黄河上游宁蒙大型灌区生态系统水分利用效率变化及其影响因素

Variations of water use efficiency in ecosystem of large irrigation districts along Ningxia-Inner Mongolia section of the upper reaches of the Yellow River

水分利用效率(WUE)是评估生态系统植被固碳量与水消耗关系的关键指标。宁蒙灌区位于黄河上游的西北干旱区,主要依赖黄河水灌溉,研究该灌区WUE变化及其影响因素,对提升水分利用效率具有重要意义。文中利用遥感、气象和植被等多源数据,分析了1989-2018年宁蒙灌区土地覆盖变化,并估算了灌区生态系统三种水分利用效率WUEG(总初级生产力(GPP)/蒸散发(ET))、WUEN(净初级生产力(NPP)/ET)和IWUE(GPP与饱和水汽压差(VPD)的乘积/ET),采用微分方程量化分析等方法,研究了WUE变化特征、差异及其受控因子和影响因素。结果表明:近30年宁蒙灌区荒漠面积减少了75.73%,不透水层面积则增加了239.80%,农田和草地互有转化,但总体上农田面积增加了21.39%而草地面积减少了18.14%;宁蒙灌区WUE的多年均值中较大值出现在灌区中心,灌区边缘WUE多年均值较小;农田和草地WUE在年际尺度上呈增加趋势,空间尺度上也呈显著上升趋势;WUEG受GPP控制区域及WUEN受NPP控制区域远大于两者受ET控制区域,而IWUE受GPP*VPD和ET控制区域面积较为接近;土壤含水量与WUE显著正相关,且WUE对土壤含水量的敏感性最强,温度与WUE显著负相关,VPD与不同类型WUE的相关性在农田和草地上表现不同。

Water use efficiency(WUE) is a key indicator for assessing the relationship between vegetation carbon fixation and water consumption in ecosystems.The Ningxia-Mongolia Irrigation Area is located in the arid region of the upper Yellow River Basin,mainly relying on the water in Yellow River for irrigation.Studying the changes in WUE and its influencing factors in this large-scale irrigation area is of great significance for improving water use efficiency.In this study,using multi-source data including remote sensing,meteorology,and vegetation,we analyzed the land use changes in the Ningxia-Mongolia Irrigation Area from 1989 to 2018,and estimated the three water use efficiency indices of the ecosystem in the irrigation area:WUEG(Gross Primary Productivity(GPP)/Evapotranspiration(ET)),WUEN(Net Primary Productivity(NPP)/ET),and IWUE(GPP *Vapor Pressure Deficit(VPD)/ET).By applying methods such as differential equation quantification analysis,we studied the characteristics,differences,controlled factors,and influencing factors for WUE changes.The results reveal that in the past 30 years,the desert area in the Ningxia-Mongolia Irrigation Area has decreased by 75.73%,while the impermeable layer area has increased by 239.80%.There have been conversions between farmland and grassland,but overall,the farmland area has increased by 21.39% while the grassland area has decreased by 18.14%.The larger average of WUE in the Ningmeng Irrigation District appears in the center of the district,while the smaller average of WUE distributes at the edges of the district.Both farmland and grassland WUE show an increasing trend at the interannual scale,and also show a significant upward trend at the spatial scale.The regions controlled by GPP for WUEG and by NPP for WUEN are much larger than those controlled by ET,while the regions controlled by GPPVPD and ET for IWUE are relatively close in area.Soil moisture is significantly positively correlated with WUE,and WUE shows the strongest sensitivity to soil moisture.Temperature is significantly negatively correlated with WUE,and the correlation between VPD and WUE varies in farmland and grassland.