Research On The Effects Of Shale Gas Fracturing Return Fluid On Soil-Wheat System

Although the commercial exploitation of Shale gas can alleviate the shortage of oil and gas resources and meet the needs of economic development,we cannot ignore the enormous environmental problems that Shale gas exploitation may bring.In this study,a pot experiment was conducted to investigate the effects of fracturing return fluid on soil environment and wheat growth and development by applying different concentrations of fracturing return fluid during three growth stages of wheat.Undoubtedly,results of this study can provide scientific support for environmental pollution and ecological risk assessment caused by leakage.The main results were as follows:(1)The effects of returning fluid on the soil environment were different.Generally,the returning fluid into the soil could increase the contents of soil nutrients except for available phosphorus to a certain extent.However,it would reduce the soil pH value and the content of available phosphorus to some extent,resulting in an increase of heavy metal elements and salt content in soil.Among them,only the heavy metal Cd content exceed the screening value in the Soil Environmental Quality Agricultural Pollution Risk Control Standards for Soil Environmental Quality when the returning fluid concentration?200g/kg was applied in the heading period.The water-soluble Na~+and Cl~-were the primary contributing ions for the increase of salt content.When the returning fluid(?300 g/kg)during the sowing period was applied,the heavy metal concentration in soil increased;when the concentration of returning fluid was greater than 200 g/kg,the content of soil nutrients increased;when the concentration of returning fluid was in the range of 200 g/kg~300 g/kg,the soil would be slightly salinized;When the concentration of returning fluid was 350 g/kg,the soil would be moderately salinized.When the returning fluid was applied during the tillering stage,there was no significant change in terms of the heavy metal content of the soil;when the concentration of the returning fluid was?200 g/kg,the soil nutrient content increased;when the concentrations of returning fluid was in the range from 200 g/kg to 350 g/kg,the soil would be slightly salted.When the returning fluid with a concentration higher than 200 g/kg during the heading stage was applied,both the soil nutrient and heavy metal contents increased.When the concentration of returning fluid were between 300 g/kg and 350 g/kg,the soil would be slightly salted.During the three growth stage of wheat,the soil quality would not be significantly affected when the concentration of the returning fluid entering the soil was less than 200g/kg.(2)The returning fluid entering into the soil at different growth stages of wheat has different effects on the physiological characteristics and growth of wheat.In general,grain crude protein and mineral elements the nutritional quality of the wheat grain could be improved to a certain extent by returning fluid.However,this would affect the growth of wheat and lead to a decrease in soluble sugar content and yield and an increase in heavy metal elements in the grain.Compared with the limit value in"Contaminant Limit in Food"(GB2762-2017),the excess heavy metal in grains was mainly Cd.When a low concentration of returning fluid entered into the soil,chlorophyll content,photosynthetic rate and activities of superoxide dismutase(SOD)and peroxidase(POD)of flag leaves and roots were increased to a certain extent,while the high concentration of returning fluid showed inhibition effect.When the returning fluid with a concentration higher than 300 g/kg during the sowing period was applied,the photosynthesis of flag leaves was inhibited.When the concentration of returning fluid was?200 g/kg,the activities of SOD and POD decreased,and the growth and yield were significantly affected;When the concentration of returning fluid was?50 g/kg,although the grain crude protein and mineral elements was improved,the heavy metal content of the grain would increase,and the content of Cd in the grain would exceed the standard.When the returning fluid higher than 200 g/kg during the tillering stage was applied,the activities of SOD and POD decreased,and the CR content of wheat grains exceeded the standard.When the concentration of returning fluid was greater than 150 g/kg,the photosynthesis of flag leaf was inhibited,and the growth and yield of wheat were significantly affected.When the concentration of returning fluid was greater than 100 g/kg,the grain crude protein and mineral elements was improved;When the concentration of reflux solution was more than 50 g/kg,the content of heavy metals in grains increased and the content of Cd in grains exceeded the standard.When the concentration of returning fluid was?150 g/kg at the heading period was applied,the Cr content of wheat grain exceeded the standard;when the concentration of returning fluid was?100 g/kg,the photosynthesis of flag leaves was inhibited,and the activities of SOD and POD of wheat decreased.Moreover,the growth and yield of wheat were significantly affected,but he grain crude protein and mineral elements increased.When the concentration of returning fluid applied was?50 g/kg,the content of heavy metals in the grain increased,and the content of Cd in the grain exceeded the standard.During the pre-sowing stage,tillering stage and heading stage,the growth,and development of wheat were not affected significantly,but Cd content in grains exceeded the food safety limit,when the concentrations of the returning fluid entering into the soil were less than 200 g/kg,150 g/kg and 100 g/kg,respectively.(3)In summary,wheat could not grow normally and eventually lead to death,when the concentrations of returning fluid into the soil in the three stages of sowing period,tillering stage and heading period were greater than or equal to 350 g/kg,300 g/kg and 200g/kg,respectively.During the sowing period,tillering stage and heading stages,soil quality,and wheat growth and development would not be significantly affected when the concentrations of returning liquid entering the soil were less than 200 g/kg,150 g/kg and100 g/kg,respectively.Meanwhile,the nutritional quality of wheat grain crude protein and mineral elements improved,but the Cd content of heavy metals in seeds exceeded the food safety limit.Only when the concentration of the returned fluid entering into the soil was less than 50 g/kg,it may not lead to the safety risk of agricultural products.