Effects of Atmospheric Pollution on High-Elevation Fauna in the Southern Appalachians.

摘要

The Southern Appalachians are exposed to some of the highest levels of air pollution in North America. Animals in the higher elevations where deposition is greatest may be vulnerable to the effects of acidic and mercury deposition. Because an acidified environment both enhances methylation of mercury and depletion of calcium, the adverse effects of air pollution are complex. Calcium limitation is a primary concern for animals living in acidified landscapes, where birds may experience eggshell defects, decreased nesting success and decreased fitness, and snails may experience decreased abundance and diversity. We examined the effects of acidic deposition on Dark-eyed Juncos ( Junco hyemalis) and terrestrial snails in the Southern Appalachians using a geostatistical model of lead deposition in the organic horizon as a surrogate for acidic deposition. We found a significant decrease (up to 18%) in egg calcium with increasing atmospheric deposition. We also conducted a calcium supplementation experiment to test if added calcium within junco breeding territories would yield increases in factors associated with reproductive success. We found a weak effect of calcium supplementation on clutch size and egg volume; however we were unable to detect a positive effect on daily nest survival or hatchability. Thus, although acidic deposition may be affecting the composition of calcium within eggs and clutch sizes, we were unable to detect any population-level effects in the juncos.;We found that increasing soil pH and calcium, and decreasing percent downed dead wood, but not deposition, were the strongest predictors of increasing snail abundance, diversity, and shell volume. The strong negative relationship with downed dead wood may be a function of increased habitat for salamanders, a known snail predator. Snail species richness, abundance and shell volume were also consistently lower in Fraser fir (Abies fraseri) habitat, which may be related to the major ecosystem restructuring following extensive fir mortality from the invasive balsam wooly adelgid (Adelges picea) and the subsequent rapid pulse of dead wood to the system. Snail abundance is thus a reliable indicator of overall calcium availability at the ecosystem level. As snails are the primary calcium source for higher order species such as birds and salamanders, monitoring snail populations in areas susceptible to high acidic precipitation is warranted.;We analyzed feather mercury levels in 458 individuals of 32 Southern Appalachian bird species. Our results indicate that terrestrial songbirds in the Southern Appalachians are accumulating mercury at levels similar to those recently documented in the northeastern U.S. As predicted, mercury was detected in every bird sampled (elevations ranged from 420 to 2,000 m). Mercury levels varied across species, with much of the variation related to foraging ecology. In general, higher mercury levels were found in invertivores compared to omnivores, and in birds with higher delta15N levels, indicating higher trophic position. To our knowledge, this is the first study to link trophic position to mercury levels in terrestrial birds using stable isotopes. Only one individual, a Carolina Wren from the shore of Lake Fontana, NC, had mercury levels (3.74 ug·g-1) likely to cause measurable (10--25%) reductions in nesting success. The lakeside location of this site suggests that mercury could be biomagnifying through the aquatic food web, and entering the terrestrial food web when aquatic larvae emerge as adults. We highly recommend further sampling of mercury in birds and other animals that feed at higher trophic levels in the Lake Fontana area, as lakes can act as reservoirs for mercury and support sulfate-reducing bacteria which converts inorganic mercury to the biologically toxic methylated form.