Water quality and sediments of the Marlborough Creek system

The Marlborough Creek system in Central Queensland, Australia, dominated by serpentinite geology, was studied to describe (i) its physical and chemical characteristics and (ii) their seasonal variation in relation to the proposed Marlborough Nickel mine. Nine sites on Marlborough Creek and two sites of a tributary (Spring Creek) were studied at the end of the dry season in November 1997 and results were compared with those obtained in April 1999, approximately six weeks after significant wet season flows. The flows resulted in significant changes in many of the physical and chemical parameters monitored. The stream system was generally high in conductivity (1146 - 2200 oxygen IlScm-1), pH (8.3 to 9.1) and oxygen, the last indicating a generally healthy condition. The dominant ions were CI, Mg, Na and Ca. Nutrient concentrations were mostly low. AI, Co, Cu, Mn, Ni and Zn in stream waters were naturally high in concentration. Stream sediments were enriched with Ni, Cr, Co and Zn. After the flows, water levels and flow rates increased, temperatures and conductivities decreased, oxygen levels increased at sites where levels were previously low and pH was almost unchanged. Substrate composition changed in the percentage of silt, with the largest increases at reference sites upstream of the proposed mining activities and in the tributary. Detritus cover generally decreased in the 1999 survey. To improve the design of future surveys additional reference sites are recommended.