Unsaturated hydraulic conductivity in limestone dolines: Influence of vegetation and rock fragments

Vegetation and rock fragments have a profound impact on runoff generation in the dolines of the Sierra de Gádor, southeastern Spain. This study investigated the effect of vegetation and rock fragments on unsaturated hydraulic conductivity [K(h)] in three limestone dolines and examined whether variation in K(h) was consistent with differences in runoff from simulated rainfall. Tension infiltrometers were used to measure unsaturated hydraulic conductivity at three pressure heads (h) of − 30, − 60 and − 120 mm at 70 locations within the three dolines. Generally, the trends of the K(h) were consistent with the simulated rainfall data and accounted for difference in runoff for the vegetated surfaces. Vegetation resulted in high infiltration with unsaturated hydraulic conductivities at − 30 and − 60 mm are significantly greater for the vegetated surface than for the rock fragment covered surface and bare soil surface. Rock fragments had no obvious effect on soil hydraulic conductivity as compared with bare soils. The K(h) of the non-crusted soil were 2–5 times higher than that of the crusted soil. The K(h) decreased with increasing tensions, K(60) and K(120) were only 8.4 and 0.89%, respectively, of K(30) for the vegetated surfaces, and were about 30 and 8.7%, respectively, of K(30) for both rock fragment covered surfaces and bare soils, suggesting that pores in the 0.5- to 1-mm diameter range dominate flow under unsaturated conditions. There were significant differences in K(h) among the different topographic units of the dolines, and K(h) tended to be higher in the upper position than in the lower position of the doline.