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Hydrological characterization of cave drip waters in a porous limestone: Golgotha Cave, Western Australia
Get PDFCave drip water response to surface meteorological conditions is complex due to the heterogeneity of water movement in the karst unsaturated zone. Previous studies have focused on the monitoring of fractured rock limestones that have little or no primary porosity. In this study, we aim to further understand infiltration water hydrology in the Tamala Limestone of SW Australia, which is Quaternary aeolianite with primary porosity. We build on our previous studies of the Golgotha Cave system and utilize the existing spatial survey of 29 automated cave drip loggers and a lidar-based flow classification scheme, conducted in the two main chambers of this cave. We find that a daily sampling frequency at our cave site optimizes the capture of drip variability with the least possible sampling artifacts. With the optimum sampling frequency, most of the drip sites show persistent autocorrelation for at least a month, typically much longer, indicating ample storage of water feeding all stalactites investigated. Drip discharge histograms are highly variable, showing sometimes multimodal distributions. Histogram skewness is shown to relate to the wetter-than-average 2013 hydrological year and modality is affected by seasonality. The hydrological classification scheme with respect to mean discharge and the flow variation can distinguish between groundwater flow types in limestones with primary porosity, and the technique could be used to characterize different karst flow paths when high-frequency automated drip logger data are available. We observe little difference in the coefficient of variation (COV) between flow classification types, probably reflecting the ample storage due to the dominance of primary porosity at this cave site. Moreover, we do not find any relationship between drip variability and discharge within similar flow type. Finally, a combination of multidimensional scaling (MDS) and clustering by k means is used to classify similar drip types based on time series analysis. This clustering reveals four unique drip regimes which agree with previous flow type classification for this site. It highlights a spatial homogeneity in drip types in one cave chamber, and spatial heterogeneity in the other, which is in agreement with our understanding of cave chamber morphology and lithology. © Author(s) 201
Rainfall isotope (3H, δ2H and δ18O) input to groundwater in Australia
No full textThe stable isotopes of water, δ2H and δ18O, are conservative tracers available for studying mixing of water in the
hydrosphere. Radioactive tritium (2H, half-life = 12.3 years), derived from both cosmogenic and anthropogenic
sources (nuclear testing), is an important tracer for dating of young groundwater. Measurements of stable water
isotopes and tritium in Australian rainfall have been made monthly at six coastal sites and Alice Springs since 1962 as
part of the Global Network of Isotopes in Precipitation (GNIP).
Since 2006 this network has been expanded to include seven inland sites in New South Wales, Queensland, South
Australia and Western Australia (δ2H and δ18O analysed only). In addition, event-based studies of stable water
isotopes have been conducted at four locations in the Sydney region since 2005. These data have been analysed to
determine local meteoric water lines, weighted averages and to investigate the relationships between rainfall
isotopic composition, temperature and precipitation amount. Stable water isotopes are not completely conservative
as they undergo fractionation as a result of hydrological processes such as evaporation, precipitation, ice and snow
formation and melting, and geothermal activity. The fractionation can be used to understand the provenance and
history of groundwater and to define end members for mixing studies.
