Spatially distributed hydro-chemical data with temporally high-resolution is needed to adequately assess the hydrological functioning of headwater catchments

Abstract

Abstract We demonstrated the great value of spatially distributed and temporally high-resolution hydro-chemical data to enhance knowledge about the intra-catchment variability of flow processes and the runoff composition of individual storms in a tropical alpine (Paramo) ecosystem. In this study, water sources (rainfall, spring water, and water from soil layers of Histosols and Andosols) and nested streams were sampled bi-weekly (2013–2014), including three storm high-resolution events (5–240 min). Water samples were analyzed for 14 tracers including electrical conductivity (EC) and rare earth trace elements and used as input to perform End-Member Mixing Analysis (EMMA). End-members identified for the outlet could explain the hydrological behavior of four out of the five tributaries, indicating similar hydro-geochemical processes and geomorphic features within the catchments. The runoff source contributions of the individual sub-catchments varied among (e.g. Andosols ~40% in tributaries and ~25% at the outlet) and within storm events (e.g. Histosols 15% higher in small peak discharge event), indicating a time-variable composition of streamflows. The latter was also reflected by the interaction of different sources and the chronology of flow paths in EMMA-space, evidencing a faster connectivity with hillslopes in the upper sub-catchments compared to the lower sub-catchments. We found counter-clockwise hysteresis patterns of storms in the lower catchments and clockwise hysteresis loops in the upper catchments. The latter bi-directionality can be related to lower slopes, wider riparian areas and the higher proportion of Histosols in the lower catchments compared to the upper sites.