Browsing by Author "Zawadzki, A"
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- Item12th South Pacific Environmental Radioactivity Association Conference (SPERA 2012)(Australian Nuclear Science and Technology Organisation, 2012-10-16) Heijnis, H; Payne, TE; Lickiss, J; Bruhn, F; Zettinig, M; Zawadzki, A; Hoffmann, EL; Child, DPWelcome to the 12th South Pacific Radioactivity Association Conference, welcome back in Sydney. The conference will be hosted by the Australian Institute for Nuclear Science and Engineering and the Australian Nuclear Science and Technology Organisation. The program for the 12th SPERA conference is very exciting, with key-note speakers setting the scene for a diverse range of sessions. The conference will conclude by offering the participants a tour of ANSTO’s new facilities. We would like to thank Jorden Lickiss for her tireless efforts in conference management. We also like to thank our sponsors AINSE, ANSTO and Nucletron for their financial support. We look forward to your participation and a successful conference.
- ItemA 7300 year record of environmental changes in a coastal wetland (Moawhitu), New Zealand, and evidence for catastrophic overwash (tsunami?)(Elsevier, 2020-09) Chagué, C; Cope, J; Kilroy, C; Jacobsen, GE; Zawadzki, A; Wong, HKYThree sedimentary sequences from a coastal wetland behind a sand barrier, on the west coast of d'Urville Island, New Zealand, were examined using a multi-proxy approach, including sedimentological, geochemical and microfossil (diatom) analyses, with the chronology established using radiocarbon and 210Pb dating. Data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in Moawhitu. This was followed by periods of alternating wetland encroachment and open water, displaying spatial variations, until a peatland was established about 1300 cal. yr BP. The wetland was then partially drained in the early 1900s, leading to compaction of the peat near the surface. A coarse layer containing gravel, sand and shells, with a sharp lower contact, in the northern area of the wetland, is attributed to an overwash about 2500–3000 yr BP, most probably a tsunami generated by the rupture of a local or regional fault. The high-resolution continuous record obtained with XRF core scanning revealed a geochemical signature (Ca and S) for the overwash 600 m inland in the middle area of the wetland, while it was absent from the southern site 1.1 km from the shore. This suggests that, except at the northern end of Moawhitu, the sand dune acted as an effective barrier preventing any sediment from overtopping 2500–3000 yr BP, with only a geochemical evidence marking the extent of seawater inundation. No sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in Moawhitu, as recounted in Māori oral tradition (pūrākau), although pebbles at the surface of the dune are likely to be linked to this event. Thus, the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century. However, our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years. It also shows that a high-resolution continuous XRF record can provide the evidence for short-term changes (catastrophic or not) that did not leave any clear sedimentological signature, thus providing a better insight of environmental changes in any depositional environment. © 2020 Elsevier B.V
- ItemAnalysis of uranium, thorium and radium radioisotopes in coal seam gas associated water samples(South Pacific Environmental Radioactivity Association, 2018-11-06) Maizma, S; Chellappa, J; Zawadzki, A; Apte, S; King, J; Jarolimek, C; Angel, BMThe Australian coal seam gas (CSG) industry, located mainly in eastern Australia, has grown significantly over the last decade and is now a significant contributor to natural gas production in Australia. CS6 extraction involves drilling boreholes across landscapes which intersect with coal seams. Gas is then flowed to the surface along with associated produced waters. In order to increase gas production, some wells are subjected to hydraulic fracturing which involves pumping water, chemicals and a proppant into the coal seams. The resulting flow-back waters are then collected at the surface prior to treatment and disposal. There are significant public concerns about the water quality of flow-back and produced waters associated with CSG operations, in particular the concentration of geogenic contaminants including radioisotopes such as 226Ra and 222Ra. In order to address these concerns, accurate data on water quality needs to be collected. CSG waste waters are complex, saline matrices and sensitive, robust analytical methods are required to reliably quantify the concentrations of contaminants including radioisotopes ln this work, radioisotopes of uranium, thorium and radium were analysed in CSG flow-back and produced waters samples collected from CSG bores located in Central Queensland, Australia. The water samples were processed for the determination of 233U, 238U, 228Th, 230Th, 232Th, 226Ra activity concentrations by alpha-particle spectrometry and 222Ra by gamma-ray spectrometry. GSG associated water consist of high concentrations of total dissolved solids (TDS) ranging from 800 to 10,000 mg/L. Such high salinity levels pose difficulties for the measurement of the radioisotopes of interest, resulting in low sample recoveries and poor resolution alpha spectra. This paper presents radiochemical techniques used to reduce the complex sample matrix effects in analysing CSG associated water samples. Manganese dioxide co-precipitation technique was chosen to concentrate the elements of interest, followed by the isolation of uranium and thorium using UTEVA (Eichrom) resin. The determination of 222Ra by alpha spectrometry was found to be challenging due to low sample recoveries and poor alpha spectra resolutions. This was overcome by diluting the samples in large volumes prior to lead sulphate co-precipitation, which isolates radium and barium from other metals in the samples. The developed radiochemical technique was suitable and robust for determining the radioisotopes of interest in CSG associated water samples.
