山地土壤优先流路径的染色示踪研究

在山地林区开展土壤大孔隙及优先流的实验研究，可深化对森林土壤涵养水源机理的认识，为山区的水土流失防治和植被恢复提供依据。利用剖面染色与图像分析相结合的方法，沿长江三峡大老岭-邓村一线，对山地不同垂直带内土壤优先流特征进行了调查，分析了优先流路径对剖面水分入渗过程的影响。结果显示，中山常绿落叶针阔混交林-山地黄棕壤、低山暖性针叶林-山地黄壤中大孔隙孔径大、分布广，有利于优先流的形成和入渗。受耕作扰动的弃耕土壤中大孔隙结构遭到破坏，优先流路径与森林土壤不同，且渗流强度较弱，染色区域较浅。森林土壤各发生层内优先流特征差异显著，腐殖质层内以洞穴流为主，水分与土壤基质域交换较少，多通过大孔隙快速下渗。淋溶淀积层内洞穴流消失或减弱，侧向渗透增强。低山暖性针叶林-山地黄壤质地较粗，出现以裂隙为主的大孔隙，优先流表现为裂隙流。弃耕土壤各发生层都表现为指流，染色面积随深度减小，侧向渗透基本稳定。植被-土壤垂直地带性分布是山地土壤优先流存在差异的主要原因，山区生态环境建设中应促进土壤优先流路径的发育。

To investigate soil preferential flow paths in mountain area using dye tracer

Preferential flow plays an important role in water and contaminants transporting in the soil. The aim of this study is was to investigate characteristics of soil preferential flows in different vertical traps in mountains along the Dalaoling-Dengcun section of the Three Gorges of the Yangtze River, using the section staining method coupled with image analysis, and hence to analyze impact of preferential flows on water infiltration in the profile. Results show that the mountain yellow brown earth under evergreen-decidous broadleaf mixed forest in the mid-mountain belt and the mountain yellow earth under low-mountain warm coniferous forests have soil pores large in aperture and extensive in distribution, which is conducive to formation of preferential flows, and water infiltration. In deserted farmland, the large-pored soil structure is damaged by tillage in the past, the paths of preferential flows differ from those in the forest soils, and consequently its water infiltration intensity is low and the color of the stained area is light. Characteristics of preferential flows differ significantly between soil layers. Burrow flows occur frequently in the humus horizon, and soil water percolate down rapidly through macropores, exchanging little with surrounding soil matrix. In the leaching illuvial horizon, burrow flows disappear or weaken, while lateral percolation intensifies. The low-mountain yellow earth under warm coniferous forests is rather coarse in texture, and macropores mainly in the form of crack or fissure appear, making crack flows the preferential flows. In deserted farmland, finger flows dominate in all the genetic horizons with the area of stained section diminishing with soil depth, however, lateral percolation remains basically constant in these horizons. In conclusion, vegetation-soil vertical zonal distribution is the major cause of the difference existing in preferential flow between mountain soils. In eco-environment construction in the maintain regions, it is essential to promote development of preferential flows in the soil.