Stdudys On Dynamic Changes Of Groundwater Depth And Its Infuence Factors In Minqin Oasis

The Minqin Oasis is an important production area for the people of Minqin County,which is surrounded by the Badan Jaran Desert and Tengger Desert.The unique geographical environment determines an important influence for the ecological stability of the hydrology ecosyetem to maintain the Minqin region and even the Hexi region.The existing problems in the current ecological environment are mainly manifested in serious land desertification,structural destruction of vegetation systems,reduced species,serious soil salinization,increased dust storms,decreased groundwater leveland deterioration of water quality.In this study,multiple regression statistical method was used to analyze and predict dynamic changes of groundwater level,selected representing typical natural factors such as temperature,precipitation,and evaporation to analyze meteorological factors,selected representing human factors such as amount of upstream runoff water,irrigation water consumption,industrial water,ecological water,groundwater exploitation,crop planting area,and population as research variables.The correlation was explored between groundwater level and potential impact factors to establishan optimal regression model in order to understand the dynamic changes of groundwater level in this study,and provide grounds for long-term groundwater prediction.Systematically studying effects of dynamic changes of groundwater level on vegetation?growth,coverage?and department of water use to clarify the dynamic law of groundwater level and clarify the response mechanism of groundwater level for hydrology ecosystem,and draw the following main conclusions:?1?The correlation analysis of the factors affecting groundwater level shows that the correlation coefficients with natural factors are 0.688,0.434 and 0.251,which respectively represent air temperature,precipitationandevaporation.The correlation coefficients of human factors are 0.942,0.828,0.488 and 0.290,of which groundwater exploitation,upstream inflow amount were larger,second is area of crop plants,the population is minmum factor.The variables such as air temperature,precipitation,evaporation,ecological water use,upstream runoff water,planting area of grain crops were positively correlated with groundwater depth,while the other variables were all negatively correlated with groundwater depth?Groundwater depth has a strong correlation with groundwater exploitation,irrigation water consumption and upstream inflow,while the variables which representing natural factors have no significant correlation with groundwaterdepthwhich indicating that human factors can significantly affect groundwater level changes.?2?Based on the analysis of changes for groundwaterdepth in Minqin from 2007to 2016,it is indicated that the groundwater depth in Minqin shows a upward trend inrecent many years,and the variation trend of groundwater depth shows a continuous increasing trend,increasing from 21.15m in 2007 to 23.31m in 2016,and groundwater depth was increased by 2.16m in 10 years,increasing at a rate of 0.2 m/a and increasing year by year.With the groundwater buried level in 2016 was maximum between 2007 to 2016,reaching the peak in the last recent decade.?3?The groundwater depth in June—October was generally higher than that other months in the whole year,especially in July,August and September,groundwater depth reached the peak in August,when monthly decline rate was 0.02m and the change in other months was not obvious.From February to May,the level of groundwater maintained stability,the reason was that there were no significant agricultural activities during this period.From November to January of the following year,the groundwater level was stable because there were agricultural winter irrigation activities providing appropriate supply of groundwater to keep slowrecovery for groundwater level.?4?Through stepwise regression model removing variables that have no significant effects on groundwater level,determining the optimal regression equation was:y=24.980-0.557 X₈+0.228 X₄-0.109 X₁₀(X₈ for groundwater extraction,X₄for upstream water inflow,X₁₀ for population)which showed that groundwater extraction,upstream water inflow and population size were the there main factors affecting groundwater level change,and the equation of determination coefficient was0.943,which means those three variables could explain 94.3%of groundwater level change,by the way,groundwater extraction was the dominant factor.The optimal regression equation can effectively predict the groundwater level in the Minqin Oasis.?5?Groundwater depth has obvious regulation effect on vegetation growth,coverage,etc.Suitable groundwater depth can promote good growth of vegetation.The depth of groundwater corresponding to the high vegetation density was the most appropriate level to keep vegetation community stability.Thereasonable water level which suitable for vegetation growth in Minqin Oasis was 4.5m,While the appropriate groundwater level for grassland and shrubs was1.8².25m,the corresponding vegetation probability was more higher.Vegetation above or below this water level all have poorer growth,at the same time,the vegetation probability is smaller.The appropriate groundwater mineralization degree required by different vegetations are inconsistent,but it was all reflected that in the lower mineralization of groundwater resources was more conducive to the survival and reproduction of vegetation.The dynamic changes of groundwater level are closely related to the appropriate water use of the water sectors,which is reflected in the fact that high irrigation water quota can effectively supplement groundwater and reduce the rate of groundwater decline.