PROCEEDINGS: Index of Abstracts

BIOGEOCHEMICAL CYCLING OF CARBON, NITROGEN, AND SULFUR AT THE HOWLAND INTEGRATED FOREST STUDY SITE, HOWLAND, MAINE

James W. McLaughlin, Ivan J. Fernandez, Stewart M. Goltz, Lindsey E.Rustad, and Larry Zibilske

Assistant Research Professor, Professor of Forest Soils, Research Associate Professor Emeritus of Climatology, Faculty Associate, and Associate Professor of Soil Microbiology, respectively, Department of Applied Ecology and Environmental Sciences, 5722 Deering Hall, University of Maine, Orono, ME 04469-5722.

The biogeochemistry of C, N, and S was studied for six years at the Howland Integrated Forest Study (HIFS) site by measuring those constituents in major above- and below-ground pools and fluxes. Leaching losses of C from the solum were much less than CO₂ efflux, with a mean annual leaching rate of 31.2 kg ha^-1 yr^-1. Carbon return to the forest floor via litterfall and outputs via CO₂ efflux were relatively equal. Mean annual total (wet+plus) atmospheric deposition inputs were 5.51 kg ha^-1 yr^-1 for NO₃^-N, 2.64 kg ha^-1 yr^-1 for NH₄⁺N, and 8.09 kg ha^-1 yr^-1 for SO₄^2-S; wet deposition inputs for C were 6.67 kg ha^-1 yr^-1. Sulfur-deposition, in the form of SO₂ dry deposition, and SO₄^2- in wet deposition showed significant decreasing temporal trends during the six year study period. There were no significant temporal trends for NO₃^- in neither dry nor wet deposition. Wet deposition of NH₄⁺, however, showed a significant decreasing pattern through the study period. Decreases in precipitation chemical flux was likely the result of decreases in precipitation volume through the study period because no significant decreases in concentration of SO₄^2- or NH₄⁺ occurred. There was a net ecosystem retention of NO₃^- and NH₄⁺, attributable to the N-deficiency of this forest. Mean annual input-output for SO₄^2-, however, was near zero for the study period, indicating the conservative behavior of that ion in this ecosystem. Ongoing research is attempting to further define the temporal trends in C, N, and S cycling, and to determine the mechanisms controlling these characteristics including the effects of temperature and moisture.