基于景观格局的干旱内陆河流域生态风险分析——以石羊河流域为例

The Ecological Risk Assessment of Arid Inland River Basin at the Landscape Scale:A Case Study on Shiyang River Basin

合理评估流域生态风险,对于优化流域景观格局、建立流域生态风险预警机制、降低流域生态环境风险、维护流域生态功能具有十分重要的意义。文章以干旱内陆河典型流域为研究对象,以三期遥感数据为基础,构建生态风险指数,结合ArcGIS的空间分析功能,对流域生态风险的时空特征进行分析,结果表明:1987—2010年,流域景观发生较大了变化,草地面积减少12.73×104hm2,未利用地面积增加15.59×104hm2;将生态风险划分为5个等级,其中低生态风险区向流域上游不断迁移,面积减少31.89×104hm2,较低生态风险区向上游和中游不断延伸,面积增加29.30×104hm2,高生态风险区向下游不断扩展,面积增加58.69×104hm2;流域生态风险转换方式共有7种,低向高等级转化的总面积为122.56×104hm2,高向低等级转化的总面积为6.12×104hm2,生态风险呈增高趋势。

It is significant to make a reasonable assessment of ecological risk to optimize the landscape pattern, establish the ecological risk alarm mechanisms, minimize the risk of ecological environment and maintain the ecological function in river basin. The study, based on the remote sensing data of 1987, 2000 and 2010, chooses the typical arid inland river basin as the subject, divides the study area into 20 km× 20 km risk area and analyzes the temporal-spatial distribution pattern of ecological risk in Shiyang River Basin. Proceeding from the structure of landscape ecological system, the landscape disturbance degree index, the fragile index and the loss degree index are used to build the integrated ecological risk index （ER/） in the study with the help of spatial analysis of GIS. The results show that： 1） Great changes of landscape have taken place in the study area during 1987 - 2010, arable, woodland and grassland area have respectively reduced by 2.46×104 hm2, 4.77×104 hm2 and 12.73 × 104 hm2, while the residential land, water and unused land area have increased by 1.79×104 hm2, 2.58× 104 hm2 and 15.59×104 hm2, which mean that the predominant of arable land, woodland and grassland decrease gradually, while the predominant of water, unused land and residential land increase gradually. 2） According to scope of ERI, 5 ecological risk grades are separated by ＇natural breaks＇ . If 0.12 ≤ERI ≤0.17, then the ecological risk grade is extremely low; if 0.17 〈ERI ≤0.22, the ecological risk grade is low; if 0.22〈 ERI≤ 0.27, the ecological risk grade is medium; and if 0.27 〈ERI≤0.32, then the ecological risk grade is high, or the ecological risk grade is extremely high. 3） At the early stage of the study period, the main ecological risk grades are extremely low and high, with the elapse of time, three ecological risk models coexist in the study area, i.e., extremely low, low, and extremely high, which means that the threaten of the ecosystem is increasing. It embodies in the space that the extremely low ecological risk areas shrink to upstream, and the area reduces 31.89× 104hm2; the low ecological risk areas spread to the upper and middle stream, and the area increases 29.30× 104 hm2; the extremely high ecological risk areas expand to the downstream, and the area increases 58.69 ×104 hm2. 4） There are seven conversion modes of ecological risk, among which the overall performance is from low-grade ecological risk to high-grade ecological risk. The conversion area from low-grade to high-grade is 122.56× 104 hm2, while conversion area from high-grade to low-grade is 6.12×104hm2.