黑河流域生态输水对下游植被变化影响研究

为挽救黑河下游额济纳地区严重退化的生态环境，本世纪初开始向下游实施生态输水工程。本文通过对2000-2009年的MODIS/NDVI序列分析，揭示了生态输水以来额济纳地区植被时空变化格局；基于不同时空分辨率的遥感影像和实地考察资料，分析了植被变化空间差异的主要原因。研究表明：（1）研究区内80.4 %的绿洲区植被和91.5 %的荒漠区植被呈恢复趋势。绿洲区内年累积植被指数序列趋势度大于0.14 a-1 的区域都存在农田开垦或弃耕地复播现象；荒漠植被的显著恢复主要发生在西河中、下游和东河下游地区。（2）研究区内19.6 %的绿洲区植被和5.1 %的荒漠区植被进一步退化，退化区主要分布在衬砌渠系两侧和一些干涸或径流减少的自然河流两岸，植被退化主要是乔木林的退化。（3）大范围的植被恢复主要原因在于地下水环境的整体好转，以及生态保护措施的实施；地下水环境的整体好转取决于黑河中游来水量的增加和下游输水方案的实施。（4）研究区植被退化的直接原因在于目前输水方案实施引起的局部地表水环境恶化。基于植被动态监测和局部植被对全局生态的重要性评价，确定合理的输水方案，对于区域生态环境演变进入良性循环意义重大。

Vegetation changes by environmental flow control in the lower Heihe

The environmental flow control has been implemented in Heihe river basin since 2001 in order to restore the degraded ecosystem, especially in its lower reach, the Ejina basin. In this study, the temporal-spatial pattern of vegetation change in Ejina basin was investigated through the trend analysis of MODIS NDVI time series from 2000-2009, and its causes were discussed based on the multi-scale remotely sensed images and field investigations. The results show that: (1) the vegetation in 80.4% of oasis regions and 91.5% of desert regions presented an increasing or recovery trend; the increasing magnitude larger than 0.14 a-1 mainly resulted from cultivated lands reclamation; the recovery of desert vegetation largely took place in the middle and lower reaches of the Ejina basin. (2) The vegetation in 19.6% of oasis and 5.1% of desert regions showed a decreasing or degrading trend, mainly in where water reduced or rivers diminished, and along artificial concrete canals; the degradation largely occurred in forest regions. (3) The vegetation recovery mainly resulted from the regional improvements of groundwater environments and adoption of vegetation protection counter-measures and the improvements of groundwater environments were due to the increasing of river stream from the middle reach of Heihe river and current water-transport strategy. (4) The vegetation degradation directly resulted from the deterioration of local surface water environments which were caused by current water-transport strategy. Based on the monitoring of vegetation dynamics and the importance assessment of local vegetation for regional ecological environment, more rational water-transport manner should be made to advance the ecological environment recovery.