4051 research outputs found
Sort by
The influence of groundwater/surface water exchange on stable isotopic signatures along the Darling River, NSW, Australia
No full textStable water isotopes (SWIs) have been analysed in surface waters collected from the Barwon-Darling River over the past five years (2002 to 2007). Run-of-River sampling results were compared with temporal SWI data from three gauging stations located along the river. Darling River surface water samples are generally enriched in heavy isotopes due to evaporation. Partitioning of distinctly labelled isotopic waters such as enriched surface waters and depleted groundwaters allowed for the identification of groundwater/surface water exchange. Preliminary results showed that large flood events recharge the shallow aquifer with fresh-enriched waters and during low flow conditions, saline-deleted groundwaters rebound towards the river. Consequently, during drought periods saline groundwaters discharge into the river system. The flux of saline groundwaters into the surface water system was found to not only increase the salinity of scarce fresh water supplies but also create the desired environmental conditions for cyanobacteria blooms in the Darling River
A post-wildfire response in cave dripwater chemistry
Get PDFSurface disturbances above a cave have the potential to impact cave dripwater discharge, isotopic composition and solute concentrations, which may subsequently be recorded in the stalagmites forming from these dripwaters. One such disturbance is wildfire; however, the effects of wildfire on cave chemistry and hydrology remains poorly understood. Using dripwater data monitored at two sites in a shallow cave, beneath a forest, in southwest Australia, we provide one of the first cave monitoring studies conducted in a post-fire regime, which seeks to identify the effects of wildfire and post-fire vegetation dynamics on dripwater δ18O composition and solute concentrations. We compare our post-wildfire δ18O data with predicted dripwater δ18O using a forward model based on measured hydro-climatic influences alone. This helps to delineate hydro-climatic and fire-related influences on δ18O. Further we also compare our data with both data from Golgotha Cave – which is in a similar environment but was not influenced by this particular fire – as well as regional groundwater chemistry, in an attempt to determine the extent to which wildfire affects dripwater chemistry. We find in our forested shallow cave that δ18O is higher after the fire relative to modelled δ18O. We attribute this to increased evaporation due to reduced albedo and canopy cover. The solute response post-fire varied between the two drip sites: at Site 1a, which had a large tree above it that was lost in the fire, we see a response reflecting both a reduction in tree water use and a removal of nutrients (Cl, Mg, Sr, and Ca) from the surface and subsurface. Solutes such as SO4 and K maintain high concentrations, due to the abundance of above-ground ash. At Site 2a, which was covered by lower–middle storey vegetation, we see a solute response reflecting evaporative concentration of all studied ions (Cl, Ca, Mg, Sr, SO4, and K) similar to the trend in δ18O for this drip site. We open a new avenue for speleothem science in fire-prone regions, focusing on the geochemical records of speleothems as potential palaeo-fire archives. © Author(s) 2016
Abatement of xenon and iodine emissions from medical isotope production facilities
No full textNot available
Unsaturated zone hydrology and implications for paleo-climate speleothem reconstructions
No full textSpeleothem growth relies on the supply of water which percolates from the surface,
through the unsaturated zone and discharges into cavernous voids. The flow path of
water feeding individual speleothems varies considerably depending on the karst
architecture e.g. micro-fractures, solution pipes, structural voids in the karst, storage
reservoirs, etc., all of which may alter the composition of drip waters over the flow
route. By monitoring drip waters, we can determine: 1) unsaturated zone flow
regimes; 2) connectivity between the surface and cave discharge zone; and 3)
thresholds for groundwater recharge. This information can be used to identify suitable
speleothems in caves for reconstruction of past climatic and hydrologic variability, at
least over the last few thousand years of similar mean climate state.
