The Ecotoxicological Impacts of Copper in Aquatic Systems
This dissertation examines the ecotoxicological impacts of heavy metal pollution within an aquatic ecosystem. First, the influence of point versus nonpoint sources in structuring the distribution of chemicals in a simulated flowing freshwater habitat was examined. The fine scale (molecular) spatio-temporal distribution of chemicals was measured in situ using an electrochemical detector. Molecular concentration at varying distance and height from the source was quantified using dopamine coupled with an electrochemical detection system. The fine-scale distribution of chemical plumes from point and nonpoint sources showed significant differences in how organisms will be exposed to chemicals. Overall, this study characterized plumes from nonpoint sources as having significantly longer peak lengths and rise times, as well as greater peak heights and maximum slopes than plumes from point sources, providing a significantly different exposure paradigm depending on introduction method. Next, the effects of sublethal copper toxicity on chemically mediated behavior were determined by exposing rusty crayfish (Orconectes rusticus) to ecologically relevant concentrations of copper (4.5, 45, and 450 µg/l) for 120 hours. Following exposure, crayfish were allowed to orient toward a food odor stimulus. During orientation trials, select crayfish oriented under a point or nonpoint source copper background pollutant at the same concentration as the exposure period. Significant differences were found in the overall orientation ability of O. rusticus to locate an odor source when previously exposed to copper in combination with a source of pollution in the background of orientation trials. Crayfish exposed to copper in any capacity during the experiment (regardless of concentration or background during trials) showed slower walking speeds toward the source, decreased turning angles, increased heading angles toward the source, and decreased upstream heading angles. Results from this experiment support that copper impairs the ability of crayfish to detect, process, and/or respond appropriately to chemosensory information in order to successfully localize a food odor source. Finally, impairment to a behavioral mechanism (antennular flicking) involved in chemically mediated behaviors (orientation to an odor source) of O. rusticus was investigated following 120 hours of sublethal copper exposure (450 µg/l). In second portion of this experiment, crayfish previously exposed to copper were subsequently placed in unpolluted water before behavioral assays. Crayfish exposed to copper were significantly less successful in their ability to orient to a food odor and exhibited lower flicking rates than control crayfish. Over the course of the recovery period, crayfish demonstrated significant increases in rates of successful localization of odors and antennular flicking. These results indicate that the mechanism by which copper impairs chemoreception in the rusty crayfish is reversible if copper concentrations are decreased in aquatic ecosystems. Overall, results from this dissertation demonstrated that although differing exposures were created pollution entering the water column from point and nonpoint sources, ecologically relevant levels of copper significantly impaired the performance of a chemically mediated behavior in the rusty crayfish. Results also demonstrated that impairment to this behavior was correlated to a decrease in olfactory sampling rate, which was further revealed to be a reversible impairment.