ATMOSPHERIC DEPOSITION AND FOLIAR LEACHING IN A REGENERATING SOUTHERN APPALACHIAN FOREST CANOPY

(1) Incident precipitation, throughfall and stemflow were collected to examine the importance of factors potentially determining net canopy element fluxes, and to quantify canopy exchange and dry deposition rates in a regenerating southern Appalachian forest. (2) Net throughfall fluxes (throughfall minus precipitation transfers) showed consistent canopy effects on rainfall chemistry, with SO42-, PO43-, Cl-, K+, Ca2+ and Mg2+ added to rainfall by foliage, whereas NO3--N, NH4+-N and H+ ions were absorbed from precipitation. Storm characteristics (event amount and duration) accounted for the largest portion of the variability in growing season net throughfall fluxes, suggesting that canopy exchange was the major mechanism of throughfall transfer. (3) Stemflow fluxes increased canopy exchange rates of SO4(2-), PO4(3-), Cl-, K+, and Mg2+ by greater than 20% in a regression model of total below-canopy element fluxes. (4) Cation leaching fluxes were highly variable (C.V. > 50%) over spatial scales of several m2, but could be explained largely by heterogeneity in canopy cover. (5) Foliar cation leaching losses in the early successional forest accounted for 4-13% of leaf nutrient reserves. As cation throughfall transfers were highest during storms with the greatest hydrogen ion uptake from rainwater, it is hypothesized that acid precipitation is causing accelerated foliar nutrient leaching in south-eastern hardwood forests.