- ItemAnthropogenic acceleration of sediment accretion in lowland floodplain wetlands, Murray–Darling Basin, Australia(Elsevier, 2009-07-01) Gell, PA; Fluin, J; Tibby, J; Hancock, G; Harrison, JJ; Zawadzki, A; Haynes, D; Khanum, SI; Little, F; Walsh, BOver the last decade there has been a deliberate focus on the application of paleolimnological research to address issues of sediment flux and water quality change in the wetlands of the Murray–Darling Basin of Australia. This paper reports on the research outcomes on cores collected from sixteen wetlands along the Murrumbidgee–Murray River continuum. In all sixteen wetlands radiometric techniques and exotic pollen biomarkers were used to establish sedimentation rates from the collected cores. Fossil diatom assemblages were used to identify water source and quality changes to the wetlands. The sedimentation rates of all wetlands accelerated after European settlement, as little as two-fold, and as much as eighty times the mean rate through the Late Holocene. Some wetlands completely infilled through the Holocene, while others have rapidly progressed towards a terrestrial state due to accelerated accretion rates. Increasing wetland salinity and turbidity commenced within decades of settlement, contributing to sediment inputs. The sedimentation rate was observed to slow after river regulation in one wetland, but has accelerated recently in others. The complex history of flooding and drying, and wetland salinisation and eutrophication, influence the reliability of models used to establish recent, fine-resolution chronologies with confidence and the capacity to attribute causes to documented effects. © 2009 Elsevier B.V
- ItemAtmospheric pollutants in alpine peat bogs record a detailed chronology of industrial and agricultural development on the Australian continent(Elsevier, 2010-05-01) Marx, SK; Kamber, BS; McGowan, HA; Zawadzki, ATwo peat bogs from remote alpine sites in Australia were found to contain detailed and coherent histories of atmospheric metal pollution for Pb, Zn, Cu, Mo, Ag, As, Cd, Sb, Zn, In, Cr, Ni, Tl and V. Dramatic increases in metal deposition in the post-1850 AD portion of the cores coincide with the onset of mining in Australia. Using both Pb isotopes and metals, pollutants were ascribed to the main atmospheric pollution emitting sources in Australia, namely mining and smelting, coal combustion and agriculture. Results imply mining and metal production are the major source of atmospheric metal pollution, although coal combustion may account for up to 30% of metal pollutants. A novel finding of this study is the increase in the otherwise near-constant Y/Ho ratio after 1900 AD. We link this change to widespread and increased application of marine phosphate fertiliser in Australia's main agricultural area (the Murray Darling Basin). Detailed records of atmospheric metal pollution accumulation in Australia are presented and are shown to trace the industrial and agricultural development of the continent. © 2010, Elsevier Ltd.
