Use of δ18O tracer to identify stream and spring origins of a mountainous catchment: A case study from Liddar watershed, Western Himalaya, India

SummaryWater samples from precipitation, streams and springs were collected and analyzed for oxygen isotope composition to identify the stream and spring origins in Liddar watershed, NW Himalaya, India. Samples were collected from eight precipitation sites, 14 streams and six springs on bimonthly basis from January/March 2008 to January 2009. The data generated indicated a strong spatial and temporal variation in oxygen isotope composition. An altitude effect of −0.1‰ to −0.5‰/100 m change in elevation (mean altitude effect: 0.19‰/100 m) was discernible in precipitation isotopic composition. The precipitation was 18O depleted in cooler seasons/months and at higher elevations. The δ18O of precipitation showed a narrow range (2–5‰) during the periods/months of more precipitation and wide range (8–13‰) during the other months. Like precipitation the isotopic composition of streams is also controlled by the elevations of their catchments. The stream water was 18O depleted in the mountain areas with their catchments at higher altitudes than at lower elevations. The streams/tributaries were most 18O depleted in May and least depleted in September. The oxygen isotope composition of springs is similar to that observed in the streams, being most 18O depleted in May and least 18O depleted in September. On the basis of local vertical isotopic gradient of oxygen the mean altitude of the recharge by rainfall infiltration was estimated. The widespread melting of snow, the high discharges of the streams and the springs and 18O depleted stream and spring waters indicate the dominant contribution of snow melt in May; negligible snow melting, precipitation in the form of snow only, less stream and spring discharges and less variance indicate the contribution from baseflow in January; while as exhausted snow, moderate stream and spring discharges and 18O enriched stream and spring water indicate the contribution from rainfall. The best correlation was observed between the δ18O of springs and streams.