Anthropogenic CO2-flux into cave atmosphere and its environmental impact: A case study in the Císařská Cave (Moravian Karst, Czech Republic)

The evolution of CO2 levels was studied in the ventilated and unventilated Nagel Dome chamber (the Císařská Cave) withand without human presence. Based on a simplified dynamic model and CO2/Rn data (222Rn considered as a conservative tracer), two types of CO2-fluxes into the chamber were distinguished: (1) the natural input of (2–4)×10−6 m3 s−1, corresponding to a flux of (8.5–17)×10−10 m3 m−2 s−1 and (2) an anthropogenic input of (0.6–2.5)×10−4 m3 s−1, corresponding to an average partial flux of (4.8–7.7)×10−6 m3 s−1 person−1. The chamber ventilation rates were calculated in the range from 0.033 to 0.155 h−1. Comparison of the chamber CO2-levels with chamber dripwater chemistry indicates that the peak CO2-concentrations during stay of persons (log pCO2 ∼−2.97, −2.89, and −2.83) do not reach the theoretical values at which dripwater carbonate species and air CO2 are at equilibrium (log pCO2[DW] ∼−2.76 to −2.79). This means that CO2- degassing of the dripwaters will continue, increasing supersaturation with respect to calcite (dripwater saturation index defined as SIcalcite=aCa2+aCO3 2−/10−8.4 varied in the range from 0.76 to 0.86). The pCO2[DW] values, however, would easily be exceeded if the period of person stay in the chamber had been slightly extended (from 2.85 to 4 h under given conditions). In such case, the dripwater CO2-degassing would be inverted into CO2-dissolution and dripwater supersaturation would decrease. Achieving the threshold values at which water become aggressive to calcite (log pCO2[EK] ∼−1.99, −2.02, and −1.84) would require extreme conditions, e.g., simultaneous presence of 100 persons in the cave chamber for 14 h. The study should contribute to a better preservation of cave environment.