| Soil hydraulic conductivity and macropores are important parameters determining theproportion of precipitation infiltration, and thus have great significance for simulating soilwater and solute transport and establishing watershed hydrologic model. To investigate theeffect of land use types on macropores in soils, soil hydraulic properties, macroporosityand macropore connectivity were measured by Hood infiltrometer and water retentioncurve in different land uses (Locust forestland, grassland, farmland and apple orchard) inloess region. Simultaneously, in order to understand the mechanism of macropore flowwell, the laboratory soil column infiltration experiments were conducted with man-mademacropore under different initial conditions, and the Hydrus-2D/3D sofeware was appliedto solve the model numerically. The main findings are as follows:1) Average hydraulic conductivity in Locust forestland, grassland, farmland and appleorchard were58.60×10-6,54.90×10-6,35.30×10-6,23.40×10-6m·s-1, respectively. Thedifference among land uses is statistically significant (P<0.05). The effective macroporeper unit area, macroporosity and macropore connectivity ranked a descending sequences asLocust forestland≈grassland> farmland> apple orchard. As a consequence of vegetationrestoration, macropores developed owing to root growths and animal activity wouldsignificantly improved soil infiltration capability.2) When the initial soil water content is greater than the critical soil moisture of waterrepellency, the wetting front migration distance increases with increasing of initial soilwater content for a given soil type; whereas the wetting front migration distance increasedwith the decrease of initial soil water content. For different soil types, wetting frontmigration distance deceases with increasing of clay particles content. Cumulativeinfiltration which was influenced by both the water repellency and soil water storage is different from the change of wetting front migration. Kostiakov model was used tosimulate the cumulative infiltration change with time, the results showed soil infiltrationprocess of preferential flow were fitted by Kostiakov model.3) The macropore tortuosity considerably influenced the shape of the wetting frontmigration and its movement in vertical and lateral direction; the decrease of macroporetortuosity could accelerate the migration of wetting front and increase the cumulativeinfiltration; the depth of wetting front migration and the amount of cumulative infiltrationhas exponential relationship with time. The parameters in these functions depended on themacropore tortuosity. The time for water to penetrate the soil column increased with therise of the macropore tortuosity. The relationship between penetration time and macroporetortuosity could be described by a logarithmic function.4）Macropore connectivity does not necessarily affect the wetting front shape, itsimpact depends on the position of the macropores in soils, macropores hardly affect thewetting front unless macropores connected to soil surface; Macropores connected to soilsurface wonld shorten the migration time of wetting front, O–O treatment reached thebottom of the macropore bypassing the soil matrices instantaneously, while thebreakthrough time for O-C treatment is depent on macropore depth, macropore density,macropore tuorisity, macropore angle, etc.5) Simplified dual-permeability model was established for water transport inunsaturated soil, The Hydrus-2D/3D software was applied to solve the modelnumerically．The model was validated through the contrast of measured values andsimulated values of the soil wetting front which change over time．The results showed thatthe simulated valued are in well agreement with measured values. It is not too sensitive forsimulating the wetting front of different initial soil moisture content by Hydrus-2D/3Dsoftware, the realtionship among initial soil moisture content, soil water repellency andmacropore flow still needs to be studied further. |
PDF Full Text Request