民勤湖区地下水资源时空变化对灌区景观生态安全的影响研究

以生态安全面临着严重威胁的我国干旱区民勤绿洲湖区灌区景观为例，研究地下水资源的时空变化对灌区生态安全的影响．利用GIS进行地下水的空间插值得到地下水埋深与地下水矿化度的时空变化．结果表明，地下水埋深在14年间持续下降，且灌区中心地带的地下水埋深的下降速率较边缘地带快。导致地下水降落漏斗不断加深，并逐渐由灌区中心向边缘扩展．大于3m的地下水埋深面积比例逐年增加，由1987年占湖区总面积的81．2％上升到2001年的97．4％．地下水埋深的持续下降导致土壤含水量降低是除人为破坏而引起林木自然衰败、死亡，并引起灌区自然生态安全水平降低的主要原因．当地下水埋深超过8m，地下2m处土壤含水率达到12％以下，大部分乔木林枯梢率达到90％以上，而灌木林枯梢率也达到50％以上．受地下水位下降的影响，14年间有林地、灌木林地与疏林地的斑块面积分别减少了67％、54％与31％，斑块数量减少35、42与50块．地下水矿化度的上升导致作物的安全生长格局发生显著变化，导致农业经济效益降低、种植业结构调整受到严重制约，构成对灌区经济生态安全的严重影响．合理分配流域中、下游水资源量，限制人类不合理的土地利用方式，减少灌区耕地面积，构建安全的景观格局．逐渐恢复地下水采、补平衡，阻止地下水位的进一步下降与地下水矿化度的上升是提高灌区生态安全水平的重要途径．

Impact of groundwater resource temporal-spatial change in Minqin oasis on ecological security of irrigation region landscape

By the GIS technology,this paper studied the impact of groundwater resource temporal-spatial change in the lake area of Minqin Oasis on the ecological security of irrigation region landscape.The results showed that the depth of groundwater was descending continuously,the velocity of groundwater line change in the center of irrigation region was faster than that in the edge region,and consequently,the area of the descending funnel of groundwater line was enlarged.From 1987 to 2001,the area with a groundwater depth deeper than 3 m was increased from 81.2% to 97.4%.The descending of groundwater line due to soil water reducing was the main reason that resulted in the destruction and deadness of forests.When the depth of groundwater was deeper than 8m and soil water content was less than 12%,the die-back rate of tree was morn than 90%,and that of shrub was more than 50%.Impacted by the descend of groundwater depth,the area of forest land,shrub land and open-canopy land was decreased by 67%,54% and 31%,and the number of their patches was decreased by 35,42 and 50,respectively.The mineralization degree of groundwater in northern irrigation region increased obviously,and changed the safe pattern of crop growth.The benefit of agriculture decreased,and the adjustment of planting construction was restricted seriously,which became the main impact factor on the ecological security of irrigation region.Reasonably distributing water resource between upper and lower river basin,reducing unreasonable land use,decreasing farmland area,and constructing safety landscape pattern could lead to the balance between the exploitation and replenishment of groundwater resource,prevent the descend of groundwater depth and the increase of groundwater mineralization,and improve the ecological security of the irrigation region.