1.1.7.2 Aquatic species and communities

1.1.7.2.1 Gwydir Wetlands

The Gwydir Wetlands are located on the Lower Gwydir floodplain and consist of a mosaic of wetland types, ranging from semi-permanent marshes and waterholes to floodplain woodlands only inundated by large floods (Torrible et al., 2008). Just east of the township of Moree, the Gwydir floodplain begins to broaden and forms an inland delta with the floodplains of the Barwon-Macintyre valley and Namoi valley to the south. This area covers approximately 102,000 ha (Rogers and Ralph, 2011) and is collectively referred to as the Gwydir Wetlands. It comprises three regions: Gingham Watercourse, Lower Gwydir Watercourse and Mehi, Mallowa and Moomin system (Figure 29). These wetlands are highly modified by agricultural development and water management but retain high ecological values (NSW DECCW, 2011). Environmental water is being provided to the Gwydir Wetlands to support the ongoing restoration of native wetland plant communities and maintain habitat for native animals (NSW DECCW, 2011).

Portions of the Gwydir Wetlands are listed under the Ramsar List of Wetlands of International Importance as they provide a good example of an inland terminal wetland delta system (Figure 29), support a large assemblage of species (including threatened species), are important for maintaining diversity, support many species at important life stages and can sustain large numbers of breeding colonial waterbirds when flooded (Table 18). They include the Windella, Crinolyn, Goddard’s Lease and Old Dromana wetlands. The Gwydir Wetlands are also listed in the Directory of Important Wetlands in Australia (Environment Australia, 2001) and support a diverse assemblage of rare, endangered and vulnerable species, and when flooded, sustain large numbers of waterbird breeding colonies (see Table 18).

The wetlands contain native plant communities such as marsh club-rush sedgeland and water couch (Paspalum distichum), which are inundated frequently by overbank flooding from many small channels. River cooba (Acacia stenophylla) and lignum (Muehlenbeckia florulenta) are common in and around the margins of the core wetlands (Bowen and Simpson, 2010; Keyte, 1994). On the floodplain, coolibah - black box woodlands fringe the wetlands and form extensive woodlands in a number of areas (Bowen and Simpson, 2010; Keyte, 1994). These plants have many of their natural processes, such as flowering, seeding and germination, determined by the amount of water that is available to them (NSW DECCW, 2011).

Gwydir Wetlands are recognised as a refuge for waterbirds in dry times, and for supporting some of the largest waterbird breeding colonies recorded in Australia. They include species listed as threatened both under NSW and Commonwealth legislation (Table 18), and species listed on international migratory bird agreements (Spencer, 2010). The key habitats for waterbird breeding in the Gwydir Wetlands are floodplain waterholes, in-channel lagoons and floodplain wetlands. These habitats comprise marsh club-rush sedgelands, stands of cumbungi/bulrush (Typha spp.), lignum, belah (Casuarina cristata), coolibah (Eucalyptus coolibah) and river red gum (Eucalyptus camaldulensis). Feeding habitats include floodplain waterholes, in-channel lagoons and floodplain areas with freshwater meadows, sedgelands and stands of cumbungi (Spencer, 2010). Colonially nesting species are prominent, and the great egret, intermediate egret, little egret, Nankeen night heron, glossy ibis, Australian white ibis, straw-necked ibis, little pied cormorant and little black cormorant breed in large numbers. Colonially nesting waterbirds need flooding of sufficient volume and duration to inundate colony sites and feeding areas for at least four to five months between August and April (Marchant and Higgins, 1990, 1993).

The wetlands also provide habitat for many types of frogs, fish and insects that, in turn, are food for the nesting waterbirds (Table 18). The aquatic ecological community of the Gwydir Wetlands, which is part of the natural drainage system of the lowland catchment of the Darling River, is listed under the New South Wales Fisheries Management Act 1994 as an endangered ecological community (Table 18). This listing includes all native fish (all 21 species) and aquatic invertebrates within the natural rivers, creeks, lagoons, billabongs, wetlands, lakes, tributaries and anabranches across the Gwydir Wetlands (Green et al., 2011). Threats to the ecological character of the Gwydir Wetlands Ramsar site include reduced frequency and duration of flooding, invasive plant species such as lippia and water hyacinth, feral animals including foxes, pigs and cats, and pesticide contamination (Department of the Environment, 1999).

1.1.7.2.2 Lower Macintyre River Wetlands

In the Border Rivers river basin; Morella Lagoon, Pungbougal Lagoon and Boobera Lagoon are part of a wetland complex found along a remnant channel of the previous course of the Macintyre River. Boobera Lagoon is one of the few naturally permanent water bodies in the Murray–Darling Basin. The lagoons are fringed by riparian woodland of river red gum and coolibah and are listed under the Directory of Important Wetlands in Australia (Environment Australia, 2001).

1.1.7.2.3 Groundwater-dependent ecosystems

The Gwydir subregion contains a diverse range of groundwater-dependent ecosystems, including wetlands, terrestrial vegetation, and instream ecosystems fed by baseflow and springs. The alluvial groundwater management areas of the plains have the highest yield and provide significant irrigation requirements (NSW Department of Environment and Heritage, 2010). The majority of the groundwater-dependent ecosystems identified from field mapping are centred around the Gwydir and Lower Macintyre River wetland and floodplain systems (Bureau of Meteorology, 2013), although the NSW State of the Catchments report noted that there was limited knowledge on the location of groundwater-dependent ecosystems within the Border Rivers-Gwydir river basins, especially for terrestrial ecosystems (NSW Department of Environment and Heritage, 2010). The main pressures on groundwater resources across the subregion are river regulation and agriculture. River regulation has altered the natural river behaviour and the surface water – groundwater interaction with the river system. Agriculture has altered the amount of water that leaks through the root zone from rainfall and through irrigation (NSW Department of Environment and Heritage, 2010).

Table 18 List of threatened communities and species associated with the Gwydir Wetlands

Source data: NSW Department of Environment and Heritage (2013b), NSW Department of Primary Industries (2013), Department of the Environment (2013a)