The influence of hydrologic processes on Al chemistry was investigated along an elevational gradient in a headwater stream at the Hubbard Brook Experimental Forest. Relationships between streamflow and concentrations of inorganic and organic Al, H+, and dissolved organic carbon varied within the watershed. At high elevations, increased streamflow was associated with reduced surface water acidity and decreased inorganic Al concentrations. At low elevations, however, increased streamflow was associated with increases in stream acidity and concentrations of inorganic Al. Changes in soil flow paths and variations in source areas both appear to regulate stream chemistry. Flow through upper soil horizons under high‐flow conditions appears to be the controlling hydrologic influence on stream chemistry at the high‐elevation site. At the low‐elevation site, contributions of flow from the more acidic, upper region of the watershed during high‐flow conditions appears to be the major hydrologic influence on stream chemistry. During low‐flow conditions the upper reaches of the stream become dry, so that there is no contribution to flow from this part of the watershed. Stream solutions appeared to be closest to equilibrium with respect to natural gibbsite under high‐ and low‐flow conditions, with no indication that changes in flow introduced disequilibrium conditions. Efforts to incorporate hydrologic effects into surface water acidification models must address the relationship between runoff generation mechanisms and spatial variations in watershed biogeochemistry.
ASJC Scopus subject areas
- Water Science and Technology