The effect of water extraction regime on the chemistry and macro invertebrates of a subtropical coastal freshwater wetland

In this paper it is demonstrated, through an instance of a localized short-term oscillating mode of water extraction from a large coastal oligotrophic hind-dune peat swamp, Eighteen Mile Swamp, North Stradbroke Island, that the mode of water extraction is as important as the amount of water extracted. A six-year duration, high-frequency drought-wetting cycle imposed by a point-source extraction regime has had apparently irreversible effects on the adjacent peat and macro invertebrates. The legacy of this short-term alteration in hydrological conditions has been the disintegration of the peat with consequent release oflarge amounts of otherwise captured nutrients and a significant increase in biological oxygen demand. This is associated with significant reductions in macroinvertebrate abundance and richness, with a reduction in soft-bodied taxa as Coleoptera becoming dominant. Although full suites of biota were present in nearby unaffected locations, the substrate is sufficiently altered that there can be no short-term prospect of rehabilitation of the area affected by this water extraction. This chain of events illustrates a catastrophic regime shift or 'ecological surprise'. Defining the point of no return (a threshold) would have to be demonstrated experimentally.