Analysis On The Dependency Of Salix Psammophila On Groundwater

Ordos basin is rich in energy mineral and is a new base of energy industry, which play an important role in the implementation of the western development strategy. The shortage of water resources and the fragile ecological environment because of the lack of rain in the basin heavily constrain the development of regional economy and society and the construction of energy base. In recent years,the scale of the development of groundwater increasingly rise with the increasingly development of energy and mineral resources. It has became a major problem that must be solved in the sustainable development that how to make a rational use of groundwater with the premise of ecology and vegetation protection. Therefore, the research on the relation between groundwater and vegetation and on determination of the degree of the dependence of major vegetation on groundwater has important theoretical and practical significance.A large number of research on the relationship between the groundwater and vegetation has been carried out in the basin, which mainly uses the conbining method of the ecological hydrogeology survey and remote sensing to qualitative and semi-quantitative analyse the dependence of vegetation on the groundwater and preliminarily determines the threshold value of groundwater table which affect the vegetation on regional scale, then make the division by ecological sensitivity of vegetation and established the coupling model of groundwater and the vegetation But there is still little quantitative research on the dependence of the vegetation on the groundwater. It is a hot spot and front edge problem in the ecological hydrogeology that determinate the water source of different vegetation transpiration.Based on a Asian fund project with cooperation of China and Netherland 《the research on the relation between ecological system and water in Ordos basin》, we first read literature home and abroad and analyse the status and drawback of the present quantitative research on the relation between vegetation and groundwater, based on the conduct the field work on the way of three-dimensional dynamic monitoring the atmosphere、the vegetation、the soil water and the groundwater：monitoring climate factors by Bowen ratio system、monitoring transpiration by Sap flow32, monitoring soil water content by TDR, monitoring groundwater table by Minidiver, at the same time research the vegetation roots by rootauger. The experimental data show that the total rainfall is78mm including48mm at a maximum precipitation; Net radiation is positive during the day and negative at night, maximum net radiation is847w m-2;The average air humidity is45%, and the mean wind speed is2m s-1.In the weather characteristics, salix transpiration present a characteristics of sine, transpiration halt in rain. Because of the role of transpiration by vegetation,soil water and groundwater declined while no rain, but laggingly response.According to the precipitation characteristic in the experimental period,we devided the trial period into the drought period, wet and the relative drought period. The relation between salix transpiration and climate factors is:in three periods, vegetation is positively relative with net radiation、temperature、wind speed and negative with relative humidity; The liner multivariate regression analysis shows that, during the experiment,climate factors could explain85%of the salix transpiration changes. The relation between accumulated transpiration and the groundwater and soil water suggest that in drought period the soil water and the groundwater are both the source of salix transpiration;And the change of groundwater level can be explained by accumulated transpiration linear regression, with determination of coefficient0.99; In wet period,with the effection of precipitation, soil water and groundwater is in increasing trend,but there are lag characteristic, groundwater level can be explained by the change of soil water; In the relative drought period,the soil water and groundwater become water resourcrs of transpiration again,and regression analysis shows that the change of water level can be explained by the accumulated transpiration, with determination of coefficient0.78,which is slightly smaller than in drought period.The atmosphere-vegetation-soil water-groundwater continuous dynamics system model that based on the field experiment data is described by Richards equation and is calculated by Hydrus-ld from the USA. The numerical model simulate the change characteristics of the soil water and salix transpiration during the experiment; The balance equation that based on the data from numerical model output revealed that:in the drought period,the soil water contribution to salix transpiration is42%, while groundwater58%; In the relative drought period,the soil water contribution to salix transpiration is61%,while groundwater39%. The results from the quantitative research answered the degree of salix transpiration to groundwater where the groundwater depth is large than4.8m, which provide the scientific evidence to the construction of energy base and the development of local economic.