Browsing by Author "Beck, KK"

Now showing 1 - 9 of 9
  • Thumbnail Image
    Item
    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
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    An early onset of ENSO influence in the extra-tropics of the southwest Pacific inferred from a 14, 600 year high resolution multi-proxy record from Paddy's Lake, northwest Tasmania
    (Elsevier B.V., 2017-02-01) Beck, KK; Fletcher, MS; Gadd, PS; Heijnis, H; Jacobsen, GE
    Tropical El Niño Southern Oscillation (ENSO) is an important influence on natural systems and cultural change across the Pacific Ocean basin. El Niño events result in negative moisture anomalies in the southwest Pacific and are implicated in droughts and catastrophic wildfires across eastern Australia. An amplification of tropical El Niño activity is reported in the east Pacific after ca. 6.7 ka; however, proxy data for ENSO-driven environmental change in Australia suggest an initial influence only after ca. 5 ka. Here, we reconstruct changes in vegetation, fire activity and catchment dynamics (e.g. erosion) over the last 14.6 ka from part of the southwest Pacific in which ENSO is the main control of interannual hydroclimatic variability: Paddy's Lake, in northwest Tasmania (1065 masl), Australia. Our multi-proxy approach includes analyses of charcoal, pollen, geochemistry and radioactive isotopes. Our results reveal a high sensitivity of the local and regional vegetation to climatic change, with an increase of non-arboreal pollen between ca. 14.6–13.3 ka synchronous with the Antarctic Cold Reversal, and a sensitivity of the local vegetation and fire activity to ENSO variability recorded in the tropical east Pacific through the Holocene. We detect local-scale shifts in vegetation, fire and sediment geochemistry at ca. 6.3, 4.8 and 3.4 ka, simultaneous with increases in El Niño activity in the tropical Pacific. Finally, we observe a fire-driven shift in vegetation from a pyrophobic association dominated by rainforest elements to a pyrogenic association dominated by sclerophyllous taxa following a prolonged (>1 ka) phase of tropical ENSO-amplification and a major local fire event at ca. 3.4 ka. Our results reveal the following key insights: (1) that ENSO has been a persistent modulator of southwest Pacific climate and fire activity through the Holocene; (2) that the climate of northwest Tasmania is sensitive to long-term shifts in tropical ENSO variability; and (3) that there has been possible stationarity in the spatial influence of ENSO over this region through the Holocene. © 2016 Elsevier Ltd.
  • No Thumbnail Available
    Item
    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
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    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
  • No Thumbnail Available
    Item
    The long-term impacts of climate and fire on catchment processes and aquatic ecosystem response in Tasmania, Australia
    (Elsevier, 2019-10-01) Beck, KK; Fletcher, MS; Gadd, PS; Heijnis, H; Saunders, KM; Zawadzki, A
    The impacts of fire and climate on freshwater ecosystems are not well understood, masking the potential impacts of anthropogenic climate change on these systems. A 9200 year Holocene record of sedimentary Carbon/Nitrogen, x-ray fluorescence, charcoal, pollen, and diatoms preserved within a freshwater lake in Tasmania was used to understand the influences of climate variability and fire on aquatic ecosystem response. Western Tasmania is a cool temperate environment where fire occurrence is driven by hydroclimate. High rainfall during the early to mid-Holocene drove an increase in rainforest and peat in the absence of fire, resulting in an oligotrophic and turbid aquatic environment. This also resulted in leaching of humic acid from the catchment, increasing acidity and dystrophy. The onset of a drier, more variable hydroclimate from the mid-to late Holocene drove lower lake levels and a shift to the dominant planktonic diatom species, Discostella stelligera, the result of the unusual bathymetry of Lake Vera where planktonic diatoms increase with lower lake levels. Further drying caused burning of the rainforest (at ca. 2.3 ka) and increased terrigenous deposition into the lake, leading to a productive, alkaline and disturbed diatom community. Repeated fire disturbance resulted in increased inorganic material deposition, the removal of nutrient rich peat, and an invasion of ferns and sclerophyll vegetation. These fire-driven catchment changes caused a shift in the diatom community to low productivity, oligotrophic and acidic assemblages, likely due to restricted light availability and nutrient uptake by increased deposition of terrigenous material. Therefore, the aquatic ecosystem is responding to climate-mediated changes in the terrestrial environment consistent with regional trends in nearby terrestrial-aquatic Holocene records. ©2019 Elsevier Ltd
