Wavelet transform analysis of the response mechanism of CO2 concentration to tourist activities in Zhijin Cave
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摘要: 旅游活动将导致洞穴环境发生改变,特别是对于洞穴CO2浓度短时间内变化影响,多时间尺度下两者间的关联性研究较少。为准确探讨旅游活动对洞内CO2浓度的影响及其响应机制,本文基于织金洞封控期和运营期洞内温度、CO2浓度和游客量监测数据,利用小波变换进行多时间尺度下时频和时滞性分析。结果表明:织金洞内部环境受旅游活动扰动,洞内平均温度提升0.2~0.9 ℃,但各监测点间变幅存在差异;与封控期相比,运营期旅游高峰时段洞内CO2浓度明显升高,高峰时段后,3#和4#下降过程较为缓慢,5#至7#呈快速下降特征;织金洞运营期洞内CO2浓度长周期短于封控期,存在与客流日间差异特征显著关联的短周期变化;节假日期间洞内CO2浓度与游客量存在显著的正相关性,昼夜尺度上洞内CO2浓度对旅游活动的响应具有滞后性。研究结果为旅游活动对洞穴内部微环境的扰动程度及其影响过程提供重要的数据支撑,为指导洞穴开发、利用、管理提供科学理论依据。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 °C, 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. -
Key words:
- wavelet transform /
- cave environment /
- CO2 concentration /
- tourist activities /
- response mechanism /
- Zhijin Cave
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图 5 织金洞临时封控和正常运营状况下洞穴CO2小波系数实部
注:a1~a8为2022年临时封控期;b1~b8为2023年正常运营期。
Figure 5. Real part of CO2 wavelet coefficients in Zhijin Cave under temporary lockdown and normal operation conditions
Note: a1~a8 represent the temporary lockdown period in 2022; while b1~b8 denote the normal operation period in 2023.
图 6 2023年织金洞各监测站点CO2浓度与游客量小波相干谱
注:图例表示交叉小波相关性(无量纲),黑弧线为小波影响锥边界,弧线以内表示通过α=0.05的红色噪音标准谱显著性检验,箭头方向反映了洞内CO2浓度与游客量的相位关系:箭头水平向右,表示两者同步变换;水平向左,表示洞内CO2浓度滞后游客量1/2周期;箭头垂直向上,表示洞内CO2浓度滞后游客量1/4周期;向下则提前1/4周期。
Figure 6. Coherence spectrum of CO2 concentration and tourist volume wavelet in each monitoring point of the Zhijin Cave in 2023
Note: The legend indicates the cross-wavelet coherence (dimensionless). The black arcs represent the boundaries of the wavelet cone of influence. Regions within the arcs denote areas that pass the red noise standard spectral significance test at α=0.05. The arrow directions reflect the phase relationship between cave CO2 concentration and tourist numbers:right-pointing arrows indicate in-phase synchronization between the two variables;left-pointing arrows signify that cave CO2 concentration lags behind tourist volume by half a period (1/2 period);upward-pointing arrows denote cave CO2 concentration lagging tourist numbers by a quarter period (1/4 period);and downward-pointing arrows suggest cave CO2 concentration leads tourist volumns by a quarter period (1/4 period).
表 1 织金洞监测点洞腔主要参数
Table 1. Main cavity indexes of Zhijin Cave
监测站点 景点名称 长度/m 高度 宽度 面积/
m2体积/
m3测点海拔/
m到旅游步道
距离/m最大/m 最小/m 最大/m 最小/m 1# 迎宾厅 105 26 8 70 20 4700 106218 1267 20 2# 塔林宫 91 29 12 38 5 2900 45895 1264 4 3# 苗岭大厅 281 38 19 85 50 18000 426384 1244 14 4# 苗岭大厅 281 38 19 85 50 18000 426384 1249 6 5# 灵霄殿 180 42 14 95 38 11600 362114 1306 3 6# 银雨宫 190 66 40 115 90 18600 825472 1329 25 7# 掌上明珠 120 58 21 125 39 12500 372191 1339 19 8# 雷子洞 58 14 6 23 6 800 6512 1309 4 -
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