Browsing by Author "Saunders, KM"

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    Assessing feral animal impacts on World Heritage sub-Antarctic Macquarie Island
    (International Union for Quaternary Research (INQUA), 2019-07-30) Saunders, KM; Roberts, SJ; Butz, C; Grosjean, M; Hodgson, DA
    Animals introduced by human activities to remote islands can be ecologically devastating as they often have a large proportion of endemic species with limited resilience to non-indigenous ones. Sub-Antarctic islands are remote, small islands in the vast Southern Ocean. Most have experienced some form of impact from non-indigenous fauna (e.g. rabbits, rats, mice, cats) that became feral pests soon after their deliberate and unintended introductions. Conservation and management efforts are increasingly focused on their control and/or eradication. World Heritage UNESCO Biosphere listed Macquarie Island (54°S) is one of the most impacted sub-Antarctic islands, in particular due to the introduction of rabbits in 1879, to the extent that its World Heritage values were considered threatened in the early 2000s. The values relate to Macquarie Island’s geological, geomorphic and physiographic features, and exceptional natural beauty and aesthetic importance. The latter includes the presence of a large number of lakes, tarns and ponds, and extensive peat beds. The largest rabbit and rodent eradication program for any sub-Antarctic island was undertaken from 2010-2014. Monitoring to assess recovery focused on geomorphological (including erosion) processes, vegetation and some fauna (i.e. invertebrates, burrowing petrels and albatross species) using previous studies as baselines. All of these studies were undertaken after rabbits were introduced, and no pre-introduction data exist beyond some limited historical documents after its discovery in 1810. No monitoring to assess recovery of the lakes, tarns, ponds or peat beds was undertaken. In the absence of long term data, palaeoecology may be used to determine the nature, magnitude and spatial extent of impacts in the context of long term natural variability. To provide a long-term context for assessing the island’s pre-invasion state, invasion impacts, and to provide baseline information for the waterbodies, we undertook a palaeoecological study using high-resolution x-ray fluorescence scanning and hyperspectral imaging together with biological (diatoms), geochemical (total organic carbon and nitrogen) and sedimentological (grain size) analyses of lake sediment cores in two different areas of Macquarie Island. Results showed that Macquarie Island lakes have undergone unprecedented and statistically significant environmental changes since the introduction of rabbits in 1879. Sediment accumulation rates increased by more than 10 times at one site, 100 times at another, due to enhanced catchment inputs and within- lake production. Total organic carbon and total nitrogen contents of the sediments increased by a factor of four. The diatom flora became dominated by two previously rare species in both lakes. This study provides an example of how palaeoecology may be used to determine baseline conditions prior to the introduction of non-indigenous species, quantify the timing and extent of changes, and help identify a basis for monitoring the recovery of waterbodies following successful non-indigenous species eradication programs ©The Authors
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    Biogeochemical responses to Holocene catchment-lake dynamics in the Tasmanian World Heritage Area, Australia
    (American Geophysical Union, 2018-04-30) Mariani, M; Beck, KK; Fletcher, MS; Gell, PA; Saunders, KM; Gadd, PS; Chisari, R
    Environmental changes such as climate, land use, and fire activity affect terrestrial and aquatic ecosystems at multiple scales of space and time. Due to the nature of the interactions between terrestrial and aquatic dynamics, an integrated study using multiple proxies is critical for a better understanding of climate- and fire-driven impacts on environmental change. Here we present a synthesis of biological and geochemical data (pollen, spores, diatoms, micro X-ray fluorescence scanning, CN content, and stable isotopes) from Dove Lake, Tasmania, allowing us to disentangle long-term terrestrial-aquatic dynamics through the last 12 kyear. We found that aquatic dynamics at Dove Lake are tightly linked to vegetation shifts dictated by regional hydroclimatic variability in western Tasmania. A major shift in the diatom composition was detected at ca. 6 ka, and it was likely mediated by changes in regional terrestrial vegetation, charcoal, and iron accumulation. High rainforest abundance prior ca. 6 ka is linked to increased terrestrially derived organic matter delivery into the lake, higher dystrophy, anoxic bottom conditions, and lower light penetration depths. The shift to a landscape with a higher proportion of sclerophyll species following the intensification of El Niño-Southern Oscillation since ca. 6 ka corresponds to a decline in terrestrial organic matter input into Dove Lake, lower dystrophy levels, higher oxygen availability, and higher light availability for algae and littoral macrophytes. This record provides new insights on terrestrial-aquatic dynamics that could contribute to the conservation management plans in the Tasmanian World Heritage Area and in temperate high-altitude dystrophic systems elsewhere. ©2018. American Geophysical Union
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    Carbon cycling in sub-Antarctic and Antarctic lakes
    (American Geophysical Union (AGU), 2021-12-17) McDonough, LK; Meredith, KT; Saunders, KM; Baker, AA
