A new high-resolution groundwater isoscape for South-East Germany: insights from differences to precipitation

Abstract. Stable water isotopes are important tracers to understand interactions between all compartments of the hydrological cycle. Particularly in groundwater studies they have been used to assess recharge and origin of groundwater. Based on high- density groundwater measurements, we produced a new, interpolated map of the δ¹⁸O distribution (i.e. an isoscape) in groundwater of south-east Germany. A comparison of this groundwater isoscape to the regional long-term precipitation isoscape showed differences of up to ±2 ‰ between both compartments. Groundwater was enriched in the light isotope ¹⁶O compared to precipitation in the alpine area where recharge occurs mainly during winter and at recharge areas at higher altitudes. However, groundwater was enriched in the heavy isotope ¹⁸O with respect to precipitation in drier lowland regions where summer recharge, irrigation practices and aquifer types as well as evaporation processes may play a role. Further comparative studies between precipitation and groundwater stable water isotopes by using time series are needed to improve the understanding of spatial and seasonal recharge patterns of groundwater.