The use of shallow dripwater as an isotopic marker of seepage in karst areas: A comparison between Western Sicily (Italy) and the Harz Mountains (Germany)

Abstract

The isotopic signature of slow-flowing dripwater collected in caves located in Western Sicily (Italy) was determined for evaluating its possible use as an isotopic tracer of the local groundwater recharge. These spot measures were compared with a longer series of local rain and spring compositions and with other samples taken, under different hydrogeological conditions, in caves of the Harz Mountains (Northern Germany). The slow flowing dripwater from Sicily showed δ18O/δD ratios similar to those of local rain and groundwater, demonstrating that these three are all parent waters. A parallel similarity was found in the vertical isotopic gradient (Δδ18O) of the three groups of water, accounting for their common meteoric origin. In the colder Harz Region, dripwater, spring water and rain have the same δ18O/δD ratio but fast flowing dripwater, infiltrating through open cracks, is significantly enriched in lighter isotopes and representative of short residence time percolation. These results lead to the conclusion that dripwater, even if collected as spot samples, can be considered as a good isotopic marker of the average local groundwater recharge on the condition that only slow, diffused drips due to seepages are sampled.