Ciliate epibiont effects on feeding,energy reserves,and sensitivity to hydrocarbon contaminants in an estuarine harpacticoid copepod

Although epibiotic protozoans are commonly observed on the chitinous exoskeleton of aquatic crustaceans, relatively little is known about their ecological significance. The significance of protozoan epibionts on benthic copepods has never been examined.Coullana sp., a meiobenthic harpacticoid copepod, is abundant in Louisiana salt marshes and has high incidence (∼50%) of ciliate epibionts. Field and laboratory grazing experiments indicated that ciliate epibionts did not hinderCoullana feeding on benthic or planktonic algae. Contrary to expectations,Coullana with high levels of ciliate epibionts (>8 ind⁻¹) grazed at a significantly higher rate on¹⁴C-labeled benthic diatoms added to intact sediment cores than didCoullana with no epibionts.Coullana neutral lipids (examined using Nile Red, a hydrophobic fluorophore) were not significantly influenced by the presence of ciliate epibionts, suggesting that copepods are able to compensate for any additional energetic demands imposed by epibionts. Epibiont effects onCoullana susceptibility to hydrocarbon contaminants were measured by examining survivorship in diesel-spiked sediments. The presence of ciliate epibionts significantly decreased survivorship at relatively low PAH concentrations (12.8 ppm). While ciliate epibionts onCoullana do not dramatically alter total food acquisition or energy storage, they may cause stress, which in turn makesCoullana more susceptible to contaminants and possibly other natural stressors such as food limitation.     

Monitoring and Mathematical Modeling of Contaminated Ground-Water Plumes in Fluvial Environments

Ground-water monitoring to delineate a contaminant plume in fluvial hydrostratigraphic units often is uncertain. Fluvial deposits consist typically of interbedded layers of sands, silts and clays, with buried stream channel deposits of sands or gravels. The channel deposits are often interpreted erroneously to be discontinuous between test holes and in cross section due to their sinuosity. Erroneous conclusions pertaining to the areal continuity of these geometrically complex deposits are inevitable unless the investigator thoroughly understands the depositional environment(s). The hydraulic conductivity of buried stream channel deposits may be several orders of magnitude higher than the matrix materials in which they are enclosed. The higher hydraulic conductivity of buried stream channel deposits has potentially significant ramifications with respect to ground-water monitoring to delineate the geometry of a contaminant plume migrating through these deposits. Ground-water monitoring at uranium mill waste disposal sites located in fluvial environments began on a significant scale in about 1977. A uranium mill tailing disposal site located in such an environment in central Wyoming is among the first sites monitored. Thirty-seven monitor wells were constructed at the site to delineate a seepage plume originating from one of the tailing ponds. This case history illustrates the need for a detailed under—standing of the hydrostratigraphy at a waste disposal site in order to interpret the meaning of ground-water quality data effectively. Water quality data from monitor wells located on a hit or miss basis often are misleading. The hydrostratigraphic horizon from which a water quality sample is collected must be well defined before the sample analyses can be interpreted quantitatively.