Water Transformation Mechanism Of Vadose Zone In Alpine Meadow Of Qinghai-Tibet Plateau

The hydrodynamic transformation interface dynamics of vadose zone has always been a hot and difficult problem in the field of vegetation ecology and hydrogeology.The qinghai-tibet plateau is a typical research area.The vadose zone moisture in the alpine meadow of qinghaitibet plateau was studied.The soil-gas interface,soil-root interface and frozen-melt interface water are the main clues.By means of collecting data,field investigation,in-situ test and numerical simulation,the water transformation mechanism of vadose zone in alpine meadow of qinghai-tibet plateau was studied.The following achievements have been achieved:(1)By analyzing the moisture content of different time,vadose zone profile suction head change rule,in combination with the meteorological elements of change,using the theory of vadose zone hydrothermal migration mechanics,the water transformation kinetics process of vadose zone was divided into latent heat accumulation stage,the solid melting solid to liquid phase,liquid water and gaseous water frequently translated each stage,the frozen liquid to solid phase such as four stages.such as the correct understanding of vadose zone water transformation kinetics is of great significance.(2)According to the different depth of vadose zone section geothermal gradient change rule,in combination with the meteorological elements of change,using the theory of thermodynamics transmission,heat balance of thermodynamics process of vadose zone are analyzed.In the vadose zone,the heat flux in different depths is consistent with the external temperature trend.At the beginning of march to the end of September,the heat flux on the upper boundary surface was positive.The vadose zone is absorbed from the outside.Conversely,the vadose zone is in the heat dissipation state;Each year in March and October,it belongs to the transition period of endothermic and exothermic heat.In June and December,it belongs to the extreme period of heat absorption and heat release of vadose zones.On this basis,this paper explores the access to determine the average temperature of the balance of vadose zone heat threshold value method,average temperature is established and the vadose zone near the correlation between the surface heat flux,and determines the vadose zone judgment of the heat balance of average temperature is-0.73?,the threshold for the extreme low temperature environment area outside the change of temperature of frozen layer thickness and mutual transformation between solid,liquid,water quantity research is of great significance.(3)The water equilibrium analysis shows that the vadose zone water balance in the experimental area is close to the balance of payments.Rainfall infiltration in the vadose zone after the moisture of redistribution,influenced by evaporation,part of the vadose zone water returned to the atmosphere,the root absorbing effect,part of the vadose zone water is absorbed by the meadow root transpiration,affected by the vadose zone water effect,part of the water to keep vadose zone inherent capacity stranded in the vadose zone,influenced by its own gravity,the remaining water discharge to deep vadose zone,reveals the vadose zone dynamic allocation mechanism of the surface soil infiltration quantity,provide theoretical support for very cold district vadose zone water conservation.(4)The use of reference crop transpiration in the penmen formula on the basis of the vadose zone based on water balance principle,the test area actual transpiration is calculated,the results show that the actual transpiration accounted for 68% of the reference crop transpiration,and on this basis,calculated the test area may crop coefficient of 0.18,the crop coefficient of 0.9 from june to August and September crop coefficient of 0.38,the actual crop transpiration in computing has an important significance.(5)Based on the different environmental area based on the study of the vadose zone moisture transformation mechanism,clear the discriminant basis whether the growth of the alpine meadow was by water stress.The correlation is established between water stress index and root water absorption intensity and determines the very cold district meadow growing water stress index threshold is 0.43;And test area calculating water stress index of 0.68,based on known alpine meadow status under the conditions of growth was not influenced by water stress,only low temperature stress.The time of low temperature stress distribution is from the first half of June to the middle of September.(6)The water absorption intensity of the root system was quantitatively calculated using the model constructed,and the water absorption intensity of the meadow root system in the experimental area was 169.1 mm/a;The water consumption intensity of different deep roots is 0-0.05 m and 108.4mm/a,0.05-0.1m is 44.1mm/a,0.1-0.2m is 16.6mm/a,and below 0.2m is 0mm/a;on the basis,the estimation model of water absorption of alpine meadow roots is constructed by using logarithmic normal distribution density function,and the dynamic theory and method of soil-root interface water transformation are improved.(7)According to the migration characteristics of freeze-thaw front,the migration process of freeze-thaw front is divided into three periods.Among them,the melt front migration period is from early April to early January,and its rate of ablation: 10mm/d.Freezing front migration period is from early November to early January,and its freezing rate: 15mm/d.The two fronts met in early January and disappeared into full freeze time.The total freezing period is mainly from the beginning of January to the end of march,the maximum depth of the melting front in the high cold zone is 2m,and the maximum depth of the freezing front is 0.87 m.The dynamic process of the water freezing and thawing front migration of the bag is revealed,and the causes of permafrost and the rheological theory of permafrost are enriched.Above research results for the correct understanding of vadose zone moisture transformation kinetics,improve the efficiency of governance alpine meadow,self-restraint very cold district vadose zone of water resources,protect ecological environment,alpine meadow inhibition negative effect geological environments,reveal very cold district meadow ecological succession mechanism and the influence mechanism of alpine meadow very cold district permafrost development has important theoretical and practical significance.