Effects of Acid Precipitation and Natural Processes on Cation Leaching from Four Diverse Forest Ecosystems

摘要

Four forest ecosystems (two in eastern Tennessee and two in western Washington) with a history of intensive nutrient cycling research were selected for studies on the effects of acid precipitation and natural acid production processes on cation leaching rates. At the Tennessee sites, atmospheric acid input in bulk precipitation equaled or exceeded natural leaching by carbonic acid. At the less polluted Washington sites, natural leaching by carbonic acid was slightly larger than atmospheric acid input in the Douglas-fir soil. In the red alder soil, natural nitric acid formation far exceeded atmospheric acid inputs and appeared to have caused significant acidification of both soil and soil solution. The mobility of SO sub 42- and NO sub 3- in these four soils was a major factor in their relative susceptibilities to leaching by H sub 2 SO sub 4 and HNO sub 3 entering from the atmosphere. In two of the sites (chestnut oak in Tennessee and red alder in Washington), SO sub 42- adsorption reduced the potential for sulfate-mediated leaching by H sub 2 SO sub 4 by as much as one-half. Biological immobilization of NO sub 3- prevented leaching in all but the N-fixing red alder site. Both field and laboratory soil column studies involving artificial additions of SO sub 42- and NO sub 3- verified the concept that cation leaching is controlled by the mobility of the associated anion. (ERA citation 08:047313)