黄土高原藓结皮覆盖土壤导水性能和水流特征

生物结皮具有特殊的水文物理性质,为探究其对土壤水分渗透性和水流特征的影响,以黄土高原风沙土和黄绵土上3种典型地表覆盖类型(裸地、藓结皮、藓结皮-草本植物混合)为对象,采用环刀法和染色示踪法对其导水性质与水流特征进行探究。结果表明:藓结皮对2种土壤类型0~5 cm土层土壤理化性质影响较大,与裸地相比土壤容重降低了9.85%~10.00%,土壤黏粒含量增加了1.01~1.29倍,表层有机质含量提高了2.73~3.02倍;藓结皮使0~5 cm土层土壤饱和导水率降低了61.32%~88.89%,而在5~10 cm土层饱和导水率则有明显上升。另外,由于草本植物的影响,藓结皮-草本植物0~5 cm土层与藓结皮土壤相比土壤饱和导水率提高了1.32~6.43倍;黄绵土藓结皮与藓结皮-草本植物的染色面积比均高于裸地,且水分下渗深度增加了10 cm,而风沙土藓结皮与风沙土裸地的染色面积比差异不明显。综上所述,藓结皮和藓结皮-草本植物的存在改变了表层土壤水分渗透性以及水流运动特征和水分下渗深度,影响着黄土高原土壤水分保持和生态恢复。

Study of soil water permeability and water flow characteristics under moss crusts covering the Loess Plateau

Biological soil crusts are assumed to greatly affect soil hydraulic conductivity and flow characteristics owing to their unique hydrophysical properties.Many studies have reported the effect of biocrust cover in soil water movement in arid and semi-arid areas and noted that the physicochemical properties (i.e.,bulk density,organic matter,and soil particle distribution) of topsoil are different than those of bare soil,which may have positive or negative impacts on soil water infiltration,evaporation and other properties that play an important role in the water and heat balance of arid and semi-arid areas.However,biocrust/grass mixed into soil is a common surface cover type in Loess Plateau,China,whereas the differences between biocrust cover and biocrust/grass mixed into soil are unknown in terms of water infiltration and water flow characteristics.In this study,three typical soil cover types (bare soil,soil with moss crusts,and soil with a mixture of moss crusts and grass) were selected for aeolian sandy soil and loessal soil.Their hydraulic conductivity and water flow characteristics were measured using the constant-head method in undisturbed soil samples and the dye tracing method in the field.The results show that the moss crusts had a marked influence on the physiochemical properties of surface soil.As compared with bare soil,the bulk density of the moss crust layer decreased by 9.85%-10.00%,and the clay content and organic matter content of the moss crusts layer were 1.01-1.29 times and 2.72-3.02 times that of the bare soil,respectively.Moreover,the moss crusts reduced the saturated hydraulic conductivity of the surface soil,especially for aeolian sandy soil where the value was over 88.89% that of bare soil.The moss crust/grass mix would reduce the water loss;however,grass roots can create a number of preferential flow paths.This significant effect ultimately increased the surface soil hydraulic conductivity by 1.32-6.43 times.The stained area ratios of the moss crusts cover type and moss crust/grass mix were higher than that of the bare soil at the same soil depths for the loessal soil.Moreover,the soil water infiltration depth was increased by 10 cm under moss crust cover.However,the stained area of the moss crusts cover type and the bare soil was similar for the aeolian sandy soil.More importantly,soil cracks and macropores caused by the swelling and shrinking of the moss crusts and the penetration of grass roots were important preferential flow channels for soil water infiltration and conduction;therefore,finger flow was clearly observed in the process of soil water infiltration,promoting rapid soil water infiltration and ultimately affecting the characteristics of soil water flow.In conclusion,the moss crusts cover type and moss crust/grass mix in the Loess Plateau significantly altered surface soil water permeability and water flow characteristics.Therefore,their effects on soil water conservation and vegetation restoration should be considered in arid and semi-arid climate regions.