Comparative Evaluation of the Effects of Acid Precipitation, Natural Acid Production, and Harvesting on Cation Removal from Forests.

摘要

A comparison of the effects of acid deposition, natural leaching and harvesting on base cation export from forests in Maine, Tennessee, South Carolina, North Carolina, and Washington was made. Results showed that atmospheric deposition added at least 50-100% to natural leaching rates in study sites in the eastern United States, but only 1-2% in western Washington (the latter primarily due to high natural acid production). Sulfate flux accounted for 30-80% of total cation leaching in sites in the eastern United States, and only 3-12% of leaching in the Washington sites (the latter due to very high HCO sub 3- and NO sub 3- leaching rates). Nitrate leaching was negligible in all but a red alder site where net NO sub 3- leaching is caused by excess nitrogen fixation. Total base cation export by leaching exceeded Ca exp 2+ + Mg exp 2+ + K exp + export due to whole-tree harvesting in all but one site (Camp Branch, Tennessee). (The export of Na exp + via harvesting was assumed to be negligible compared to Ca exp 2+ , Mg exp 2+ , and K exp + .) Some sites showed a net Ca exp 2+ or K exp + accumulation from atmospheric deposition until they were subjected to whole-tree harvesting. Thus, leaching need not cause a net export of all nutrient cations even if total base cation export is accelerated by acid deposition. 4 references, 2 tables. (ERA citation 10:014387)