Charakteristika Anomálního Skapu v Punkevních Jeskyních (Moravský Kras)

Abstract

Cave speleothems grow from supersaturated dripwaters and store information about various karst processes along the water fl ow path. Anomalous non-saturated waters may occur if (1) rainfall water passes very rapidly through karst profi le or if (2) two saturated waters of diff erent compositions are mixed. Th e low mineralization close to saturation could be reached also as (3) result of calcite precipitating prior the water enters the cave. Th e hydrogeochemistry of four dripwaters in the Punkva Caves (Moravian Karst) was systematically studied for anomalous properties during one-year period. Th e drips are situated in a passage behind Přední Dóm Chamber (CP1 and CP2, 24 samples each), in Tunnel Corridor (TC1, 24 samples), and in Zadní Dóm Chamber (ZD1, 6 samples). Th e dripwaters CP1, CP2, and ZD1 show various fl ow regimes but very similar hydrogeochemical properties: electric conductivity (EC = 550-630 μS/cm), saturation (SI calcite = 0.8-1.2), and Mg/Ca ratio (1000*(Mg/Ca) = 15-20). In contrast, the dripwater TC1 shows stable drip rate and EC = 275-350 μS/cm, SI =-0.1 to 0.3, and almost thrice as high Mg/Ca ratios as other drips. High and stable discharge of the drip TC1, combined with low EC, SI close to zero, and high Mg/Ca ratio indicate that a prior precipitation of calcite is responsible for the anomalous composition of the dripwater. Th e slightly negative SI values that were occasionally observed indicate that further minor processes probably participate on the water formation.