- ItemBlooms of cyanobacteria in a temperate Australian lagoon system post and prior to European settlement(European Geosciences Union, 2016-06-22) Cook, PLM; Jennings, M; Holland, DP; Beardall, J; Briles, C; Zawadzki, A; Doan, P; Mills, K; Gell, PABlooms of noxious N2 fixing cyanobacteria such as Nodularia spumigena are a recurring problem in some estuaries; however, the historic occurrence of such blooms in unclear in many cases. Here we report the results of a palaeoecological study on a temperate Australian lagoon system (the Gippsland Lakes) where we used stable isotopes and pigment biomarkers in dated cores as proxies for eutrophication and blooms of cyanobacteria. Pigment proxies show a clear signal, with an increase in cyanobacterial pigments (echinenone, canthaxanthin and zeaxanthin) in the period coinciding with recent blooms. Another excursion in these proxies was observed prior to the opening of an artificial entrance to the lakes in 1889, which markedly increased the salinity of the Gippsland Lakes. A coincident increase in the sediment organic-carbon content in the period prior to the opening of the artificial entrance suggests that the bottom waters of the lakes were more stratified and hypoxic, which would have led to an increase in the recycling of phosphorus. After the opening of the artificial entrance, there was a ˜ 60-year period with low values for the cyanobacterial proxies as well as a low sediment organic-carbon content suggesting a period of low bloom activity associated with the increased salinity of the lakes. During the 1940s, the current period of re-eutrophication commenced, as indicated by a steadily increasing sediment organic-carbon content and cyanobacterial pigments. We suggest that increasing nitrogen inputs from the catchment led to the return of hypoxia and increased phosphorus release from the sediment, which drove the re-emergence of cyanobacterial blooms. © Author(s) 2016.
- ItemCentennial-scale trends in the Southern Annular Mode revealed by hemisphere-wide fire and hydroclimatic trends over the past 2400 years(Geological Society of America, 2018-02-15) Fletcher, MS; Benson, B; Bowman, DMJS; Gadd, PS; Heijnis, H; Mariani, M; Saunders, KM; Wolfe, BB; Zawadzki, AMillennial-scale latitudinal shifts in the southern westerly winds (SWW) drive changes in Southern Ocean upwelling, leading to changes in atmospheric CO2 levels, thereby affecting the global climate and carbon cycle. Our aim here is to understand whether century-scale shifts in the SWW also drive changes in atmospheric CO2 content. We report new multiproxy lake sediment data from southwest Tasmania, Australia, that show centennial-scale changes in vegetation and fire activity over the past 2400 yr. We compare our results with existing data from southern South America and reveal synchronous and in-phase centennial-scale trends in vegetation and fire activity between southwest Tasmania and southern South America over the past 2400 yr. Interannual to centennial-scale rainfall anomalies and fire activity in both these regions are significantly correlated with shifts in the SWW associated with the Southern Annular Mode (SAM; atmospheric variability of the Southern Hemisphere). Thus, we interpret the centennial-scale trends we have identified as reflecting century-scale SAM-like shifts in the SWW over the past 2400 yr. We identify covariance between our inferred century-scale shifts in the SWW and Antarctic ice core CO2 values, demonstrating that the SWW-CO2 relationship operating at a millennial scale also operates at a centennial scale through the past 2400 yr. Our results indicate a possible westerly-driven modulation of recent increases in global atmospheric CO2 content that could potentially exacerbate current greenhouse gas–related warming. © 2021 Geological Society of America
- ItemChanges in hydrology and carbon cycling following Late Holocene deforestation in a New Zealand lake catchment(European Geosciences Union (EGU), 2018-04-13) Woodward, CA; Hua, Q; Tyler, JJ; Meredith, KT; Moss, PT; Gadd, PS; Zawadzki, ANew Zealand was one of the last major land masses to be impacted by humans, with two waves of settlement occurring in the last 800 years. Polynesian (Maori) settlers arrived in New Zealand ca. 1250 A.D., while major European settlement occurred after 1840 A.D. A major impact of both phases of settlement was clearance of indigenous forest. An increasing number of pollen and macroscopic charcoal records reveal the timing and extent of past forest clearance in New Zealand. Only a few records explore the wider implications of this land use change in terms of catchment biogeochemical cycles and aquatic ecosystem functioning. We used multiple proxies from a lake sediment core from a cleared catchment to explore changes in catchment hydrology and carbon cycling after forest clearance. One of the most interesting findings emerged from paired radiocarbon dates on terrestrial targets (e.g. leaves and charcoal) and seeds from the aquatic plant Myriophyllum. The offset between terrestrial and aquatic radiocarbon ages increased to 1000 years and then decreased to 100 years within three centuries of local Maori