Acid-deposition-induced Calcium Depletion from Adirondack Forests and the Response of Biotic Communities to Calcium Amendment

Timothy McCay1, Michele Hluchy2, Richard April3 and Randall Fuller1

We aimed to better understand how calcium availability has changed in forests of the Adirondacks and determine how biotic communities respond to calcium amendment at one acid-deposition-impacted forest in the western Adirondacks. We re-sampled soils at sites initially sampled in the 1980s and analyzed samples for total exchangeable calcium and other soil parameters. We amended soil calcium in forest uplands by adding powdered limestone (lime) to each of four 1590-m2 plots to effect a treatment of 10 tonnes lime per hectare. Each limed plot was paired with an untreated plot, and a stream ran between the two plots. We added CaCl2 to one of these episodically acidified streams and both CaCl2 and NaHCO3 to another episodically acidified stream for 6 weeks. Preliminary analysis suggests that total cation abundance at Adirondack forests has decreased since the 1980s and that the greatest decreases have occurred at sites in the central and eastern Adirondacks where losses had been modest prior to the 1980s. Liming raised the soil pH in the upper horizons of our plots as expected and, over time, that effect is being translated lower into the soil profile. Similarly, exchangeable calcium is increased in the upper horizons of limed soils, although that increase is only seen down to about 15 cm even 3 years after the first application of lime. Leaves of overstory plants showed an increased concentration of elemental calcium within 6 months of the first application of lime, thus increasing calcium availability for animals that consume leaf litter. Responses by animal taxa have been mixed with some groups, such as snails, increasing and many others decreasing after liming. Generally, this community of forest organisms is acidophilic and community change may require immigration of taxa from less acidified habitats. In streams, increasing Ca concentrations alone had no effect on alkalinity and no effect on abundance of macroinvertebrates and periphyton or rate of leaf decomposition. In the stream receiving both CaCl2 and NaHCO3, we observed an increase in alkalinity; however, again there was no effect on macroinvertebrates, periphyton, or rate of leaf decomposition. Thus, our 6 week manipulations of calcium and bicarbonate in these streams were probably not long enough to overcome the legacy effects of episodic acidification events. In sum, our results suggest that recovery of forests from chronic acidification will be slow because of cation loss and the adaptation of forest and stream communities to acidified conditions.

1 Biology and Environmental Studies, Colgate University, Hamilton, NY 13346
2 Geology and Environmental Studies, Alfred University, Alfred NY 14802
3 Geology, Colgate University, Hamilton, NY 13346