HYDROLOGIC PROCESSES CONTROLLING SULFATE MOBILITY IN A SMALL FORESTEDWATERSHED

Hydrologic controls on sulfate mobility were investigated in a foreste d catchment in the Georgia Piedmont using a watershed mass balance app roach. Variations in annual sulfate export were governed primarily by differences in runoff rather than by differences in sulfate deposition or in total annual precipitation. However, 2 years with similar total runoff had substantially different sulfate export. A residual analysi s indicated that a shift in the concentration-discharge relationship a ccounted for 72% of the difference in sulfate export and that a change in the pattern of discharge accounted for the remainder of the differ ence. Stream water sulfate concentrations reflected past hydrologic co nditions. Concentrations at the same discharge were higher following a n extended dry period than following average periods. The elevation in stream water sulfate concentrations following dry periods persisted f or several months. The influence of rainfall patterns on sulfate expor t underscores the need for long-term records to adequately characteriz e the acidification status of the watershed and to understand trends i n water quality.