基于分形分析的干热河谷区典型地类土壤优先路径分布特征

Distribution characteristics of typical soil-specific routes in dry-hot valley regions based on fractal analysis

【目的】定量分析土壤优先路径的分布特征,为探究土壤优先流运动及土壤水资源管理提供参考。【方法】基于分形理论,以云南省楚雄市元谋县老城乡苴那小流域4种典型地类(林地、荒草地、农地、园地)为研究对象,在各地类区域内依据地形分别设置4个10 m×10 m或10 m×15 m的样方,利用染色示踪法提取和分析土壤染色特征参数,将染色影响半径分为≤1 mm、>1~≤2.5 mm、>2.5~≤5 mm、>5~≤10 mm和>10 mm等5个等级,研究各典型地类土壤优先路径分布特征及其与大孔隙的关系。【结果】4种地类各个土壤剖面的计盒维数基本均随土壤深度的增加而逐渐减少,不同影响半径的优先路径连通性以林地发育程度最好,其次是农地,园地最差;同一地类不同半径范围的优先路径连通性从大到小排列,园地依次为>1~≤2.5 mm、>5~≤10 mm、>10 mm、≤1 mm和>2.5~≤5 mm;荒草地和林地均为>1~≤2.5 mm、>2.5~≤5 mm、≤1 mm、>10 mm和>5~≤10 mm;农地为>2.5~≤5 mm、>1~≤2.5 mm、≤1 mm、>10 mm和>5~≤10 mm。4种地类中,荒草地优先路径数量最多,其次是林地和农地,园地最少;荒草地和园地在同一土壤深度上优先路径数量由大到小依次为≤1 mm、>1~≤2.5 mm、>2.5~≤5 mm、>5~≤10 mm和>10 mm,林地为>1~≤2.5 mm、≤1 mm、>2.5~≤5 mm、>5~≤10 mm和>10 mm,农地为>1~≤2.5 mm、>2.5~≤5 mm、≤1 mm、>5~≤10 mm和>10 mm。土壤中大孔隙数量随土壤深度的增加而逐渐减少,且孔隙半径为>1.5~≤2.0 mm和>2.0~≤3.7 mm的大孔隙数量与稳定出流速率具有极显著相关性(P<0.01)。【结论】优先路径分布具有自相似性,可用分形分析中的计盒维数对优先路径在土壤中的分布特征进行表征;优先流的发生与土壤中大孔隙的分布和数量关系密切,大孔隙分布密集区更易发生优先流。

【Objective】Quantitative analysis of distribution characteristics of soil priority paths was studied to provide reference for exploring soil priority flow movement and soil water resources management.【Method】Based on the fractal theory,four typical land types including forests,grasslands,agricultural lands and gardens in Juna river basin in Laocheng,Yuanmou County,Chuxiong City of Yunnan were studied.Four 10 m×10 m or 10 m×15 m plots were set according to the topography in each area.The samples were extracted and analyzed by dyeing tracer method,and the influence radius of the dyeing path was divided into five grades of≤1 mm,>1-≤2.5 mm,>2.5-≤5 mm,>5-≤10 mm and>10 mm.Then the distribution characteristics of typical soil-specific path and its relationship with macropores were analyzed.【Result】The box-counting dimension of each soil profile of the four land types decreased gradually with the increase of soil depth.The priority path connectivity of different impact radius was the best in forest land development,followed by farmland and garden land.The priority path connectivity of garden was in the decreasing order of>1-≤2.5 mm,>5-≤10 mm,>10 mm,≤1 mm and>2.5-≤5 mm.The order of grassland and forest all were>1-≤2.5 mm,>2.5-≤5 mm,≤1 mm,>10 mm and>5-≤10 mm and that of farmland was>2.5-≤5 mm,>1-≤2.5 mm,≤1 mm,>10 mm and>5-≤10 mm.Among the four land types,the number of priority paths for grassland was the largest,followed by forest land,agricultural land and garden.The number of soil priority path in the same soil depth of grassland and garden land was in the decreasing order of≤1 mm,>1-≤2.5 mm,>2.5-≤5 mm,>5-≤10 mm and>10 mm,that of woodland was>1-≤2.5 mm,≤1 mm,>2.5-≤5 mm,>5-≤10 mm and>10 mm,and that of agricultural land was>1-≤2.5 mm,>2.5-≤5 mm,≤1 mm,>5-≤10 mm and>10 mm.The number of macropores decreased with the increase of soil depth.The number of macropores was significantly correlated with steady outflow rate when the thickness was>1.5-≤2.0 mm and>2.0-≤3.7 mm(P<0.01).【Conclusion】The priority path distribution had self-similarity.The distribution characteristics of the priority path in soil can be characterized by the box-counting dimension in fractal analysis.The occurrence of preferential flow had close relationship with distribution and quantity of macropores in soil.Pore-distributed areas were more likely to cause preferential flow phenomena.