对冲效应弱化了土地利用变化对干流水文情势的影响——以中国金沙江流域为例

Global extreme hydrological events pose considerable challenges to the sustainable development of human society and river ecology.Land use/cover change(LUCC)is a visible manifestation of human activity and has caused substantial alterations in extreme hydrological regimes across rivers worldwide.The Jinsha River lies upstream of the Yangtze River and its hydrological variability has had profound socioeconomic and environmental effects.In this study,we developed Hydrological Simulation Program–FORTRAN(HSPF)and land-use simulation models of the entire watershed to simulate the effects of LUCC on hydrological extremes and quantify the inter-relationships among them.The main land-use changes between 1995 and 2015 were those associated with cropland,forest land,and grassland.Between 2015 and 2030,it is estimated that the coverage of forest land,grassland,construction land,and unused land will increase by 0.64%,0.18%,69.38%,and 45.08%,respectively,whereas that of cropland,water bodies,and snow-and ice-covered areas will decline by 8.02%,2.63%,and 0.89%,respectively.LUCC has had irregular effects on different hydrological regimes and has most severely altered stream flows.The responses of hydrological extremes to historical land-use change were characterized by spatial variation.Extreme low flows increased by 0.54%–0.59%whereas extreme high flows increased by 0%–0.08%at the lowest outlet.Responses to future land-use change will be amplified by a 0.72%–0.90%reduction in extreme low flows and a 0.08%–0.12%increase in extreme high flows.The hedging effect caused by irregular changes in tributary stream flow was found to alleviate the observed flow in mainstream rivers caused by land-use change.The extreme hydrological regimes were affected mainly by the net swap area transferred from ice and snow area to forest(NSAIF)and thereafter to cultivated land(NSAIC).Extreme low flows were found to be positively correlated with NSAIF and NSAIC,whereas extreme high flows were positively correlated with NSAIC and negatively correlated with NSAIF.

青藏高原土壤氮矿化速率及其温度敏感性的海拔差异

土壤氮矿化速率的变化会影响营养物质的可利用性,进而影响植物生长。然而,温度升高如何影响不同海拔高山草地土壤净氮矿化速率仍不清楚。在青藏高原北部的祁连山脉一处坡地上,我们从海拔3200至4200m每隔200m设立一观测样地,用树脂芯法开展了沿海拔梯度土壤净氮矿化速率的原位观测实验。同时我们以海拔3800、4000和4200m的样地作为基准,通过分别向低海拔移栽土壤样方的实验方法评估土壤净氮矿化速率及其温度敏感性(Q_(10))受升温的影响。研究结果表明,土壤净氮矿化速率随海拔升高而降低:结构方程模型分析结果显示沿海拔梯度土壤净氮矿化速率主要受土壤温度的影响;海拔间移植实验导致的温度增加显著提高了土壤净氮矿化速率;基于海拔4200m开展的移植实验表明土壤净氮矿化速率的Q_(10)值达到3.4,这大约是基于海拔4000和3800m的Q_(10)值的两倍。