Victorian Highlands Research Articles

Tracing the migration of mantle CO2 in gas fields and mineral water springs in south-east Australia using noble gas and stable isotopes

Abstract Geochemical monitoring of CO2 storage requires understanding of both innate and introduced fluids in the crust as well as the subsurface processes that can change the geochemical fingerprint of CO2 during injection, storage and any subsequent migration. Here, we analyse a natural analogue of CO2 storage, migration and leakage to the atmosphere, using noble gas and stable isotopes to constrain the effect of these processes on the geochemical fingerprint of the CO2. We present the most comprehensive evidence to date for mantle-sourced CO2 in south-east Australia, including well gas and CO2-rich mineral spring samples from the Otway Basin and Central Victorian Highlands (CVH). 3He/4He ratios in well gases and CO2 springs range from 1.21 to 3.07 RA and 1.23–3.65 RC/RA, respectively. We present chemical fractionation models to explain the observed range of 3He/4He ratios, He, Ne, Ar, Kr, Xe concentrations and δ13C(CO2) values in the springs and the well gases. The variability of 3He/4He in the well gases is controlled by the gas residence time in the reservoir and associated radiogenic 4He accumulation. 3He/4He in CO2 springs decrease away from the main mantle fluid supply conduit. We identify one main pathway for CO2 supply to the surface in the CVH, located near a major fault zone. Solubility fractionation during phase separation is proposed to explain the range in noble gas concentrations and δ13C(CO2) values measured in the mineral spring samples. This process is also responsible for low 3He concentrations and associated high CO2/3He, which are commonly interpreted as evidence for mixing with crustal CO2. The elevated CO2/3He can be explained solely by solubility fractionation without the need to invoke other CO2 sources. The noble gases in the springs and well gases can be traced back to a single end-member which has suffered varying degrees of radiogenic helium accumulation and late stage degassing. This work shows that combined stable and noble gas isotopes in natural gases provide a robust tool for identifying the migration of injected CO2 to the shallow subsurface.

Development of a powerful microsatellite marker panel for Trichosurus cunninghami

Here we describe the development of 11 microsatellite markers (9 autosomal and 2 sex-linked) for Trichosurus cunninghami. These markers will enable in-depth population genetic studies of this species; contributing to long-term research on the responses of arboreal marsupials to the loss of tree cavities in the tall eucalypt forests of the central Victorian highlands, Australia.

Riparian zones provide for distinct bird assemblages in forest mosaics of south-east Australia

Riparian zones are a characteristic component of many landscapes throughout the world and increasingly are recognised as key areas for biodiversity conservation. Their importance for bird communities has been well recognised in semi-arid environments and in modified landscapes where there is a marked contrast between riparian and adjacent upslope vegetation. The value of riparian zones in largely intact landscapes with continuous vegetation cover is less well understood. In this study, birds were surveyed at 30 pairs of riparian and adjacent non-riparian sites in extensive mesic forests of the Victorian Highlands, Australia. Riparian sites were floristically distinct from non-riparian sites and had a more complex vegetation structure, including a mid-storey tree layer mostly absent from non-riparian sites. Bird assemblages at riparian sites had significantly greater richness, abundance and diversity of species than was recorded at adjacent non-riparian sites. Species composition also differed significantly between these habitat types. Compositional differences in assemblages were due to a suite of distinctive species in each habitat and to significant contrasts in the densities of species that occurred in both habitat types. Many species (36%) attained a significantly greater abundance in riparian habitats. The distinctiveness and richness of the riparian avifauna contribute to the diversity of continuous forest landscapes. The spatial patterning of the avifauna, the occurrence of complementary assemblages, the presence of rare species and the potential for riparian habitats to serve as refuges, all point to the value of riparian zones and highlight the importance of landscape-level planning and management for avifaunal conservation.

Habitat use and distribution of the Beautiful Firetail (Stagonopleura bella) in foothill forests of the Victorian Highlands, Australia

The Beautiful Firetail (Stagonopleura bella) is an uncommon, granivorous finch from coastal south-eastern Australia, with a distribution extending from mid-coastal New South Wales to south-eastern South Australia, including Tasmania. This paper presents a quantitative assessment of habitat use by the Beautiful Firetail based on data collected from 30 paired riparian and non-riparian sites in the foothill forests of the Victorian Highlands, Australia. The Beautiful Firetail occurred in two of the three forest blocks surveyed and was found almost exclusively at riparian sites. The Beautiful Firetail was most likely to occur at riparian sites on the coastal fall of the ranges at sites with high sedge cover and low cover of shrubs and bare ground. The species occurred at low densities (0.10–0.19 individuals ha−1) throughout the year. Records from the Atlas of Victorian Wildlife were used to describe the distribution of Beautiful Firetails in Victoria. Notable observations inland of the Great Dividing Range were recorded during the present study. Further study is required to understand the ecological requirements of the Beautiful Firetail throughout its range.

