Environmental changes and their cause of the Zhijin cave in Guizhou Province

The Zhijin cave is located in the northeast of Zhijin county in western Guizhou Province. The area of Zhijin cave world geological park is 307 km2, and its central scenic spot lies at the intersection of the Liuchong river and Sancha river, where developed the Huangchun dam (T1y2) Formation of Lower Triassic Yelang Group (T1y). Because of the magnificent and unique landscape, the Zhijin cave has been honored with national geological park in 2004 and the world geological park in 2015. From January 2015 to May 2016, monthly monitoring has been conducted to the temperature, air CO2 concentration, air pressure, air humidity and wind speed in this cave. The cave air CO2 concentration was measured by Telaire7001 portable infrared CO2 instrument, of which the resolution and the range are 1 ppm and t 0-10,000 ppm, respectively. The humidity, temperature, air pressure of cave air and wind speed in the tunnel were observed by the Kestrel4500 anemometer. The data on visitor amount are provided by the Zhijin Cave Management Bureau. The previous research data are collected from the literature and compared with the new monitoring data point by point. Then this work analyzes the change of the environment and the number of tourists from the initial stage of opening of the Zhijin cave to the present and the relationship between the environment and the visitor amount and the influence of artificial light sources on the environment inside the cave. Thus the impact of human activities on environmental factors in the cave are quantified, and the main factors affecting the environment inside the cave are identified, which could provide a scientific basis for protection of the cave environment and landscape. The results show that the CO2 concentration and temperature level have been increased significantly since the initial stage of opening of the Zhijin cave, with amplitudes reaching 1,000 ppm and 2-3 ℃, respectively. The maximum CO2 difference was up to 465 ppm between 2011-2013 and 2015-2016. The main factors of the environmental change are tourism activities and artificial light. The amount of tourists has increased from less than 50 thousand in 1985 to 594.571 thousand in 2015, leading to increase of the CO2 concentration with time. The annual temperature difference was not large, but the overall trend was still decreasing year by year and the gap of humidity was not obviously except 2011. The maximum temperature difference between surrounding environment and artificial lights can reach 33 ℃, and the maximum humidity difference between the cave interior and surrounding environment is up to 66.7%.