Variations in seepage water geochemistry induced by natural and anthropogenic microclimatic changes: Implications for speleothem growth conditions

Abstract

During an annual cycle the affect of microclimatic changes (of natural and anthropogenic origin) on the geochemical characteristics of seepage water and mineral precipitation rates was analyzed for two karstic caves which contrast in environmental stability and energy exchange with exterior. On the one hand, Castañar cave (Caceres, Spain) is an extremely controlled show cave with limited visitation showing a minimum exchange rate of energy with the external atmosphere and, secondly, Canelobre cave (Alicante, Spain), is a widely visited cave where the anthropogenic impact generates rapid and high-energy environmental changes. Mineral saturation state of seepage water of both caves is controlled by microclimatic variations, such as: 1) natural underground air renewal through the porous system of the upper soil and the network of host-rock fissures, or elso through the cave entrance, 2) cumulative disruptions in the pCO2 levels of cave air due to the presence of visitors, and 3) forced ventilation of the subterranean atmosphere due to the uncontrolled opening of cave entrances. The obtained results reinforce the significance of the microclimatic fluctuations on short time scales in the dynamics of the subterranean karst systems, in terms of rates of mineral precipitation and growth of speleothems, as well as their key role for cave conservation.