The Hydrological Eff ects of Lateral PreferenƟ al Flow Paths in a Glaciated Watershed in the

Despite observaƟ onal evidence of lateral preferenƟ al fl ow paths in northeastern U.S. water-sheds, their eff ects on the sources of runoff remain unclear. An intense fi eld survey was undertaken during the 2007 growing season to determine the sources of stream runoff from a 2.51 km2 watershed in the Catskill Mountains, New York State. Lateral preferenƟ al fl ow paths are caused by groundwater springs and soil piping in this region. A two-component hydrograph separaƟ on using δ18O showed that event water (rain water) was a signifi cant source of runoff during nine rainfall events (from July to October). With these rainfall events, 14 to 37 % of the volume and 18 to 49 % of the peak streamfl ow was aƩ ributable to event water. Further, end-member mixing analysis (EMMA), using δ18O, Si, and dissolved organic carbon (DOC), showed that saturated areas accounted for 2 to 24 % of the total volume and 4 to 59 % of peak streamfl ow but that groundwater was the dominant source of runoff volume during all events. Field surveys of saturated areas also suggested that near-stream areas were insuffi cient to generate the observed stream chemistry during rainfall events larger than 8 mm. A connecƟ on with the hillside saturated areas was therefore required to explain the results of the hydrograph separaƟ ons, which were corroborated by the Ɵ ming of the tran