Isotopic Composition of Waters in the Demänovská dolina Valley and Its Underground Hydrologic System During Winter and Spring of 2010/2011

In the Demänovská dolina Cave system (Slovakia) and its vicinity, 32 sampling places for regular observation (in 2-months interval) of δ¹⁸O and δ²H in water were established. This monitoring included precipitation waters, waters in the surface streams, waters of the underground hydrological system as well as the dripping seepage waters of the cave system. Altitudinal extent of the area was from 800 m a.s.l. (lowermost cave entrance) to 2024 m a.s.l. (Chopok Mt. on the top of the crystalline range). Initial results show some similarities but also differences within the analyzed water types. For precipitation, a high variability of isotopic composition was confirmed, from quite depleted up to more enriched waters (δ¹⁸O from -16.8‰ up to -5.7‰; δ²H from -121.6‰ to -32.7‰). During the recharge process and groundwater/surface water formation, precipitation water is homogenized, what is reflected in much more stable isotope content. The most depleted (δ¹⁸O ≈ -11.7‰ to -10.8‰; δ²H ≈ -78.9‰ to -73.4‰) were the waters of surface streams, running from the northern slopes of the Nízke Tatry Mts., formed by crystalline rocks, alochtonous to the underground hydrological system. Smaller autochtonous surface water streams (formed in the side valleys of the main karstic canyon) are slightly enriched (heavier, as δ¹⁸O ≈ -11.4‰ to -10.6‰; δ²H ≈ -78.3‰ to -71.5‰), what reflects lower altitudes of their watersheds. Interesting is the distribution of the isotope content of the underground streams in the cave system. The most depleted are the underground streams directly (visibly) communicating with surface waters (δ¹⁸O≈-11.33±0.13‰; δ²H≈-76.88±1.68‰). Extent of the relationship of underground streams to the autochtonous seepage waters (slow circulation through the fissures) is manifested by respective portion of isotopically enriched waters–as the underground streams show different isotope composition. The combination of the alochtonous water components (from surface streams reaching the karstic area from the adjacent crystalline via swallow holes) and autochtonous water components (recharged directly in karstified limestones) is visible especially on the subsurface stream of Demänovka. The most isotopically enriched (heaviest) of all water types are dripping seepage waters (δ¹⁸O ≈ -10.4‰ to -9.4‰; δ²H ≈ -71.6‰ to -65.0‰).