Solution Chemistry of a New Hampshire Subalpine Ecosystem: A Biogeochemical Analysis

Abstract

Field studies were conducted to examine the processes and environmental factors which influence or control ion transport in ecosystems receiving chronic acid precipitation. Specifically, these studies focused on changes in solution chemistry during rainfall percolation through a cool, moist balsam fir forest in the subalpine zone of the White Mountains of New Hampshire. Patterns of solution chemistry exhibit the following distinctive trends: (1) atmospheric sulfate is the dominant anion in the leachate from this system, although organic ligands were probably the major anionic species in solution in the past; (2) soil aluminum leaching appears to be increasing in response to acid precipitation, resulting in comparatively high dissolved aluminum concentrations in the soil solution; and (3) most neutralization of atmospheric sulfuric acid occurs at depth in the mineral soil, rather than in the fir forest canopy or forest floor. The behavior of individual ions in the fir zone system appears to depend upon the differential effects of the following major factors: atmospheric input rates, biological demand, ion exchange affinities, acidity of the percolate, and rates of ion release and consumption in weathering, mineralization, and geochemical buffering reactions.