Stable isotopes and water chemistry in ?achtice Cave and Hladovy prameň Cave in relation to karst topology, soil cover, and past land-use

摘要

The ?achtické Karpaty Mts. are the northernmost part of the Malé Karpaty Mts. The studied area belongs to the ?achtice Karst area built by Middle to Upper Triassic Wetterstein limestone and dolomite. The Hladovy prameň and ?achtická caves represent two contrasting cave systems, which were formed along steeply dipping fault structures with N–S and NW–SE strikes, respectively. The stable isotopes of CO2 in water samples from both caves point to microbially produced soil CO2 as main source of carbon in dissolved bicarbonate. We observed lighter carbon in water of the Hladovy prameň, probably due to thicker pile of decomposing leaf litter above the cave and thus more soil CO2 production. The study of carbon isotopes in grasses and soils with different histories of land-use ruled out presence of grasslands dominated by C4 plant species producing heavier carbon. In speleothems, the lightest oxygen occurs in soda-straws, while in flowstones and helictites the oxygen is heavier due to evaporation prior to calcite crystallization. Dripwater sampled simultaneously in the Hladovy prameň and ?achtická caves slightly differ, reflecting a lagged response to rainfall events due to much thicker overburden in the ?achtická Cave. According to chemical analyses, the spring water at the Hladovy prameň Cave has developed in shallow circulating system within Wetterstein Limestone, without significant contact with underlying dolomites.