基于多重分形理论的多年冻土区高寒草甸退化过程中土壤粒径分析

为阐明青藏高原多年冻土区高寒草甸退化过程中土壤粒径分布(PSD)非均匀性和异质性的变化特征, 在青藏高原长江源区, 根据高寒草甸的退化梯度, 选取了未退化区域、 轻度退化区域、 中度退化区域、 重度退化区域和极重度退化区域, 测定了高寒草甸退化过程中土壤的粒径分布、 饱和导水率、 孔隙度与有机质含量. 运用多重分形理论, 并结合土壤颗粒分布与土壤理化特性等参数的相关性进行分析, 为高寒草甸退化对长江源高寒土壤性质变化的影响的定量研究提供一种精确的分析方法. 结果表明: 随着青藏高原多年冻土区高寒草甸退化程度的增加, 土壤颗粒呈粗粒化趋势, 多重分形参数中容量维数(D₀)随之增大, 表征PSD宽度随之增大; 信息维数(D₁)、 信息维数/容量维数(D₁/D₀)、 关联维数(D₂)、 奇异谱宽(Δα)可从不同角度反映的土壤PSD的非均匀性与局部异质性随着高寒草甸退化有先增大后减小的趋势, 中度退化区域的土壤PSD不均匀性最大. 研究发现, 研究区土壤多重分形参数与细砂含量、 土壤的孔隙度、 有机质含量具有较明显的相关性. 多重分形参数能准确描述高寒草甸退化过程中土壤粒径分布的细微差别, 可作为反映土壤性质的潜在指标.

Heterogeneity analysis of soil particle size distribution in the process of degradation of alpine meadow in the permafrost regions based on multifractal theory

The study purpose was to investigate the changes of the heterogeneity of the soil particle-size distribution (PSD) in the process of degradation of alpine meadows of permafrost regions in the Tibetan Plateau and to develop a precise quantitative analytical method of quantitative research on the evolution of soil properties in the developing process of alpine meadow ecosystem. In this paper, alpine meadows in the source regions of the Yangtze River were divided into five stages (no degradation, slight degradation, moderate degradation, severe degradation and extreme degradation). Three soil samples were collected from every degradation stage area. PSD, saturated hydraulic conductivity, porosity and organic matter content of the soil samples were measured. Multifractal theory was used combined with the correlation analyses between physical and chemical characteristic parameters of soil and soil particle size distribution. The result showed that with increasing degradation degree of alpine meadow in the Tibetan Plateau permafrost regions, the soil particles trend to coarsen and increase dimension (D₀) in multifractal parameter, which means PSD width increasing; information dimension (D₁), ratio of information dimension to capacity dimension (D₁/D₀), correlation dimension (D₂), the singular spectrum width Δα could represent the trend of soil PSD inhomogeneity changing with degradation degree of alpine meadow, first increasing and then decreasing; in moderate degradation area the inhomogeneity is the maximum. The study also found that the multifractal parameters of soil in the study region are obviously correlated with fine sand content, soil porosity, soil organic matter content. The multifractal parameters could accurately describe the subtle changes in soil particle size distribution in the process of degradation of alpine meadow and could be used as potential indicators of soil properties.