| This study investigated the soil nematode community structure along Yellow River in the Lanzhou area of China,and analyzed the impact of heavy metals(Cd,Pb, Cr,Cu and Zn) and polycyclic aromatic hydrocarbons(PAHs) on the nematode community.Soil samples came from seven locations(A site:Xidagou Drain of Baiyin City, B sites:Matan Village of Lanzhou City,C site:Qiangwan Village of Lanzhou City,D site:Qingbaishi Village of Lanzhou City,E site:Jianting Village of Yuzhong County, F site:Lanzhou University garden and G site:Liujiaxia Village of Yongjing County). The results were showed as follows:1.The sampling sites showed significant differences(p＜0.05) in the moisture of the soil,organic matter,total nitrogen,C/N ratio,and pH.Average soil moisture content ranged between 10.33%and 19.30%.Soil was weakly alkaline,with pH ranging from 7.70 to 7.96.2.It was appeared that the soil samples were mainly contaminated by heavy metals.A significant difference on heavy metals contents in soils was also found in soil samples of different sites(p＜0.05).The highest Cd,Pb,Cu and Zn concentrations were found in site A(p＜0.05) and the lowest Pb,Cr,Cu,and Zn concentrations were found in site G,and Cd even could not be detected in site A.3.In accordance with environmental quality standard for soils(China,GB15618, 1995),all soil samples except site G were polluted by Cd(Pi＞1),especially in site A with PI of Cd equaling 40.35.The soil samples of A,C and F site were polluted by Pb Pi＞1).In site A and B,the soil samples were polluted by Cu.Zn polluted soils of sites A,B and F.In all sites,pollution of Cr was not found.4.Concentrations of PAHs were lower in all soil samples than expected.Among seven sites,only six PAHs were found.In A,B and F,soil sample concentrations of PAHs were higher.Lower concentrations of PAHs were found at other sites.5.A total of 29 nematode families and 53 nematode genera were identified. Population of nematode individuals of A site had a population of 1555.48 nematode individuals in 100g soil,which was significantly higher(p＜0.05) than other sampling sites.At B,C,D and G site,the nematode population densities did not have a distinct difference(p＞0.05).Site C was the lowest in nematode population size among all locations(p＜0.05).6.Bacteriovores were found to be the most abundant trophic group in the study area.A significant location effect was found(p＜0.05) among the bacteria feeder nematodes,reaching a mean maximum of 1451.25(93.30%) at location A.The plant-parasite population was the second most common trophic group in all sites.In sites E and G,the omnivorous-predatory proportions were the highest(p＜0.05). Fungivores nematode taxa were found in low numbers in all trophic groups.7.The nematode quantity of which the c-p value was 1 and 2,occupied over 50% of investigated all nematode population numbers.In site A,the nematode numbers of c-p 1-2 were much more than others locations(p＜0.05).In G sites,numbers of c-p 3-5 nematode population were higher than other sites(p＜0.05),but c-p 1 nematode only occupied 5.92%.8.In heavy pollution sites,∑MI,MI and H' were low,on a contrary,they were high.In site G,∑MI and MI were the highest(p＜0.05).Site A has the lowest∑MI,MI, H' and PPI,but the highest WI(p＜0.05).PPI was the highest in site B(p＜0.05).9.Negative correlations were found between Pi of heavy metals(such as Cd,Pb Cu and Zn so on),PAHs and nematode index(such as∑MI,MI,and H') respectively, but positively correlated with WI and PPI(p＜0.01).The results of this study indicated that heavy metals and PAHs influenced or changed soil nematode diversity and tropical structure.The trophic groups,especially bacterivores and plant parasites,presented big fluctuation with the increase contaminant level.The ecological indexes(such as Diversity Index H' and MI) were significantly correlated with soil environment condition,concentration of heavy metals and PAHs.Therefore the nematode community and the nematode indexes is a sensitive bioindicator for monitoring pollution by heavy metal and polycyclic aromatic hydrocarbons.
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