the effluent or the river samples were primarily of a chronic nature. Overall, survival of C. dubia was affected more frequently at the upstream site than in the effluent or …

Geographic information systems (GIS) technology was used to analyze factors influencing habitat use by an endangered species, the red-cockaded woodpecker. The study area was the western part of the Raven Ranger District of the Sam Houston National Forest, Texas. The factors considered included both structural characteristics and spatial relationships among stands of trees in the habitat.

Changes in trophic status are often related to increases or decreases in the allocthonous inputs of nutrients from changes in land use and management practices. Lake and reservoir managers are continually faced with the questions of what to monitor, how to monitor it, and how much change is necessary to be considered significant. This study is a compilation of four manuscripts, addressing one of these questions, using data from six reservoirs in Texas.