Linking wetland hydrology to ecological outcomes in the Lowbidgee wetlands in Southern New South Wales

Abstract

The Lowbidgee Floodplain (Lowbidgee) is an ephemeral wetland system located in semi-arid southern New South Wales. The wetlands provide critical fish and waterbird habitats, and are a refuge for biodiversity. In its natural state, many of the wetlands in Lowbidgee are characterised by variable and unpredictable patterns of high and low flows and water levels. Previous studies indicate that the Lowbidgee floodplain is undergoing accelerated ecological degradation since the 1960s. The ecological degradation can be recognised through declining biodiversity, encroachment of terrestrial species, colonisation by exotic species, and deterioration of the floodplain forests. This degradation is primarily due to changes in the flooding regime, and principally a decrease in flooding frequency due to river regulation. There has been a renewed investment in providing water for the environment to address this declining ecological condition. To optimise environmental water management, the LYNC decision support system (DSS) was developed based on the Eco Modeller framework. 60 key wetlands in the Lowbidgee are represented in LYNC. LYNC applies habitat models to daily hydrological time series for each of these 60 key wetlands to transparently evaluate and report the relative ecological outcomes of different watering scenarios. . LYNC contains habitat models for interpreting the hydrological regime for 17 species. In this paper we focus on river red gum (Eucalyptus Camaldulensis) in the Yanga National Park, an area of the Lowbidgee that is predominantly a river red gum forest. We ran the cell-based IQQM hydrological model for eight scenarios that investigated different options in the amount and timing of delivery of environmental water. The LYNC DSS was used to model habitat condition for each hydrological scenario. The best overall habitat scores across the wetlands are provided under the predevelopment scenario. The environmental water application scenarios indicated that, given a set volume of water, the timing of water delivery has a significant effect on the suitability of the habitat conditions. Additionally the method of water delivery (over-bank flooding versus active diversions) gives a different spatial pattern to habitat suitability. This study has demonstrated the potential value of habitat models to quantitatively test environmental water planning options. As with all modelling, the habitat models represent our current understanding of the water needs of the different target species and it is important to continue to refine and test the underlying assumptions of the habitat models as more ecological data becomes available.