Separation of run-off components of a glacierized catchment in Kyrgyzstan, Central Asia, by tracer methods (mainly δ2H, δ18O) and meteorological data

Since 2014 the glacierized Ala Archa catchment (ca. 230 km2) in the Kyrgyz Alatau mountains south of Bishkek is investigated for run-off contributions of precipitation, groundwater, snow-melt, and glacier melt by tracer methods (δ2H, δ18O, electrical conductivity) and hydro-meteorological data (run-off, precipitation, air temperature, albedo). The investigation period is characterized by a high inter-annual variability in precipitation amount and summer run-off. The isotopic composition of run-off water is found to be governed more by the interplay of air temperature, precipitation history, and snow coverage than by its origin from direct precipitation, snow- or glacial melt. The isotopic composition of base flow in winter and early spring time is found to vary probably not due to a reservoir (mixing) but due to a phase exchange process (fractionation). In the light of these results a separation of all run-off components in such an environment simply with isotope methods appears to be unrealistic.