A Study On Eco-hydrologic Process Of Small Basin Of Desert Steppe In Inner Mongolia

Desert steppe is a fragile ecologic system and limited by water.We analyzed community characteristics,evapotranspiration,rainfall-runoff process,water balance,and eco-hydrological characteristics of small watershed via field experiment and rainfall simulator experiment in ShangDong River to determine the eco-hydrologic inter-relationship and water cycle process in desert steppe,and provide decision-making basis for biodiversity conservation and sustainable water resources management.The results are followed:?1?We found the precipitation and air temperature has a positive increasing trend,andthe average variation rates were 1.6 mm and 0.46?per decade by analyzing sixtyyears meteorological data of ShangDong River.The soil thickness,soil moisturecontent,soil nutrients and hydrothermal condition are the dominant factors ofaffecting community characteristics.?2?In ShangDong river,the research plots community coverage,height andaboveground biomass followed the order of fenced>light degraded>moderatedegraded>heavy degraded;the plant species decreased,but aboveground biomass,community coverage and height increased with increase of enclosure years;enclosure significantly increased the soil nutrient content.In addition,stipa,Leymus chinensis,Agropyron cristatum and Cryptomeria scabra were the majordominant species of community composition after fenced 13 years.?3?The community coverage had significantly positive relationship withevapotranspiration.Precipitation has a great impact on communitevapotranspiration,and difference of community structure had marked impact onevapotranspiration when soil water content was higher.The evapotranspiration indesert stepped was less than 1 mm d^-1 if there is no rain in one week;precipitationhas greater effect on evapotranspiration than the difference of communitystructure;There had significant positive correlation between aboveground biomassand evapotranspiration;The interaction between radiation and surface temperaturehad significant effect on the evapotranspiration;the daily evapotranspiration inShangDong Rive obtained by inversion of SEBAL model and OILremote sensing data of Landsat8 is higher than measured value,but the results ofmodel were better after calibrated according ground measured data.Theevapotranspiration ratio range from 92%to 94%in growing season?15 April-15September?in ShangDong River.Most of precipitation to provide the waterconsumption for plant growth,and total precipitation in growing season haspositive correlation with the total evapotranspiration.?4?Artificial rainfall experiment showed that,when the rainfall intensity were 20,40and 60 mm h^-1,the runoff lag time were 27min 18s,22min 5s and 5min 8s,respectively,in light degraded plots,and 17min 21s,14min 56s and 5min 4s,respectively,in moderate degraded plots,and 14min 59s,13min 17s and 3min 20sin heavy degraded plots.Plant can delay the runoff and promote waterseep into the soil.Rainfall intensity has significantly positive correlation withrunoff amount.They had a significantly positive linear correlation between therunoff coefficient and rainfall intensity in heavy degraded plots?P<0.05?,andthey had a positive exponential correlation in light and moderate degraded plots?P<0.05?.Runoff coefficient is significantly negative linear correlated witaboveground biomass when rainfall intensity was 20 mm h^-1,and they had asignificant negative correlations and described by power function when rainfallintensity was 40-60 mm h^-1?P<0.05?.The runoff coefficientincreased with grassland degradation.The runoff coefficient increased from 10.58%to 32.29 in heavy degraded plots,from 6.27%to 31.49%in moderate degradedplots and from 2.98%to 31.34%in light degraded plots,respectively,when therainfall intensity increased from 20 to 60 mm h^-1.The runoff coefficient wasstrongly influenced by the degradation degree of community.The runoff coefficient showed significant negative dependence on community coverage and exhibited the quadratic polynomial function?P<0.05?,and showed significant positive dependence on slopes and followed an exponential trend.The relationship between runoff coefficient???,slopes?i?and community cover?C?followed the equation:?=-62.26C+2.472i+15.775,when the rainfall intensity was40-60 mm h^-1,then get the runoff coefficient spatial distribution map of ShangDong River Basin.?5?Infiltration process in soils during rainfall.Infiltration depth of soil water within20 cm after 60 minutes when the rainfall intensity range from 20 to 40 mm h^-1 andindicated that lower speed of soil water infiltration and rainfall runoff was Hortonrunoff.We used a physical model was established by filtration equations and finiteelement software to simulated soil water infiltration,and the error of simulatedresult is less than 9.6%,the method is reliable.?6?We have established the equation of water balance of ShangDong River Basin.The all precipitation in growing season,92%for evapotranspiration,1.3%forsurface runoff,-2.1%for variables of soil water storage and 1.3%for leakage,respectively,in 2015,and these value were 93.9%,1.3%,0.4%,4.5%,respectively,in 2016,and 93.1%,0,-3.3%,10.2%,respectively,in 2017.The rainfall is mainlyused for evapotranspiration of plant community and average deep percolation ofthree years between 9.8 and 19 mm based on analyses water quantity balance.?7?Annual rainfall had significant effects on aboveground biomass,plant height andcommunity coverage.There was a linear positive correction between abovegroundbiomass and soil water content in the slope.Evapotranspiration after rain haslinear positive correlation with rainfall amount.The grads of precipitation havean effect on specific leaf area?SLA?.Precipitation has no effect on the SLA ofAgaricus rotundifolia,and has significant positive correlation with the SLA of C.scabra.And the SLA of Stipa kirssii increased firstly and then decreased withincrease of precipitation.The belowground biomass and roots volume increasedwith increase of precipitation.Through this study,we realized eco-hydrological characteristics of ShangDong River Basin in desert steppe,and have far-reaching significance to ecosystem restoration and the sustainable use of water.