Sediments, nutrients and pesticide residues in event flow conditions in streams of the Mackay Whitsunday Region, Australia

The Mackay Whitsunday region covers 9000 km² in northeastern Australia. A study of diffuse pollutants during high flow events was conducted in coastal streams in this region. Sampling was conducted in the Pioneer River catchment during a high flow event in February 2002 and in Gooseponds Creek, Sandy Creek and Carmila Creek in March 2003. Concentrations of five herbicides; atrazine (1.3 μg l^-1), diuron (8.5 μg l^-1), 2,4-D (0.4 μg l^-1), hexazinone (0.3 μg l^-1) and ametryn (0.3 μg l^-1) and high concentrations of nutrients (total nitrogen 1.14 mg l^-1, total phosphorus 0.20 mg l^-1) and suspended sediments (620 mg l^-1) were measured at Dumbleton Weir on the lower reaches of the Pioneer River. Drinking water guidelines for atrazine and 2,4-D were exceeded at Dumbleton Weir, low reliability trigger values for ecosystem protection for diuron were exceeded at three sites and primary industry guidelines for irrigation levels of diuron were also exceeded at Dumbleton Weir. Similar concentrations were found in the three smaller streams measured in 2003. Herbicides and fertilisers used in sugarcane cultivation were identified as the most likely major source of the herbicide residues and nutrients found.