Study On Ecological Utilization Of Underground Saline Water In Coastal Saline-alkali Region

The low groundwater depth and high salinity of the soil in coastal area are highly responsible for the phenomenon of soil salinization in the coastal area.To some extents,the soil salinization has become one of the important obstacle to the restoration of local ecological environment.Since Tianjin is a city lacking fresh water resources,the wise use of shallow groundwater becomes more and more important.It will do good to the ecological restoration of coastal areas.This thesis aims at utilizing the shallow saline water to restore ecological environment.Through the design of indoor simulation experiment device and low temperature evaporation device,the author can study the behavior of different experimental soils under different evaporating temperatures.The experimental data of soil moisture,water potential,temperature and conductivity are monitored during the experiment.By analyzing the relationship between these data and the results of different circumstances,it is found that:1.The soil temperature fluctuated periodically under the condition of low temperature evaporation.Among three different kinds of soils,the sand soil is most affected by the low temperature evaporation device.The temperature varies enormously with different depth of the sand soil: the surface temperature was lower than that of the bottom layer.The soil water content of the sand soil is the highest,the clay comes the second,and the loam is the lowest.In addition,the soil moisture content fluctuates greatly.Because the clay itself has high salt content,the conductivity of clay is high and the conductivity of sand changes nonlinearly.The conductivity of loam is the lowest and the fluctuation is small.The change of soil water potential decreases once the low temperature evaporation device is opened,and it increases with the closure of the low temperature evaporation device.Besides,the soil water potential will decrease with the approaching of low temperature evaporation device.2.With the comparison of four different preset temperatures,it is found that: The water potential of the bottom layer is lower than that of the surface layer,and the temperature near the low-temperature evaporation device is higher than that of the surface layer.With the rising of temperature,the maximum temperature of soil layer are increased.However,the soil layer conductivity changes very little during the rising of temperature.Since soil moisture and water potential gradient are largely affected by soil temperature gradient,the water content will reach its maximum at the depth of 10 cm.3.By monitoring the changes of soil moisture,water potential,temperature and conductivity,it can be concluded that: there is a high correlation between soil moisture,water potential and temperature;whereas these three indictors have little correlation with conductivity.Considered that the high temperature may have a negative impact on the growth of surface plants,this thesis analyzes the behavior of soil surface under four different temperature conditions.It is found that 45? is the most appropriate low temperature for the growth of surface plants.Comparing with the data of soil salt content before and after the operation,it is found that low temperature evaporation can effectively prevent salt accumulation in surface soil and delay secondary soil salinization.