三江平原别拉洪河流域湿地农田化过程研究

自20世纪50年代以来,三江平原的别拉洪河流域在经历了3次大规模开荒后,大面积的湿地被农田所替代,耕地面积迅速增加,湿地农田化过程干扰和破坏了原有的湿地环境。在遥感和地理信息系统技术支持下,应用景观生态学方法,利用1954年、1976年、1986年、2000年和2005年的土地利用数据,分析了研究区近50 a来的湿地农田化过程。结果显示,湿地农田化过程中大面积的湿地斑块被农田斑块所取代,破碎化的小耕地斑块又逐渐合并为大的耕地斑块,并导致斑块形状复杂度指数逐渐增大,景观均匀度指数呈现波动变化;耕地面积在1954~1986年期间增长幅度较大,特别是在20世纪70年代末和80年代初的改革开放初期,研究区景观动态度为0.201,远高于其它时期;目前,农田景观已成为主要景观类型,农田面积占研究区总面积的63.69%,湿地面积占研究区总面积的比例由1954年的64.83%减小到2005年的19.44%。质心模型的分析结果显示,近50 a来研究区耕地景观质心平移幅度明显大于湿地景观,湿地景观质心不断地向东北方向移动,偏移了约20.5 km,而农田景观质心逐渐向东平移,平移了约44.7 km。农业开垦是研究区湿地大面积消退的主要原因。

Process of Wetland Reclamation in the Bielahong River Basin of the Sanjiang Plain

Since the 1950s several reclamations of wetlands have been carried out in the Bielahong river basin of the north of the Sanjiang plain.Farmland instead of wetland has been the main landscape through the large-scale reclamation.The wetland ecosystem was badly disturbed and destroyed while continuing cultivation to the Bielahong river basin.Using theory and methods of landscape ecology,land use and land cover changes in 1954,1976,1986,2000 and 2005 were analyzed based on RS and GIS.The data sources mainly came from the Landsat TM digital images,topographic maps and statistical data.The landscapes changes,especially analyzing the process of land reclamation and wetland shrinkage was focused on in the paper.As a result,Large area of wetland patches were replaced by fragmental farm patches that were then combined into large patches gradually.This resulted in the increase of patch shape index and the fluctuant change of landscape evenness index.From 1954 to 1986,the farm area grew rapidly,especially in the early stage of reform and opening policy from the end of 1970s to the beginning of 1980s when the walue of landscape dynamical index reached as high as 0.201.The analysis results on the ecological landscape patterns of land use indicated that farmland was the main landscape types which occupied 63.69% of the total study area,comparatively wetland occupying nearly 19.44% in 2005.The study results on centroids of landscapes showed that the shift degree of farmland centroid was much higher than that of wetland centroid in recent 50 years,that the centroid of farmland moved from west to east with a distance of 44.7 km while wetland centroid moved 20.5 km to the northeast.Based on the analysis of the spatial and time variations of wetlands,the causes of wetland shrinkage were further analyzed that the agricultural cultivation with the population increasing was the primary factor,while the mean annual temperature increases and the annual precipitation decreased obviously in the study area in recent 50 years.