A REVISION OF THE SPIDER GENUS TAURONGIA (ARANEAE, STIPHIDIOIDEA) FROM SOUTH-EASTERN AUSTRALIA

Abstract The spider genus Taurongia Hogg 1901 and the species T. punctata (Hogg 1900) are redescribed. Taurongia punctata is shown to be a rather variable species with a widespread distribution across the eastern central Victorian highlands. Taurongia punctata is a robust spider, contrasting with a more gracile new species, T. ambigua, described from the western Victorian highlands. The placement of the latter in Taurongia is provisional and may change once other undescribed ‘Taurongia group’ genera from eastern Australia have been examined. The Taurongia species dealt with here differ from the latter taxa in having an increased number of cylindrical spigots and a large palpal median apophysis.

O, H, C isotope geochemistry of carbonated mineral springs in central Victoria, Australia: sources of gas and water–rock interaction during dying basaltic volcanism

Waters discharging from carbonated cold mineral springs in the central Victorian Highlands of Australia have δ2H and δ18O values of −45 to −35‰ and −8 to −5.5‰, respectively, that suggest that they were derived from local meteoric water recharged under cooler climatic conditions than present. δ13C values of entrained CO2 (−10.4 to −7.0‰) and dissolved inorganic carbon (−3.9 to −0.1‰) imply that the C was probably derived from outgassing of Recent igneous rocks within the Newer Volcanic Province. The waters lie to the left of both local and global meteoric water lines due to CO2 exsolution from waters that were never involved in high-temperature water–rock interaction.

Predicting water yield from a mountain ash forest catchment using a terrain analysis based catchment model

The structure, capabilities and performance of a distributed parameter hydrologic model are described. The model, called Topog-Yield, permits a transient analysis of unsaturated-saturated flow and evapotranspiration to be performed across complex terrain using a one-dimensional framework. It is applied to a 0.32 km 2 mountain ash ( Eucalyptus regnans) forest catchment in the central Victorian highlands, Australia. We compare observed and predicted daily runoff values for the site over a continuous 12 year period (1972–1983) when the catchment vegetation was in an undisturbed climax condition. All input parameter values were based on published or measured data, although some variables were adjusted within the range of known variability to yield a best fit between predicted and observed streamflow in the first year of simulation, 1972. Although the model was ‘calibrated’ for the first year, all variables other than climatic inputs remained fixed for the following 11 years. Modelled and observed daily runoff values compare well throughout the period of simulation, despite a wide range of climatic conditions. When modelled daily runoff values were lumped on a monthly basis, the model was able to explain 87% of the variation in observed monthly streamflows over the 12 year period. Modelled annual runoff was within ±5% of observed values for 6 of the 12 years of record. Annual runoff prediction errors exceeded ±10% of observed values in only 2 of the 12 years. By the end of the 12 year simulation, the model had over-predicted runoff by less than 5%. Input data requirements and model results are discussed in the light of a preliminary sensitivity analysis.

Forest succession and habitat management for Leadbeater's possum in the State of Victoria, Australia

The aim of the study was to develop models which predict habitat availability for a rare and endangered marsupial, Leadbeater's possum ( Gymnobelideus leadbeateri), in space and time. Measures of forest age, structure and floristics were correlated with the density of Leadbeater's possum at 32 sites in montane ash forests of the Victorian Highlands of south-east Australia. The density of leadbeater's possum was significantly correlated with the number of trees with hollows (PNTs), the number and biomass of Acacia spp., canopy and understory closure, and forest age. Peak densities occurred in regrowth forests (15–50 years), with abundant tree hollows (greater than 6 PNTs per 3 ha), and a high biomass of acacias (20–50% of stand basal area). Leadbeater's possums also occurred at low frequencies and densities in old-growth-regrowth forest ecotones, and in mature and multi-aged forests with an understory of eucalypts and acacias. Models of trends in habitat availability predict a massive decline over the next 30 years, followed by a population bottleneck lasting until the year 2075. Survival of Leadbeater's possum during the bottleneck will depend on protection of refuge habitats, particularly patches of mature, multi-age and old-growth forest. Recovery after the bottleneck is expected to depend on the extent to which current silvicultural practices can be modified to guarantee recruitment of PNTs within timber production forests.