    Between 2000 and 2010, anthropogenic carbon emissions rose at rates of 2.2% year-1, a 70% increase above the annual rates observed between 1970 and 2000. This has accelerated global temperature increases. As a result, carbon fluxes to and from aquatic environments have changed, affecting microbial community compositions, and impacting the ability of some environments to act as carbon stores. Whilst the factors influencing nutrient cycling in many aquatic environments, including major rivers and oceans, have been well studied, little is known about the biogeochemical processes driving aquatic carbon cycling in sub-Antarctic and Antarctic lakes, and how this may be impacted by climate change. This is in part because sampling programs designed for such isolated environments take years to plan and require international collaboration. The isolation of these lakes however mean that many are relatively undisturbed by human activities, making them ideal locations to study the interactions between hydrological and biogeochemical processes, and the impact of climate change on natural carbon sources, transformation and storage. We aim to analyse Antarctic and sub-Antarctic lake water using organic carbon characterisation techniques such as fluorescence, liquid chromatography organic carbon detection and synchrotron characterisation, as well as radiocarbon and stable carbon isotopes of dissolved organic carbon (14CDOC and 13CDOC) and dissolved inorganic carbon (14CDIC and 13CDIC). This will allow us to identify key carbon sources such as terrestrial vegetation, groundwater and permafrost thaw, carbon age, and cycling via biodegradation or other processing mechanisms. The data collected for this project will form the first comprehensive spatial and temporal survey of dissolved carbon in both organic and inorganic phases in lakes across the region, aimed at understanding present-day environmental processes and their drivers. These data also have the potential to calibrate palaeo-records such as peat and lake archives which will assist in the understanding of the impacts of large-scale climate variability and environmental changes that may occur in the future.
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    Centennial-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, A
    Millennial-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
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    Coupling of the Intertropical Convergence Zone and Southern Hemisphere mid-latitude climate during the early to mid-Holocene
    (Geological Society of America, 2017-10-27) Mariani, M; Fletcher, MS; Drysdale, RN; Saunders, KM; Heijnis, H; Jacobsen, GE; Zawadzki, A
    Conceptual models predict a tight coupling between the Intertropical Convergence Zone (ITCZ) and the Southern Westerly Winds (SWW) in response to glacial-interglacial transitions, yet little is known about this relationship under Holocene boundary conditions. Here we present a synthesis of Holocene pollen data from the southwest Pacific mid-latitudes that tracks changes in the SWW. Comparison of our SWW paleoclimate records with data tracking the ITCZ, oceanic circulation, and insolation reveals clearly synchronous and in-phase ITCZ-SWW dynamics between 12 and 5 ka, indicating a tight coupling between the tropics and southern mid-latitudes in response to ocean circulation and insolation. An apparent decoupling of the SWW and ITCZ in the Pacific region after 5 ka is attributable to the overriding influence of the El Niño-Southern Oscillation (ENSO) over the proxy data. © 2017 Geological Society of America
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    Critical 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, A
    Aquatic 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.
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    Ecosystem impacts of feral rabbits on World Heritage sub-Antarctic Macquarie Island: a palaeoecological perspective
    (Elsevier, 2013-11) Saunders, KM; Harrison, JJ; Hodgson, DA; de Jong, R; Mauchle, F; McMinn, A
    The introduction and establishment of non-indigenous species through human activities often poses a major threat to natural biodiversity. In many parts of the world management efforts are therefore focused on their eradication. The environment of World Heritage sub-Antarctic Macquarie Island has been severely damaged by non-indigenous species including rabbits, rats and mice, introduced from the late AD 1800s. An extensive eradication programme is now underway which aims to remove all rabbits and rodents. To provide a long-term context for assessing the Island's pre-invasion state, invasion impacts, and to provide a baseline for monitoring its recovery, we undertook a palaeoecological study using proxies in a lake sediment core. Sedimentological and diatom analyses revealed an unproductive catchment and lake environment persisted for ca. 7100 years prior to the introduction of the invasive species. After ca. AD 1898, unprecedented and statistically significant environmental changes occurred. Lake sediment accumulation rates increased >100 times due to enhanced catchment inputs and within-lake production. Total carbon and total nitrogen contents of the sediments increased by a factor of four. The diatom flora became dominated by two previously rare species. The results strongly suggest a causal link between the anthropogenic introduction of rabbits and the changes identified in the lake sediments. This study provides an example of how palaeoecology may be used to determine baseline conditions prior to the introduction of non-indigenous species, quantify the timing and extent of changes, and help monitor the recovery of the ecosystem and natural biodiversity following successful non-indigenous species eradication programmes. © 2014 Elsevier Ltd.
