Study catchment
Chenqi catchment is located in the Puding Karst Ecohydrological Observation Station of Guizhou Province, southwest China, and has an area of 1.25 km2 (Fig. 1). It is a typical cockpit karst landscape, with surrounding conical hills separated by star-shaped valleys (Zhang et al., 2011; Chen et al., 2018). The catchment, which is drained by a single underground channel/conduit, can be divided into two units: depression areas with low-elevation (<1340 m) and steeper hillslopes with high elevation ranging from 1340 to 1500 m. The site has a subtropical wet monsoon climate with mean annual temperature of 20.1 °C, and the highest temperatures in July and lowest in January. The annual precipitation is 1,140 mm, with a distinct wet summer season from May to September and a dry winter season from October to April. The average monthly humidity ranges from 74 to 78%.
Geological strata in the study basin include dolostone, thick and thin limestone, marl and Quaternary soil. Limestone formations 150–200 m thick lie above an impervious marl formation, which allows precipitation to recharge perched groundwater on the marl that discharges in the lower areas (mostly as hillslope springs). On hillslopes, Quaternary soils developed on carbonate rocks are very thin, and the average soil thickness is less than 30 cm. Some limestone fragments are mixed in with the soils, and the rock outcrop area is 10–30%. The vegetation characteristics include deciduous broad-leaved forest at the top and middle of the hillslope and crops (including rice paddies) on the depression where soils are also thicker.
At Chenqi, discharge of a hillslope spring (HS) located at the foot of the eastern steep hillslope and the underground channel at the catchment outlet were measured (Fig. 1). An automatic weather station was established on the upper hillslope to record precipitation, air temperature, wind, radiation, air humidity and air pressure. Additionally, precipitation, hillslope spring discharge and catchment outlet flows were sampled daily for hydrogen and oxygen isotopes analysis. These hydrometric and isotopic data were used to analyze the seasonal cycles, and short-term dynamics of stream water and precipitation isotopes and aid model calibration.