民勤绿洲天然植被生长与地下水埋深变化关系

甘肃石羊河流域民勤盆地水资源短缺，生态环境脆弱，弄清地下水埋深与天然生态植被生长的关系，是精准调控地下水开采、针对性制定生态保护政策的重要理论依据。利用民勤盆地2000—2017年LANDSAT遥感数据，计算归一化差值植被指数（NDVI）年均值，结合85眼监测井的地下水埋深实测数据，分析了植被生长与埋深的关系。结果显示：研究区植被NDVI较低，多年均值约0.1，2012年后NDVI趋于增大，反映人工造林等措施成果明显。地下水埋深总体趋于增大，2008年后增幅减缓，目前埋深西部大于20 m，东部、北部小于20 m。区内适宜植被生长的埋深范围为2.5~3.9 m，多年平均适宜生态水位约2.66 m；埋深小于4 m时，NDVI与埋深表现为高度负相关(R<-0.8)，即埋深越小，NDVI越高；埋深大于4 m时，两者无明显关系。较前人成果，文章从长序列时间、盆地空间尺度分析了民勤绿洲区天然植被生长与地下水埋深的变化，得到浅埋区生态水位，进而圈定了生态治理重点靶区。

Changes in natural vegetation growth and groundwater depth and their relationship in the Minqin oasis in the Shiyang River Basin

The Minqin Basin is short of water resources and has a weak ecological environment. Understanding the relationship between groundwater table depth and growth of natural ecological vegetation is an important theoretical basis for precisely controlling groundwater exploitation and targeted protecting ecological environment. Previous studies lack correlation analyses, especially determination of ecological groundwater levels in the shallow buried area. In this study, we analyzes the spatial and temporal variation in the NDVI of the natural ecological vegetation and groundwater depth and the relationship, based on the LANDSAT remote sensing data and the measured data at 85 wells during 2000—2017.The results show that (1) NDVI was generally low in the study area, with the annual mean value of 0.1, and the value of NDVI became greater after 2012, reflecting the significant effect of the measurs of artificial afforestation and the like; (2) groundwater depth showed an increasing trend during 2000—2017, but the increase slowed down after 2008, and the groundwater table depth was greater than 20 m in the western part, but less than 20 m in the eastern and northern parts; (3) the groundwater depth suitable for vegetation growth is about 2.5~3.9 m, the NDVI is highly negative correlated with groundwater depth when the groundwater depth is less than 4 m, and the correlation coefficient between them was generally less than -0.8; (4) there was no obvious correlation between them when the groundwater depth was greater than 4 m. In this paper, the relationship between the growth state of natural vegetation and groundwater table depth in the Minqin oasis area was studied synthetically in the long time series and on the basin spatial scale, and the ecological groundwater level in the shallow buried area was obtained, and the key target area of ecological governance was preliminarily delineated.