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Water and air dynamics within a deep vadose zone of a karstmassif: Observations from the Lukina jama–Trojama cavesystem (−1, 431 m) in Dinaric karst (Croatia)

Extreme heterogeneity of karst systems makes them very challenging to study. Variousprocesses within the system affect its global response, usually measured at karstsprings. Research conducted in caves provides a unique opportunity for in situ analysisof separate processes in karst underground. The aim of the present study was toresearch the water and air dynamics within a deep karst system. Air and water basicphysical parameters across the Lukina jama–Trojama cave system (−1, 431 m) werecontinuously monitored during a 1‐year period. Recorded hydrograph of the siphonlake at the bottom of the cave was used to interpret the characteristics of an unex-plored phreatic/epiphreatic conduit network. Water origin in the siphon was deter- mined based on temperature and electrical conductivity. Air temperature andhumidity monitoring revealed a strong inflow of air of sub‐zero temperature into theupper portion of the cave during winter. Cave passage morphology was interpretedas the main determinant of air dynamics, which caused ice to accumulate extensivelyin the upper portions of the cave and caused the temperature on the top of thehomothermic zone to be significantly below the mean outside temperature. Air dynam-ics also lowered the temperature of water flowing through the cave vadose zone andfeeding the phreatic zone of the massif. The pronounced temperature differencebetween the phreatic zone and the top of the homothermic zone probably contributedto the thermal gradient observed in the cave, which is steeper than in ice‐free caves inthe area. Our results enabled the development of a conceptual model that describescoupling between air and water dynamics in the cave system and its surroundings.

cave meteorology, Dinaric karst, epiphreatic flow, karst hydrology, Lukina jama–Trojama cavesystem, Northern Velebit, thermal gradient, vadose zon

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