Occurrence of water ponding on soil surfaces depending on infiltration rates on Mongolian rangeland

摘要

The occurrence of water ponding on soil surfaces during and after heavy rainfall produces surface run-off or surface water accumulation in low-lying areas, which might reduce the water supply to soils and result in a reduction of the soil water that plants can use, especially in arid climates. On Mongolian rangeland, we observed ponded water on the surface of a specific soil condition subjected to a heavy rainfall of 30mm/hr. By contrast, ponded water was not observed for the same type of soil where livestock grazing had been removed for 6-8 years via a fence or for nearby soil containing less clay. We measured the infiltration rate (the saturated hydraulic conductivity of the surface soil, K-s) of the three sites by applying ponded water on the soil surface (an intake rate test). The results showed that K-s in the rangeland was lower than the rainfall intensity in the site where water ponded on the soil surface; however, K-s of the soil inside of the fence has recovered to 3 times that of the soil outside of the fence to exceed the rainfall intensity. Heavy rainfall that exceeds the infiltration rate occurs several times a year at the livestock grazing site where we observed ponded water. Slight water repellency of the soil reduces rain infiltration to increase the possibility of surface ponding for the soil.