Karst region has a dual hydrological system where extremely fast water flow can be found in karst aquifer, while high heterogeneity is the most important characteristic of the aquifer. Under the context of global climate change, it is urgent to find out the hydrological process of karst watershed and its regulation mechanism.

Compared to non-karst areas where the hydrological processes are regulated by soil layer, how to assess the storage and transit function of the critical zone that compose of soil, epikarst coupling with conduit, fissure and matrix in karst area are critical issues.

A research team led by Prof. CHEN Hongsong from the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences investigated the springs and stream recharge processes in a small karst catchment, and assessed the transfer and storage function of karst aquifer.

The study was based on the hydrological monitoring in the Huanjiang Observation and Research Station for Karst Ecosystems, CAS, coupling with geophysical technology and isotope/hydrochemistry tracer technique.

Scientists found that rain water recharged springs and stream via homogeneous mixing with groundwater. The difference of response sensitivity to rainfall between intermittent and perennial springs was attributed to the combined effect of relatively higher proportions of rocky outcrops, thinner soil and epikarst thickness, and better karstic development in intermittent spring aquifer.

Different from the catchment that spring water dominated the recharge source of stream, the springs did not recharge stream directly but was regulated by the soil in the depression, and most of recharge flow were subsurface and epikarst flows in our study area.

In addition, epikarst water contributed more than 83% of the total flow during rainfall event and more than 90% during seasonal scale.

They also found that although conduit flow could contribute approximately 11.4% of the total flow during the wet season and rainfall scales, matrix flow dominated the recharge of the stream water (>55%).

Therefore, scientists suggested that the permeability of the epikarst matrix dominates the storage and transfer function in the dolomite kart aquifers with low karstification.

Related findings were published in Science of The Total Environment and Journal of Hydrology. The researches were supported by the National Natural Science Foundation of China, the Guangxi Natural Science Foundation of China, and the International Partnership Program of Chinese Academy of Sciences.

Contact: Chen Hongsong

E-mail: hbchs@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences

Figure 1: Estimation of mean residence time in spring and stream waters (Left) and season variation characteristic of new water contribution proportion (Right) （Image by Wang Fa）

Figure 2: Season variation characteristic of sources (conduit flow, fissure flow and matrix flow) recharging stream water（Image by Wang Fa）