Impact of alpine meadow degradation on soil water conservation in the source region of three rivers

Research on the effects of grassland degradation on soil water conservation in the Sanjiangyuan region of China is essential as it can provide a scientific basis for evaluating and monitoring water conservation in this important water conservation area. Its regional strategic position is extremely important as 1.2% of the total water in the Yangtze River, 40% of the total water in the Yellow River, and 15% of the total water in the Lancang River comes from this area. As a result of climate change and human activity, grassland degradation had been more severe in the Sanjiangyuan region since the 1970s. Rangeland degradation not only impacts vegetation, it can also have great effects on soil physical and chemical properties. Changes to the physical and chemical properties of soil can subsequently affect the efficiency of soil water conservation. The vegetation in this region is dominated by grassland. In grassland ecosystems 99% of water conservation capacity comes from the capacity of soil to retain water. While soil water conservation efficiency is influenced by many factors such as vegetation type, land use and land cover, studies have shown that water yield in this region has decreased year by year and that water conservation capacity has declined sharply. These findings show that further studies exploring the impacts of grassland degradation on the function of soil water conservation are of great significance. Field surveys and experimental analyses were applied to detect vegetation biomass, soil moisture and physical characteristics, and soil water conservation capacity of alpine meadows in different soil types in this area. Results showed that above-ground biomass, under-ground biomass, capillary porosity, total porosity, natural water-holding capacity, maximum water holding capacity, and soil water conservation capacity decreased significantly at severely degraded alpine meadows (P < 0.05). When an alpine meadow deteriorated from not degraded alpine meadow status to moderately degraded and severely degraded alpine meadows, soil bulk density increased gradually. Soil non-capillary porosity, minimum water-holding capacity and capillary water-holding capacity did not change dramatically. The ranges of soil water conservation capacity at the three degradation stages were 1884.32--1897.44t/hm super(2), 1360.04--1707.79t/hm super(2) and 1082.38--1550.10t/hm super(2) respectively. Compared with not degraded alpine meadows with different soil types, soil wat