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Browsing by Author "Gell, PA"

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Anthropogenic 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, B
Over 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
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
Blooms 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, PA
Blooms 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.
Changing 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, F
The 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
Climate 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, GE
Climates 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.
Environmental change in the coastal wetlands near Adelaide, Australia.
(Elsevier, 2007-07) Nicholson, ED; Krull, ES; Smernik, RJ; Zawadzki, A; Gell, PA; Gillanders, BM
The 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.
A fine-resolution reconstruction of climatic variability in southeastern Australia over the last 1500 years
(18th INQUA Congress, 2011-07-21) Barr, C; Tibby, J; Gell, PA; Jacobsen, GE; Zawadzki, A
High-resolution palaeoclimate records extend knowledge of long- and short-term climatic variability beyond the limit of instrumental data. However, to date, no millennial-length, sub-decadal resolution climate records have been produced from mainland Australia. In part, this is due to the absence of suitable archives of proxies amenable to high-resolution analysis. Here, we present a study of two crater lakes in western Victoria, southeastern Australia. A diatom-conductivity transfer function was developed specifically for application to oligosaline and mesosaline lakes, such as the two study sites; Lake Elingamite and Lake Surprise. A sub-decadal resolution sampling regime was undertaken and results demonstrate that over the past 1500 years, both lakes responded to a common regional-scale climate signal. Reconstructed conductivity, a proxy for moisture balance, indicates distinct periods of contrasting climates. Both lakes record evidence of a severe, and prolonged, dry phase centered around AD 700, which was more extreme than any subsequent drought. Between ca. AD 900 and 1500, the climate was highly variable, with substantial fluctuations in effective moisture. Thereafter, a period of positive moisture balance is evident from ca. AD 1500-1850, with a marked reduction in the amplitude of variability. Correlations with studies from further afield suggest that ENSO, and possibly the Indian Ocean Dipole, are the key drivers of the observed shifts in moisture balance. These records constitute the first high-resolution evidence of centennial- and decadal-scale climatic variability over the last 1500 years from mainland Australia. This enables a recent major drought to be viewed in an historical context for the first time and provides insight into past climate regimes across southeastern Australia in general, and western Victoria in particular.Copyright (c) 2011 INQUA 18
Increasing the understanding and use of natural archives of ecosystem services, resilience and threholds to improve policy, science and practice
(SAGE, 2014-12-04) Pearson, S; Lynch, AJJ; Plant, R; Cork, S; Taffs, K; Dodson, JR; Maynard, S; Gergis, J; Gell, PA; Thackway, R; Sealie, L; Donaldson, J
Despite the great potential of palaeo-environmental information to strengthen natural resource policy, science and practical outcomes naturally occurring archives of palaeo-environmental and ecosystem service information have not been fully recognised or utilised to inform the development of environmental policy. In this paper, we describe how Australian palaeo-environmental science is improving environmental understanding through local studies and regional syntheses that inform us about past conditions, extreme conditions and altered ecosystem states. Australian innovations in ecosystem services research and palaeo-environmental science contribute in five important contexts: discussions about environmental understanding and management objectives, improving access to information, improved knowledge about the dynamics of ecosystem services, increasing understanding of environmental processes and resource availability, and engaging interdisciplinary approaches to manage ecosystem services. Knowledge of the past is an important starting point for setting present and future resource management objectives, anticipating consequences of trade-offs, sharing risk and evaluating and monitoring the ongoing availability of ecosystem services. Palaeo-environmental information helps reframe discussions about desirable futures and collaborative efforts between scientists, planners, managers and communities. However, further steps are needed to translate the ecosystem services concept into ecosystem services policy and tangible management objectives and actions that are useful, feasible and encompass the range of benefits to people from ecosystems. We argue that increased incorporation of palaeo-environmental information into policy and decision-making is needed for evidence-based adaptive management to enhance sustainability of ecosystem functions and reduce long-term risks. © 2020 by SAGE Publications
Industrial past, urban future: using palaeo-studies to determine the industrial legacy of the Barwon Estuary, Victoria, Australia.
