三江源区高寒草甸退化对土壤水源涵养功能的影响

三江源区是我国重要的水源涵养区,研究草地退化对土壤水源涵养功能的影响,可为三江源区水源涵养功能的科学评估与合理监测提供科学依据。以实地采样与室内测试分析相结合的方法研究了三江源区内不同土壤类型高寒草甸生物量特征、土壤水文物理性质及土壤水源涵养量。结果表明:高寒草甸在重度退化阶段地上生物量、地下生物量、毛管孔隙度、总孔隙度、自然含水量、最大持水量、土壤水源涵养量显著低于未退化和中度退化阶段(P<0.05)。随着高寒草甸退化程度加剧,土壤容重逐渐增大,且非毛管孔隙度规律不显著。未退化、中度退化、重度退化草甸的土壤水源涵养量范围分别为1884.32—1897.44t/hm2、1360.04—1707.79t/hm2、1082.38—1550.10t/hm2。中度退化草甸土壤水源涵养量比未退化草甸低9.37%—10.35%,重度退化草甸低18.31%—27.82%。草甸退化进程中土壤总孔隙度与毛管孔隙度的降低是影响土壤水源涵养量下降的直接原因,而草甸退化进程中地上生物量与地下生物量的减少则是间接原因。度量三江源区高寒草甸土壤水源涵养功能时应着重考虑毛管孔隙度的蓄水作用。研究表明高寒草甸地上生物量与土壤水源涵养量之间存在显著的正相关关系(P<0.05),该结果能够推动水源涵养功能评估向空间化、精细化发展,为探索利用遥感技术监测三江源区水源涵养功能提供参考依据。

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/hm², 1360.04-1707.79t/hm² and 1082.38-1550.10t/hm² respectively. Compared with not degraded alpine meadows with different soil types, soil water conservation capacity was reduced by 9.37%-10.35% at moderately degraded meadows, and by 18.31%-27.82% at severely degraded meadows. Reduced soil water conservation capacity was caused by diminished total porosity and capillary porosity and was also indirectly caused by a reduction of above-ground biomass and under-ground biomass associated with the degradation of the alpine meadows. The contribution of capillary porosity to water conservation should be taken into account when evaluating alpine meadow soil water conservation capacity in the Sanjiangyuan region. The results of the correlation analysis showed that soil water conservation capacity was positively correlated with above-ground biomass and under-ground biomass (P<0.05). In addition to promoting the evaluation of water conservation function, our findings can be used to provide guidelines and methods for water conservation function monitoring in the Sanjiangyuan region by remote sensing.