forest clearance. There was a further increase in the radiocarbon age offset to 1500 radiocarbon years within decades of the start of the European forest clearance. We argue that the offset between terrestrial and aquatic radiocarbon ages results from an increased contribution of old dissolved inorganic carbon from groundwater to the lake after forest clearance. Forest clearance reduced evapotranspiration, increased aquifer recharge and increased the contribution of groundwater to the lake. This interpretation is supported by a major increase in the δ 13C of Myriophyllum seeds following Maori deforestation. At the time of abstract submission the results are pending for δ 18O analysis on Myriophyllum seeds and aquatic insects. This will provide a further test for changes in catchment hydrology following deforestation. Reviews of catchment impacts on hydrology and carbon cycling have shown an increased catchment water yield and flux of old carbon in disturbed catchments. Our study provides one of the most comprehensive records of forest clearance and provides valuable insights into the causal mechanisms and consequences of these changes. © Author(s) 2018. CC Attribution 4.0 license.
- ItemChanging fluxes of sediments and salts as recorded in lower River Murray wetlands, Australia(International Association of Hydrological Sciences (IAHS), 2006-07-06) Gell, PA; Fluin, J; Tibby, J; Haynes, D; Khanum, SI; Walsh, B; Hancock, G; Harrison, JJ; Zawadzki, A; Little, FThe River Murray basin, Australia’s largest, has been significantly impacted by changed flow regimes and increased fluxes of salts and sediments since settlement in the 1840s. The river’s flood plain hosts an array of cut-off meanders, levee lakes and basin depression lakes that archive historical changes. Pre-European sedimentation rates are typically approx. 0.1–1 mm year-1, while those in the period after European arrival are typically 10 to 30 fold greater. This increased sedimentation corresponds to a shift in wetland trophic state from submerged macrophytes in clear waters to phytoplankton dominated, turbid systems. There is evidence for a decline in sedimentation in some natural wetlands after river regulation from the 1920s, but with the maintenance of the phytoplankton state. Fossil diatom assemblages reveal that, while some wetlands had saline episodes before settlement, others became saline after, and as early as the 1880s. The oxidation of sulphurous salts deposited after regulation has induced hyperacidity in a number of wetlands in recent years. While these wetlands are rightly perceived as being heavily impacted, other, once open water systems, that have infilled and now support rich macrophyte beds, are used as interpretive sites. The rate of filling, however, suggests that the lifespan of these wetlands is short. The rate of wetland loss through such increased infilling is unlikely to be matched by future scouring as regulation has eliminated middle order floods from the lower catchment. © 2006 IAHS Press
- ItemClimate variability in south-eastern Australia over the last 1500 years inferred from the high-resolution diatom records of two crater lakes(Pergamon-Elsevier Science Ltd, 2014-07-01) Barr, C; Tibby, J; Gell, PA; Tyler, JJ; Zawadzki, A; Jacobsen, GEClimates of the last two millennia have been the focus of numerous studies due to the availability of high-resolution palaeoclimate records and the occurrence of divergent periods of climate, commonly referred to as the 'Medieval Climatic Anomaly' and The Little Ice Age'. The majority of these studies are centred in the Northern Hemisphere and, in comparison, the Southern Hemisphere is relatively understudied. In Australia, there are few high-resolution, palaeoclimate studies spanning a millennium or more and, consequently, knowledge of long-term natural climate variability is limited for much of the continent. South-eastern Australia, which recently experienced a severe, decade-long drought, is one such region. Results are presented of investigations from two crater lakes in the south-east of mainland Australia. Fluctuations in lake-water conductivity, a proxy for effective moisture, are reconstructed at sub-decadal resolution over the past 1500 years using a statistically robust, diatom-conductivity transfer function. These data are interpreted in conjunction with diatom autecology. The records display coherent patterns of change at centennial scale, signifying that both lakes responded to regional-scale climate forcing, though the nature of that response varied between sites due to differing lake morphometry. Both sites provide evidence for a multi-decadal drought, commencing ca 650 AD, and a period of variable climate between ca 850 and 1400 AD. From ca 1400-1880 AD, coincident with the timing of the 'Little Ice Age', climates of the region are characterised by high effective moisture and a marked reduction in interdecadal variability. The records provide context for climates of the historical period and reveal the potential for more extreme droughts and more variable climate than that experienced since European settlement of the region ca 170 years ago. © 2014, Elsevier Ltd.
