PROCEEDINGS: Index of Abstracts

ALUMINUM MOBILIZATION AND CALCIUM DEPLETION IN THE FOREST FLOOR OF RED SPRUCE FORESTS IN THE NORTHEASTERN UNITED STATES

Gregory B. Lawrence-1, Mark B. David-2 and Walter C. Shortle-3

1-Research Hydrologist, US Geological Survey, 425 Jordan Rd., Troy, NY 12180. 2-Associate Professor, Dept. of Natural Resources and Environmental Sciences, University of Illinois, W-503, Turner Hall, 1102 S. Goodwin Ave., Urbana, IL 61801. 3-Supervisory Research Plant Pathologist, USDA Forest Service, Northeastern Forest Experiment Station, Durham, NH 03824.

Mechanisms of Ca depletion were investigated as part of a regional study of relations among acidic deposition, soil chemistry and red spruce decline. Comparison with results from studies in the Adirondack Mountains of New York and the White Mountains of New Hampshire indicates that current acid-extractable Ca concentrations in the Oa horizon are less than one-half the average measured in the 1930's. A statistically significant decrease of similar magnitude was also observed for both exchangeable and acid-extractable Ca, over the past two decades, in archived Oa horizon samples collected in red spruce stands at the Hubbard Brook Experimental Forest, N. H. The same samples indicated increases in exchangeable and acid-extractable Al concentrations over this period. Our results indicated no relation between concentrations of exchangeable Ca and exchangeable H in the forest floor, whereas a strong inverse relation was observed between concentrations of exchangeable Ca and exchangeable Al. We also found that exchangeable Al concentrations were related to the concentrations of acid-extractable Al (mostly organically complex Al), but unrelated to mineral Al concentrations. Furthermore, the exchangeable Al content of the forest floor was positively correlated with the molar ratio of inorganic Al to Ca in the soil solution of the B horizon. We propose that Al mobilized within the mineral soil by acidic deposition is an important contributor to the pools of exchangeable and acid-extractable Al in the forest floor. Once mobilized in the mineral soil, Al is transported by water movement and root uptake into the forest floor, where it can replace Ca on exchange sites through its strong affinity for organic functional groups.