典型冶炼厂大气沉降区农田耕层土壤重金属(Cd、Cu、Pb)输入输出平衡研究

Input and Output Balance of Heavy Metals(Cd,Cu,Pb)in Arable Soils in Atmospheric Deposition Area of Typical Smelter

为探究不同大气沉降区农田耕层土壤镉(Cd)、铜(Cu)、铅(Pb)的质量平衡特征,以距离贵溪冶炼厂34 km(背景区)、6 km(中沉降区)、1 km(高沉降区)的0~20 cm农田耕层土壤为研究对象,通过化学质量平衡方法对土壤重金属的主要输入途径(大气沉降、灌溉水、农药肥料)和输出途径(地表径流、土壤淋溶、籽粒带走)开展为期三年的监测与定量分析。结果表明:背景区、中沉降区、高沉降区由大气沉降导致的Cd年均输入通量分别为0.84、2.26、9.01 mg·m^(-2)·a^(-1),分别占比43.18%、38.33%、100%;Cu年均输入通量分别为17.62、99.68、747.6 mg·m^(-2)·a^(-1),分别占比80.76%、86.24%、100%;Pb年均输入通量分别为13.93、27.43、73.17 mg·m^(-2)·a^(-1),分别占比97.75%、92.36%、100%。背景区和中沉降区由灌溉水导致的Cd年均输入通量分别为1.05、3.60 mg·m^(-2)·a^(-1),分别占比54.62%和60.82%;农药肥料带入的重金属年均输入量占比小于5%,可忽略不计。不同沉降区土壤的主要输出途径均为地表径流和土壤淋溶,输出占比介于86.66%~100%;籽粒带走的重金属输出占比介于2.88%~13.34%。2019—2021年,背景区、中沉降区、高沉降区土壤Cd、Cu、Pb的年均净输入通量均大于0,Cd年均净输入通量分别为1.54、1.96、4.38 mg·m^(-2)·a^(-1);Cu年均净输入通量分别为12.72、28.02、184.0 mg·m^(-2)·a^(-1);Pb年均净输入通量分别为13.03、21.31、55.04 mg·m^(-2)·a^(-1)。综上,建议加强研究区域大气污染源和灌溉水质的长期监测并采取一定的控制措施,同时避免秸秆直接还田。本研究可为区域农田环境质量保护及重金属污染修复治理提供理论支持。

【Objective】This study aimed to investigate the input and output characteristics of cadmium(Cd),copper(Cu),and lead(Pb)in different atmospheric deposition areas.【Method】The arable soils(0-20 cm)of Guixi Smelter with main wind direction at 34 km(background site),6 km(moderate deposition site)and 1 km(high deposition site)were selected as the research objects.The main input(atmospheric deposition,irrigation water,pesticides,and fertilizers)and output pathways(surface runoff,leaching water,and grain harvest)were monitored and quantitatively analyzed for three years by using the chemical mass balance(CMB)method.【Result】The results showed that the average annual input fluxes of Cd in the background,moderate,and high deposition sites by atmospheric deposition were 0.84,2.26,9.01 mg·m^(-2)·a^(-1),accounting for 43.18%,38.33%,and 100%,while the average annual input fluxes of Cu were 17.62,99.68,747.6 mg·m^(-2)·a^(-1),accounting for 80.76%,86.24%,100%,respectively.Also,the average annual input fluxes of Pb were 13.93,27.43,73.17 mg·m^(-2)·a^(-1),accounting for 97.75%,92.36%,and 100%,respectively.Specifically,the average annual input fluxes of Cd in the background and moderate deposition sites due to irrigation water were 1.05 and 3.60 mg·m^(-2)·a^(-1)and accounted for 54.62%and 60.82%,respectively,whereas the annual heavy metal input fluxes by pesticides and fertilizers accounted for less than 5%,which could be ignored.The main output pathways of arable soil in different atmospheric deposition areas were surface runoff and leaching water,with the output ratio ranging from 86.66%to 100%,and the output ratio of the grain harvest ranging from 2.88%to 13.34%.From 2019 to 2021,the average annual net input fluxes of Cd,Cu,and Pb were all greater than 0 in the background site,moderate deposition site,and high deposition site.For example,the average annual net input fluxes of Cd were 1.54,1.96,and 4.38 mg·m^(-2)·a^(-1),for Cu were 12.72,28.02,and 184.0 mg·m^(-2)·a^(-1),and for Pb were 13.03,21.31,55.04 mg·m^(-2)·a^(-1)in the background site,moderate deposition site,and high deposition site,respectively.【Conclusion】In general,it is advisable to strengthen the long-term supervision of atmospheric pollution sources and irrigation water quality in the study area and avoid the direct return of straw to the field.This study provided theoretical support for the remediation of heavy metal pollution and the protection of environmental quality in regional arable soils.