Study On Water Balance Of Urban Green Space And Effects Of Reclaimed Water Irrigation On Soil Water

The arid and humid transition zone?north China section?is a fragile zone sensitive to the change of ecological environment,and water resources are extremely scarce.With global warming,climate fluctuations make precipitation,the region's main water source,more unstable.On the other hand,with the rapid development of urbanization,the green space area has doubled and doubled.Meanwhile,due to the drought and strong evaporation of vegetation,the water demand of urban green space in this region keeps increasing.In summary,the use of reclaimed water for irrigation has become the preferred method to solve the problem of large water consumption of green land in the context of water resources shortage.However,the reclaimed water is rich in pollutants and contains a large amount of salt,so the effects of irrigation on vegetation,soil,vaduct water environment and groundwater are urgently needed to be studied.This study investigated the water balance process of urban green space in the arid and humid transition zone?north China section?and the changes of soil water quality after the use of reclaimed water irrigation,and discussed the changes and causes of soil water quality under different irrigation water quality conditions.First in terms of urban green space of water balance,this study the main vegetation types in urban green space,the lawn as the research object,based on the reference of lawn evaporation calculation method combined with actual evaporation evapotranspiration,Penman-Monteith comprehensive method,analysis on daily and monthly time scales to kown the grass water consumption;Second,and through the contrast test,this study made a comparison with three different irrigation water,namely the guarantee other experimental conditions?before the experiment of soil physical and chemical properties,soil box size,lawn grass varieties,irrigation system,maintenance level,etc.?of the same premise,uses the clear water,recycled water,reclaimed water three double concentration to turfgrass irrigation water quality for irrigation water.The pH,total nitrogen,total phosphorus,ammonia nitrogen and chemical oxygen demand?COD?in irrigation water and its corresponding percolating solution were detected and analyzed,and the changes of soil water quality and the main causes under different irrigation water quality conditions were investigated,and the changes of soil environment under different irrigation treatments were also investigated.It provides a basis for evaluating the feasibility of long-term irrigation with reclaimed water.The specific contents are as follows:?1?According to the principle of water balance,the daily and monthly time scales of the lawn evapotranspiration during the experiment period were analyzed.On the daily time scale,the evapotranspiration of the lawn increased first and then decreased,and the peak appeared between 12:00 and 15:00,that is,the phenomenon of"siesta"of plants existed.On the monthly time scale,the total evapotranspiration of the lawn from August to October is 324.07mm,and the change trend of the evapotranspiration of the lawn is basically the same as the change trend of the temperature in the same period.The evapotranspiration of the lawn increases with the increase of the temperature,and decreases with the decrease of the temperature.In addition,rainfall will increase the relative air humidity,resulting in a sudden drop in lawn evapotranspiration.?2?Through comparative tests,the pH,total nitrogen,total phosphorus,ammonia nitrogen and chemical oxygen demand in the corresponding leakage solution of irrigation water under three different experimental treatments of fresh water,reclaimed water and twice the concentration of reclaimed water for irrigation water were detected and analyzed:?1?In the comparison and analysis of the water quality of the lawn percolate and the irrigation water after the reclaimed water irrigation,it was found that the pH and ammonia nitrogen concentration in the irrigation water did not affect the change of soil water.However,the higher the concentration of TN in the irrigation water and the longer the irrigation time,the higher the load of the soil system will be.COD entering the soil system by irrigation water is basically not absorbed and absorbed,and nearly84%of COD infiltrates into the percolating liquid.?2?In different irrigation water treatment of the seepage water quality changes,found that the use of recycled water irrigation can reduce the soil pH value to a certain extent.The high content of organic matter,total phosphorus,total carbon,total nitrogen and other substances in the reclaimed water can accelerate the growth rate of the grass root system and promote the development of the grass root system.Therefore,the use of reclaimed water instead of fresh water for irrigation in the short term will not affect the soil water quality,but can promote the growth and development of the grass.?3?The physical and chemical properties of the soil at a depth of 0-50cm before and after the experiment period were compared under different irrigation water treatment,and it was found that different irrigation water treatment also affected the spatial distribution of soil nutrients.On the whole,the alkali-hydrolyzed nitrogen and rapidly available potassium in the soil at 0-50cm depth increased.The contents of organic matter,conductivity,K⁺,Mg²⁺and Cl^-ions all increased in the surface layer.On the contrary,Ca²⁺and NO₃^-ions in soil decreased in the dgree depth from 0 to50cm.Although there is no obvious soil pollution in the short term,if the quality and concentration of reclaimed water are not controlled,there may be pollution risk after long-term irrigation.Secondly,through the real-time monitoring of the soil moisture detector,it is found that the volume moisture content of the soil under the condition of reclaimed water irrigation is higher than that under the condition of clean water irrigation,and the difference mainly occurs in the 0-10cm soil layer.In addition,irrigation of reclaimed water will not have a significant impact on soil conductivity in a short period of time.However,after increasing the concentration of reclaimed water,the soil increases significantly at 20cm,50cm and 90cm.