High-frequency, spatially-dense monitoring was conducted in Harrie Wood Cave,
Yarrangobilly, Snowy Mountains over a 15 month period to characterise the flow
regimes at 14 sites along a depth profile within the cave. Sites were monitored using
acoustic drip loggers (stalagmates®). Discharge rates and response to significant
rainfall events were highly variable between sites. A moderate relationship was found
between decreasing discharge rates and increasing depth (r2 = 0.40). We suggest
unsaturated zone storage and mixing, unrelated to depth, also have a significant
impact on flow regimes. Using a statistical approach, five different drip types, which
often had no spatial commonality, were identified. This information was used to
inform the choice of speleothems for paleo-climate reconstruction, using stalagmites
with differing hydrological regimes feeding growth, of which the preliminary data
18
will be presented here. The study highlights the need to understand unsaturated zone
hydrology at the individual drip discharge level, prior to any speleothem study for
paleo-climate, to truly appreciate the drip water signal it is recording. Copyright (C) The Authors
Not just salt - the 11 March 2011 Tohoku-oki Tsunami and the significance of geochemical proxies
No full textResearchers most often rely on the extent of sandy deposits to assess the magnitude and extent of palaeotsunamis, assuming that the landward limit of the deposit approximates the maximum runup of the tsunami. While it has been reported in many modern examples, it is not always the case. One such example is the 11 March 2011 Tohoku-oki tsunami, which inundated c. 4.5 km inland in the Sendai plain. However, a recognisable (>0.5 cm thick) sand deposit was recorded only up to c. 2.8 km inland (~ 62% of the inundation distance). Further inland, the deposit was dominated by mud containing at least a one-grain thick sand lamina up to the inundation limit. Therefore, relying on the extent of sandy deposits may lead to a gross underestimate of the generating event, and extent of tsunami inundation. The magnitude of the 869AD Jogan earthquake, which was based on the extent of the sandy deposits reported in the Sendai Plain, was estimated at ~8.4. Data acquired after the Tohoku-oki tsunami suggest it was an underestimate. Then the question arises - how will one be able to distinguish mud deposited by a tsunami from terrestrial mud and soil? Geochemical markers might provide the answer. We reported brackish and saline ponded water up to 2.6 km inland, despite >60 mm of precipitation in the two months since the tsunami, and we also observed salt crusts on numerous paddy fields up to the limit of tsunami inundation, where the water had evaporated. Elevated concentrations of chloride (salt), sulphate, magnesium, calcium and other associated elements were measured not only in mud deposits, but also in sandy deposits, where seawater had stagnated and then evaporated. The preservation of the marine geochemical signature (mostly salt but also sulphur) is problematic in sandy deposits, mainly due to leaching and post-depositional diagenetic processes. On the other hand, it has been proven in organic-rich sediments, such as mud, and has been used as an additional proxy to identify palaeotsunami deposits. Other geochemical markers, which are specific to each source area, can also be used. Geochemical markers could be used in conjunction with other proxies, such as microfossil data (e.g. marine diatoms), which have also been found to occur beyond the limit of recognisable tsunami deposits. They can provide the clues to identify the maximum inundation limit of palaeotsunamis that extends beyond the limit of the recognisable sandy deposits. The marine geochemical signature of the 2011 Tohoku-oki tsunami was found up to the limit of tsunami inundation near the Tobu Highway, and even beyond, where the waves reached through the underpasses. As geochemical markers show a good preservation potential in fine-grained and organic-rich sediments, we could use them to estimate the inundation distance of the Jogan tsunami beyond the preserved sand layer. © American Geophysical Unio
Reinterpretation of megatsunami inundation in Southeast Australia and the implications for palaeotsunami identification
