Analysis on seasonal distribution characteristics of heavy metals on riverbed of Dapuhe River Estuary, China

摘要

Dapuhe River, located in Qinhuangdao, China, is one of the most contaminated rivers due to the wastewater from its watershed discharging into the river. Since contaminants (especially heavy metals) can easily stick on sediments and then deposit on the riverbed, sediments contaminated by heavy metals become the potential secondary pollution sources to aquatic system. To assess the effects of heavy metals on the estuarine environment, seasonal distribution characteristics of heavy metal in surface sediments on riverbed of Dapuhe River were investigated in this study. Sediment samples were collected at 6 sites along the river estuary during August (i.e. the flood season) and November 2011 (i.e. the dry season). They were analyzed by polarization spectrometer for heavy metals to examine the element distribution pattern and pollution status. The concentrations (mg/kg) of heavy metals were for Cu in 10.2-322.0, Zn in 19.7-435.2, Cd in 0.04-0.59, Pb in 4.2-142.0, Cr in 37.0-154.6, Hg in 0.02-0.73, As in 0.6-36.7, respectively. A primary assessment with Geo-accumulation Index and Potential Ecological Risk Index indicated that the pollution status associated with heavy mental in sediments was unpolluted to moderate polluted which posed a light potential ecological risk to the aquatic environment. The pollution status of the river in the flood season was worse than that in the dry season, and the middle reach of the river (especially the branch of Guhe River) may suffer more pollution than the upper and the lower reaches. It was also found that the contaminated degree of heavy metal on the riverbed sediments was: Cu>Pb>Zn>Hg>As>Cd>Cr and some heavy metals from metallic wastewater discharges along the river were likely to result in harmful effects on river ecosystem. Although the concentrations of metals were lower than the threshold level in the study area, an attention still should be paid to the potentially ecological risk of heavy metal on bed sediments of Dapuhe River estuary.