A comparative ecological and toxicological investigation was conducted on a secondary wastewater treatment plant point—source discharge and the receiving system, a fourth—order freshwater stream in the Kentucky River basin. Biological, chemical, hydrological and on—site toxicological studies were performed at 10 monitoring stations, including reference sites. The principal objectives were to assess downstream persistence of aquatic contaminants, to quantify their effects on structure and function of aquatic communities and to evaluate the 8—d fathead minnow embryo—larval test for measuring instream toxicity and estimating chronic effects on aquatic biota. The principal ecological endpoints included species richness, diversity (H'), density and dominance (D) of macroinvertebrates and diversity of fish species. Macroinvertebrates were further analyzed by trophic groups. Marked downstream gradients existed for effluent dilution, decreasing concentration of selected chemicals, improvement in ecological conditions and decreasing toxicity, as measured in on—site static—renewal tests. A good predictive correlation was found between embryo—larval survival and independent ecological parameters, especially species richness of macroinvertebrates. In addition, static—renewal and flow—through toxicity tests were performed with effluent dilutions to determine LC50 and toxicity threshold values (LC1), expressed as percent effluent by volume. The estimated toxicity thresholds correlated closely with the actual percent instream effluent dilution observed at the first downstream station at which no ecological impact was discernible.
Spatial changes in structural and functional characteristics of fish and macroinvertebrate communities in eastern Kentucky were investigated in a drainage system chronically exposed to high levels of chloride salts from nearby oilfield operations. Salinity levels at biological monitoring stations ranged from 0.12-31.3%. Lotic regions with salinities greater than 10% were dominated by larvae of the dipterans Ephydra and Culicoides. In regions with salinities less than 10%o species richness increased more or less linearly with decreasing levels of chloride salts. Ephemeropterans appeared to be one of the major invertebrate groups least tolerant of elevated NaCl levels and were absent in regions with salinities greater than 2%0. Availability of food resources, such as periphyton and particulate organic matter, did not appear to be grossly altered in disturbed regions, and it is suggested that the observed distribution of macroinvertebrate fauna was largely in response to taxonomic differences in salt tolerance. Fish seemed to be more tolerant of highly saline conditions, and several species were observed in regions experiencing salinities as high as 15%,. Accordingly, assemblages of fish taxa along the salinity gradient may have been influenced by trophic factors, such as spatial limitations in availability of invertebrate prey.
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