Marek Lang

Variances in airflows during different ventilation modes in a dynamic U-shaped cave

Airflow dynamics were studied in Cisařska Cave (Moravian Karst, Czech Republic) under different seasonal conditions. The dependence of airflows on the difference between external and cave temperatures is nonlinear and roughly obeys the Darcy-Weisbach equation. The upward airflows were found to be systematically higher than the downward airflows under comparable driving forces. The principle reason is nonlinearity between air temperature and air density. U-shaped cave geometry magnifies this effect by feedback between external temperature and airflow driving forces. Whereas this feedback is positive during the upward airflow ventilation mode, it is negative during the downward airflow mode. To discuss the behavior in detail, a simplified model based on balancing the masses of two equivalent air columns of different temperatures and densities is proposed. The results contribute to a better understanding of cave microclimate evolution, cave CO2 dynamics, and speleothem growth.

The impact of door opening on CO2 levels: A case study from the Balcarka Cave (Moravian Karst, Czech Republic)

The impact of door opening on cave carbon dioxide (CO2) levels was studied in the Entrance Chamber and the Gallery Chamber of the Balcarka Cave (Moravian Karst, Czech Republic). The effect of door opening differed with cave ventilation modes. Under upward airflow mode, the cave door opening led to the increase of output advective CO2 fluxes from the cave and to the decrease of CO2 levels. This effect was evident especially in the Entrance Chamber near the cave entrance and then suppressed in the Gallery Chamber situated deeper in the cave. Under the downward airflow mode, the cave door opening changed airflow paths and main CO2 sources/fluxes. This resulted in the increase of CO2 level in the Entrance Chamber while the levels in the Gallery Chamber decrease. Modeling indicates that the increase could be result of input advective CO2 fluxes from epikarst (up to 5.9 × 10-2 mol s-1). To reduce the impact on cave microclimate, a careful control of the visiting regime without overlapping of individual doors’ openings is recommended.