No full textThe 2004 Indian Ocean tsunami resulted in a marked increase in concern regarding regions previously considered low risk of tsunami inundation. The southeast coast of Australia has a record suggesting low tsunami risk, with only 47 small tsunamis striking since European arrival. However, the controversial megatsunami hypothesis suggests patterns of massive inundation of the east Australian coast. Given the extreme vulnerability of the NSW coastline due to population concentration and the reliance on boulder deposit evidence, there is a need to provide thorough re-evaluation of the Australian tsunami risk. This re-examination has led to research at four back-beach locations on the south coast of New South Wales, located close to sites reported to contain evidence of megatsunami inundation. Analysis of stratigraphy, sediments, geochemistry and microfossils, plus an extensive radiocarbon chronology of these sites allows for a full reconstruction of the Holocene environments. This success highlights the importance of using multi-proxy diagnostic techniques in investigating potential tsunami inundation sites with relatively short historical records. In the case of NSW, no evidence of Holocene tsunamis has been identified, casting serious doubt on the existing understanding of tsunami risk on the NSW coast and the diagnostic criteria used for identifying tsunami deposits
Climatic variations over the last 4000 cal yr BP in the western margin of the Tarim Basin, Xinjiang, reconstructed from pollen data
No full textThe nature of Holocene climate patterns and mechanisms in central Asia are open areas of inquiry. In this study, regional vegetation and climate dynamics over the last ca. 4000 years are reconstructed using a high resolution pollen record from the Kashgar oasis, on the western margin of the Tarim Basin, central Asia. Ephedra, Chenopodiaceae and Cannabaceae dominate the pollen assemblages, and Chenopodiaceae/Ephedra ratios and percentages of long-distance transported pollen taxa are used to infer regional variations in moisture and vegetation density. Three periods of increased humidity are identified, from ca. 4000–2620 cal yr BP, ca. 1750–1260 cal yr BP and ca. 550–390 cal yr BP and these periods coincide with the respective Holocene Bond Events 2, 1 and 0, which are reported in the North Atlantic. Any increase in strength, or southward migration, of the mid-latitude westerlies would result in more precipitation and meltwater on mountains surrounding the study site. Warm and dry conditions are detected between ca.1260 and 840 cal yr BP (AD 690–1110), and cool and wet conditions are detected between ca. 840 and 680 cal yr BP (AD 1110–1270), during the Medieval Warm Period (ca. AD 800–1200). The climate variations in the Kashgar region over the last 4000 years appear to have been dominated by changes to the westerly circulation system and glacier dynamics on surrounding mountains. However, the question of whether the Asian monsoon delivers precipitation to the western Tarim Basin, a region that is influenced by several climate systems, is still open to debate. © 2012 Elsevier B.V
26Al/10Be dating of an aeolian dust mantle soil in western New South Wales, Australia
No full textAeolian dust mantle soils are an important element of many landscapes in south-eastern Australia, though the age of these aeolian deposits has not been radiometrically determined. At Fowlers Gap in western New South Wales, surface cobbles of silcrete and quartz overlie a stone-free, aeolian dust mantle soil, which has a thickness of about 1.6 m. The clay-rich aeolian dust deposit in turn lies upon a buried silcrete and quartz stone layer. Modelling in-situ cosmogenic 26Al and 10Be concentrations measured in both the surface quartz stones and in the buried quartz layer of rocks, reveals that each has experienced a complex exposure-burial history. Due to the absence of quartz stones or sand at intermediate depths, our cosmogenic 26Al and 10Be modelling was not able to determine a definitive mechanism of stone pavement formation and stone burial. Various scenarios of stone formation, transport, burial and exhumation were tested that constrain the age of the deposit to range from 0.9 ± 0.2 Ma to 1.8 ± 0.2 Ma, based largely on different assumptions taken for the time-dependency of the net sedimentation rate. This corresponds with the initiation of the Simpson Desert dune fields and the deflation of lakes in central Australia, which probably responded to the shift to longer-wavelength, larger-amplitude Quaternary glacial cycles at around 1 Ma. Sensitivity analyses were carried out to identify those parameters which better constrained model outputs. Within model errors, which largely are the result of analytical errors in measured 26Al and 10Be concentrations, all three competing theories of colluvial wash, upward displacement of stones, and cumulic pedogenesis are possible mechanisms for the formation of the surface stone pavement. © 2014 Elsevier B.V
‘Age’, recharge rates and connectivity of groundwater 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 δ
13C 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. © Geological Society of Australia In