Restoring biodiversity in the Gwydir Wetlands through environmental flows

As part of the Water Reforms process, environmental flow rules have been progressively implemented in New South Wales rivers. The Integrated Monitoring of Environmental Flows (IMEF) is a major project established to better understand how rivers and associated wetlands respond to environmental water allocations. The results presented here represent the vegetation data collected for the testing of the hypothesis that "protecting or restoring a portion of freshes and high flows and otherwise maintaining natural flow variability will replenish anabranches and riverine wetlands, restoring their biodiversity". The study site is the Ramsar listed Gwydir Wetlands, located on the Gingham and Gwydir (Big Leather) Watercourses in the Lower Gwydir Valley, 100 km west of Moree. The expansion of irrigated agriculture in the lower Gwydir valley has severely altered flow regimes in the wetlands. The spread of the weed Phyla canescens (Lippia) is of major concern to landholders in the Gwydir Wetlands. Results indicate that Paspalum distichum (Water couch) and Eleocharis plana (Ribbed spike-rush) can maintain dominance over Phyla canescens if flooding occurs on a semi-regular basis. Conversely, Eichhornia crassipes (Water hyacinth) is a rampant noxious weed of open water in the Gwydir Wetlands, and has quickly spread in areas that are inundated for long periods. Management of this weed requires periodic drying of the wetlands to cause desiccation and death of the plants. The flooding requirement of individual species and plant associations in the Gwydir Wetlands are currently not fully understood. By providing better information on the consequence of different flows, the IMEF project will help to develop better management strategies to shift the dominance from introduced species such as P. canescens and E. crassipes to more desirable native plant species.