Anuran response to the contamination and reclamation of Nahant Marsh, an environmental protection agency superfund site.

摘要

In this study, the focal response of an anuran community to contamination, reclamation, and succession at Nahant Marsh, an Environmental Protection Agency (USEPA) Superfund reclamation site in Davenport, Iowa was assessed. Anurans were monitored at both the population and community levels using a Before-After/Control- Impact-Pairs (BACIP) study design. This was undertaken by conducting simultaneous anuran-calling surveys over a six-year period to evaluate anuran biodiversity within natural wetland pools in the Nahant Marsh Complex and an ecologically compromised Nahant Marsh pool that was contaminated with polycyclic aeromatic hydrocarbons and lead shot associated heavy metals during a 26-year period of skeet and trap shooting by the Scott County Sportsmen's Association.;As the first postulation of this study, it was hypothesized that marsh contamination had a negative effect on the anuran communities within Nahant Marsh pool 1 (route 1). Secondly, it was predicted that anuran populations within this pool would increase in the years following the USEPA Superfund reclamation, while those of adjacent Nahant wetland pools (route 2) would remain within the range of natural variability. The third expectation was that the USEPA Superfund reclamation of pool 1 would cause spatial and temporal shifts in anuran community composition.;Contamination of pool 1 had a negative effect on the anuran community and, for the most part, anuran populations increased post-reclamation while anuran populations along route 2 remained within the range of natural variability. The dramatic increase in the average number of calling males per survey indicates that the pool 1 anuran community responded positively to the USEPA Superfund reclamation, with pool 1 able to sustain, on average, almost as many calling male anurans as route 2 by the end of the study. Evenness within the anuran community was also increasing in 2003, an indication that anuran community composition is shifting and becoming more balanced as time progresses, which is a trend that is expected to continue in the years to come.;The third hypothesis was also substantiated, with individual species shifting in abundance spatially and temporally post-reclamation. The intensity of response varied with species, with response quick and dramatic for some, while others were slow to respond or did not respond at all. Also of interest is the response of the route 2 anuran populations to low Mississippi River levels, with spatial and temporal shifts in species abundance, dominance, and community evenness documented during and after this natural disturbance event. It is interesting to note that the average number of calling males per survey contracted from a peak of 45 back to a baseline of between 21 - 27 calling males once the low river level effect subsided. Furthermore, the average number of calling males per survey along route 1 increased post-reclamation to 25 by year 2003. The centralization of mean number of calling males per survey along both routes may be an indication of anuran carrying capacity for the Nahant Marsh Complex.