Can conductivity and stable isotope tracers determine water sources during flooding? An example from the Elbe River in 2002

Abstract Despite drastic runoff variations, stable isotope data of water in the upstream part of the Elbe River showed remarkable similarity during, and two months after the flood of 2002. This homogeneity indicates that water sources remained the same and most likely represents dominant groundwater input regardless of the flood. While the latter remains the most plausible explanation, it was difficult to prove with water stable isotopes for the upstream part of the river. Overlapping isotope compositions of long‐term average precipitation data (as a proxy for the groundwater end member) and of the weighted average from precipitation events in August 2002 did not allow quantification of the groundwater component during flooding. This shows that better spatial and temporal sample resolution is necessary for enhanced understanding of water sources and mass balances during floods. Such mass balances were only possible in the estuary where conductivity and stable isotope tracers both revealed much stronger fr...