Precipitation, stream, and groundwater sample collection: Precipitation samples for water chemistry and isotope analysis were collected in wet deposition collectors at KPBS headquarters as part of the National Atmospheric Deposition Program (NADP). Water from the collectors was collected every Tuesday morning (whenever water was available) following NADP protocols. Subsamples(1-2 mL) were then collected from each precipitation sample for isotopic analysis. Each sample therefore integrates the stable isotopic signature of any preciptiation events over the previous seven days. Wet deposition collectors remain in a sealed closed position except during active precipitation events, eliminating the potential for evaporative isotopic enrichment of the precipitation samples. Samples are immediately frozen after collection. Stream samples were collected near the USGS weir locations on each watershed (N1B, N2B, N4D) three times per week in the mornings when water was available. Samples were collected from the middle of the stream and immediately frozen after collection. Groundwater samples from Edler Spring were also collected three times per week and immediately frozen after collection.
 
Stable isotope analyses: All water samples were analyzed for δ18O and δ2H using a Picarro WS-CRDS isotopic water analyzer at the Kansas State University Stable Isotope Mass Spectrometry Lab (SIMSL). Isotopic ratios were expressed in per mil (‰) relative to the international standard V-SMOW (Vienna Standard Mean Ocean Water). The long-term precision of water isotope analyses was assessed using three in-house standards to calculate a calibration curve, along with a laboratory working standard (n=16 per run) used for within-run drift correction. Assessed as standard deviation, the precision across and within runs was <0.3‰ for δ2H and <0.15 ‰ for δ18O.