- ItemComparison of Be-7 analysis using two gamma spectrometry systems and software packages(South Pacific Radioactivity Association, 2008-11-26) Zawadzki, A; Mokhber-Shahin, L; Fierro, D; Shamnugarajah, K; Ciufici, JNaturally occurring radioisotope, Be-7, can be used to study short term deposition and resuspension cycle of surficial bed sediments. The activity of Be-7 can be determined by gamma spectrometry. Due to Be-7 short half life, samples must be analysed within a few days of collection on several gamma spectrometry systems. To test the precision of Be-7 data from two gamma spectrometry systems and software packages, multiple analysis of a sediment sample was performed over 6 months. A statistical procedure was used to investigate the precision of the analytical data as the activity of Be-7 decreases over time. The sample was prepared from a sediment sample spiked with Be-7 activity, collected from fresh rain water, and counted on High Purity Germanium (HPGe) gamma spectrometry systems from EG&G Ortec and Canberra. Software packages Gamma Vision and Genie-PC were employed to determine peak areas and activity calculations. Calculations were also performed manually by visual determination of the Be-7 peak region of interest and simple gamma spectrometry calculation procedure.
- ItemComparison of radium-228 determination in water among Australian laboratories(Elsevier, 2017-11) Zawadzki, A; Cook, M; Cutmore, B; Evans, F; Fierro, D; Gedz, A; Harrison, JJ; Loosz, T; Medley, P; Mokhber-Shahin, L; Mullins, S; Sdraulig, SThe National Health and Medical Research Council and Natural Resource Management Ministerial Council of Australia developed the current Australian Drinking Water Guidelines which recommend an annual radiation dose value of 1 mSv year−1. One of the potential major contributors to the radiation dose from drinking water is radium-228, a naturally occurring radionuclide arising from the thorium decay series. Various methods of analysing for radium-228 in water have been established and adapted by analytical radiochemistry laboratories. Seven laboratories in Australia participated in analysing radium-228 spiked water samples with activity concentrations ranging from 6 mBq L−1 to 20 Bq L−1. The aim of the exercise was to compare and evaluate radium-228 results reported by the participating laboratories, the methods used and the detection limits. This paper presents the outcome of the exercise. Crown Copyright © 2017 Published by Elsevier Ltd.
