半干旱区湿地-干草原交错带边界判定及其变化

鉴于目前国内对于半干旱区及小尺度上湿地-干草原交错带边界界定的研究较少,利用交错带对其周围环境变化具有提前指示作用的原理,以宁夏盐池四儿滩湿地为例,首先探讨游动分割窗技术在半干旱区湿地-干草原交错带边界判定中的可行性,其次再对2006年—2010年湿地-干草原交错带的宽度和边界进行判定,通过交错带的宽度和边界变化并结合交错带内植被的变化情况,综合对整个湿地生态系统的健康状况和湿地退化进行研究。结果表明:研究的尺度大小以及交错带过渡性是否明显将决定适宜窗口宽度的大小,这点在选择最小适宜窗口宽度时体现更为显著;降雨量是决定该区交错带的位置与宽度的最主要因素,但降雨量并不是决定该区交错带内植被变化状况的最主要因素,交错带距湿地核心区的距离是影响交错带内物种丰富度指数变化的最主要因素;由于保护区的成立,四儿滩湿地在2006年—2007年间,交错带宽度变大,湿地状况转好,2008年—2010年,由于铁路建设,湿地遭到破坏,交错带萎缩,湿地出现退化现象。湿地-干草原交错带作为一个敏感地带,它的变化情况可以对整个湿地生态系统的变化情况作出一定的提前预示;在半干旱区湿地的健康评价和退化研究中,通过交错带的变化来反映整个湿地生态系统的健康情况是一种可行的思路和方法。

Research on boundary definition and changes of wetland-dry grassland

Functioned as the "kidneys" of the earth, wetlands provide comprehensive eco-environmental and productive services in terms of flood mitigation, climate control, pollution prevention, soil-erosion reduction, environment beautification, biodiversity maintenance and bio-productivity protection. In China, most wetlands are distributed in the northwest part. Research on wetlands in semi arid region is very important and meaningful. Defining the location and width of interlaced zone is the basement to have quantitative study of its ecological process. In consideration of there is little research on identifying the interlaced zone boundary of semi arid area and small-scale wetland-dry grassland, this paper is based on the theory that changes of ecotone boundary can indicate the transformation of ambience in advance. Si'er Tan wetland, which is located in Yanchi county, Ningxia province, was studied by line transect methods. Four transect lines, centered on the wetland, ran into four directions: N, E, S and W respectively. These lines went through three main ecological areas including wet zone, interlaced zone and typical dry zone. Field investigations have been done every July to September during the year 2006 and 2010. In this paper, we first discussed the feasibility of using Moving Split-Window Technique in determining the interlaced zone boundary between wetland and dry grassland in semi arid area. Secondly, take Si'er Tan wetland for instance, Moving Split-Window Technique was used to identify the width and boundary of wetland and dry grassland from the year 2006 to 2010. Health condition of the whole wetland ecosystem can be known through analyzing the changes of width, boundary and vegetation of the interlaced zone during these five years. The results show that: Moving Split-Window Technique can be used to define the interlaced zone boundary. According to the dimension of investigatory scale and the visibility of ecotone transitivity, appropriate window width can be chosen especially in the selection of appropriate smallest window width. What's more, precipitation is the primary determinant factor of defining the location and width of interlaced zone but does not have substantial influence on vegetation variation. The distance between interlaced zone and the core area of the wetland can determine species richness index. By analyzing the data and making comparisons, wetland health condition shows significant differences. Owing to the built of the reserve, interlaced zone width got larger in the year 2006 and 2007, as a result, Si'er Tan wetland health condition had turned better. While from the year 2008 to 2010, the shrink of interlaced zone indicated the degradation of wetland, which as a result of railway construction disturbance. Results above prove that wetland-dry steppe alternated zone, which is always very sensible, can predict the transformation of the whole wetland ecosystem. In future development and degradation research of semi arid region wetland, we can focus on the study of interlaced zone evolvement. This method is feasible and much easier to make health evaluation for the whole wetland ecosystem. It can also provide new solutions and ideas to find and solve protection and improvement problems of wetlands in semi arid region.