Wavelet transform analysis of the response mechanism of CO2 concentration to tourist activities in Zhijin Cave

ZHANG Hongzhi; WU Kehua; LUO Shuwen

doi:10.11932/karst20250607

Abstract：Karst caves are among the most frequented visited geological sites worldwide.However,their stable environments are vulnerable to changes caused by tourist activities,including variations in temperature,CO2 concentrations,humidity,airflow,microbial communities,and groundwater chemistry.Therefore,it is imperative to investigate the impact of tourist on cave ecosystems and to implement strategies aimed at enhancing the overall environmental quality of these caves.These efforts are crucial for ensuring the sustainable development of tourist caves. As a principal driver of karst processes,CO2 has garnered considerable attention in the fields of regional carbon cycling,weathering of cave sedimentary landscapes,and the analysis of cave ecological capacity.Prior research primarily focused on the characteristics of CO2 concentration variations,their sources,and influencing factors within tourist caves.Observations of diurnal and nocturnal fluctuations in CO2 concentrations clearly indicate that tourist activities exert a significant influence on these variations.However,monitoring of CO2 concentrations prior to development has not been conducted in most tourist caves,which limits the ability to accurately assess the extent of tourist impact on CO2 dynamics.The closure of tourist caves during the COVID-19 pandemic has provided a unique opportunity for comparative analyses.Currently,statistical analyses of CO2 concentrations in tourist caves predominantly rely on line graphs and scatter plots,which illustrate magnitude and variability but fail to accurately capture frequency variations across multiple temporal scales.Moreover,the depth of data exploration remains limited.Additionally,studies exploring the temporal variations of CO2 concentrations in relation to tourist volume often involve a degree of subjectivity.While,wavelet transform techniques can effectively reveal the periodic temporal-frequency characteristics of time series data across various scales,while precisely depicting the lag between dynamic changes in time series and their influencing factors.This methodological approach effectively addresses the existing gaps in research concerning CO2 levels in tourist caves.This study utilizes monitoring data on temperature,CO2 concentrations,and tourist volume from Zhijin Cave during both the lockdown and operation period.By employing wavelet transform for comprehensive time-frequency and lag analysis across multiple temporal scales,this research aims to provide an accurate assessment of the impact of tourist activities on CO2 concentrations within the cave,ultimately offering a scientific foundation to enhance predictive capabilities regarding CO2 levels in Zhijin Cave. The results reveal that following disturbances caused by tourist activities,the average temperature within Zhijin Cave increased by 0.23 to 0.86 ℃,with notable variations observed among different monitoring sites.Compared to the lockdown period,CO2 concentrations within the cave exhibited a marked increase during peak tourist hours of the operation period.Subsequently,the decline in CO2 levels at monitoring points 3 and 4 was relatively gradual,whereas points 5 through 7 demonstrated a rapid decrease.During the operation period,the long-term periodicity of CO2 concentrations in Zhijin Cave was shorter than that recorded during the lockdown,with significant short-term fluctuations closely associated with variations in daytime visitor flows.During the holiday period(September 30 to October 4),a significant positive correlation was identified between CO2 concentrations and tourist volume within the cave.The response of CO2 concentrations to tourist activities displayed a distinct lag effect across both diurnal and nocturnal time scales.Overall,it was found that larger cave volumes were associated with longer lag times for CO2 concentrations in response to changes in tourist volume.These findings provide valuable insights for analyzing the changes in CO2 concentrations within tourist caves under relatively natural conditions and offer a scientific foundation for effective cave management. However,it is important to note that this study did not include monitoring of CO2 concentrations in the overlying soil,which limits the availability of direct data to characterize soil CO2 variations during the lockdown period.Additionally,the elevated visitor numbers during peak holiday periods influenced the correlation between CO2 concentrations and visitor counts during non-holiday intervals.Therefore,a comprehensive consideration of data comparisons during non-holiday periods is warranted.Furthermore,the analysis was conducted over a limited timeframe,which restricts its broader applicability.It is suggested that future research should adopt innovative analytical methodologies to investigate the response of CO2 concentrations in the cave to tourist volume across seasonal and interannual scales.