Seven Decades of Calcium Depletion in Organic Horizons of Adirondack Forest Soils

We used repeated sampling of the forest floor to determine if there was a net loss of Ca from organic horizons of Adirondack forest soils between 1930 and 2004. In 1984, we established 48 permanent plots in spruce-fir, northern hardwood, and pine stands located in areas sampled by Carl C. Heimburger in the early 1930s. Following Heimburger's protocols and analytical methods, we measured pH and dilute-HCl-extractable Ca in Oe and Oa horizons, and determined that there was a statistically significant decrease in Ca concentration during the 1932 to 1984 interval. In the 36 plots that we could locate in 2004, we again sampled organic horizons. During the > 70-yr interval, HCl-extractable Ca concentrations in the Oe and Oa horizons decreased in each forest type (P < 0.05). We also measured NH4Cl-extractable Ca and Al in the 1984 and 2004 samples and found a significant decrease in Ca concentration in the pooled Oe horizons. High-elevation spruce-fir plots showed a Ca loss rate between 1984 and 2004 of 7.6 to 9.8 kg ha(-1) yr(-1). This compares well with a 4-yr Ca cycling study conducted in an equivalent spruce-fir forest at Whiteface Mt. in the Adirondacks, which showed an annual forest floor Ca loss of 8.4 kg ha(-1) yr(-1). Based on uptake and anion flux data from the Whiteface Mt. study, we estimated that about 25 to 30% of the 1984 to 2004 forest floor Ca loss in the spruce-fir plots is attributable to leaching driven by atmospheric SO42- deposition.