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    Emerging biological archives can reveal ecological and climatic change in Antarctica
    (Wiley, 2022-07-28) Strugnell, JM; McGregor, HV; Wilson, NG; Meredith, KT; Chown, SL; Lau, SCY; Robinson, SA; Saunders, KM
    Anthropogenic climate change is causing observable changes in Antarctica and the Southern Ocean including increased air and ocean temperatures, glacial melt leading to sea‐level rise and a reduction in salinity, and changes to freshwater water availability on land. These changes impact local Antarctic ecosystems and the Earth's climate system. The Antarctic has experienced significant past environmental change, including cycles of glaciation over the Quaternary Period (the past ~2.6 million years). Understanding Antarctica's paleoecosystems, and the corresponding paleoenvironments and climates that have shaped them, provides insight into present day ecosystem change, and importantly, helps constrain model projections of future change. Biological archives such as extant moss beds and peat profiles, biological proxies in lake and marine sediments, vertebrate animal colonies, and extant terrestrial and benthic marine invertebrates, complement other Antarctic paleoclimate archives by recording the nature and rate of past ecological change, the paleoenvironmental drivers of that change, and constrain current ecosystem and climate models. These archives provide invaluable information about terrestrial ice‐free areas, a key location for Antarctic biodiversity, and the continental margin which is important for understanding ice sheet dynamics. Recent significant advances in analytical techniques (e.g., genomics, biogeochemical analyses) have led to new applications and greater power in elucidating the environmental records contained within biological archives. Paleoecological and paleoclimate discoveries derived from biological archives, and integration with existing data from other paleoclimate data sources, will significantly expand our understanding of past, present, and future ecological change, alongside climate change, in a unique, globally significant region. © © 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd. Open Access.
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    First evidence of plutonium and uranium fallout on a Southern Ocean Island (Macquarie Island, 54°S, 158°E)
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Saunders, KM; Child, DP; Griffiths, AD; Harrison, JJ; Hotchkis, MAC; Motta, G; Roberts, SJ; Zawadzki, A
    Plutonium and uranium concentrations and isotopic signatures may be used to trace the changing patterns and locations of nuclear testing activities and the resulting spatial distribution of fallout. Virtually nothing is known about the fallout distribution of plutonium and uranium in the Southern Ocean region. Although only 10% of the atmospheric nuclear weapons detonations between 1945 and 1980 were conducted in the Southern Hemisphere, atmospheric transport meant that it received a much larger proportion of fallout – about one third of the total inventory. Lake sediment and peat records from the few remote sub-Antarctic islands in the Southern Ocean provide unique and undisturbed archives for investigating fallout histories, and an opportunity to bridge the spatial gap between the Southern Hemisphere mid-latitudes, where records show mixed regional and global signatures, and Antarctica, where global signatures dominate. Here, we present the first nuclear weapons testing fallout history for a sub-Antarctic island using a lake sediment core from Macquarie Island. Macquarie Island is nearly equidistant from Tasmania, New Zealand and Antarctica at 54°S, 158°E. It has an area of 120 km2 and lies just north of the Polar Frontal Zone in the core belt of the Southern Hemisphere westerly winds, which dominate the climate of the Southern Hemisphere mid-high latitudes. A 54.0 cm sediment core was collected from a small lake on the western edge of the Macquarie Island plateau. It was sampled at 0.5 cm increments, dated using 210Pb (ages calculated using the constant flux, constant sedimentation model) and 14C, and scanned with micro x-ray fluorescence and hyperspectral (400-1000 nm) core scanners to identify stratigraphic and geochemical variations through time. The core spanned ca. 2000 years, with the upper 18.0 cm dating back to ca. 1900 based on 210Pb dating. Plutonium and uranium fallout isotopes 239Pu, 240Pu, 241Pu and 236U were measured on this part of the core. The profile demonstrated the onset of