For age dating of groundwater using tritium the rainfall tritium composition is required. In addition to the 50-year
tritium record available from GNIP for six sites, data for an additional eleven locations throughout eastern Australia
were compiled for varying periods mainly between 1970 and 1991, thereby improving the spatial resolution of the
tritium time series in Australia. Unlike δ2H and δ18O, the spatial distribution and seasonal variation of tritium in
rainfall is largely controlled by the stratosphere to troposphere exchange of anthropogenic tritium from nuclear
testing, with the highest concentrations occurring at Adelaide and Melbourne during the early spring. Modern
concentrations appear to be stabilising with average annual concentrations in the range 1–3 TU increasing with
latitude. These data have also been used to estimate the tritium composition of rainfall resulting in the January 1974
Queensland floods, which are believed to have resulted in significant recharge to aquifers in Queensland and
northern NSW. © Geological Society of Australia In
Recharge rates and connectivity of grouwater in deeper aquifers of the Sydney Basin
No full textThe Permo-Triassic Sydney Basin covers almost 50 000 km2 and extends from the outer continental shelf inland to
the Great Diving Range, from Newcastle in the north to Batemans Bay in the south. Major lithological units broadly
include the Permian Coal Measures, the Permo-Triassic Narrabeen Group, the Triassic Hawkesbury Sandstone and
the Wianamatta Shale. The Hawkesbury Sandstone is generally made of very thick heavily compacted quartz sands,
with minor discontinuous shale units. Its aquifer system is a complex, dual porosity, deep fractured system with
three aquifers typically recognised. The shallow and intermediate aquifers contribute to spring and base stream
flows as well as groundwater dependent ecosystems, and the deep regional aquifer system. It is this deeper system
that is investigated in this study.
Groundwater from the Sydney Basin, and in particular Hawkesbury Sandstone aquifers, forms part of emergency
supply strategies for coping with future severe droughts, with >5 million people living in the region, in addition to
large industrial development. Despite the significance of these resources there are still large gaps in our knowledge
of these aquifers including aspects such as age recharge and mixing rates. Filling these knowledge gaps has become
even more critical in order to understand impacts of existing and planned coal and coal seam gas (CSG) mining of the
underlying Illawarra Coal Measures. Community concerns over risks associated with CSG extraction have reached
fever pitch in recent years, and there is public demand for research into these aquifers. Understanding of these
systems has been complicated by the poor quality of existing data – commonly relying solely on driller bore-logs,
reporting only being carried out for specific mine or extraction activities, and therefore conducted over localised
zones, and the lack of communication between companies and agencies with data. Additionally, large variations in
hydraulic properties have been noted over localised areas.
This study sampled bores along a loosely east–west transect across urban Sydney, targeting the deeper Hawkesbury
Sandstone and Narrabeen group aquifers. Very high salinities are recorded by several samples, interpreted to relate
to the influence of the overlying Wianamatta Group and Cumberland Basin sediments in those locations. Equally
however, this signal may record the impact of interaction with coal seams. Results also show inconsistencies
between tritium and radiocarbon groundwater ‘ages’ in multiple locations, suggesting that extensive mixing occurs
between aquifers. A relationship between bicarbonate, depth and δ13C isotopic ratios highlights the influence of
methanogenesis for deeper samples and either interaction with localised organic matter or deeper inputs derived
from the coal measures. These findings have implications for potential coals seam gas extraction in the region,
demonstrating that impacts could be significant in areas of high fracturing and connectivity. This supports previous
assessments of groundwater vulnerability and the need for further detailed research
Radiotracer methods for understanding contaminant dynamics in aquatic environments
No full textRadioactive tracers have a distinct advantage in tracing contaminant migration in natural systems and characterizing contaminant mobility and uptake into living organisms in already-contaminated environments or at trace (environmental) levels. To use the contaminant itself in its non-radioactive form, concentrations significantly higher than the normal contaminated background level are commonly required which may be undesirable from a
toxicological, chemical or regulatory perspective by impacting on the very processes under study. In contrast, radioactive forms of the contaminant can often be more easily measured
(often in situ or non-destructively) and imaged at trace levels (using autoradiography), and usually have the advantage of a short half-life to remove residual contaminant. As such
radiotracers have a valuable role to play in contaminant dynamics studies from the lab
scale to the field. In the lab, radiotracers are well established in studies of contaminant kinetics and bio-distribution in living organisms, in interactions with non-living natural environments, e.g., sorption to soils and sediment, rocks and organics matter, and in tracing contaminant flow pathways and rates.
Radioisotopes of heavy metal contaminants (e.g., Cd, As, Se, Zn, Pb, Hg), nutrients (P, C) and the shorter-lived isotopes of longer lived radioactive contaminants such as Cs and Sr are commonly used in environmental contaminant studies. Recently, there is increasing interest and benefit in using radiotracer versions of emerging environmental contaminants such as persistent organic compounds or nanoparticles.
