三峡库区典型流域“源”“汇”景观格局时空变化对侵蚀产沙的影响

以三峡库区王家桥流域为研究对象,基于五期遥感影像(1995、2000、2005、2010和2015)提取流域景观格局,采用马尔科夫模型研究"源""汇"景观格局时空变化,并结合野外多年实测数据建立景观格局指数与产沙量之间的关系,分析景观格局对流域侵蚀产沙的影响。结果表明:1995—2015年,王家桥流域景观格局时空变化明显,呈破碎化发展趋势。"源"景观面积持续下降,"汇"景观面积持续增长。在降雨量时序曲线相似的条件下,斑块类型尺度的景观指数对侵蚀产沙量的解释能力高于景观尺度。斑块类型尺度,"源""汇"景观指数与径流输沙量的复相关系数分别为0.946和0.903,均显著相关。对于"源"景观而言,相似邻近百分比(PLADJ)与斑块结合度(COHESION)是影响流域侵蚀产沙的重要指标。径流输沙量与PLADJ和COHESION指数呈正相关关系,输沙量随指数的增大而增大。对于"汇"景观而言,斑块密度(PD)、边界密度(ED)、景观形状指数(LSI)是影响流域侵蚀产沙的重要指标,径流输沙量与PD和LSI呈负相关关系,输沙量随着指数的增大而减小。斑块类型尺度上,流域景观格局时空变化对泥沙输出影响显著。研究结果可为建立其他流域景观格局变化与土壤侵蚀响应关系提供参考。

Effects of temporal and spatial variations in source-sink landscape patterns on soil erosion and sediment yield from typical watershed in the Three Gorges Reservoir area, China

Taking the Wangjiaqiao watershed as the study region, the landscape patterns of the watershed were extracted based on remote sensing images over five periods (1995, 2000, 2005, 2010, and 2015). The temporal-spatial evolution characteristic of the source-sink landscape patterns were analyzed using transfer matrixes with the Markov model. In addition, the relationship between landscape pattern indexes and sediment yield were established based on field measured data of the Wangjiaqiao watershed for many years, and the influence of landscape patterns on the sediment yield of the watershed was analyzed. The results concluded that temporal and spatial variations in landscape patterns were obvious in the Wangjiaqiao watershed from 1995 to 2015, showing a fragmentation trend of development. The area of source landscape continued to decline, while the area of sink landscape continued to increase. Under the condition that the time-series curves of precipitation are similar, the landscape index at patch scale had a higher interpretation ability to erosion sediment yield than at landscape scale. At patch scale, the multiple correlation coefficients between sediment yield and landscape indexes of source and sink were 0.946 and 0.903 respectively, showing a significant correlation. The Proportion of Like Adjacency (PLADJ) and Patch Cohesion index (COHESION) were important landscape indexes affecting sediment yield in the watershed for the source landscape. Both PLADJ and COHESION were positively correlated with the sediment yield, and the sediment yield increased with the increasing value of the above two indexes. As for the sink landscape, Patch Density (PD), Edge Density (ED), and the Landscape Shape Index (LSI) were important indexes of soil erosion and sediment yield. Both PD and LSI were negatively correlated with sediment yield, and the sediment yield decreased with an increasing value of the two indexes. At patch scale, the influence of temporal and spatial variation of landscape patterns on sediment yield was significant. These results could provide references for establishing the relationship between variations in landscape patterns and responses of soil erosion to other watersheds.