nuclear weapons testing at 12.0-12.5 cm (late 1940s based on 210Pb dating) with a 240/239Pu atom ratio of 0.24. This coincides with ratios typical of US testing in the Pacific Proving Grounds, which were the dominant source of global fallout at the time. Concentrations of all isotopes sharply increased between 12.5-9.5 cm and peaked at 9.5-10.0 cm, which, based on 210Pb dating corresponds to ca. 1963. In the late 1950s and early 1960s, there was a change to a lower 240/239Pu atom ratio of 0.17 coinciding with the shift from US testing dominating global fallout to that of the former Soviet Union. A replicate sediment core from another lake on Macquarie Island is currently being analysed to verify these findings, as well as records from other sub-Antarctic islands, with the aim of tracing the changing patterns and locations of nuclear testing activities and resulting spatial distribution of fallout in the mid-late 20th century. © The Authors
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    A global database of holocene paleotemperature records
    (Springer Nature Limited, 2020-04-14) Kaufman, DS; McKay, N; Rouston, C; Erb, M; Davis, B; Heiri, O; Jaccard, SL; Tierney, J; Dätwyler, C; Axford, Y; Brussel, T; Cartapanis, O; Chase, BM; Dawson, A; de Vernal, A; Engels, S; Jonkers, L; Marsicek, J; Moffa-Sánchez, P; Morrill, C; Oris, A; Rehfeld, K; Saunders, KM; Sommer, PS; Thomas, E; Tonello, M; Tóth, M; Vachula, R; Andreev, A; Bertrand, S; Biskaborn, B; Bringué, M; Brooks, S; Caniupán, M; Chevalier, M; Cwynar, L; Emile-Geay, J; Fegyveresi, J; Feurdean, A; Finsinger, W; Fortin, MC; Foster, L; Fox, M; Gajewski, K; Grosjean, M; Hausmann, S; Heinrichs, M; Holmes, N; Ilyashuk, B; Ilyashuk, E; Juggins, S; Khider, D; Koinig, K; Langdon, P; Larocque-Tobler, I; Li, JY; Lotter, A; Luoto, T; Mackay, A; Magyari, E; Malevich, S; Mark, B; Massaferro, J; Montade, V; Nazarova, L; Novenko, E; Pařil, P; Pearson, E; Peros, M; Peinitz, R; Płóciennik, M; Porinchu, D; Potito, A; Rees, ABH; Reinemann, S; Roberts, SJ; Rolland, N; Salonen, S; Self, A; Seppä, H; Shala, S; St-Jacques, JM; Stenni, B; Syrykh, L; Tarrats, P; Taylor, K; van den Bos, V; Velle, G; Wahl, E; Walker, I; Wilmshurst, J; Zhang, E; Zhilich, S
    A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format. © 2020 The Authors
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    High-resolution palaeodust archive from subantarctic Macquarie Island
    (Australasian Quaternary Association, 2022-12-06) Johansen, A; Stromsoe, N; Saunders, KM; Marx, SK
    Mineral dust drives climate variability both during atmospheric transport and upon deposition. During transport, dust influences radiative forcing and cloud properties. Upon deposition, nutrients supplied by dust can drive primary productivity and subsequent drawdown of atmospheric carbon. Inputs of Australian dust may be especially critical in the nutrient-limited ecosystems of the South Pacific Southern Ocean and subantarctic islands. This study seeks to understand dust flux to Macquarie Island since the mid-Holocene, and the potential response of plants to changing dust inputs. Peat cores from Macquarie Island were selected to reconstruct the dust flux history as peat plants can effectively capture dust and preserve the dust signal. Peats develop in water-saturated areas where plant decomposition is slowed in the anoxic and reduced conditions. As new growth accumulates over decaying plants, some elemental components of dust are preserved in place in the peat column. We developed high-resolution age-depth models with 210Pb, 239,240Pu, and 14C analysis. We applied 210Pb dating to the top 25 cm of each core, with additional age-control from the peak concentration of anthropogenic 239,240Pu identifying the Southern Hemisphere peak from nuclear weapons testing (about 1964). These data, along with radiocarbon ages to the mid-Holocene, were used to inform the age-depth model, which indicates variability in peat accumulation rates. The quantity and quality of organic matter (OM) were indicated by loss-on-ignition and Fourier-transform infrared (FTIR) spectroscopy. The δ15N values indicated minimal animal inputs. Preliminary inductively coupled plasma mass spectrometry (ICP-MS) data indicates dust inputs by increases in the stable isotopes of Pb in the early and mid-20th century. Dust scavenges Pb during transport, and the Australian production of Pb increased with the opening of the Broken Hill mine in 1885. Work is currently in progress to confirm these findings and extend the dust record prior to the 20th century.