While most radiotracer work is conducted in laboratories, this approach can be up-scaled
to field environments. There are obvious scientific benefits of conducting studies in situ, where the tracer interacts with the complex natural environment rather than an artificially simplified laboratory representation. However there are few examples where this has been done. Since the first field scale uses of radiotracer in the mid-1950s, the majority of field scale radiotracer applications have been in the nexus between industry and environment sediment transport in harbours and dams, effluent dispersion from outfalls and in mining and oil extraction. Exceptions include whole ecosystem studies in the Canadian Experimental Lakes in the 1970s, heavy metals downstream of a uranium mine in Kakadu NP in Australia,
and studies demonstrating the retardation of metals and nutrients in studies in Sweden.
Increasingly public and regulatory concern about the potential impact and perception of
radiotracing in field environments has made these methods appear largely inaccessible to
the research community. However, the introduction of new biota dose modelling tools and guidelines over the past two decades has provided improved evaluation of the environmental impact of radiotracer releases to the environment and ensure and demonstrate their safe use
99mTc vs Rhodamine WT for tracing coastal hydrodynamics
No full textRhodamine WT is a tracer commonly used to quantitatively and visibly trace currents and contaminant plumes. Radioactive tracer 99mTc can also be used for these applications. Both of these tracers were injected simultaneously in a study of currents in a nearshore area of Darwin Harbour, Australia. Five subsurface drifters were released at one minute intervals during the tracer releases as an additional method of determining dispersive processes. Aerial photography was used to observe the Rhodamine WT plume. These methodologies provided data on dispersion and advection for calibration of a 2D hydrodynamic model of the harbour, which was in turn used to design the extension of a sewage outfall.
Using this case study we contrast and compare the independent analysis of the two tracer methods. Some differences in the initial tracer plume are expected due to different deployment methods. Differences in detection systems may lead to time lags between datasets. The methods used to quantify tracer concentration will also be discussed. Once these technical aspects are accounted for it should be possible to directly compare the behaviour of the two tracers and their suitability for determining dispersion. Logistical aspects relating to tracer availability, detection systems, human safety, environmental impact and cost will also be addressed. Unexpected regulatory obstacles existed for Rhodamine WT – a tracer specifically designed for surface water and 99mTc was the favoured tracer out of the two for regulators in the Northern Territory of Australia on the basis of environmental impact
The potential of 14CO in glacial ice as a tracer for past cosmic ray flux and atmospheric hydroxyl radical abundance
No full textThe amount of 14C-containing carbon monoxide (14CO) in glacial ice is determined by
trapping of atmospheric 14CO into air bubbles in the ice and in situ cosmogenic production
of 14CO in relatively shallow ice and firn. Earlier studies of 14CO in ice cores showed large
disagreements with regard to rates of in situ cosmogenic production as well as with regard
to whether 14CO produced in the firn layer is well retained or largely escapes to the
atmosphere via the interconnected pore space. We have reviewed previously published work
that included 14CO measurements in ice or firn air, and compared with our more recent
high-precision measurements on very large ice and firn samples. The available evidence
suggests that very little in situ cosmogenic 14CO is retained in the diffusive part of the firn
(the upper ≈ 40 – 100m). In situ cosmogenic 14CO production rates below the firn diffusive
zone are non-negligible, with production due to deeper-penetrating muons. At sites with low
snow accumulation rates, the in situ cosmogenic 14CO component is expected to be larger
than the trapped atmospheric component. This potentially allows to use ice core 14CO
measurements from such sites to improve our understanding of past cosmic ray flux
variations. In contrast, at sites with very high accumulation rates, trapped atmospheric 14CO
is expected to be dominant over the in situ cosmogenic component. This potentially allows
14CO records from such sites to be used for reconstructions of past atmospheric hydroxyl
radical (OH) variations
Late quaternary environmental change at Lake McKenzie, Southeast Queensland: evidence from microfossils, biomarkers and stable isotope analysis
