短时间高强度旅游活动下洞穴CO_2的变化特征及对滴水水文地球化学的响应

Variation of CO_2 and its response to the drip hydrogeochemistry in caves under the short-time high-strength tourism activities

洞穴高强度旅游活动产生的CO_2对洞穴滴水水文地球化学及洞穴沉积物沉积具有重要影响。本文于2017年9月30日-10月9日对贵州绥阳大风洞洞穴CO_2、温度、相对湿度、游客数量及洞穴滴水水化学指标等进行连续监测,运用系统分析方法对各要素进行综合分析。结果发现:(1)受游客数量和洞穴通风效应等因素影响,洞穴空气CO_2分压(PCO_2(A))在时间序列上呈现明显的昼夜变化和日际变化,表现为白昼高、夜间低,游客多的天数高,游客少的天数低。在空间变化上,由于通风程度和洞腔体积不同,不同监测点PCO_2(A)存在明显差异,由洞内深处至洞口分别为3#(神泉玉露)>1#(时光隧道)>2#(夜明珠);(2)通过比较PCO_2(A)和滴水水温,前者对CO_2溶解度影响比后者更为显著,表明PCO_2(A)是洞穴沉积过程中最重要的驱动因素之一;(3)洞穴滴水水温、滴水PCO_2分压(PCO_2(W))与PCO_2(A)变化趋势大体一致,也呈现出明显的昼夜变化和日际变化。p H、SIc和HCO_3^-变化趋势大体上与PCO_2(A)相反,EC和Ca2+则无明显的昼夜变化,但存在一定的日际变化。随着旅游活动强度的增加,滴水水化学变化幅度逐渐增大。此外,不同滴水点所在洞腔结构、大小、封闭程度等不同,使PCO_2(A)的扩散和通风程度存在差异,进而影响洞穴滴水水化学组分和洞穴沉积物沉积状况。因此,本研究对于洞穴环境保护和管理及其岩溶洞穴碳循环的研究具有重要意义。

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 （PCO2 （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 PCO2（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 PCO2（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 （PCO2（W）） of cave generally had the same trend of variation with that of PCO2（A）, and also presented obvious diurnal and interdiurnal variations. The pH, Sic, and HCO; generally had a trend of variation in the opposite way to that of PCO2 （A）, EC and Ca^2＋ had no obvious diurnal variation but certain interdiumal 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 PCO2（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.