生态输水工程对水系连通的多维影响:以塔里木河为例

Multi-dimensional response of hydrological connectivity to ecological water conveyance project

生态输水工程一方面缓解了水资源时空分布不均的难题,另一方面改变了水系自然连通状态。本文结合图论与景观格局指数法,从形态、结构、功能三个维度构建水系连通评价指标体系,分析塔里木河干流生态输水工程实施前后,上、中、下游水系连通格局的时空演变。综合水系连通指数计算结果表明,生态输水以来上、中游水系连通指数先上升后渐趋稳定。生态输水之前由于断流,下游各维水系连通指数均呈下降趋势,生态输水以来下游水系连通指数开始上升,其中形态与结构连通指数响应较快,功能连通指数响应较慢。从趋势来看,水系连通指数不会随着生态输水工程的实施持续上升,而是存在一定的阈值。形态连通方面,生态输水后,上、中游水域由大面积连续斑块向小面积破碎斑块转化,下游大面积水域斑块增多。结构连通方面,水系连通时长增加,其中下游最为显著;生态输水前期上、中游水域面积减少,下游水域面积增加;输水后期流域整体水域面积增加,但上、中游持续和周期连通水域面积增幅减小,而下游增幅显著。功能连通方面,上、中游以供给和支持功能占主导,下游随着生态输水的进行,各类功能占比渐趋均衡。生态输水水量与各维水系连通指数均表现为正相关,水系形态、结构连通指数响应较快,功能连通指响应较慢,由此可见生态输水对塔里木河干流水系连通的提升具有积极效益。研究结果可为生态输水实践提供技术支撑。

On the one hand,the ecological water conveyance project solves the problem of uneven distribution of water resources in time and space;on the other hand,it changes the natural connection status of the water system.This paper constructed a hydrological connectivity evaluation system from three dimensions:morphology,structure and function.The hydrological connectivity of upstream,midstream and downstream in the mainstream of Tarim River are evaluated before and after the implementation of the ecological water conveyance project.The calculation results of the integrated hydrological connectivity index indicated that the connectivity of the upstream and midstream,of the Tarim River increased first and then became stable.Before the implementation of the ecological water conveyance project,the hydrological connectivity index of the downstream showed a downward trend due to the cut off.Since the implementation of the ecological water conveyance project the downstream hydrological connectivity index began to rise,with the morphological and structural connectivity index responding more quickly,while the functional connectivity index responded more slowly.In terms of trends,the hydrological connectivity index did not continue to rise,but had a certain threshold value.The results of morphological connectivity showed that after implementation of the ecological water conveyance project the large continuous water patches converted into small fragmented water patches in upstream and midstream,and large area water patches increased in downstream.In terms of structural connectivity,the duration of hydrological connectivity was prolonged,especially in downstream.In the early stage of the ecological water conveyance project,the water area decreased in upstream and midstream but increased in downstream.The total water area increased in the later stage of the ecological water conveyance project.The area of continuously and periodically connected water area in upstream and midstream decreased,while that in downstream increased significantly(by 11% and 6% respectively).In terms of functional connectivity,the upstream and midstream were dominated by provisioning and supporting functions.After the implementation of the ecological water conveyance project,provisioning and supporting functions gradually increased and the proportion of the four functions became balanced in downstream.There was a positive correlation between the ecological water conveyance volume and each dimensional hydrological connectivity index.The morphological connectivity index was most sensitive to the changes in the water conveyance volume,followed by the structural and functional connectivity indexes.Obviously,the ecological water conveyance project has positive benefits for the improvement of the hydrological connectivity in the mainstream of Tarim River.This study can provide technical support for the ecological water conveyance practice.