Development of a model to simulate soil heavy metals lateral migration quantity based on SWAT in Huanjiang watershed,China

Lateral transportation of soil heavy metals in rainfall events could significantly increase the scope of pollution. Therefore, it is necessary to develop a model with high accuracy to simulate the migration quantity of heavy metals. A model for heavy metal migration simulation was developed based on the SWAT(Soil and Water Assessment Tool) model. This model took into consideration the influence of soil p H value, soil particle size, runoff volume, sediment amount,concentration of water-soluble heavy metals dissolved in runoff and insoluble absorbed to the soil particles. This model was reasonable in Huanjiang watershed, Guangxi Zhuang Autonomous Region, south China, covering an area of 273 km^2. The optimal drainage area threshold was determined by analyzing the effects of watershed subdivision on the simulation results to ensure the simulation accuracy. The main conclusions of this paper were:(1) watershed subdivision could affect simulation migration quantity of heavy metals;(2) the quantity of heavy metals transported by sediment accounted for 97%–99% of the total migration quantity in the study watershed. Therefore, sediment played the most important role in heavy metal migration;(3) the optimal drainage area threshold percentage to ensure high simulation accuracy was determined to be 2.01% of the total watershed;(4) with the optimal threshold percentage, this model could simulate the migration quantity of As, Pb and Cd accurately at the total watershed and subwatershed level. The results of this paper were useful for identifying the key regions with heavy metal migration.

Identifying factors that influence soil heavy metals by using categorical regression analysis:A case study in Beijing,China

Identifying the factors that influence the heavy metal contents of soil could reveal the sources of soil heavy metal pollution.In this study,a categorical regression was used to identify the factors that influence soil heavy metals.First,environmental factors were associated with soil heavy metal data,and then,the degree of influence of different factors on the soil heavy metal contents in Beijing was analyzed using a categorical regression.The results showed that the soil parent material,soil type,land use type,and industrial activity were the main influencing factors,which suggested that these four factors were important sources of soil heavy metals in Beijing.In addition,population density had a certain influence on the soil Pb and Zn contents.The distribution of soil As,Cd,Pb,and Zn was markedly influenced by interactions,such as traffic activity and land use type,industrial activity and population density.The spatial distribution of soil heavy metal hotspots corresponded well with the influencing factors,such as industrial activity,population density,and soil parent material.In this study,the main factors affecting soil heavy metals were identified,and the degree of their influence was ranked.A categorical regression represents a suitable method for identifying the factors that influence soil heavy metal contents and could be used to study the genetic process of regional soil heavy metal pollution.