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    Holocene dynamics of the Southern Hemisphere westerly winds and possible links to CO2 outgassing
    (Springer Nature, 2018-07-23) Saunders, KM; Roberts, SJ; Perren, B; Butz, C; Sime, L; Davies, S; van Nieuwenhuyze, W; Grosjean, M; Hodgson, DA
    The Southern Hemisphere westerly winds (SHW) play an important role in regulating the capacity of the Southern Ocean carbon sink. They modulate upwelling of carbon-rich deep water and, with sea ice, determine the ocean surface area available for air–sea gas exchange. Some models indicate that the current strengthening and poleward shift of these winds will weaken the carbon sink. If correct, centennial- to millennial-scale reconstructions of the SHW intensity should be linked with past changes in atmospheric CO2, temperature and sea ice. Here we present a 12,300-year reconstruction of wind strength based on three independent proxies that track inputs of sea-salt aerosols and minerogenic particles accumulating in lake sediments on sub-Antarctic Macquarie Island. Between about 12.1 thousand years ago (ka) and 11.2 ka, and since about 7 ka, the wind intensities were above their long-term mean and corresponded with increasing atmospheric CO2. Conversely, from about 11.2 to 7.2 ka, the wind intensities were below their long-term mean and corresponded with decreasing atmospheric CO2. These observations are consistent with model inferences of enhanced SHW contributing to the long-term outgassing of CO2 from the Southern Ocean. © 2021 Springer Nature Limited
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    How old is the Tasmanian cultural landscape? A test of landscape openness using quantitative land-cover reconstructions
    (John Wiley and Sons, 2017-06-19) Mariani, M; Connor, SE; Fletcher, MS; Theuerkauf, M; Kuneš, P; Jacobsen, GE; Saunders, KM; Zawadzki, A
    Aim To test competing hypotheses about the timing and extent of Holocene landscape opening using pollen-based quantitative land-cover estimates. Location Dove Lake, Tasmanian Wilderness World Heritage Area, Australia. Methods Fossil pollen data were incorporated into pollen dispersal models and corrected for differences in pollen productivity among key plant taxa. Mechanistic models (REVEALS—Regional Estimates of VEgetation Abundance from Large Sites) employing different models for pollen dispersal (Gaussian plume and Lagrangian stochastic models) were evaluated and applied in the Southern Hemisphere for the first time. Results Validation of the REVEALS model with vegetation cover data suggests an overall better performance of the Lagrangian stochastic model. Regional land-cover estimates for forest and non-forest plant taxa show persistent landscape openness throughout the Holocene (average landscape openness ~50%). Gymnoschoenus sphaerocephalus, an indicator of moorland vegetation, shows higher values during the early Holocene (11.7–9 ka) and declines slightly through the mid-Holocene (9–4.5 ka) during a phase of partial landscape afforestation. Rain forest cover reduced (from ~40% to ~20%) during the period between 4.2–3.5 ka. Main conclusions Pollen percentages severely under-represent landscape openness in western Tasmania and this bias has fostered an over-estimation of Holocene forest cover from pollen data. Treeless vegetation dominated Holocene landscapes of the Dove Lake area, allowing us to reject models of landscape evolution that invoke late-Holocene replacement of a rain forest-dominated landscape by moorland. Instead, we confirm a model of Late Pleistocene inheritance of open vegetation. Rapid forest decline occurred after c. 4 ka, likely in response to regional moisture decline. © 2017 John Wiley & Sons Ltd
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    How significant is atmospheric metal contamination from mining activity adjacent to the Tasmanian Wilderness World Heritage Area? A spatial analysis of metal concentrations using air trajectories models
    (Elsevier, 2019-03-15) Schneider, L; Mariani, M; Saunders, KM; Maher, WA; Harrison, JJ; Fletcher, MS; Zawadzki, A; Heijnis, H; Haberle, SG
    This study investigated metal contamination from historical mining in lakes in the Tasmanian Wilderness World Heritage Area (TWWHA) and surrounding region. The largest increase in sedimentation and metal contamination occurred ca. 1930 when open-cut mining commenced and new mining technology was introduced into the region. The geochemical signal of lake sediments changed from reflecting the underlying geology and lithology to that reflecting mining activities. The HYSPLIT air particle trajectory model explains metal distribution in the lakes, with those in the northwest region closest to the mines having the highest metal contamination. Lake metal concentrations since mining activities commenced are in the order: Owen Tarn > Basin Lake > Perched Lake > Lake Dove > Lake Dobson > Lake Cygnus, with Perched Lake and Lakes Dove, Dobson and Cygnus in the TWWHA. Metal contamination affected centres up to 130 km down-wind of mining sites. Enrichment factors (EF) for Pb, Cu, As and Cd are >1 for all lakes, with Owen Tarn and Basin Lake having very high EFs for Cu and Pb (98 and 91, respectively). Pb, Cu, As and Cd concentrations are above the Australia/New Zealand lower sediment guidelines, with Pb, Cu and As above the high guidelines in Owen Tarn and Basin Lake. This study demonstrated the legacy of metal contamination in the TWWHA by mining activities and the consequences of a lack of execution of environmental regulations by past governments in Tasmania.