Spatial Distribution And Change Trend Of Cadmium In Paddy Field Based On GIS:a Case Study Of Youxian County

Cadmium(Cd)pollution in paddy soil in China is serious.Excessive Cd content in rice occurred frequently,which seriously threatens the safety of regional agricultural products and human health.The prevention and control of Cd pollution in paddy fields is the premise to ensure the safety production of rice,of which the key is to accurately simulate the trend of Cd accumulation in paddy soil.Youxian County of Hunan Province,is one of the most important rice-producing areas in south China.In recent years,the “Cd-contaminated rice” incident has seriously affected the agricultural production and economic development in this area,and endangered the health of local residents.In this research,Youxian County was selected as the research area,model simulation was developed based on the data of regional investigation and the laboratory analysis,associated with application of GIS spatial analysis,geostatistical analysis,Monte Carlo simulation,parameter sensitivity analysis and scenario analysis.This research systematically analyzed and revealed the changing patterns of Cd accumulation in regional paddy soil,quantified the effects of different input approaches of Cd,evaluated the effectiveness and sustainability of long-term application of different control measures in regional paddy soil,providing a scientific basis for the safety management of regional paddy fields.Main research results are as follows:(1)Through regional investigation and statistical analysis,Youxian County had a high risk of Cd accumulation in soil-rice system and significant Cd enrichment in rice.The Cd pollution in soil in the study area was mainly light to moderate degree,while the pollution degree in the eastern and western area was high.It should be of attention that the Cd in most of the soil had a ecological risk above moderate degree.The spatial prediction results showed that the spatial distribution of soil and rice Cd was heterogeneously,and there was soil and rice Cd polluted parts due to the influence of different human activities and intensity and the difference of Cd sources.There was a certain correlation between the spatial distribution of Cd in soil and rice but not significant.(2)Based on the multiple environmental media sampling and the mass balance principle,the Cd accumulation unit flux model in paddy soil was established,and the trend and risk of Cd accumulation in regional paddy soil were predicted by Monte Carlo simulation.The results showed that the cumulative risk of soil Cd in the study area would increase annually.After 50 years,the probability of slight Cd pollution in the paddy soil would be 82.1% and the probability of moderate pollution increased to 12.4%,indicating the Cd pollution of Youxian paddy soil is severe under the current Cd import model.Therefore,sufficient attention should be paid when risk managing and effective measures should be taken to reduce the Cd accumulation risk in the region.Sensitivity analysis confirmed that atmospheric deposition,irrigation and straw returning are the key environmental processes of Cd accumulation in paddy soil.(3)Combined with geostatistics and GIS spatial analysis,the spatial prediction model of soil Cd accumulation was built in Arc GIS 10.5 to realize the spatial calculation of unit flux model,and the spatial-temporal changing process of soil Cd in study area in the next 50 years was simulated.The simulation results showed that the Cd accumulation level and ecological risk in study area increased with the passage of time.Affected by the industrial and mining activities,human settlements and agricultural activities,the spatial distribution of high Cd soil mainly distributed in the northeast and central south of Youxian County,and the northeast area was a potential high-risk area,which should be of attention.The results showed that the spatial model could effectively simulate the dynamic changes of regional soil Cd accumulation process and predict the potential high-risk areas,which could be of great guiding significance to regional soil Cd pollution prevention and control.(4)The results of multi-scene simulation showed that optimizing the layout of industrial and mining enterprises and cleaning irrigation water could slow down the accumulation rate of Cd in soil,but could not reduce Cd,which could mainly reflect in the long-term effect.Not returning straw to the field could significantly reduce soil Cd,which was an effective control measure for regional soil Cd pollution control.Based on not returning straw to the field,the comprehensive treatment measures further reduced the regional Cd accumulation level by reducing input flux from the atmospheric deposition and cleaner irrigation water.After 50 years of application of the comprehensive treatment measures,Cd in more than 80% of the county soil could be reduced to a pollution-free level.Through the regional spatial prediction model of soil Cd,the scenario simulation could effectively analyze the soil Cd accumulation trend under the long-term application of different control measures in the paddy field,evaluate the effectiveness and sustainability of each measure,and provide a scientific reference for the prevention and control of regional farmland soil Cd pollution.