| The lake-groundwater hyporheic zone is a sensitive area for the material energy transmission between surface water and groundwater.Influenced by various factors such as landform,geomorphology,meteorological conditions,characteristics of water-bearing medium,etc,the processes of water movement,hydrochemistry and heat transfer in the cross zone are extremely complex.And the hydrological processes in the cross zone are closely related to regional water quality,ecological environment,species distribution and human life.For a long time,the cross zone has not been considered as a research system in the development and management of surface water and groundwater,especially in the arid areas of northwest China where water resources are relatively scarce.Therefore,carrying out the study of lake-groundwater hyporheic zone has important theoretical and practical significance for lake ecological environment protection and optimal allocation of water resources in arid areas.Taking the Yuehai Lake water-groundwater hyporheic belt of the Yinchuan Plain as the research object,and Helan Mountain-Yuehai Lake-the Yellow River hydrogeological section as the starting point,the changes of the hydrodynamic field,based on the field investigation,sample collecting test,in situ test and numerical simulation method,the variation of hydrodynamic field,hydrochemical field and water temperature field in the hyporheic zone are analyzed to reveal the hydrodynamic mode and the mechanism of hydrochemical hyporheic in the hyporheic zone,and divide the hydrodynamic exchange zone,biochemical hyporheic zone and forced convection of temperature in the interactive zone tropical.The following major achievements and understandings have been achieved:(1)Influenced by the geomorphologic type of the whole Helan mountain-Yuehai lake-the Yellow River profile,the western side of the hyporheic zone receives lateral replenishment of the piedmont valley subsurface current.Due to the existence of the water source in the hyporheic zone,the groundwater level of the lakeshore in the wet and dry seasons is lower than that of the lake,and the east side of the hyporheic zone receives the water recharge from the lake.The farther away from the lake shore,the smaller the degree of change of the hydrodynamic field in the hyporheic zone is affected by the fluctuation of the lake water level.And when it is more than 3.89 km away from the lake bank,it is basically not affected by the lake level.(2)The formation mechanism was studied from the source of water in the cross zone.By analyzing the deuterium-oxygen isotope relationship of water bodies,it was found that the water in the cross zone received less replenishment from atmospheric precipitation,mainly from groundwater runoff and surface water,and the recharge elevation was close to the elevation of Yuehai Lake and western piedmont plain.(3)The distribution of hydrochemical composition in the interactive zone is spatially different.Affected by the replenishment of the lake,the hydrochemical indexes of the surrounding around the lake are close to the lake,while those far from the lake shore are greatly different from the lake.With the increase of distance from the lakeside,TDS and common ions showed gradual gradient change in the horizontal direction.Affected by human domestic water and agricultural irrigation,the content of nitrogen compounds are the highest in agricultural irrigation areas away from the lake shore.Under the combined influence of water flow velocity and temperature,the DO,Eh,and COD of the water body in the high-water season are lower than those in the dry season.And the p H is higher compared to the dry season.The spatial distribution of hydrochemical types is also largely affected by the water-rock hyporheic in the Helan mountain-Yuehai Lake-Yellow River section.(4)The temperature field of the Helan Mountain-Yuehai Lake-the Yellow River profile shows a decreasing trend from west to east.Affected by the water supply in the front of the Helan Mountain,the temperature in the west side of the hyporheic zone also shows a gradient change in the horizontal and vertical directions.The surface receives solar radiation and lake water heat flow near the lake shore.The water temperature in the hyporheic zone is relatively high,while away from the surface and lake shore,the water temperature decreases due to less influence from heat conduction,and it remains basically stable on the time scale.There is a qualitative relationship between water temperature change and water exchange,and water temperature fluctuation has a hysteresis effect due to the influence of lake water-groundwater exchange.Combined with the two-dimensional temperature field model based on seepage,it is calculated that there is a functional relationship between the temperature and seepage velocity in the hyporheic zone.(5)Based on the principle of isotopic mass balance,hydrochemistry gradient method and temperature gradient method,the range of hydrodynamic exchange zone,biochemical action zone and temperature forced convection tropical zone in the hyporheic zone are obtained respectively.The range of the hyporheic zone shows a fan-shaped distribution around the wet circumference of the lake,and with the deepening of the depth,the boundary of the hyporheic zone gradually approaches the lake shore.Under the influence of meteorological conditions and artificial water replenishment and other comprehensive factors,the fluctuations of water bodies in the hyporheic zone,especially the decline zone,formed a pattern that the vegetation type evolved between herbaceous plants and woody plants,and the land type changed between saline land and shallow water. |
PDF Full Text Request