Soil animals and their responses to soil heavy metal pollution in sewage irrigated farmland: A case study of the sewage irrigated area of Huafei River, Kaifeng City

Abstract

The sewage irrigated area of Huafei River is located in the eastern suburbs of Kaifeng City,Henan Province.Soil animals were collected twice in spring and autumn of 2007.Soil macrofauna were collected by hand-sorting method,small and medium-sized soil animals were collected by Tullgren funnel method and humidogene soil animals were collected by Baermann funnel method.Soil samples(0-20 cm)were collected in spring of 2007,and five heavy metals(Cu,Zn,Pb,Cd and Ni) and main soil properties(pH,organic matter content and texture) were analyzed using the corresponding national standard methods.According to heavy metal pollution,soils in the sewage irrigation area were divided into three types of different pollution levels.Further,soil animal distributions,soil animal group characteristics,and their responses to soil pollution were analyzed by use of ecological analysis and statistical analysis methods.The research results showed that:(1)Throughout the sewage irrigated area,Nemata and Isotomidae were dominant groups.The number of soil animals in spring was 3158 heads,much more than 1963 heads in autumn,and the number of groups performed similarly,with 74 species in spring and 57 species in autumn.(2)However,in soils of three different pollution levels the group number of spring was less than that of autumn.Similarity coefficients of groups between sampling sites were higher in spring than that in autumn.(3)Heavy metal pollution had a great influence on the horizontal distribution of soil animals,which resulted in a significant difference of soil animal quantities between polluted soil and control soil.The more serious the pollution was,the lower the surface aggregation of soil animals was.(4)The heavy metals pollution resulted in a decline of the density-group index,which was bigger in autumn than in spring.(5) The responses of the soil animals to heavy metals pollution showed that: the individual number was more sensitive than the group number,the horizontal distribution was more significant than the vertical distribution,and their responses were more obvious in spring than in autumn.