Twelve 0.1-ha rectangular ponds (mesocosms) were constructed during 1986 and 1987 to test ecosystem-level responses to a pyrethroid insecticide containing esfenvalerate. Treatment consisted of 10 weekly drift and 5 biweekly runoff simulations of formulated esfenvalerate between July 9 and September 17, 1988. Control ponds received only untreated runoff, while low, medium, and high treatments received total loadings of 0.23, 4.1, and 23.3 g active ingredient (a.i.)/ pond. The top vertebrate predator in the mesocosms was bluegill (Lepomis macrochirus). Once adult bluegill spawned and young fish were present, microcrustaceans declined in number. Following esfenvalerate applications, nauplii in medium-and high-rate ponds underwent further significant reductions, indicating a response to esfenvalerate not observed in control and low-rate ponds. Relative to other treatments, high-rate ponds were found to have significantly increased metabolism and reduced macroinvertebrates following application. Bluegill exhibited no significant differences in population structure among treatments, although 2-cm-size bluegill were missing from high-rate ponds at harvest. Patterns of response emerged in this whole ecosystem test of esfenvalerate. Variation measured among communities was high as is typical of natural ecosystems; however, we suggest that this experiment provided an acceptable way of detecting impacts at both the community and the ecosystem level.

Twelve 0.1‐ha rectangular ponds (mesocosms) were constructed during 1986 and 1987 to test ecosystem‐level responses to a pyrethroid insecticide containing esfenvalerate. Treatment consisted of 10 weekly drift and 5 biweekly runoff simulations of formulated esfenvalerate between July 9 and September 17, 1988. Control ponds received only untreated runoff, while low, medium, and high treatments received total loadings of 0.23, 4.1, and 23.3 g active ingredient (a.i.)/ pond. The top vertebrate predator in the mesocosms was bluegill (Lepomis macrochirus). Once adult blue‐gill spawned and young fish were present, microcrustaceans declined in number. Following esfenvalerate applications, nauplii in medium‐ and high‐rate ponds underwent further significant reductions, indicating a response to esfenvalerate not observed in control and low‐rate ponds. Relative to other treatments, high‐rate ponds were found to have significantly increased metabolism and reduced macroinvertebrates following application. Bluegill exhibited no significant differences in population structure among treatments, although 2‐cm‐size bluegill were missing from high‐rate ponds at harvest. Patterns of response emerged in this whole ecosystem test of esfenvalerate. Variation measured among communities was high as is typical of natural ecosystems; however, we suggest that this experiment provided an acceptable way of detecting impacts at both the community and the ecosystem level.

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The Southeastern USA is currently experiencing a period of rapid growth of human populations that is likely having profound effects on the region's unique aquatic biota. Using both survey data and experimental protocols, we assessed the influences of water and habitat quality on freshwater mussel populations in a small Piedmont stream. Chewacla Creek is a high-quality stream located near the rapidly growing towns of Auburn and Opelika in east-central Alabama. From 1999 to 2007 we monitored freshwater mussel populations and measured substrate and water chemistry variables in Chewacla Creek. Surveys revealed that mussel abundance decreased substantially concomitant with degraded habitat and water quality downstream of three highly urbanized tributaries. We conducted sentinel trials using adult mussels (Villosa lienosa) in Chewacla Creek and a tributary (Parkerson Mill Creek) that receives wastewater discharge. Sentinel mussels were placed in cages at three locations downstream of the effluent discharge point and at one upstream site (control). Sentinel mussels exposed to wastewater discharge exhibited lower survival rates compared to control animals. Together, survey and experimental data suggest that degraded tributary subcatchments may fragment mussel populations in highquality streams. Moreover, our data indicate that protection of sensitive aquatic taxa necessitates effective management of water quality across large spatial scales.

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