Response of water cycle to precipitation in Shizhiyan underground river system in Huixian wetland of Guilin

Karst wetland is an important regulator of karst ecosystems in southwest China and is of great significance to the sustainable development of the region. Water cycle, as the core factor to maintain the healthy operation of karst wetlands, has become a hot topic in current researches. Based on the field monitoring data of the Shizhiyan underground river system in the Guilin Huixian Wetland from April 15, 2020 to May 30, 2020, hydrological dynamic analysis and water balance are used to study the water cycle of the underground river system. The results show that (1) surface runoff, soil water, surface karst zone water and karst groundwater are sensitive to atmospheric rainfall, but the sensitivity degree is different. The sensitivity of karst groundwater is the highest, the sensitivity of surface runoff and surface karst zone water is weak, and the sensitivity of soil water is greatly affected by depth. (2) The proportion of all kinds of water circulation in the underground river system is different at different grades of rainfall, and the proportion of soil water in the system is the largest in light rain (24 h cumulative rainfall ranges from 4.2 mm to 10 mm), which accounts for about 75.87%. The proportion of soil water and karst groundwater in moderate rain (24 h cumulative rainfall is 17.8 mm) is the largest, which is about 43.38% and 44.12%, respectively. The proportion of karst groundwater in heavy rain (24 h cumulative rainfall is 24 mm) and heavy rainstorm (24 h cumulative rainfall ranges from 110.8 mm to 128.2 mm) is the largest, accounting for about 66.48%. (3) The average coefficient of regulation and storage in the study area is about 0.53, which is significantly higher than that of other karst areas, showing strong regulation and storage capacity. With the increasing rainfall, the coefficient of regulation and storage gradually decreases. (4) The conceptual model of water cycle of underground river system includes the transformation relationship and transformation amount among atmospheric rainfall, surface runoff, soil water, surface karst zone water and karst groundwater. The establishment of the conceptual model can provide a theoretical basis for the development and utilization of water resources and wetland protection of karst wetland.