Features Of Preferential Flow And Its Influence Factors In Typical Forests Root Zone In Rocky Mountain Area Of Northern China

Preferential flow in forest soils'root zone affects the process of soil water infiltration,nutrient leaching and pollutant migration.Spatial distribution features of roots,soil macropores and rock fragments are the main influence factors of the preferential flow transport.The study of preferential flow in different forests soils root zone could help to understand the laws of soil water and solute transport under different tree species,and provide data support for the allocation and management of forests.This work also with a view to provide basic theoretical references for ensuring ecological security of regional soil and water resources.This study investigated the preferential flow and its main influence factors in a deciduous forest(Quercus variabilis Bl.)and a coniferous forest(Platycladus orientalis(L.)Franco.)in rocky mountain area by dual-tracer experiments(brilliant blue FCF and sodium bromide)under different infiltration amount(40 and 70mm).Meantime,industrial CT technology and 3D image reconstruction analysis method were used.This study analyzed the distribution features of preferential flow paths,investigated the transport law of soil water,brilliant blue FCF and Br~-,explored the root distribution patterns and structure indexes,rebuilt and quantified the 3D structures of macropores and rock fragments.Finally,we explored the features of preferential flow and its influence factors in typical forests root zone in rocky mountain area.The main results of our investigations are as follows:(1)Preferential flow existed in both vertical and horizontal direction of soils.In typical forests soils'root zone,the main types of soil water flow were homogeneous matrix flow,heterogeneous matrix flow and fingering,and macropore flow with high interaction.The macropore flow was the main type.When the infiltration amount increased from 40 to 70mm,the preferential flow in both forest soils could carry solutes quickly infiltrate into deep soil layer,which were more obvious in coniferous forest soils with greater degree of preferential flow and higher spatial variability of preferential flow paths.(2)There were spatial variations of soil water content in region contain preferential flow and soil matrix.Generally,the soil water content in region contain preferential flow was larger than which in soil matrix.The concentrations of brilliant blue and Na Br accumulated in upper soil layer,and decreased along soil depth in both forest soils.Although the Br~-had a wider and deeper transport range than Brilliant Blue,a significant aggregation appeared in the preferential flow paths.The higher degree of preferential flow was,the higher solutes'concentrations retained in deeper soil layer.(3)The spatial distribution features of roots were the main factors for the preferential flow transport process in forest root zone.In deciduous forest,accumulated roots in the upper soil layer induce larger lateral preferential flow as compared to the coniferous forest soil.Compared with coarse roots(d>5mm),the positive effects of fine roots(d?5mm,accounting for a larger proportion of total roots)on preferential flow was stronger.Additionally,fine roots with less diameter contribute more to preferential flow transport.(4)In the limiting soil layer,the spatial distribution of different rock fragments'3D features varied in different soil layers.However,the features of 3D spatial structures of soil macropores decreased along with soil depth.Compared with deciduous forest,the soil macroproe surface area density,volume density and average of the maximum and minimum Feret diameter were higher in coniferous forest.However,compared with coniferous forest,the number density of soil macropore in deciduous forest was larger.The influences of rock fragments on soil macopores was mainly manifested in the effects on the number density,the average maximum and minimum Feret diameter of macroproes.The soil saturated conductivity increased with the increase of volume density,average maximum and minimum Feret diameter of the soil macropores.However,when the volume density of rock fragments increased,the soil saturated conductivity showed an obvious decreased.Generally,the features of 3D structures of soil macropores had a greater influence on saturated hydraulic conductivity compared with rock fragments.