Yanco-Billabong Creek Broad-scale Wetland Monitoring Project: Frog communities of the Yanco-Billabong creek system

Amelia Walcott, Ben Wolfenden, Andrew Hall, Skye Wassens

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Limited information is available on the biota of the Yanco-billabong creek system, particularly for aquatic animals and plants, and this information is critical to making informed, evidence-based natural resource management decisions. This project has been developed in partnership with Charles Sturt University and Murray Local Land Services to increase knowledge of the ecology and ecological function of wetlands through the Yanco-Billabong creek system. This final report synthesises the research activities and outcomes achieved for the Yanco-Billabong Creek Wetland monitoring Project between April 2017 and April 2018.
Fifteen wetlands were selected across the system for their potentially high conservation value via consultation with Jim Parrett (Rural & Environmental Services). Wetland boundaries for 18 candidate wetlands were delineated using high resolution digital terrain models (spatial analysis). Subsequently, wetland areas were estimated and stratified according to depth classes, a useful tool for the delivery of environmental water and other natural resource management activities. Rapid habitat assessment described over and under story vegetation allowing for classification of the different wetland types occurring throughout the system. 
Broad scale frog surveys were conducted on two occasions in 2017. First in October, following a small delivery of environmental water and again in early December, following very heavy rainfall. Frogs were very widespread, identified at 14 of the 15 wetlands (all wetlands which held at least residual water during the surveys). Overall, eight frog species were identified across the system: spotted marsh frog, barking marsh frog & eastern sign-bearing froglet, eastern banjo frog, Sudell’s frog, inland banjo frog, Peron’s tree frog; and one threatened species, the southern bell frog. A key finding of this study was observation of the southern bell frog which was heard calling in low numbers at two wetlands along the mid-Yanco creek. Also, higher frog species diversity (number of frog species) was related to a higher diversity of microhabitat types (e.g. submerged vegetation, tall standing emergent vegetation). 
Frog calling activity, a proxy for breeding activity, was also monitored on an hourly basis from 25th October 2017 until 7th February 2018. Daily calling by the same frog species varied considerably between the two sites considered and this likely reflected the strong influence of hydrology on resident frog species breeding. The findings of this study suggest that Bundure provided an important breeding habitat for the endangered southern bell frog, as well as a range of other frog species during the monitoring period. Based on the findings of this study, natural resource management actions which improve/sustain aquatic vegetation diversity and provide aquatic habitats which persist during spring and summer (and longer to cater for southern bell frog metamorphosis) could sustain and even improve frog occupancy in this system. 
A single waterbird survey was conducted alongside the day time frog surveys in December 2017. Overall, 17 waterbird species were identified, in addition numerous (90-100) inactive nests (likely cormorant species) were identified. Further surveys are required following wetland inundation to better understand waterbird diversity in the system. 
Inland wetlands are attributed with being the earth’s largest stores of terrestrial carbon and in this way are considered important for offsetting the impacts of greenhouse gas emissions. Multiple factors influence the capacity for wetlands to sequester carbon. Hydrology controls the amount and type of vegetation that grows in wetlands as well as the rate at which the organic matter of these plants produce accumulates within the soil over time. Using the wetland maps stratified according to depth, the relationship between carbon stores (soil and standing stock) and wetland depth (a proxy for hydrological regime) was assessed (from May 2017). Carbon stock ‘hotspots’ were identified and extended to the lower reaches of the catchment which are likely to have suffered the compounding effects of lower water volumes. The results of this pilot study suggest that wetland soils more frequently inundated, stored significantly higher proportions of carbon. Further analysis of soil carbon stable isotopes was conducted to determine whether the source of carbon also differed among wetlands, or sites within wetlands, with different hydrological regimes. For example, we might expect sites that are more frequently inundated will have a higher proportion of soil carbon contributed by wetland plants, and so the composition of soil carbon isotopes may reflect changes in carbon sources. Stable isotope δ13C ‰ analysis also revealed a relationship with wetland depth, showing that deeper (more frequently inundated) sites within wetlands were more enriched in 13C. It isn’t clear whether this trend reflects alternative source materials at drier sites that have a contrasting isotopic signature, or if the less depleted signature is the result of microbial processing. These findings are an important consideration when assessing the potential environmental impacts of future management decisions that result in reduced water delivery to this system. Based on the findings of this pilot study, the delivery of water to these hotspots is recommended and emphasised. These findings demonstrate key differences in the amount and type of soil carbon accumulated by different wetlands in the Yanco Creek system and provide a benchmark for which future reassessment can be compared against to quantify the benefits of rehabilitation.
Original languageEnglish
Place of PublicationAlbury/Wodonga
PublisherInstitute of Land Water and Society
Commissioning bodyMurray Local Land Services
Number of pages104
Publication statusPublished - 01 Jun 2018

Grant Number

  • 0000102106


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