Coal mine-affected water releases, turbidity and metal concentrations in the Fitzroy River Basin, Queensland, Australia

Historical water quality datasets from the Fitzroy Basin, a large river system that receives mine-affected water from more than 40 mines, and drains into the Great Barrier Reef Lagoon, were analysed. There is great public and environmental interest in these waters that are used for agriculture, recreation and raw drinking water supplies. Aside from one AMD-impacted area, waters were generally alkaline. Turbidity data regularly exceeded the regional water quality objective (< 50 NTU), indicating the presence of particulates that may accumulate or transport metal contaminants within the waters. Analyses of data for 14 metals showed dissolved Cu and Al, followed by Zn, were the parameters that were most often greater than Australian toxicant guideline values. Analysis of coal mine-affected water samples and the receiving creek data, showed that median turbidity was greater downstream than upstream of the mine water release points, suggesting release-water may contain particulate-bound metals. Median dissolved Al and Cu concentrations were lower downstream than upstream and were above guidelines. Preliminary modelling using WHAM7 suggested downstream dissolved Cu (2–5 µg/L) was bound to fulvic acid and was likely not bioavailable. Dissolved Al (170–550 µg/L) may have existed as Al(OH)4−. Overall, suspended particulate matter appeared to be a water quality parameter of interest in this mine-affected river basin. Further targeted sampling, direct measurement of particulate-bound metals and multivariate statistical analysis are needed to help better understand metal partitioning in these turbid, alkaline waters.