- ItemCritical thresholds in aquatic ecosystems: a case study of Tasmanian diatom community response to regional and local environmental change(Australian Society for Limnology, 2016-09-29) Beck, KK; Fletcher, MS; Saunders, KM; Benson, A; Gadd, PS; Heijnis, H; Wolfe, B; Zawadzki, AAquatic ecosystems are often hyper-sensitive and rapid responders to local and regional environmental change, in large part, due to fast reproduction and short lifespans of organisms relative to, for example, terrestrial vegetation. Here, we explore the response of a local diatom community to rapid shifts in rainforest vegetation driven by climate and fire over the last 2,400 years. We use a suite of palaeolimnological data to determine changes in vegetation, nutrient cycling, sediment delivery and diatom community structure to test the response of the local aquatic ecosystems to climate-driven terrestrial environment changes. We find that the diatom community in our study lake, Lake Vera in southwest Tasmania, Australia, remains complacent through phases of substantial changes in the terrestrial environment, hinting at a degree of resilience to both regional climatic and local terrestrial ecosystem change. We also identify a major compositional changes in diatom community – a shift from a planktonic dominance (i.e. Discostella stelligera) to a benthic dominance (i.e. Fragilaria spp. and Achnanthes didyma) – at ca. 930 cal yr BP, prior to a climate-driven terrestrial ecosystem change at ca. 800 cal yr BP. This aquatic ecosystem state-shift reflects the crossing of a critical threshold/tipping point in response to regional drivers and/or local dynamics that, thus, provides critical insights in to the long-term drivers and responses of aquatic ecosystem dynamics.
- ItemA detailed study of Holocene climate variability in south-east Australia based on cellulose inferred lake water isotopes and monitoring and modelling approach at Lake Surprise, western Victoria.(Australasian Quaternary Association Inc., 2022-12-06) Dharmarathma, A; Tyler, JJ; Tibby, J; Barr, C; Cadd, H; Ankor, MJ; Jones, MD; Tadros, CV; Hua, Q; Child, DP; Zawadzki, A; Hotchkis, MAC; Gadd, PS; Klaeb, RM; Hall, TDuring the Holocene, southeast Australia experienced intense climate conditions including extended droughts. However, knowledge of the frequency and intensity of such episodes is restricted due to the scarcity of quantitative, high-resolution climate records from the region. Where conditions are possible, oxygen isotopes preserved in lake sediments are a useful tool for retracing the past climatic and environment. Here we present a well-dated, highly resolved Holocene record based on δ18O values of aquatic cellulose, alongside organic carbon isotopes and carbon/nitrogen ratios from sediments at Lake Surprise in western Victoria. Our interpretation of the palaeo-data is supported by both monitoring of water and sediment accumulation and lake isotope mass balance modelling to track the modern hydrology of the lake. The lake is highly groundwater dependant alongside its evaporative enrichment of major ions and stable isotopes. The cellulose record indicates a trend of gradually increasing aridity towards the present day, with notable extreme wet periods prevailing from 10900 – 10000, 7600 – 7000 and 5600 – 4500 cal yr BP. the lake represent a significant climate transition to towards aridity at 4500 cal yr BP and remained consistent over the last 4000 years, along with the driest period recorded from 2000 – 1550 cal yr BP. while our record is consistent with other studies from western Victoria, we demonstrate a strong coherence with SWW variability suggesting that the southern Ocean processes were the dominant controls of Holocene climate change at least over the study area. Further, we suggest an increasing influence of ENSO and IOD during the last two millennia. Our record also agrees with the pattern of variation in solar forcing to some extent which may symbolize a connection to proxy data and climate drivers. However, detailed analyses focused on solar activity and climate modes are required to understand teleconnections among these climate drivers and their mechanisms.
- ItemDetermining flow patterns and emplacement dynamics from tsunami deposits with no visible sedimentary structure(John Wiley and Sons, 2016-09-16) Kain, CL; Wassmer, P; Goff, JR; Chagué-Goff, C; Gomez, C; Hart, DE; Fierro, D; Jacobsen, GE; Zawadzki, AIn the absence of eyewitness reports or clear sedimentary structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K-means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub-perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infrastructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: (1) samples deposited from laminar flow; and (2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large-scale investigations can be more easily performed. Copyright © 2016 John Wiley & Sons, Ltd.
