Impacts of deep open drains on water quality and biodiversity of receiving waterways in the Wheatbelt of Western Australia |
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Authors: | Barbara Stewart Karin Strehlow Jenny Davis |
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Institution: | (1) Centre of Excellence in Natural Resource Management, University of Western Australia, PO Box 5771, Albany, WA, 6332, Australia;(2) School of Environmental Science, Murdoch University, Murdoch, WA, 6150, Australia |
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Abstract: | Extensive networks of deep drains are being built in Western Australia to reduce the effects of dryland salinity on agricultural
lands. Most of these drains discharge into natural river and wetland systems, with little consideration given to the environmental
impacts. This study examined the downstream ecological impacts of one of the oldest deep drain networks in Western Australia,
located in the Wakeman subcatchment near Narembeen. Twelve sites were sampled bi-monthly from October 2004 to September 2006.
On each occasion, water quality parameters were measured and the macro-invertebrate fauna was sampled. Significant differences
in water quality and macro-invertebrates were observed between the untreated sites and those affected by the drain discharge.
Surface water at untreated sites was always fresh (<3 ppt), alkaline (pH 7.6–8.9) and turbid (49–600 NTU), whereas treatment
sites were always saline (28–147 ppt), acidic (pH 1.9–3.8) and mostly clear (0–100 NTU). No recovery of water quality was
observed with distance from discharge point (20 km). Invertebrates reflected differences in water quality, with drain discharge
resulting in a sharp decline in species richness, and significant changes in macro-invertebrate community composition. Sites
affected by drain discharge were dominated by fly larvae such as Orthocladiinae and Ceratopogonidae. Microcrustaceans were
far more abundant at sites unaffected by drainage. The ecological values of Wheatbelt streams are likely to be further compromised
by discharge of poor water quality from deep drainage.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Handling editor: K. Martens |
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Keywords: | Secondary salinisation Downstream impacts Water quality Acidity Biodiversity Macro-invertebrates |
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