© 2018 Elsevier B.V
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    Hydrochemical and isotopic baselines for understanding hydrological processes across Macquarie Island
    (Springer Nature, 2022-12-08) Meredith, KT; Saunders, KM; McDonough, LK; McGeoch, M
    Isotopic and hydrochemical data from lakes provide direct information on catchment response to changing rainfall, evaporation, nutrient cycling, and the health of ecosystems. These techniques have not been widely applied to lakes in the Southern Hemisphere high latitudes, including Southern Ocean Islands (SOIs) experiencing rapid, significant shifts in climate. Historical work has highlighted the localised nature of geochemical drivers in controlling the hydrochemical evolution of lakes, such as geology, sea spray contribution, vegetation, geographical location, and ice cover extent. The role of groundwater in lake hydrology and hydrochemistry has not been identified until now, and its omission will have major implications for interpreting soil–water–air processes affecting lakes. Here we present the first comprehensive, island-wide hydrochemical and isotopic survey of lakes on a SOI. Forty lakes were examined across Macquarie Island, using comparable methods to identify key environmental processes and their geochemical drivers. Methods include stable carbon (δ13CDOC: dissolved organic carbon and δ13CDIC: dissolved inorganic carbon), oxygen (δ18O), hydrogen (δ2H) and strontium isotopic ratios (87Sr/86Sr) in water. These provide essential baseline data for hydrological, biological, and geochemical lake processes. Lakes on the western side of the island are influenced by sea spray aerosols. In general, it was found that lakes at higher elevations are dilute and those located in lower elevation catchments have experienced more water–rock interactions. The hydrochemical and isotopic tracers suggest that lakes in lower elevations contain more terrestrial sourced ions that may be contributed from groundwater. Increasing temperatures and changing rainfall patterns predicted for the region will lead to shifts in nutrient cycles, and impact the island’s unique ecosystems. Future research will focus on long-term monitoring to understand seasonal, annual, and long-term variability to test fundamental hypotheses concerning ecosystem function and the consequences of environmental change on SOIs. © 2024 The Authors - Open Access CC-BY 4.0.
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    Identifying the key sources of metal (loid) deposition to remote Tasmanian lakes: is legacy mining a problem?
    (Springer Nature, 0202-03-07) Stevens, H; Barmuta, LA; Chase, Z; Saunders, KM; Zawadzki, A; Gadd, PS; Proemse, BC
    Reports have shown that even remote lakes have been negatively affected by anthropogenic activities. This study used metal concentrations and enrichment factors to comprehensively determine key metal sources and identify potential impacts of recent anthropogenic activity in remote Central Highland Tasmanian (Australia) lakes. Metal concentrations (Al, As, Cd, Cu, Fe, Pb, and Zn) in these lakes remain below Australian interim sediment quality guidelines but have been slowly increasing since the start of the twentieth century. This increase is likely related to increasing organic matter content, rather than any direct, increased input of metals. The largest anthropogenic impact to these systems was damming, which typically led to an increase in organic matter content either directly, by the trapping of particles and nutrients, or indirectly, by stimulating primary production in the lake. This increased organic matter content, in turn, increased the retention of metals, manifesting as an increase to measured metal concentrations. Minor impacts are the historical use of lead shot, leaded petrol, and industrial processes, which may have contributed to the higher Pb enrichment, compared to the other studied metals, in these lakes. Despite recent concerns of metal contamination in the Tasmanian Wilderness World Heritage Area from distant mining activities, there is no strong evidence in this study indicating that lakes in the Central Highlands (a similar distance away) have been impacted by long-distance atmospheric deposition. This is likely related to the decreased rainfall, and thus decreased rates of wet deposition of aerosols in the east of Tasmania, compared to that of the west and in the Tasmanian Wilderness World Heritage Area. © The Author(s) 2024. - Open Access - This article is licensed under a Creative Commons Attribution 4.0 International License
