Response of zooplankton communities to liquid creosote in freshwater microcosms

In this study, the response of zooplankton communities to single applicatio ns of liquid creosote in model aquatic ecosystems (microcosms) was evaluate d. Liquid creosote was applied to 14 microcosms at concentrations ranging f rom 0.06 to 109 mg/L. Two microcosms served as controls. Zooplankton sample s were collected from each microcosm on days 7 and 1 before treatment and o n days 2, 5, 7, 14, 21, 28, 43, 55, and 83 following treatment. Temporal ch anges (response-recovery) in composition of the zooplankton community were assessed using principal response curves (PRC). Creosote induced a rapid, c oncentration-dependent reduction in zooplankton abundance and number of tax a, with maximum response (50-100% reduction in population densities) occurr ing between 5 and 7 d after treatment. Taxa that dominated at the time of t reatment experienced the greatest impact, as indicated by large, positive s pecies weight values (>1) from the PRC analysis. Many of these taxa recover ed to pretreatment or control levels during the posttreatment period, with the degree and duration of recovery being strongly dependent on concentrati on. Creosote had little effect on species composition at less than 1.1 mg/L , because changes in the types and relative proportion of species contribut ed from Cladocera, Rotifera, and Copepoda were comparable to those observed in control microcosms. However, a significant shift in species composition was observed at concentrations greater than 1.1 mg/L; these microcosms wer e generally dominated by low numbers of rotifers, some of which had not bee n collected before treatment. Community-level effect concentrations (EC50s) were 44.6 and 46.6 mug/L at 5 and 7 d, respectively, based on nominal creo sote. Corresponding no-effect concentrations were 13.9 and 5.6 mug/L. The r esults of this field study indicate that creosote may pose a significant ri sk to zooplankton communities at environmental concentrations potentially e ncountered during spills and/or leaching events.