Effects of Basin Size on Low-flow Stream Chemistry and Subsurface Contact Time in the Neversink River Watershed, New York

The e€ects of basin size on low̄ow stream chemistry and subsurface contact time were examined for a part of the Neversink River watershed in southern New York State. Acid neutralizing capacity (ANC), the sum of base cation concentrations (SBC), pH and concentrations of total aluminum (Al), dissolved organic carbon (DOC) and silicon (Si) were measured during low stream ̄ow at the outlets of nested basins ranging in size from 0.2 to 166.3 km. ANC, SBC, pH, Al and DOC showed pronounced changes as basin size increased from 0.2 to 3 km, but relatively small variations were observed as basin size increased beyond 3 km. An index of subsurface contact time computed from basin topography and soil hydraulic conductivity also showed pronounced changes as basin size increased from 0.2 to 3 km and smaller changes as basin size increased beyond 3 km. These results suggest that basin size a€ects low̄ow stream chemistry because of the e€ects of basin size on subsurface contact time. # 1997 by John Wiley & Sons, Ltd. Hydrol. Process., Vol. 11, 1273±1286 (1997). (No. of Figures: 6 No. of Tables: 2 No. of Refs: 30)