Abstract:

The presence of CO₂ in the caves affected by intense tourism activities has a significant impact on the drip hydrogeochemistry and sedimentation. In this investigation, a continuous monitoring on the indexes such as CO₂, temperature, relative humidity, tourist number and drip hydrochemistry was conducted in Guizhou Suiyang Dafeng Cave from 30 September 2017 to 9 October 2017. Following the collection of data, different methods were applied systematically to analyze a number of elements comprehensively. The observed results show that, under the influence of factors such as tourist number and ventilation effect of cave, the partial pressure of CO₂ in the cave (PCO_{2 (A)}) presented obvious diurnal and interdiurnal variations in the time sequence, and showed a higher value in daytime whereas a lower value at nighttime, and also a higher value on days with many tourists and a lower value on days with few tourists. In space variation, due to different ventilation degrees and cavity volumes, the PCO_2(A) of different monitoring points had obvious differences, from the deep cave to the entrance of cave as 3# (Magical Spring and Dewdrop) >1# (Time Tunnel)>2# (Legendary Luminous Pearl). Through the comparison of PCO_2(A) and drip temperature, the former had more significant influence on the solubility of CO₂ than the latter did. Moreover, the drip temperature and drip partial pressure of CO₂ (PCO_2(W)) of cave generally had the same trend of variation with that of PCO_2(A), and also presented obvious diurnal and interdiurnal variations. The pH, SIc, and HCO₃^- generally had a trend of variation in the opposite way to that of PCO_{2 (A)}, EC and Ca²⁺ had no obvious diurnal variation but certain interdiurnal variation. With an increase in the strength of tourism activities, the variation amplitude of drip hydrochemistry gradually increased. Furthermore, the differences in the factors such as cavity structure, size and closeness caused differences in the diffusion speed of PCO_2(A) and cave ventilation degree, and further influenced the hydrochemistry of the constituents of cave drip and sedimentation conditions of cave. Overall, this study will have a significant impact on the research on protection and management of cave environment as well as its karst cave carbon cycle.

Key words: anthropogenic CO₂, short-time scale, high intensity tourism activity, cave drip water, hydrogeochemistry, Dafeng Cave