Study On The Characteristics Of Deep Sandy Soil Recharge In Typical Arid And Semi-arid Region

Land desertification has become one the biggest ecological environmental problems faced by arid and semi-arid regions.Water resource is the main limiting factor to influence a region's degree of desertification.In arid and semi-arid regions,water resource is scares.Soil water the main form of water resource to maintain a region's vegetation development and ecological environment stability.In arid and semi-arid regions,recharging source for water resource are precipitation and groundwater.Groundwater recharge is related to storage depth.Human society unreasonable development and utilization caused a sharp drop in groundwater level.Precipitation in arid regions is small and unevenly distributed.When precipitation reaches ground surface,part of it reenters the atmosphere through evapotranspiration,and the other part infiltrates into the soil to become soil water.Internationally,the shallow soil unsaturated moisture zone is called the key zone of the earth.Shallow soil water directly influences vegetation environment development.The study on soil water distribution in arid and semi-arid regions has very important scientific significance for vegetation restoration,ecological environment construction,and sustainable development.This study uses typical arid and semi-arid regions in Northern China as case studies(arid region: Ulan Buh Desert bare sand land;semi-arid region: artificial Pinus sylvestris var.mongolica forest,artificial Artamisia sphaerocephala Krasch sandfixing forest,and natural bare sand land in Mu Us Sandy Land).The study uses rain sensor,soil moisture sensor,and deep soil moisture infiltration sensor,independently developed by the team.The study conducts real-time,continuous,and multi-element simultaneous monitoring of hourly precipitation in various types of experimental areas in arid and semi-arid regions.The study monitors soil moisture content at different soil depth: 20 cm,40cm,60 cm,80cm,120 cm,160cm,and 200cm;as well as deep soil moisture infiltration at 200 cm.Through monitoring soil moisture movement,shallow soil moisture reserve,and moisture content infiltrated into deep soil(200cm),the study systematically analyzed:(1)soil moisture's response to precipitation in wind and sandfixing tree forest,artificial bush sand-fixing forest,and natural bare sand land under natural conditions in arid and semi-arid regions;(2)deep soil moisture infiltration's response to precipitation recharge;(3)several special phenomenon and boundary conditions of deep infiltration during precipitation infiltration process in arid and semi-arid regions.The study statistically calculated different water balance factors in different regions,and evaluated moisture elements in artificial afforestation that required attention.The study discussed sand land moisture distribution characteristics,and evaluated the sustainable development of artificial forests.The study finally demonstrates the feasibility of constructing sand-fixing forest under rain-fed conditions,and provides guidance for sand land artificial afforestation and water balance evaluation.Main conclusions of the experiment are:1.The capillary water holding height in the arid and semiarid region is 30-77 cm.According to this result,a new type of instrument is designed to accurately measure the DSR.This study try to establish a new method that no needs to measure the soil surface vegetation coverage and meteorological conditions to realize the goal of calculate evapotranspiration.2.Precipitation intensity(greater than 10 mm/d)and temperature influence infiltration speed.In order to clarify how soil temperature influence precipitation infiltration speed,further experimental monitoring is needed.3.Result shows that there are two obvious moisture recharge processes in an annual base for the Pinus sylvestris var.mongolica forest soil in Mu Us Sandyland.Evaporation and soil temperature can significantly influence the infiltration rate of precipitation.Compared with the two seasons in the spring and autumn,it was found that the deep soil recharge delay time was different when the precipitation intensity was similar,and the maximum delay time was 78 days.4.The snow melted water infiltration-recharge process in the spring.The precipitationrecharge process in the summer.The recharge depth of the first process is 160 cm.The second process results in DSR(referring to recharge that can reach a depth more than 200 cm and may eventually replenish the groundwater reservoir).5.The 40-year-old Artamisia sphaerocephala Krasch forest have considerably changed the soil particle distribution.The distribution range of rain-fed Artamisia sphaerocephala Krasch is 0-120 cm,and the root system is mainly concentrated in the 40-60 cm deep soil layer.The little precipitation event in spring and winter frozen seasons still have DSR to groundwater.In arid regions,partial heavy precipitation does not have obvious recharging effect on the local DSR,and the water from heavy precipitation can only redistribute in the form of run-off.6.Snow has moisture recharging effect on seasonal frozen soil(although the annual precipitation is only 48.2mm),and has recharging effect on DSR,but these effects are long undermined.In arid regions,the infiltration capacities of seasonal frozen soil and unfrozen soil are the same.The results of this study unveil the transformation process between moisture source and water resource,which is a long undermined process in arid regions.This has important guidance significance for the accurate assessment of water resource in arid and semi-arid regions.7.This study conclude that under the current precipitation conditions,a sizable DSR can occur,thus the groundwater system underneath the forest may be replenished,meaning that the artificial Pinus forestry can probably develop sustainably.This study confirms that developing limited amount forestry in semi-arid regions is likely in a sustainable fashion.Using of a constant recharge coefficient for estimating DSR in bare sand land in arid and semi-arid regions is questionable and could lead to considerable errors.It appeared that DSR in those regions was influenced by precipitation pattern,and was closely correlated with spontaneous heavy precipitation.