Water chemistry and heavy metal distribution in an AMD highly contaminated river

Environmental impacts of acid mine drainage (AMD) from Dexing Copper Mine, the largest open pit copper mine in Asia, on Le An River were well documented 10 years ago. However, ore production of the mine has increased fourfold and the contamination situation of the river now is unknown. Our studies indicated that heavy metal concentrations in riverwaters (dissolved), suspended solids (SS) and sediments all showed highly localized distribution patterns closely associated with two AMD-contaminated tributaries (Dawu River and Ji River) and are significantly different from the previous findings. Compared with the previous reports, most of the sampling sites in Le An River displayed lower contents of sediments of 2005 because several historical upstream and downstream heavy metal sources disappeared or became unimportant. The surprised decrease of copper contents in sediments at the mixing location with Dawu River was mainly due to dilution from the sufficient input of poor copper ore (<0.3%).