Heavy metals in a typical city-river-reservoir system of East China: Multi-phase distribution, microbial response and ecological risk

The rapid construction of artificial reservoirs in metropolises has promoted the emergence of city-river-reservoir systems worldwide.This study investigated the environmental be-haviors and risks of heavy metals in the aquatic environment of a typical system composed of main watersheds in Suzhou and Jinze Reservoir in Shanghai.Results shown that Mn,Zn and Cu were the dominant metals detected in multiple phases.Cd,Mn and Zn were mainly presented in exchangeable fraction and exhibited high bioavailability.Great proportion and high mobility of metals were found in suspended particulate matter (SPM),suggesting that SPM can greatly affect metal multi-phase distribution process.Spatially,city system (CiS) ex-hibited more serious metal pollution and higher ecological risk than river system (RiS) and reservoir system (ReS) owing to the diverse emission sources.CiS and ReS were regarded as critical pollution source and sink,respectively,while RiS was a vital transportation aisle.Mi-crobial community in sediments exhibited evident spatial variation and obviously modified by exchangeable metals and nutrients.In particular,Bacteroidetes and Firmicutes presented significant positive correlations with most exchangeable metals.Risk assessment implied that As,Sb and Ni in water may pose potential carcinogenic risk to human health.Never-theless,ReS was in a fairly safe state.Hg was the main risk contributor in SPM,while Cu,Zn,Ni and Sb showed moderate risk in sediments.Overall,Hg,Sb and CiS were screened out as priority metals and system,respectively.More attention should be paid to these priority issues to promote the sustainable development of the watershed.