| Precipitation infiltration is an important water source for the stability of dunes and,healthy growth of vegetation in semi-arid desertification areas.It reveals the mechanism of precipitation infiltration and accurately estimates the water flux in the process of precipitation infiltration.It has important theories for vegetation restoration and ecological environment construction in semi-arid areas.And realistic meaning.In this paper,seven types of landform-soil-vegetation combination units of semi-mobile,semi-fixed,semi-slope fixed,shady fixed dunes,meadow land,corn field,and woodland are taken as research objects.Based on in-situ monitoring data,the mechanism of precipitation infiltration in different landform-soil-vegetation combination units of Horqin sandy land was clarified,the driving factors affecting the precipitation infiltration process were identified,a model of precipitation infiltration process was established,and various water balances were accurately estimated.Based on this,the system systematically analyzes the deep water leakage of semi-flowing dunes and its response to rainfall patterns.The main conclusions are as follows:(1)The soil moisture of different landform-soil-vegetation combination units in Horqin Sandy Land has typical spatiotemporal changes.On the time scale,the dune soil moisture showed a "normal distribution" type,which is in good agreement with rainfall.Meadow meadow,woodland,and corn land only had obvious fluctuations in surface soil moisture,and deep soil moisture was relatively stable;In the vertical section,the change trend of soil moisture in the dunes gradually transitioned from the "mirror S" type of semi-mobile dunes to the "S" type of fixed dunes on the shady slope.As the depth increases,the ground decreases first and then increases.(2)The soil moisture is weak and moderate.Among them,semi-mobile,semi-fixed,shady fixed dunes and meadows all show reduced variability with increasing depth.Woodland and semi-yang slope fixed dunes are on the soil profile.The performance is "S"type,and the variability of the fixed dune at Banyang slope reaches a maximum value of 75.45%at 80 cm.The variability of corn field increases with the increase of soil depth and then decreases.(3)The process of rainfall infiltration and replenishment of soil moisture in meadow,corn and woodland is more complicated than that in sand dunes.After the occurrence of a small rainfall event,different landform-soil-vegetation combination units tend to form a divergent zero-flux surface on the topsoil,which gradually moves downward with the increase of rainfall.After the heavy rainfall event,the dunes produce a single infiltration replenishment process,while meadow land,corn land,and woodland are liable to form infiltration and wetting front recharge processes.(4)The deep layer leakage and leakage rate of different types of sand dunes are significantly correlated with rainfall levels and vegetation composition.Semi-mobile and semi-fixed sand dunes have greater rainfall or accumulated rainfall,the faster the leakage rate,the shorter the time for the peak of the leakage rate,the greater the leakage volume and its replenishment coefficient,and the semi-slope and fixed slope Sand dunes can only cause deep leakage under heavy rainfall.The change of groundwater level in meadow land,corn land and forest land has a significant positive correlation with rainfall,that is,the groundwater level increases with the increase of rainfall.(5)The main influencing factors of precipitation infiltration during semi-mobile,semi-fixed,and semi-slope fixed dunes and woodland precipitation are dry bulk density,sand content,powder content,and saturated hydraulic conductivity;sand dunes are mainly affected by sand grains.Content,silt content,organic matter,and saturated hydraulic conductivity;the main influencing factors of meadow land are sand content,silt content,clay content,and organic matter;the main affecting factors of corn land are sand content,silt content,and clay Content and saturated hydraulic conductivity.(6)The Hydro-1D model after optimizing the soil hydraulic parameters can well describe the precipitation infiltration process under different landforms,revealing that the deep leakage of semi-mobile and semi-fixed dunes is the main conversion form of rainfall.It accounted for 57.35%and 54.56%of the total rainfall;fixed-semi-slope,fixed-slope dune and meadow transpiration were the main forms of water conversion,accounting for 77.15%,54.88%,and 76.49%of the total moisture,respectively.(7)The average leakage of semi-mobile dunes from 2016 to 2019 is 254.31mm,accounting for 61.82%of the rainfall in the same period;in the concentrated rainfall from June to August,the average leakage below 200cm soil layer is as high as 185.05mm,accounting for the average leakage.The total leakage was 72.76%.Different rainfall levels have a significant impact on the changes in deep leakage.The rainfall events of 22.1mm,37.3mm,and 70mm reached their peak leakage rates at 94h,81h,and 24h,which were 0.173mm/h,0.3mm/h,and 0.94mm/h.High-frequency rainfall events are easy to recharge to a depth of 200 cm,and the leakage rate increases and the peak appears earlier,the leakage replenishment process is prolonged and its coefficient is increased.16?18 mm rainfall is the threshold for the leakage of 200 cm soil depth. |
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