- ItemDiatom community response to climate variability over the past 37,000 years in the sub-tropics of the Southern Hemisphere(Elsevier Science BV, 2014-01-15) Hembrow, SC; Taffs, K H; Atahan, P; Parr, J; Zawadzki, A; Heijnis, HClimate change is impacting global surface water resources, increasing the need for a deeper understanding of the interaction between climate and biological diversity. This is particularly the case in the Southern Hemisphere sub-tropics, where little information exists on the aquatic biota response to climate variations. Palaeolimnological techniques, in particular the use of diatoms, are well established and can significantly contribute to the understanding of climatic variability and the impacts that change in climate have on aquatic ecosystems. A sediment core from Lake McKenzie, Fraser Island (Australia), was used to investigate interactions between climate influences and aquatic ecosystems. This study utilises a combination of proxies including biological (diatom), geochemical and chronological techniques to investigate long-term aquatic changes within the perched-dune lake. A combination of Pb-210 and AMS C-14 dates showed that the retrieved sediment represented a history of ca. 37,000 cal. yBP. The sedimentation rate in Lake McKenzie is very low, ranging on average from 0.11 mm to 0.26 mm per year. A sediment hiatus was observed between ca. 18,300 and 14,000 cal. yBP suggesting a period of dry conditions at the site. The diatom record shows little variability over the period of record, with benthic, freshwater acidic tolerant species dominating. Relative abundance of planktonic species and geochemical results indicates a period of increased water depth and lake productivity in the early Holocene and a gradual decrease in effective precipitation throughout the Holocene. Results from this study not only support earlier work conducted on Fraser Island using pollen reconstructions but also demonstrate that diatom community diversity has been relatively consistent throughout the Holocene and late Pleistocene with only minor cyclical fluctuation evident. This record is consistent with the few other aquatic palaeoecological records from the Southern Hemisphere sub-tropics. © 2014, Elsevier Ltd.
- ItemDust deposition tracks late-Holocene shifts in monsoon activity and the increasing role of human disturbance in the Puna-Altiplano, northwest Argentina(SAGE, 2020-04-01) Hooper, J; Marx, SK; May, JH; Lupo, LC; Kulemeyer, JJ; Pereira, EdlÁ; Seki, O; Heijnis, H; Child, DP; Gadd, PS; Zawadzki, AThe Puna-Altiplano plateau represents a regionally significant dust source, which is critically located at the nexus between the tropical and sub-polar synoptic systems that dominate the South American climate. Dust emissions in this region would therefore be expected to be sensitive to changes in these systems, in particular the strength and position of the South American Summer Monsoon (SASM). Here, we present a late-Holocene multi-proxy study where changes in dust flux, reconstructed from a high-altitude peat mire, are examined in light of climate variability and human impacts. Results show that for most the 4300 cal. yr BP record, dust flux sensitively tracked changes in SASM activity. Prior to 2600 cal. yr BP relatively high dust flux implies dry conditions prevailed across the Puna-Altiplao in association with reduced SASM activity. The chemistry of dust deposited at this time matched the large endorheic basins on the Puna, which host ephemeral lakes and terminal fans, indicating these were actively supplying dust to the airstream. After 2600 cal. yr BP, SASM activity increased while dust flux decreased and the dust chemistry changed, collectively implying the shutting down of the Puna-Altiplano as a significant dust source. Dust flux increased after 1000 cal. yr BP during the ‘Medieval Warm Period’, associated with a return to drier conditions and reactivation of dust sources across the endorheic basins of the Puna. Natural variability in dust flux was dwarfed, however, by the very significant increase in flux after 400 cal. yr BP following Spanish Colonisation and associated changing landuse practices. This finding attests to the globally significant role of humans on dust emissions. © 2020 by SAGE Publications