  • Thumbnail Image
    Item
    A northward shift of the southern westerlies during the Antarctic cold reversal: evidence from Tasmania
    (Australasian Quaternary Association, 2018-12-10) Alexander, J; Fletcher, MS; Pedro, JB; Mariani, M; Beck, KK; Blaauw, M; Hodgson, D; Heijnis, H; Gadd, PS; Lisé-Pronovost, A
    The Last Glacial Termination (LGT) was interrupted in the Southern Hemisphere by the Antarctic Cold Reversal (ACR; 14.7 to 13 ka), a millennial-scale cooling event that coincided with the Bølling– Allerød warm phase in the North Atlantic (14.7 to 12.7 ka). This inter-hemispheric asynchrony of climate change through the LGT, the bipolar seesaw, has been theoretically linked to latitudinal shifts in the southern westerly wind belt (SWW) and their proposed influence over the global carbon cycle via wind-driven upwelling of CO2 rich deep waters in the Southern Ocean (SO). However, while climate models and theory predict a northward shift of the SWW during the ACR in response to ocean-atmosphere heat dynamics, proxy-based reconstructions disagree on the behaviour of the SWW through this interval, and the role of the SWW during the LGT remains contested. Here we present terrestrial proxy palaeoclimate data (pollen, μXRF geochemistry, charcoal) from multiple lakes across Tasmania (40-44⁰S), an island located at the northern edge of the SWW. Our data reveal a clear SWW increase over Tasmania during the ACR, synchronous with reduced SWW-driven upwelling in the SO at the southern edge of the SWW. When combined with evidence from Antarctic ice cores and terrestrial records from New Zealand and Patagonia our results suggest a hemisphere-wide migration of the SWW during the LGT, lending support to the hypothesis that changes in wind-driven ventilation of CO2 from the Southern Ocean were a key driver of the global carbon cycle during the LGT. © The Authors.
  • Thumbnail Image
    Item
    Variance and rate-of-change as early warning signals for a critical transition in an aquatic ecosystem state: a test case from Tasmania, Australia
    (American Geophysical Union (AGU), 2018-02-21) Beck, KK; Fletcher, MS; Gadd, PS; Heijnis, H; Saunders, KM; Simpson, GL; Zawadzki, A
    Critical transitions in ecosystem states are often sudden and unpredictable. Consequently, there is a concerted effort to identify measurable early warning signals (EWS) for these important events. Aquatic ecosystems provide an opportunity to observe critical transitions due to their high sensitivity and rapid response times. Using palaeoecological techniques, we can measure properties of time series data to determine if critical transitions are preceded by any measurable ecosystem metrics, that is, identify EWS. Using a suite of palaeoenvironmental data spanning the last 2,400 years (diatoms, pollen, geochemistry, and charcoal influx), we assess whether a critical transition in diatom community structure was preceded by measurable EWS. Lake Vera, in the temperate rain forest of western Tasmania, Australia, has a diatom community dominated by Discostella stelligera and undergoes an abrupt compositional shift at ca. 820 cal yr BP that is concomitant with increased fire disturbance of the local vegetation. This shift is manifest as a transition from less oligotrophic acidic diatom flora (Achnanthidium minutissimum, Brachysira styriaca, and Fragilaria capucina) to more oligotrophic acidic taxa (Frustulia elongatissima, Eunotia diodon, and Gomphonema multiforme). We observe a marked increase in compositional variance and rate-of-change prior to this critical transition, revealing these metrics are useful EWS in this system. Interestingly, vegetation remains complacent to fire disturbance until after the shift in the diatom community. Disturbance taxa invade and the vegetation system experiences an increase in both compositional variance and rate-of-change. These trends imply an approaching critical transition in the vegetation and the probable collapse of the local rain forest system. ©2018 American Geophysical Union - Open Access