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.