Impacts of alpine meadow degradation on the soil moisture and hydrological processes in the three river source region on the Qinghai Tibetan plateau

To explore the effects of mattic epipedon (ME) on soil moisture and hydraulic properties in the alpine meadow of three-river source region, the soil moisture, water infiltration, evapotranspiration, soil bulk density and soil water holding capacity of original vegetation (OV), light degradation (LD), moderate degradation (MD) and severe degradation (SD) was conducted in this study, respectively. The results showed that: (1) the alpine meadow degradation reduced the soil moisture in the shallow layer (0-10 cm) and had no significant effects on the soil moisture in the deep layer (20-30 cm). (2) The effects of alpine meadow degradation on infiltration was depend on the presence of ME or not, when the ME existed on the land surface (from OV treatment to MD treatment), the alpine meadow degradation had no significant effects on infiltration. Once the ME disappeared on the land surface (from MD treatment to SD treatment), the alpine meadow degradation mainly increased the infiltration. (3) With the aggravation of alpine meadow degradation, the daily evapotranspiration first decreased and then significantly increased when the gravimetric soil water content at 0-5 cm in SD treatment (GWC5) was exceeded 19.5%, the daily evapotranspiration gradually decreased when GWC5 ranged from 9.3% to 19.5%, and had no significant changes on the evapotranspiration when GWC5 was less than 9.3%. Considering the characteristics of precipitation in alpine meadow, it was concluded that the alpine meadow degradation accelerated the evapotranspiration during the plant-growing season. (4) The effect of alpine meadow degradation on soil bulk density and saturated water capacity was concentrated at 0-10 cm. With the aggravation of alpine meadow degradation, the bulk density at 0-10 cm was first stable and then significantly increased and the saturated water capacity at 0-10 cm was first gradually increased and then significantly decreased. Our results suggested that the ME is vital for water conservation of alpine meadow and the protection of ME should be emphasized to promote the sustainable development of the ecosystem and the water supply of water towers in China.