Study On Groundwater Ecological Threshold In Western Plain Of Jilin Province

Groundwater is one of the supporting elements of the ecological environment,and is the regulator of maintaining the balance of water,salt,heat and biodiversity on the earth’s surface.Any plant has its own optimal threshold and tolerance limit to water,salt and heat.Therefore,an appropriate groundwater level(phreatic water level)is an important condition for maintaining the stability of vegetation communities and ensuring the benign development of ecological environment,especially in arid and semi-arid areas,whose surface ecology is closely related to the groundwater level.The western plain of Jilin Province is selected as the research area.The basic conditions of vegetation,landform,lithology of vadose zone and groundwater in the research area are analyzed by various technical methods.The relationship between the capillary rise height and soil type,dry density and phreatic water mineralization is determined by experimental methods;At the same time,an ecological environment risk identification system(RIS-GET system)based on groundwater ecological threshold is established to identify the ecological environment risk in the study area;Three methods are used to determine the reasonable groundwater ecological threshold in the typical area;Through the selection of typical area method,the suitable method is applied to the calculation of groundwater ecological threshold in the western plain area,and the spatial distribution map of groundwater ecological threshold in the western plain area of Jilin Province is obtained;GMS software is used to simulate the regional groundwater flow field and study the water regulation based on the groundwater ecological threshold in the region,so as to guide the rational development of groundwater resources,maintain the groundwater burial depth within a reasonable range,maintain the normal growth of ecological vegetation,reduce the soil ecological environment risk,and promote the coordinated and sustainable development of social economy and ecological environment.(1)Established a risk identification system based on groundwater ecological threshold(RIS-GET system)The western plain area of Jilin Province is located in arid and semi-arid areas,which are prone to ecological and environmental geological problems.In order to address the issue of soil primary and secondary disasters that are prone to occur in a targeted manner,a risk identification system based on groundwater ecological thresholds(RIS-GET system)was established.The ecological environment issues in the study area were analyzed and evaluated from aspects such as groundwater depth,groundwater mineralization,drought index,evaporation,precipitation,geomorphic types,aeration zone lithology,normalized vegetation index,and vegetation types.(2)A series of field measurements and laboratory tests were carried out on the important index of soil capillary rise height.The relationship between capillary rise height and soil dry density and phreatic salinity was explored through experiments: the maximum capillary rise height of soil increased by 10 cm on average for every 1g / L increase in phreatic salinity;The relationship between soil dry density and maximum capillary rise height is similar to the parabola of normal distribution.With the increase of dry density,the capillary rise height increases continuously.When it reaches the critical value,the capillary rise height decreases with the increase of dry density.The relationship between capillary rise height and phreatic mineralization and dry density of different soil types is explored through multiple linear regression models.(3)The comprehensive analysis and calculation method under the coordination of multiple methods is used to analyze and calculate the ecological threshold of groundwater in typical areas.Based on the correlation of dynamic data and the threshold calculation method of actual measurement,the upper limit of groundwater ecological threshold in typical saline areas is 2.76-4.66 m,and the lower limit of desertification typical areas is 6.24-8.30m;Using high-precision remote sensing statistical methods to study the vegetation status of typical areas,and using Arcgis and Envi software to jointly analyze,it was found that the ecological threshold of groundwater in saline typical areas is 2.8m,the suitable groundwater mineralization degree is 0.37-1.25g/L,and the ecological threshold of groundwater in desert typical areas is 8m;By simulating the upper and lower limits of groundwater ecological thresholds in typical areas using Hydras software,it was found that the groundwater ecological threshold based on Hydras soil water salt simulation method is 3-6m.(4)By selecting the calculation method suitable for the whole western plain area in the typical area,the groundwater ecological threshold value of the western plain area of Jilin Province is calculated and studied,and the spatial distribution status of the groundwater ecological threshold value in the western plain area of Jilin Province is obtained,which provides a basis for groundwater regulation in the region.(5)Establish a numerical model of groundwater flow in the study area,simulate the groundwater flow field in the current year and predict the groundwater flow field in the study area in the next five years.According to the distribution map of the suitable range of groundwater ecological threshold in the western plain of Jilin Province,regulate the water volume in the study area based on the groundwater ecological threshold.Establish a numerical model of groundwater flow in the research area,simulate the current annual groundwater flow field,and predict the groundwater flow field in the study area five years from now.Based on the distribution law of the suitable range of groundwater ecological threshold in the western plain area of Jilin Province,adjust the corresponding water volume in the research area.The innovation points of this article are as follows:(1)The concept of groundwater ecological threshold has been further clarified,and a method for determining groundwater ecological threshold has been proposed that fully considers various factors such as soil,aeration zone lithology,vegetation,groundwater depth,and freeze-thaw soil.This paper synthesizes the hydrogeological conditions,including the factors such as groundwater level burial depth,groundwater salinity and aquifer thickness,groundwater mining output,geomorphic and micro geomorphic characteristics,vadose zone lithology,soil characteristics and other factors,and also considers the controlling role of aquifer and groundwater mining output on groundwater ecological threshold and the impact of frozen soil in Northeast China on the ecological environment,The concept of "groundwater ecological threshold" has been further clarified,and a calculation method for groundwater ecological threshold under the influence of multiple factors has been proposed: the groundwater ecological threshold is usually represented by the depth of groundwater level,which is a range value with upper and lower limits.It is a limit value to ensure the safety of the ecological environment and water supply;At the same time,taking into full consideration various factors such as soil,aeration zone lithology,vegetation,groundwater depth,freeze-thaw soil,etc.,three methods based on dynamic data correlation,high-precision remote sensing statistical method,and mathematical model simulation method are used to calculate the upper and lower limits of groundwater ecological threshold separately.Based on this,the calculation results of multiple calculation methods are further analyzed,and the calculation method with good accuracy and easy parameter selection is selected,Used for regional calculations.(2)Established a groundwater ecological threshold risk identification system(RISGET)and proposed corresponding evaluation methodsTaking the western plain area of Jilin as an example,a groundwater ecological threshold risk identification system is constructed with four criteria layers and nine indicator layers of meteorological factors,geological factors,hydrogeological factors,and vegetation factors.The constructed risk identification system starts from the influencing factors of groundwater ecological threshold,selects easily available,widely affected,and highly correlated risk assessment factors,and establishes a groundwater ecological threshold risk identification system.The indicator factor method adopted has a stronger causal relationship and can more comprehensively and completely identify the ecological security status of a region.(3)For the first time,the groundwater ecological threshold is used to regulate the groundwater mining output,which points out the direction for rational development and utilization of groundwater.Based on the identification results of the groundwater ecological threshold range and the risk identification system of groundwater ecological threshold in the western plain area of Jilin Province,and relying on the proposed and existing water conservancy projects in Jilin Province,a groundwater development and utilization plan is designed to keep the groundwater level within the range of groundwater ecological threshold,reducing the possibility of ecological environment risks.