An interpretation of the tectonostratigraphic framework of the Murray Basin region of southeastern Australia, based on an examination of airborne magnetic patterns

New pixel map representations of regional total magnetic intensity data reveal previously unknown characteristics of the basement concealed beneath thin Cainozoic sediments of the Murray Basin in southeastern Australia. Interpretations of magnetic patterns in terms of structural features allow a revised interpretation of the nature of the tectonostratigraphic framework underlying and flanking the basin. The magnetic data indicate that arcuate or curvilinear structural trends under the Murray Basin do not conform with those of the exposed Lachlan Fold Belt to the east and suggest that the basement concealed beneath the basin, together with that exposed in the Victorian Highlands to the south, forms a distinct composite tectonostratigraphic terrane. Beneath the southwestern Murray Basin ?Proterozoic-Lower Cambrian metasediments of the Padthaway Ridge of the Kanmantoo Fold Belt display a northwesterly trending structural grain and a previously unsuspected continuity of structural trend with Adelaidean-Cambrian rocks of the Mount Lofty Ranges to the west. In the south, Cambrian volcanics of the Black Range and Stavely greenstone belts have similar magnetic response and appear to be components of a single elongate and strongly magnetic domain which extends to the northwest for at least 400 km (Stavely Belt). To the north a similar but entirely concealed northeasterly trending magnetic domain can also be interpreted as volcanics (Lake Wintlow Belt). Together these two magnetic domains appear to form an arcuate zone of volcanics, with a concave-to-the-east configuration, located at a possible suture between the Lachlan and Kanmantoo Fold Belts beneath the western Murray Basin. In the south the magnetic imagery indicates that metasediments of the ?Cambro-Ordovician Stawell Belt produce magnetic patterns distinct from those produced by the metasediments of the adjacent Ordovician Bendigo Belt, which can itself be subdivided into a number of areas of distinct magnetic pattern. Magnetic domains can be interpreted in terms of concealed Proterozoic and Palaeozoic structural belts and tectonostratigraphic terranes. Reconstructions suggest that much of the Murray Basin may be underlain by a former microcontinental block or rifted marginal plateau of Precambrian crust, now welded to the Precambrian craton to the west. Deformation of the Kanmantoo and Adelaide Fold Belts adjacent to and beneath the western and southwestern margins of the basin, can be attributed to Late Cambrian-Early Ordovician convergence between the microcontinental block and the craton. Volcanics of the arcuate Stavely and Lake Wintlow Belts are interpreted to be located at the suture between the microcontinental block and the craton. In addition, the presence of concave-to-the-east, curvilinear magnetic trends in the Cambro-Ordovician metasedimentary belts beneath the Murray Basin suggests that these successions, as well as the volcanics of the Heathcote and Mount Wellington Belts, may form allochthonous sheets. These were possibly emplaced from the east during Late Ordovician-Devonian deformation, possibly related to convergence of a further microcontinental block underlying the adjacent Lachlan Fold Belt to the east of the Murray Basin.

A short pollen diagram from rainforest in highland eastern Victoria

Pollen data from the Rooty Breaks swamp – a Sphagnum bog surrounded by Atherosperma-Elaeocarpus rainforest – in the eastern Victorian highlands appears to reflect changes in the mode of pollen and spore deposition at the study site, from the time sediments began accumulating at about 5500 BP until the present day. In the lower half of the deposit, pollen of rainforest taxa is more common than it is in the top half, while Eucalyptus pollen reflects the reverse situation. Although the pollen changes may reflect climatic change it is suggested that most of the pollen and spores in the lower sediment were stream-borne. Later the stream moved away from the site and the records became more representative of atmospheric pollenrain. Throughout the period covered by the pollen diagram the Rooty Breaks swamp itself was dominated by Leptospermum grandifolium. The pollen record shows that the association of important taxa in rainforests of the highlands of eastern Victoria was established by at least 5500 BP. The presence of sparse old eucalypts throughout the area dominated by rainforest suggests that sclerophyll forest was replaced by rainforest in the recent past. However, this change is not evidenced in the pollen diagram.