Menindee Lakes Aquatic Fauna: The effect of rapid drawdowns on productivity and diversity in ephemeral deflation basin lakes (EDBL)

"April 2002".

Project Number: Menindee Lakes ESD Project: Aquatic Fauna - M/03/5107; SKM Project WCO1357.3.

MDFRC item.

Report is part of a serious of 5 reports see (Menindee Lakes Ecologically Sustainable Development Project / [compiled and edited by Stephen Moore and Tania Midgley] – ISBN: 0734751710).

Executive summary only available.

Document not available.

This study compared the effects of an imposed accelerated drawdown event with slower, more natural, evaporation driven lake drying on water quality, productivity and biodiversity in ephemeral deflation basin lakes (EDBL). Because of difficulties associated with the manipulation of natural systems, a series of small-scale experimental trials were used. Key environmental responses to the imposition of accelerated drawdown events on EDBL, such as the Menindee Lakes include: - Increased removal of salt from lakes via surface water discharges rather than the localised movement of salt back into the ground; - Increased frequency and duration of lake 'dry’ phases promotes sediment surface nutrient transformations and the post-inundation mobilisation of nutrients from the sediments; - Increased frequency and duration of lake 'dry’ phases promotes the mobilisation of deeper sediment nutrient reserves by lakebed terrestrial vegetation; - Submerged terrestrial lakebed vegetation increases aquatic habitat complexity and represents a potentially significant organic matter source as it decomposes; - Depending on the timing of drawdown relatively more nitrogen than phosphorus may be removed from lakes; - Changes in the partitioning of aquatic primary production may result in the modification of trophic structures, - Whilst this study indicated no significant effect on egg/cyst reserves or emergence from a single drawdown event, multiple sequential drawdowns may result in a gradual reduction of egg/cyst reserves within the sediments thereby increasing the potential for species loss and increasing the reliance upon riverine species to re-colonise newly flooded lakes.