- ItemEngineers or opportunists? Examining the role that Australian native plants play in constructing fluvial landforms in subtropical river corridors(American Geophysical Union (AGU), 2019-12-14) Garber, J; Rutherfurd, I; Ghisalberti, M; Zawadzki, A; Hua, Q; Gadd, PSSediment deposition around even-aged stands of riparian trees has been observed in many fluvial systems leading to the theory that most rheophytic species have biologically evolved to trap suspended sediment (SS), and construct fluvial landforms. That is, they are ecosystem engineers. However, few studies have attempted to show the causal relationship between vegetation by calculating the hydraulic impact of vegetation on flow and SS deposition. Furthermore, many of these examples of ecosystem engineering occur at locations in the river where SS deposition is already expected. Here we assess the question: does vegetation really influence deposition to a great extent, or is it more likely exploiting an area where deposition would have occurred anyway? We assess the effect of riparian vegetation on SS deposition in South East Queensland, Australia, where recent floods have scoured out much of the inner channel, and triggered recruitment of even aged cohorts of Casuarina cunninghamiana and Meleleuca bracteata. Using hydraulic theory from recent flume studies we explore whether these vegetation patches can induce deposition and creating new fine sediment deposits in the river corridor? We used Terrestrial LiDAR scanning (TLS) to estimate the physical effect of even-aged vegetation patches on SS deposition. In addition, we measured diameter at breast height and stem densities at even aged stands on the Brisbane, North Pine, and Mary River corridors in SEQld, while constraining patch ages via historic aerial imagery, and unconventional dendrochronology. By applying cutting edge hydraulic theory to our TLS data, we generate a process based estimate of the sediment trapping capability of these vegetation patches as they mature. We find that these patches will only trap fine sediment when channel velocities are less than 0.1 m/s, far lower velocities than experienced through any of the floods, limiting ecosystem engineering potential. These patches must first take advantage of the geomorphology in order to influence it. This methodology can be used elsewhere to determine where the “hotspots for ecosystem engineering” occur in a river corridor, and the relative effectiveness of different species of vegetation in constructing landforms and reducing SS yields. © 2019 American Geophysical Union
- ItemEnvironmental change in the coastal wetlands near Adelaide, Australia.(Elsevier, 2007-07) Nicholson, ED; Krull, ES; Smernik, RJ; Zawadzki, A; Gell, PA; Gillanders, BMThe coastal wetlands located near metropolitan Adelaide are comprised almost exclusively of the Grey Mangrove (Avicennia marina). This native vegetation is a natural resource that has numerous suggested functions, including coastal buffering, mitigation of terrestrially derived nutrient runoff, fish nursery habitat and also ecotourism. The coastal wetlands that are the focus of this study exist primarily within two aquatic reserves. As such, it is important to understand how this coastal environment once existed so as to provide a reference for assessing its current condition. In the relatively calm marine environment provided by the Grey Mangrove, sediments are trapped amongst the roots and pneumatophores. Within these sediments, a number of proxies exist, by which past environmental conditions may be reconstructed. These proxies include microfossils, such as diatoms and forams, macrofossils, such as pollen and seeds, but also relatively indistinguishable fractions of the soil matrix generally referred to as OM (organic matter). The ultimate question being asked within the larger context of this palaeoecological study is, “What impact has European settlement had on the coastal environment near Adelaide?” The research presented here will focus on the palaeoecological utility of OM, found in mangrove sediments, toward answering this question. Sediment samples were collected and analysed from among twenty-three modern sites and three sediment cores. In addition, plant samples representing the types of organic matter typically found in the study region (e.g. samphire OM, mangrove OM, seagrass OM, macroalgal OM), were collected from the same modern sites. An analysis of 13C and 15N isotopes was performed, as organic matter sources may be differentiated based upon recognisable isotopic signatures (e.g. marine vs. terrestrial plant origins). 13C-NMR spectroscopy was then used to supplement the stable isotope analysis, providing an additional means of differentiating carbon types and their sources. In order to make inferences about post-European impacts upon the study region, a modern chronology was obtained. 210Pb profiling of the sediment cores was performed in combination with an analysis of exotic Pinus pollen occurrences. This study describes the environmental changes that have occurred in Adelaide’s coastal wetlands since European settlement and the level of impact that may be attributable to anthropogenic influence.
- ItemEnvironmental changes indicated by grain-size and trace-metal analysis over the past 700 years at Annaburroo Lagoon, NT, Australia.(Australasian Quaternary Association, 2010-07-16) Zhang, X; Heijnis, H; Dodson, JR; Zawadzki, A