Central Wengniute-banner Xiangshui Different Vegetation Coverage Along The River Sand Dunes Of Ecological Hydrology Effect

Thispaper analyzes the rainfall characteristics of Xiangshui River from 1959 to 2015.The river is located at Ongniud Banner which is to the west of Horqin Sandy land.During the growing season in 2015,the analysis of eco-hydrological features,rainfall redistributioncharacteristics,canopy transpiration and soil water evaporation of various dunes along Xiangshui River,were performed by observing the soil eco-hydrological processes of three important types of sand-fixing community and analyzing the data of rainfall,throughfall,stemflow,transpiration,evaporation,and runoff.The following conclusions are drawn after exploring the eco-hydrological effects of dunes covered by different amount of vegetation.(1)Results show a slight downward trend in annual rainfall through the analysis of the recent 57 years' rainfall data in the study area.The recent 17 years(1999-2015)is a typical period of below-average precipitation when the drought has become more severe year by year in the area.During the growing season in 2015,most times the research area has seen short duration and low intensity rainfall.(2)The percentages of throughfall(TF)amounts in the rainfall of the corresponding periods are 74.38%?57.66% and 81.68% respectively for Caragana microphylla Lam,Salix gordejevii and Arternisia halodendron.Caragana microphylla Lam and Salix gordejevii have similar spatial distribution patterns of throughfall;TF(the outer edge of the canopy)>TF(1/2 canopy radius)> TF(the root area).Understandably,there is a critical point in the changing process of the spatial heterogeneity of shrub throughfall.This infers that canopy structure is a key factor influencing the spatial heterogeneity of throughfall when the rainfall is below the point and that other factors play a more important role when the rainfall is above the point.The critical points of Caragana microphylla Lam,Salix gordejevii and Arternisia halodendron are 6mm,9mm,and 5mm respectively.Based on the acquired data,the relationship between the percentages of stemflow in rainfall of the three species is as follows:Caragana microphylla Lam(4.53%)>Salix gordejevii(3.12%)>Arternisia halodendron(2.25%).By “S” model,the relationship between the three species when rainfall is enough can be calculated(Caragana microphylla Lam(5.35%)>Salix gordejevii(3.92%)>Arternisia halodendron(2.95%)).The percentages of canopy interception in the rainfall of the corresponding time are 25.78%,47.38%and 20.72% for Caragana microphylla Lam,Salix gordejevii and Arternisia halodendron respectively.Since “S” model applies to the threespecies when it comes to the ratio of interception to rainfall,by “S”model,the stable values of the three canopy interceptions can be estimated,which are 2.65 mm,5.24 mm and 1.91 mm.Theoretically,when the amount of rainfall increases indefinitely,the interception rate decreases indefinitely.(3)Statistics show that the leaf sizes of the three kinds of shrubs during the growing season become larger before they become smaller.For Caragana microphylla Lam and Salix gordejevii,the leaf size reaches its summit in July;however,the leaf size of Arternisia halodendron summits in August.In the growing season,the total amount of water lost through transpiration for Caragana microphylla Lam,Salix gordejevii and Arternisia halodendron is 160.19 mm,305.39 mm and 139.53 mm respectively.Daily consumed water varies from 0 to 1.88 mm for Caragana microphylla Lam,0 to 3.67 mm for Salix gordejevii and 0 to1.5mm for Arternisia halodendron.(4)The main components of different dunes are fine sand and medium sand.Sand particles whose diameters are less than 0.1mm take1.29% in migratory dunes,2.36% in semi-drifting sand dunes,and 3.78%in stabilized dunes.The approximate depth of dry sand on the shady side of bare dunes is 9cm;the depth on the sunny side and top of bare dunes is around 12 cm.(5)The impacts of the spatial distribution of water contained in duneson the vegetation were explored by experimenting on Caraganamicrophylla Lam.The result shows a similar spatial changing pattern of soil water content below canopy after it stops raining for 6hours,48 hours and 72 hours.The depth of water infiltrated in soil in different areas is regarded here as D.Thus the relations between Ds in different areas can be presented as D(bare area)> D(root area)> D(canopy edge)> D(1/2 canopy radius).By comparing the spatial heterogeneity of soil water content of the three types of dunes,the conclusion can be drawn that the percentages of soil moisture content in different areas of mobile dunes and semi-drifting dunes change in similar patterns.For the two types of dunes,the percentage of soil moisture content increases from the lowland between dunes to the shady side then it continues increasing from the sunny side to the top of the dunes.The soil 60 cm to 80 cm beneath contains most moisture with mobile dunes containing 3.47% moisture and semi-drifting dunes containing 3.34%.For stabilized dunes,the percentage of soil moisture content increases from the lowland between dunes to the sunny side and it continues increasing from the top to the shady side of the dunes.The soil 40 cm to60cm underground contains most water,which is 3.4%.Factors contributing to the different soil moisture content are sunlight,wind,vegetation etc.(6)The amount of water evaporated from different areas of a baredune varies.The water evaporates the most from the top area and the leastfrom the shady side.Besides,more water evaporates from the sunny side than the lowland between dunes.Moreover,water evaporates the most from the area covered by Arternisia halodendron.and the least from bare dunes.Besides,more water evaporates from the area covered by Caragana microphylla Lam than the area covered by Salix gordejevii.The amount of water evaporated increases from stabilized dunes to semi-drifting dunes and mobile dunes.During the growing season,the three types of shrubs all experience water stress.Salix gordejevii experiences the most severe water stress,and water needed by Salix gordejevii can be as much as 1.6758 mm per day.Precipitation cannot satisfy the need of Salix gordejevii but the shrub can still survive from water stress by absorbing groundwater.Caragana microphylla Lam suffers less from water stress;the average daily amount is about 0.4669 mm.Arternisia halodendron experiences the least water stress whose average daily amount is as low as 0.3198 mm.Generally speaking,precipitation is almost enough for Caragana microphylla Lamand Arternisia halodendron to grow.During the process of afforestation,shrubs like Caragana microphylla Lam and Arternisia halodendron should be chosen over Salix gordejevii to reduce dependence on groundwater.(7)Bare dunes benefit the most from rainfall.During the growingseason,bare dunes can absorb 246.18 mm of water which takes up83.79% of the rainfall.In a way,a bare dune can be regarded as a waterreservoir.Some of the absorbed water remains in the bare dunes and other water joins underground water.During the growing season,bare dunes absorb the most water and stabilized dunes the least.Furthermore,mobile dunes absorb more water than semi-drifting ones.(8)The research is based on the ecosystem consisting of atmosphere,vegetation,dunes,and rivers,aiming at the analysis of regional water balance.For the stabilized dunes which are covered by a lot of vegetation,when the rainfall is scarce and unable to infiltrate into the phreatic zone,the plants have to survive from water stress by absorbing water from deep layer soil.This leads to the consumption of groundwater,which causes the shrinking of rivers.On the contrary,the mobile dunes which are covered by little vegetation is a good source for the excessive rainfall to infiltrate into the phreatic zone,thus leading to the increase of groundwater and growing rivers.The decrease in mobile dunes in the east part of Ongniud Bannar leads to the shrinking groundwater,which ultimately reduces the ability of mobile dunes to keep the water balance in the ecosystem.During the process of afforestation and sand dune fixation,the positive influence of mobile dunes on regional ecosystem should not be neglected.As it was mentioned in the paper,the region has seen a progressive drop in rainfallyear by year.As a result,it is crucial to realize the important role that mobile dunes are playing as a buffer in protecting regional groundwater.