Submitted to: Geological Society of America Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2003
Publication Date: N/A
Technical Abstract: The goal of this research is to use environmental tracers to quantify the contributions of subsurface and surface runoff to rivers at multiple scales (field to catchement). The study area is the Missouri Flat Creek watershed, a 7,000 hectare (ha) semi-arid dryland agricultural setting located near Pullman, WA. Surface and ground water samples are collected at two-week intervals from an ephemeral stream and a tile drain located in actively farmed and topographically constrained fields (~6 ha) and from three stream-gauging stations. Samples were analyzed for two pesticides,the insecticide lindane and the herbicide triallate, the environmental tracers, electrical conductivity (EC) and silica, turbidity, nitrate, and oxygen-18. Our conclusions are the following. Point-wise lindane predictions are the best at the small and large watershed scale and most overpredicted at the edge of field scale. Yearly mass discharge predictions are underpredicted using the regression method compared to the Hydrograph method. Overestimation of predicted pesticide mass discharges are likely attributable to the following reasons: 1) Differences between observed and interpolated end-member chemistries for both tracers and pesticide; and 2)attenuation by sorption or sedimentation, volatilization, and transformation reactions. The variations in nitrate and lindane concentrations in streams illustrates the complexicities of instream processes. Hydrograph separation is a economical and non-time intensive method to track chemical mass discharges over various scales in a watershed because it is cheap, easy, and non-site specific.