Accounting for Time and Space Variations of δ\u3csup\u3e18\u3c/sup\u3e in a Snowmelt Isotopic Hydrograph Separation in the Boise Front

Results from isotopic hydrograph separations in the Bogus Experimental Catchment are highly dependant on the method used to account for the new water chemistry. Spatial and temporal variations in snowmelt δ18O are the source large errors resulting in outcomes of the hydrograph separation that range from 25% to 99% old water. Spatial variations in δ18O are significant on the catchment- and meter scales. A reliable isotopic hydrograph separation is possible for a snow melt event if spatial and temporal variability in δ18O, and travel time of snowmelt to the stream can be taken into account. Spatial variability of melt δ18O in the Bogus Experimental Catchment cannot be accounted for with elevation, slope, or aspect. Standard deviations of δ18O on the meter scale range between 1.29% and 0.40%. The proposed method of constructing a new water isotopic signal distributes a daily averaged isotopic time series across the basin according to the Darcy Velocity. 68% of the 2003 snowmelt hydrograph at the Bogus Experimental catchment is old water