No full textUnravelling links between climate change and vegetation response during the
Quaternary is a research priority, and needed if the climate-environment interactions of
modern systems are to be fully understood. Using a sediment core from Lake McKenzie,
Fraser Island, we reconstruct changes in the lake ecosystem and surrounding vegetation over
the last ca. 36.9 cal kyr BP. Evidence is drawn from multiple sources, including pollen,
micro-charcoal, biomarker and stable isotope (C and N) analyses, and is used to improve
understanding about the timing and spatial scale of past changes that have occurred locally
and in the southeast Queensland region. The glacial period of the record, from ca. 36.9-18.3
cal kyr BP, is characterised by lower lake water levels and increased abundance of, or closer
proximity to, plants of the aquatic and littoral zone. High abundance of biomarkers and
microfossils of the colonial green alga Botryococcus occur at this time and include high
variation in individual botryococcene
13C values. A distinct period of dry or ephemeral
conditions at the site is detected during deglaciation, causing a hiatus in the sedimentary
record covering the time period from ca. 18.3-14.0 cal kyr BP. The recommencement of
sediment accumulation around 14.0 cal kyr BP occurs with evidence of lower fire activity in
the area and reduced abundance of terrestrial herbs in the surrounding sclerophyll vegetation.
The Lake McKenzie record conforms to existing records from Fraser Island by containing
evidence for a mid-Holocene dry period, spanning the time period from ca. 6.1-2.5 cal kyr
BP. © The Author
Vertical radon-222 profiles in the atmospheric boundary layer
No full textRadon-222 (radon) is a naturally occurring radioactive tracer of air mass transport on different time and space scales. In particular, the vertical distribution of radon has been demonstrated to
be useful for characterisation of exchange and mixing processes within the atmospheric boundary layer.
In 2006 we started a program of research, using radon-222 to advance our understanding of these processes as part of a broader goal to improve parameterisation schemes for vertical
mixing in the lower atmosphere. Two types of experiments have been conducted. The first is based on continuous hourly estimates of radon-222 concentration gradients at two meteorological towers, one focussing on near-surface gradients (2-50m) recorded on a 50m tower at Lucas Heights in New South Wales (34.05ºS, 150.98ºE), and the other on boundary
layer gradients (20-200 m) measured on a 213m tower at the Cabauw Experimental Site for Atmospheric Research in the Netherlands (51.971ºN, 4.927ºE). The second experiment type relies on the collection of high resolution radon-222 vertical profiles up to 4,000 m above
ground level using radon samplers mounted on an instrumented motorised research glider.
In this presentation, we discuss selected results from a unique set of high resolution vertical radon profiles measured in 2007-2010 in clear and cloudy daytime terrestrial boundary layers
over rural New South Wales. The profile examples reveal the characteristic structure and variability of three major types of daytime boundary layer: 1) dry convective boundary layers,
2) mixed layers topped with residual layers, and 3) convective boundary layers topped with coupled non-precipitating clouds. We demonstrate that important boundary layer processes are
identifiable in the observed radon profiles, including ‘‘top down’’ mixing associated with entrainment in clear-sky cases and strongly enhanced venting and sub-cloud layer mixing when
substantial active cumulus are present.
A related presentation (Chambers et al. 2011) outlines some recent results based on our radon gradient measurements at the Lucas Heights tower. © 2011 CSIRO and the Bureau of Meteorology
Actinides isotopic analysis using a 1 MV AMS system
No full textThe VEGA 1 MV AMS system at ANSTO has been custom-designed to cover analysis
of a wide range of long-lived radioisotopes, including routine radiocarbon analysis and
multiple-isotope analysis of actinides. The system incorporates 1.0 m radius injection
and analysing magnets with o -axis cups on high and low mass sides. Following the
analysing magnet, rare isotope beams pass through a 1m radius spherical electrostatic
analyser and a 120 1 m radius magnet. The detector station consists of a two-anode gas
detector, with o -axis options to direct isotopes to either a Faraday cup or an electron
multiplier ion counter. All three analysing magnets are fitted with electrostatic bouncer
systems. At the LE end, the bouncer works in the usual way for all isotope combinations
of interest, including 12C-13C-14C and actinides. The HE bouncers are used to transmit a range of masses of interest for actinides analysis, for example mass 239 to 244 Pu isotopes.
