located on the opposite site could be a possible cause as the
sewage was carried along the river fl ow.
Alarmingly, heavy metal pollution, except Mn, was shown to be
steadily deteriorating since 1979. The disparate pattern of Mn is
enigmatic but it might be due to its strong association with the
geochemical matrix with iron or early diagenetic processes
(Jonathan et al., 2010 ). The trend of heavy metal pollution in the
present study was generally consistent with the previous study
in which heavy metals were seriously contaminated in the top
45 cm sediment in Qi’ ao Island owing to the rapid socio-economic