Predicting the Resilience of Dryland Wetlands Affected by Droughts

The Macquarie Marshes are one of the most important ecological assets of the Murray-Darling Basin in NSW, Australia. This dryland wetland has an extremely variable flow regime driven by El Nino/La Nina cycles but also modulated by river regulation (dams and irrigation diversion canals). Recorded flows over the last decade show extended drought periods followed by periods of considerable precipitation and environmental flow releases. After the last extended drought period, better known as the Millennium drought, the flood dependent wetland vegetation showed resilience and persistence due to their capacity to recover when flow regimes returned to more suitable conditions. However, during the drought conditions deteriorated in many sites and wetland vegetation transitioned to terrestrial species.

Models that allow quantification of these vegetation transitions can provide estimates of the resilience and persistence of the wetland and provide a tool for regulatory authorities to better manage environmental flow releases. In this contribution, we apply an eco-hydraulic model to quantify changes in the wetland vegetation of the Macquarie Marshes. This system is composed of semi-permanent wetland areas that have reed beds, lagoons, and mixed marsh that host a variety of precious fauna. Additionally, there are extensive and unique communities of Eucalyptus forests and woodlands. Some of the areas in the Macquarie Marshes have been declared as a Ramsar site, as they serve as a sanctuary for migratory and colonial waterbirds. The eco-hydraulic model links detailed description the flow regime obtained with hydrodynamic simulations to the inundation preference of each vegetation in order to assess vegetation transitions in the site. We have continuously simulated the period from 1989 to 2018, which includes the Millennium drought and the recovery that occurred in the wetland after the break of drought. We have also proposed different scenarios based on current projections of climate change in order to quantify the resilience of the wetland vegetation as a response to different water regimes.