ANALYZING THE SHORT-TERM REDUCTION IN STREAMFLOW PH RESULTING FROM ACIDIC PRECIPITATION

The effects of acidic precipitation on stream chemistry were measured on an east-central Pennsylvania basin. When combined with flow and che mical mass balances, the data can help quantify hydrological source ar eas and their contributions to acidic storm hydrographs. For small sto rms on the well-buffered agricultural basin, small volumes of acidic p recipitation falling directly on the stream surface react with more al kaline inflows from subsurface flow and surface runoff components to r educe streamflow pH temporarily by approximately one-half unit. During larger storms, the pH of surface runoff approaches that of precipitat ion, causing a relatively large acidic loading to the stream. However, this large input is buffered by a correspondingly larger subsurface f low component which results in stream pH reductions similar to those o bserved during the smaller events. Hydrological interpretations derive d from a pH based mass balance are reinforced by a mass balance based on electrical conductivity and are consistent with the variable source area concept of basin hydrology.