Anthropogenic acidic deposition deposits acidic nitrogen and sulfur compounds over large regions of forest in the eastern US. Long-term acidic deposition leads to forest soil acidification, depletion of soil calcium reserves, and lower foliar and litter calcium levels. These decreases in soil and plant calcium pools may cause a reduction in populations of calcium containing invertebrates, and thus transmit the effects of acidic deposition into higher trophic levels that have high calcium requirements. This research focuses on the effect of acidic deposition on populations of polydesmid millipedes and was conducted at the Fernow Experimental Forest long-term soil productivity (LTSP) site. The LTSP is an experimental acidification study composed of four blocks containing three treatment plots, and has been ongoing since 1996. The treatments accelerate acidification through addition of ammonium sulfate and add dolomitic lime as a potential method of amelioration. Previous unpublished work on this site has shown decreased pH and decreased calcium levels in foliage in the acidified plots. Millipede populations were sampled 4 times and analyzed for calcium content in attempt to show that chronic acid deposition may lead to decline of millipede populations and the standing pool of calcium they contain.

Results/Conclusions

After removal of data affected by an obvious outlier, our results indicate that experimental acidification decreased millipede populations by about 50% (p=0.011) and that addition of dolomitic lime did not restore the populations. The calcium content per millipede and individual millipede mass were unchanged by acidification or lime addition. Taken together, this means that the total amount of millipede calcium harvested per plot was lower in the acidified plots and that any animals relying on millipedes as a food source or source of calcium may be impacted by acidic deposition. Since songbirds eat millipedes, which are rather common and one of their only arthropod sources of calcium, songbirds may be affected—potentially contributing to recent declines in their populations. Also, any reduction in millipede populations has the potential to create nutrient cycling feedback effects because millipedes are important as processers of litter on the forest floor.