For uranium analysis, the less rare isotopes can be directed to o axis cups or
the ion counter. Software has been implemented to enable a high degree of exibility in
analysing up to 8 isotopes at a time. In this paper we present details of the system and
its performance and applications. © The Author
Erosion and the sediment conveyor in central Australia
Get PDFWhy are the Neogene sedimentary fills across central Australia generally thin and discontinuous?
One long-standing explanation is that sluggish tectonism and intensified aridity have combined to
suppress rates of erosion and sediment production yielding a landscape crowded with inherited, preMiocene forms. Quantifying rates of sediment production, residence time and transport is possible
with numerous methods, but the recent growth of cosmogenic nuclide (CN) analysis has provided
unprecedented quantitative insights to rates of landscape evolution. Measurements of in situ
produced cosmogenic 10Be and 26Al integrate rates of surface processes over million-year
timescales—the last part of the Neogene in which aridity has strengthened across the continental
interior. We present a compilation of ~600 published and unpublished 10Be and 26Al measurements
from central Australia with a focus on the Neogene Eyre Basin and its periphery.
Outlying and inlying bedrock uplands serve as engines of sediment production via erosion of bedrock.
Surrounding the bedrock outcrops are vast sediment conveyors of varying efficiency and tempo:
hillslopes, pediments, and alluvial fans are interim storage/burial zones for sediment in transit to the
network of low-gradient rivers, dunes, and playas towards base level. Interactions between fluvial and
aeolian processes are especially pertinent to sediment flux in the Eyre Basin. Major rivers such as the
Cooper and Finke traverse dunefields in their lower reaches where quantities of alluvia are
recirculated into dunes and vice versa. Tracking the trajectories of sediment from source-to-sink
(including aeolian recirculation) remains a major challenge, but is central to unravelling the
sedimentary dynamics of central Australia's Neogene basins. Based on the CN compilation we
estimate 1) spatially averaged erosion rates at the scale of a hillslope or river catchment; 2) pointbased erosion rates on bedrock surfaces; 3) residence time of sediment in hillslope regolith and
alluvial fans; and 4) cumulative burial history of sediments in transit.
Catchment-scale erosion rates (n~100) are consistently low (<10 m/Myr) and include some of the
lowest rates ever measured (~0.3 m/Myr); however, a small group of catchments in the Flinders Ras
yield higher erosion rates (~30–60 m/Myr). Bedrock hillslopes (n~200) tend to erode even slower (<5
m/Myr), with a subset of Flinders Ras sites again being the exception (~10–30 m/Myr) and suggesting
the influence of recent tectonism. Several CN depth-profiles measured on hillslopes and alluvial fans
indicate sediment residence times >0.5 Myr, and high-resolution sampling along three hillslopes with
differing morphology (linear, convex, and concave) reveals major variations in sediment production
and transport rates that hint at the long-term evolution. In the rivers, fluvial sediments show a weak
tendency to increase cumulative burial history downstream (1–2 Myr), consistent with the expanding
accommodation space for storage and burial. Dune sediments sampled in the Simpson and Tirari
dunefields (n~16) contain cumulative burial histories (up to 1.5 Myr) similar to that of the intersecting
rivers. This points to an intimate mix of fluvial and aeolian processes in areas approaching base level.
Curiously, these sediments occur in the lowest part of the continent and contain the longest histories
of cumulative burial, yet do not form part of the thickest sedimentary fills in the Eyre Basin