The relationship between carbon dioxide concentration and visitor numbers in the homothermic zone of the Balcarka Cave (Moravian Karst) during a period of limited ventilation

The evolution of CO2 levels with and without human presence was studied in a selected site
(Gallery Chamber) of the homothermic zone of the Balcarka Cave (Moravian Karst, Czech
Republic) during the fall, a period of limited ventilation. There were recognized various factors
controlling the cave CO2 levels under different conditions in the exterior and interior. When
visitors were absent, CO2 levels were controlled by the advective CO2 fluxes linked to cave
airflows and reaching up to ~1.5 x 10-3 mol s-1. These fluxes exceed by orders of magnitude
the exchanged diffusive fluxes (up to 4.8 x 10-8 mol s-1) and also the natural net flux (from
1.7 x 10-6 to 6.7 x 10-6 mol s-1) imputing given chamber directly from overburden. The natural
net flux, normalized to unitary surface area, was estimated to be 2.8 x 10-8 to 1.1 x 10-7 mol m-2
s-1, based on a perpendicular projection area of the chamber of ~60 m2. When visitors were
present, the anthropogenic CO2 flux into the chamber reached up to 3.5 x 10-3 mol s-1, which
slightly exceeded the advective fluxes. This flux, recalculated per one person, yields the value
of 6.7 x 10-5 mol s-1. The calculations of reachable steady states indicate that anthropogenic
fluxes could almost triple the natural CO2 levels if visitors stayed sufficiently long in the cave.