The negative effects of upstream development on aquatic environments downstream have been documented by many studies. Foremost among species impacted by development are the amphibians, a group perceived as potential sentinels of environmental change because the life histories of many amphibian species are structured around terrestrial and aquatic habitats susceptible to alteration. We sampled amphibians from 12 different riparian forested wetlands downstream of watersheds with varying degrees of upland development in southeastern Virginia. In those wetlands we measured amphibian density using the standard coverboard method in relation to environmental features including degree of upstream development, stream incision, and stream water quality.
Results/Conclusions
A total of 173 amphibians were observed during the study, including two-lined salamanders (Eurycea bislineata), three-lined salamanders (Eurycea guttolineata), and leopard frogs (Rana pipiens). Using exponential decay models, average amphibian density was negatively correlated with upland development, water temperature, and conductivity. Development upstream was positively correlated with incision downstream. All other habitat variables (upstream watershed area, stream pH, SRP, NO3+NO2, and NH4), however, were not significantly correlated with average amphibian density. Collectively, the impacts of development are to reduce downstream habitat suitability for amphibians. With a lowering of stream elevation is a concomitant lowering of the floodplain water table. The wetlands become drier with greater stream incision. Thus, we suggest that fewer amphibians downstream of development is a potential outcome due to both decreases in stream water quality (temperature and conductivity) for eggs and larvae and decreases in water availability (stream incision and lowering of the wetland water table) for adults.