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    The impacts of intensive mining on terrestrial and aquatic ecosystems: A case of sediment pollution and calcium decline in cool temperate Tasmania, Australia
    (Elsevier, 2020-10-01) Beck, KK; Mariani, M; Fletcher, MS; Schneider, L; Aquino-López, MA; Gadd, PS; Heijnis, H; Saunders, KM; Zawadzki, A
    Mining causes extensive damage to aquatic ecosystems via acidification, heavy metal pollution, sediment loading, and Ca decline. Yet little is known about the effects of mining on freshwater systems in the Southern Hemisphere. A case in point is the region of western Tasmania, Australia, an area extensively mined in the 19th century, resulting in severe environmental contamination. In order to assess the impacts of mining on aquatic ecosystems in this region, we present a multiproxy investigation of the lacustrine sediments from Owen Tarn, Tasmania. This study includes a combination of radiometric dating (14C and 210Pb), sediment geochemistry (XRF and ICP-MS), pollen, charcoal and diatoms. Generalised additive mixed models were used to test if changes in the aquatic ecosystem can be explained by other covariates. Results from this record found four key impact phases: (1) Pre-mining, (2) Early mining, (3) Intense mining, and (4) Post-mining. Before mining, low heavy metal concentrations, slow sedimentation, low fire activity, and high biomass indicate pre-impact conditions. The aquatic environment at this time was oligotrophic and dystrophic with sufficient light availability, typical of western Tasmanian lakes during the Holocene. Prosperous mining resulted in increased burning, a decrease in landscape biomass and an increase in sedimentation resulting in decreased light availability of the aquatic environment. Extensive mining at Mount Lyell in the 1930s resulted in peak heavy metal pollutants (Pb, Cu and Co) and a further increase in inorganic inputs resulted in a disturbed low light lake environment (dominated by Hantzschia amphioxys and Pinnularia divergentissima). Following the closure of the Mount Lyell Co. in 1994 CE, Ca declined to below pre-mining levels resulting in a new diatom assemblage and deformed diatom valves. Therefore, the Owen Tarn record demonstrates severe sediment pollution and continued impacts of mining long after mining has stopped at Mt. Lyell Mining Co. ©2020 Elsevier Ltd
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    The impacts of intensive mining on terrestrial and aquatic ecosystems: a case study from cool temperate Tasmania, Australia
    (International Union for Quaternary Research (INQUA), 2019-07-30) Beck, KK; Mariani, M; Fletcher, MS; Gadd, PS; Heijnis, H; Saunders, KM; Zawadzki, A
    Mining has caused extensive damage to aquatic systems worldwide with acidification, heavy metal pollution, increased sediment loading and Ca decline of freshwaters. While some aquatic ecosystems are thought to be recovering from past mining, a long-term context is needed to determine if pre-impact conditions have been restored. Here we explore the palaeoenvironmental history of Owen Tarn, western Tasmania, to assess the impacts of mining from Mt. Lyell on aquatic ecosystems. Analysis of a new sediment core using radiometric dating, sediment geochemistry, pollen, and diatoms are used to examine the full extent of mining and heavy metal pollution on aquatic and terrestrial ecosystems pre- and post-mining in this region. Our analysis indicates four key phases of environmental change: (1) A pre-mining phase (550-1160 CE); (2) an early impact phase (British invasion) shows land clearance and vegetation removal by burning during mineral exploration; (3) an intense mining period (1950 CE) had severe negative impact on the diatom community in which sediment pollution from a lack of vegetation and heavy erosion, rather than acidification, was the main driver of change; and (4) a post-mining phase (2006 CE) in which vegetation on the landscape began to recover and aquatic productivity increased. Despite this apparent recovery of the system, the aquatic community continues to experience impacts from mining. The diatom community has not returned to its pre-impact state, but rather there is evidence of a secondary impact from declining Ca in the system. The relevance of these findings demonstrates the importance of well dated palaeoecological records to inform management and mitigate human impacts on the environment.
