Stable oxygen isotope variations in rain, snow and streamwaters at the Schluchsee and Villingen sites in the Black Forest, SW Germany

Results of oxygen isotopic measurements for rain, snow and streamwaters in three catchments in the Black Forest, SW Germany, for a full range of hydrological events (snowmelt and heavy rain following dry and wet antecedent conditions) are used to assess the contribution of rainfall and snowmelt to stream flow generation. Contrasting isotopic behaviour occurs. For three of the 11 events examined, the change in streamwater isotopic composition reflects that of the rainfall or snowmelt generating the hydrological response. For three other events, the direct contribution of rainfall and snowmelt to the stream flow generation must be small, as the opposite pattern occurs. For the remaining events, the stream isotopic composition remains constant. For most of the year, all three sites show similar isotopic patterns, indicating that similar controls regulate the isotopic composition in the stream. The isotopic patterns show that direct runoff from rainfall or snowmelt is only a minor source of stormflow response. In some cases at least two pre-event water types can be inferred.