Floodplain wetlands play a significant role in the storage of sediment and water and support high levels of nutrient cycling driven by intermittent inundation. In regulated rivers, the frequency and duration of floodplain inundation are often reduced. Managed water inundation is used as a tool to help restore floodplains, but its outcome on wetlands requires further quantification. We examined the effects of environmental floodplain watering on water quality and 3 groups of invertebrates, including benthic and pelagic micro invertebrates and macroinvertebrates, in 2 wetlands systems on the Gwydir River system in the north of the Murray-Darling Basin. We hypothesised that a wetland inundated for longer periods would alter water quality and support a greater richness and abundance of invertebrates, thus altering their assemblage structures. Water quality and the assemblage structure of all 3 invertebrate groups in the wetlands were significantly influenced by the time since connection (TSC) to their rivers and therefore the length of inundation. However, the response of water quality and the micro invertebrate assemblages to TSC differed between the 2 wetlands. Water quality was affected by an increase in 6 variables, including total nitrogen, and a decrease in soluble reactive phosphorus. Micro invertebrate abundance was positively associated with TSC, but the abundance of macroinvertebrates was not. The relationships demonstrated between TSC and invertebrates indicate that the duration of inundation is important for ecological structure and food webs in these and other semiarid floodplain wetlands.

The Basin-wide Environmental Watering Strategy forms a part of a program of water reform in the Murray-Darling Basin to deliver water to instream channels and wetlands through environmental flows. A key objective of the Strategy is 'Improved Ecological Processes' based on more productive and diverse food webs and ecological communities supported by the increased movement of carbon and nutrients. In turn, achieving these productivity and water quality objectives supports the Basin Plan Objectives of improving the life cycle completion of key plants and animals, and meeting the needs of the whole fish and waterbird community. Therefore, key Basin Environmental Watering Strategy targets of successful fish and waterbird recruitment can only be achieved if environmental water delivers sufficient energy that is both available to, and accessible by aquatic biota.

In this report we assess the responses of three groups of aquatic invertebrates, including epi-benthic and zooplankton microinvertebrates and macroinvertebrates to the environmental water releases and natural flows that occurred in the channels in Gwydir River Selected Area during the Long term Intervention Monitoring (LTIM) program. We found that the responses in either richness or abundances of individual taxa due to various associations with channel hydrology significantly affected in assemblage structure of all three invertebrate groups. The response of invertebrates to channel hydrology was mainly demonstrated for epibenthic and zooplankton microinvertebrates and not macroinvertebrates but those associations were not strong. Due to the presence of invertebrates at all sites and times when water was available environmental water can play a significant role in contributing to the basal food resources in the Gwydir Selected Area.