贵州织金洞CO_2浓度不同时间尺度变化及其影响因子分析

Variation of CO_2 Concentration in Zhijin Cave,Guizhou Province Relative to Time Scale and Its Affecting Factors

作为影响洞穴沉积物沉积的重要因素,洞穴空气CO_2浓度对洞穴次生沉积物景观的稳定性以及旅游环境的舒适性具有重要影响。通过对贵州织金洞2015年1月至2016年6月连续18个月的洞内外环境(CO_2浓度和温湿度)、水文地球化学指标、洞顶上覆土壤CO_2浓度、降水量和游客数量等要素的监测,并结合2015年"十一"期间洞穴空气环境连续5昼夜的系统监测,探讨织金洞洞穴空气CO_2浓度时空变化特征及其控制因素,结果显示:(1)在空间尺度上,织金洞CO_2浓度呈现明显的空间变化,从洞口至洞内深处,CO_2浓度呈非线性上升,至洞内越深CO_2浓度变化越稳定。这主要是洞内外气流交换作用程度、洞道结构、洞内海拔差异等因素综合导致的;(2)季节变化上,织金洞洞内空气CO_2浓度总体上存在明显的雨季高旱季低的特点,这主要受旅游活动和岩溶作用吸收大量上覆土壤CO_2、滴水、池水脱气作用等因素控制;日际和昼夜变化上,"十一"期间随着进入洞内游客数量的增加,CO_2浓度白天较夜间高,随着游客数量不断攀升,CO_2浓度总体呈上升趋势;温湿度对洞内空气CO_2浓度变化有一定的调控作用,但相对较弱。(3)总体上CO_2浓度变化主要是由洞内外气流交换作用(通风效应)、洞道结构、旅游活动以及洞外自然环境的变化和岩溶作用等要素相互耦合的结果。因此在洞穴环境保护方面需要综合考虑各方面要素,通过科学管理促进洞穴旅游的可持续发展。

Being an important factor affecting deposition of sediments in a cave,CO_2 concentration in the air of the cave influences significantly stability of the secondary sediment landscape and amenity of the tourist environment. Monitoring of CO_2 concentration,temperature and relative humidity of the environments inside and outside the Zhijin Cave of Guizhou Province hydrogeochemical indices,CO_2 concentration in the overlying soil,precipitation and flow of tourists was carried out consecutively for 18 months from January,2015 to June,2016,in addition to the 5 consecutive days of round-theclock monitoring of the air environment in the cave during the national holiday period,2015,to investigate spatio-temporal variation of CO_2 concentration in the air inside the cave and its controlling factors. Results show that spatial variation of CO_2 concentration from the entrance to the deep corner of the cave did exist in the Zhijin Cave at all temporal scales and CO_2 concentration rose nonlinearly and tended to level off with the cave going deeper,which might be the result of the joint effect of the airflow exchange in and out of the cave,tunnel structure,as well as variation of elevation inside the cave. Seasonally,CO_2 concentration in the air of the cave on the whole was significantly higher in rainy seasons than in dry seasons,which is attributed mainly to tourist activities,karstification that absorbs a large volume of CO_2 containing water drips from the overlaying soil layer,and degassing of the water inside the cave,while daily,CO_2 concentration varied sharply around the clock,especially during the National Holidays when the flow of tourists visiting the cave in day time increased drasti-cally in volume,making CO_2 concentration much higher by day than by night and on the whole on a rising trend,with temperature and humidity being two factors affecting variation of air CO_2 concentration inside the cave,but relatively weak in effect. Generally speaking,variation of the CO_2 concentration in the air of the cave is regulated mainly by the joint effect of air exchange( ventilation effect),between in and out of the cave,tunnel structure,tourist activities changes in the natural environment and karstification. It is,therefore,essential to take into consideration all the aspects or factors listed above in protecting the cave environment,and adopt scientific management to promote sustainable development of cave tourism.