Hydrograph separation using isotopic, chemical and hydrological approaches(Strengbach catchment, France)

The streamflow components were determined in a small catchment located in E astern France for a 40 mm rain event using isotopic and chemical tracing wi th particular focus on the spatial and temporal variations of catchment sou rces. Precipitation, soil solution, springwater and streamwaters were sampled and analysed for stable water isotopes (O-18 and H-2), major chemical paramete rs (SO42-, NO3-, Cl-, Na+, K+, Ca2+, Mg2+, NH4+, H+, H4SiPO4, alkalinity an d conductivity), dissolved organic carbon (DOC) and trace elements (Al, Rb, Sr, Ba, Pb and U). O-18, Si, DOG, Ba and U were finally selected to asses the different contributing sources using mass balance equations and end-mem ber mixing diagrams. Isotopic hydrograph separation shows that the pre-event water only contribu tes to 2% at the beginning of the stormflow to 13% at the main peak flow. D OC associated to Si and U to Ba allow to identify the different contributin g areas (upper layers of the saturated areas, deep layers of the hillslope and rainwater). The streamflow (70%) originates from the deep layers of the hillslope, the remaining being supplied by the small saturated areas. The combination of chemical (both trace and major elements) and isotopic tr acers allows to identify the origin of water pathways. During the first sta ge of the storm event, a significant part of the runoff (30-39%) comes from the small extended saturated areas located down part of the basin (overlan d runoff then groundwater ridging). During the second stage, the contributi on of waters from the deep layers of the hillslope in the upper subcatchmen t becomes more significant. The final state is characterised by a balanced contribution between aquifers located in moraine and downslopes. Indeed, this study demonstrates the interest of combining a variety of hydr ometric data, geochemical and isotopic tracers to identify the components o f the streamwater in such conditions. (C) 2001 Elsevier Science B.V. All ri ghts reserved.