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    Imprint of recent Glacial Lake Outburst Floods (GLOFs) in Baker fjord sediments (Chile, 48 °S)
    (International Union for Quaternary Research (INQUA), 2019-07-30) Vandekerkhove, E; Bertrand, S; Reid, B; Saunders, KM; Kylander, M; Pantoja, S
    Glacial Lake Outburst Floods (GLOFs) constitute a major threat in glacier-covered regions. These catastrophic events occur when a lake dammed by a glacier or moraine suddenly empties, resulting in abrupt flooding. This issue is particularly pronounced in the Baker region (47 – 48 °S) of Patagonia, where 21 GLOFs have been documented in the last decade. During such events, the Baker River, which drains most of the eastern side of the Northern Patagonian Icefield, triples in discharge and suspended sediment concentrations increase by more than one order of magnitude. The recent occurrence and the vast impact of these large-scale events on the Baker River raises the question of how these events are recorded in Baker fjord sediments. The goal of this project is therefore to understand how GLOFs are registered in Baker fjord sediments, in order to reconstruct their occurrence in the past, i.e., when river discharge was not monitored. To do so, the bathymetry of the prodelta region of Baker fjord was mapped at high resolution and a total of ten sediment cores were collected. The sediment cores were described, photographed, and scanned at 2 mm resolution on a Geotek MSCL for magnetic susceptibility, gamma density, and spectrophotometry. Additionally, XRF scanning was performed at 2 mm resolution. A core chronology was established on the most promising core using 210Pb concentrations. Results show that the subaquatic delta in Baker fjord is deeply incised with well-developed sinuous channels (maximum depth of 26 m). The most prominent channel has an average width of 140 m and extends up to 8 km in Baker fjord. The morphology of the channels and the occurrence of sediment waves within the axial channels imply recent sediment transport by turbidity currents. The sediment cores, which display at least seven turbidites in a time span of 46 ± 7 years, confirm the occurrence of active turbidity currents. Although several potential triggering processes are plausible for the occurrence of dense underflows in Baker fjord and detailed monitoring of the subaquatic delta is required to pinpoint the exact triggering process(es), we believe that elevated river discharge during GLOFs is the main cause of the turbidite currents within the fjord. Although seasonal increases in river discharge due to snowmelt may trigger turbidity currents, it is more likely that the turbidites observed in the deepest sediment cores represent large-scale turbidity currents triggered by GLOFs. The lower number of turbidites in the sediment cores compared to the number of recent GLOF events however suggests that only the largest GLOFs are recorded as turbidites. This study demonstrates that GLOFs might be of key importance in shaping the fjord’s morphology, and that their occurrence in the past may be reconstructed using turbidite stratigraphy. © 2019 The Authors.
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    The indirect response of an aquatic ecosystem to long-term climate-driven terrestrial vegetation in a subalpine temperate lake
    (John Wiley & Sons, Inc, 2017-12-15) Beck, KK; Fletcher, MS; Kattel, G; Barry, LA; Gadd, PS; Heijnis, H; Jacobsen, GE; Saunders, KM
    Aim To assess whether climate directly influences aquatic ecosystem dynamics in the temperate landscape of Tasmania or whether the effects of long-term climatic change are mediated through the terrestrial environment (indirect climate influence). Location Paddy's Lake is located at 1065 m a.s.l. in temperate north-west Tasmania, a continental island south-east of mainland Australia (41°15–43°25′ S; 145°00–148°15′ E). Methods We developed a new 13,400 year (13.4 kyr) palaeoecological dataset of lake sediment subfossil cladocerans (aquatic grazers), bulk organic sediment carbon (C%) and nitrogen (N%) and δ13C and δ15N stable isotopes. Comparison of this new data was made with a recently published pollen, geochemistry and charcoal records from Paddy's Lake. Results Low cladoceran diversity at Paddy's Lake is consistent with other temperate Southern Hemisphere lakes. The bulk sediment δ15N values demonstrate a significant lagged negative response to pollen accumulation rate (pollen AR). Compositional shifts of dominant cladoceran taxa (Bosmina meridionalis and Alona guttata) occur following changes in both pollen AR and pollen (vegetation) composition throughout the 13.4 kyr record at Paddy's Lake. The δ15N values demonstrate a significant positive lagged relationship to the oligotrophic:eutrophic cladoceran ratio. Main conclusions Long-term changes in cladoceran composition lag changes in both pollen AR and terrestrial vegetation composition. We interpret pollen AR as reflecting climate-driven changes in terrestrial vegetation productivity and conclude that climate-driven shifts in vegetation are the principal driver of the cladoceran community during the last ca. 13.4 kyr. The significant negative lagged relationship between pollen AR and δ15N reflects the primary control of vegetation productivity over within-lake nutrient status. Thus, we conclude that the effects of long-term climate change on aquatic ecosystem dynamics at our site are indirect and mediated by the terrestrial environment. Vegetation productivity controls organic soil development and has a direct influence over lake trophic status via changes in the delivery of terrestrial organic matter into the lake. © 2017 John Wiley & Sons Ltd