基于景观结构的沱江流域土地利用生态风险时空变化

Spatiotemporal Changes in Ecological Risks of Land Use in the Tuojiang River Basin Based on Landscape Structure

本文以沱江流域为研究对象,基于2005—2020年的遥感数据,从景观结构的角度,利用GIS和GeoDa软件,同时结合土地利用类型转移矩阵,构建景观土地生态风险评价模型,分析了研究区土地生态风险的时空变化特征。结果表明:①耕地为研究区的景观本底值,受自然和人为因素的影响,15年间,耕地和林地面积减少,建设用地、水域、草地、未利用地面积增加,新增建设用地面积最多,91.95%来源于耕地,是建设用地的主要来源。②2005—2020年的生态风险指数,经计算,全局莫兰指数(Moran’s I)值均为正数,在99%的置信度标准下,通过了显著性检验,说明生态风险区在空间上具有显著的正相关关系且呈现空间聚集状态,“高-高”聚集是土地生态风险的主要聚集模式。③15年间,在空间分布上,低风险等级整体上有向中下游转移的趋势,研究区以高风险区和较高风险区为主,分别呈片状和条带状较集中地分布于流域上游的山区和中下游的丘陵地区,分别占到研究区总面积的49.20%和48.98%;从面积变化的趋势来看,低风险区、较低风险区、中等风险区面积逐年分别增加了1122.91、3581.10、21698.83 hm2,较高风险区面积先增加后减少,总体增加了582436.94 hm2,高风险区面积先减少后增加,总体减少了608839.78 hm2,沱江流域土地利用生态风险整体上趋于减弱;总体来看,除较高风险区向高风险区少量转化外,其余均以较高等级风险区向较低风险区转移占比较多,风险区的转化均表现为相邻等级之间的互相转化,说明研究区生态风险变化相对稳定,没有急剧变化的区域。

In this paper,Tuojiang River Basin was selected as the study object,based on the remote sensing data from 2005 to 2020,from the perspective of landscape structure,GIS,GeoDa software and land stochastic matrix were used to build a landscape land ecological risk assessment model,and to analyze the temporal and spatial changes of land ecological risk.The results showed that:1)Cultivated land was the landscape background value of the study area.Affected by natural and human factors,the areas of cultivated land and forest land were decreased over the past 15 years,while the areas of construction land,water body,grassland,and unused land were increased.The area of newly added construction land was the largest,with 91.95%coming from cultivated land(main source of construction land).2)Ecological risk indexes from 2005 to 2020 were calculated,and the Moran's I were all positive.At a 99%confidence level,the significance test was passed,indicating that ecological risk area had a significant positive correlation in space and exhibited a spatial aggregation state.The high-high aggregation was the main aggregation mode of land ecological risk.3)Over the past 15 years,in term of spatial distribution,the low-risk level showed an overall trend of transferring to the middle and lower reaches.The study area was mainly composed of high-risk and higher-risk areas,which were concentrated in the mountainous areas in the upper reaches of the basin and the hilly areas in the middle and lower reaches,and accounting for 49.20%and 48.98%of the total area of the study area,respectively.From the trend of area change,the areas of low-risk areas,lower-risk areas,and medium-risk areas were increased by 1122.91,3581.10,and 21698.83 hm2 respectively year by year.The areas of higher-risk area first increased and then decreased, with an overall increase of 582 436.94 hm2. The areas of high-risk area first decreased and then increased, with an overall decrease of 608 839.78 hm2. The overall ecological risk of land use in the Tuojiang River Basin tended to weaken. Overall, except for a small amount of transformation from higher- risk areas to high-risk areas, most of the other areas were transferred from higher-level risk area to lower-level risk area. The transformation of risk area was manifested as mutual transformation between adjacent levels, indicating that the ecological risk changes of land use in the Tuojiang River Basin were relatively stable and no areas with sharp changes.