(CSIRO Publishing, 2015-11-27) Reeves, JM; Gell, PA; Reichman, SM; Trewarn, AJ; Zawadzki, A
Around the globe, heavy industry has often been associated with estuaries, which provide water for operations, waste disposal and navigation. Many of these practices leave a legacy of contamination, which accumulate in the estuaries, which act as sediment sinks. Heavy metal contaminants may remain buried, even after the industrial practices are ceased. The Connewarre Complex is a series of wetlands, within the Port Philip and Bellarine Ramsar site. Through a unique combination of techniques, including diatom assemblages, biogeochemistry (δ13C, δ15N, C/N) and heavy metal content, the major anthropogenic influences over the last 170 years and the biotic response has been determined. Key features that can be elucidated include regulation of the waterways, establishment of heavy industry and major shifts in climatic conditions. In combination, these drivers have acted to rapidly shift the condition of the wetland from early in settlement such that the perceived ‘natural ecological character’ is actually an artificial one. The legacy of contamination is common to many Ramsar-listed wetlands. The lesson from this site is that, when making plans to manage the ecological condition of a wetland, past use needs to be considered to ensure that well meaning interventions do not exacerbate risk of mobilising contaminants best left undisturbed. © CSIRO 1996-2020
Interaction between a river and its wetland: evidence from the Murray River for spatial variability in diatom and radioisotope records
(Springer, 2012-02-01) Grundell, R; Gell, PA; Mills, K; Zawadzki, A
Sinclair Flat is small wetland, located within the gorge section of the Murray River floodplain. situated near Blanchetown, South Australia, the wetland is closely linked to the River and, since regulation, has become permanently inundated. High summer evaporation rates deplete the volume of water within the wetland. However, this is compensated by perennial inflow via a permanent inlet from the River. This site provides an opportunity to explore the relative contribution of river and wetland diatomflora to the sediment record, and the fluvial and aerial contribution of radiometric isotopes to the system. The geochronological and biostratigraphic data provide an insight into the history of the water quality of Sinclair Flat. Evidence exists for the River being a source of sediments and isotopes and of diatom species typical of the main river channel. Prior to 1950, Sinclair Flat was an oligotrophic, oligosaline, clear-water wetland. The wetland shifted gradually to an environment that favoured clear-water benthic species, most likely as a consequence of changes following river regulation in the 1920s, although the capacity to date these sediments is limited. During the 1950s, the wetland became plankton dominated. Peaks in epiphytic diatoms during the 1960s suggest increased emergent macrophyte cover. The contemporary condition is of a connected, turbid, eutrophic and mesosaline lagoon. The ecological condition of Sinclair Flat has diverged considerably from its historical range of condition. This record supports evidence from upstream of widespread state switches in the Murray-Darling Basin floodplain wetlands. This record also lends considerable weight to modern studies attesting to the degraded state of the waterways of the Murray-Darling Basin and the impact of river regulation practices on the water quality of these ecosystems.© 2012, Springer.
Late holocene evolution of the coastal and estuarine lakes of the Snowy River floodplain (SE Australia): salinity regimes, nutrient dynamics and anthropogenic impacts
(Elsevier, 2007-07) MacGregor, A; Gell, PA; Tibby, J; Harrison, JJ; Jacobsen, GE; Hancock, G
Coastal lake and estuarine systems across south eastern Australia act as both sedimentary and biological amplifiers, and are more sensitive to cumulative catchment-driven hydrological change than previously recognised (see Tibby et al., this volume). Deciphering natural responses to climate change and geomorphology, and ensuing historical responses to catchment clearance and regulation reveals whether these systems now lie within pre-disturbance variability, and the extent to which anthropogenic change is unidirectional. A multi-proxy palaeoecological assessment of the terminal coastal and estuarine lakes of the Snowy River floodplain will be presented. The Snowy River is one of Australia’s hallmark river systems. Its catchment has been substantially modified since the mid 1800s. The ecological and water quality impacts of a major inter-basin transfer of up to 99% of its flow since the mid 1960s are poorly understood. Incorporating a diatom-water quality inference model, stable isotope and fossil pigment reconstruction, this study has examined (a) notions of variability in the progressive evolution of the system (b) how the records compare to that of a relatively un-impacted (control) system nearby (c) the influence of natural perturbations on the ecology of these lakes (with respect to salinity and nutrient status), as well as (d) the nature and timing of anthropogenic disturbance. Explained as a combination of land clearance, drainage practices, and more recently, substantial flow diversion in the Snowy River, recent water quality changes are as pronounced as any experienced through the Holocene. However, they have occurred at a rate faster than those brought on by past climatic or geomorphic change.
Palaeoecological evidence for sustained change in a shallow Murray River (Australia) floodplain lake: regime shift or press response
(Springer Link, 2017-02-01) Kattel, G; Gell, PA; Zawadzki, A; Barry, LA
Paleolimnological techniques can reveal long-term perturbations and associated stable state transitions of lake ecosystems. However, such transitions are difficult to predict since changes to lake ecosystems can be abrupt or gradual. This study examined whether there were past transitions in the ecological regime of Kings Billabong, a shallow River Murray wetland in southeast Australia. A 94-cm-long core, covering c. 90 years of age, was analysed at 1 cm resolution for subfossil cladocerans, diatoms and other proxies. Prior to river regulation (c. 1930), the littoral to planktonic ratios of cladocerans and diatoms, and bulk sediment δ13C values were high, while the period from c. 1930 to c. 1970 experienced considerable changes to the wetland ecosystem. The abrupt nature of changes of planktonic cladocerans and diatoms, particularly after the onset of river regulation (1930s), was triggered by inundation, high rates of sedimentation and shifts in bulk sediment δ15N values. However, the transition of a once littoral-dominated community, to one favouring an increasingly turbid, plankton-dominated trophic condition following river regulation was relatively slow and lasted for decades. The progression to a new regime was likely delayed by the partial recovery of submerged plant communities and related internal dynamics.© 2016, Springer International Publishing Switzerland.
Paleoclimate studies and natural-resource management in the Murray-Darling Basin I: past, present and future climates
(Taylor & Francis, 2013-06-19) Mills, K; Gell, PA; Hesse, PP; Jones, R; Kershaw, P; Drysdale, RN; McDonald, J
This paper provides an incisive review of paleoclimate science and its relevance to natural-resource management within the Murray-Darling Basin (MDB). The drought of 1997–2010 focussed scientific, public and media attention on intrinsic climate variability and the confounding effect of human activity, especially in terms of water-resource management. Many policy and research reviews make statements about future planning with little consideration of climate change and without useful actionable knowledge. In order to understand future climate changes, modellers need, and demand, better paleoclimate data to constrain their model projections. Here, we present an insight into a number of existing long-term paleoclimate studies relevant to the MDB. Past records of climate, in response to orbital forcing (glacial–interglacial cycles) are found within, and immediately outside, the MDB. High-resolution temperature records, spanning the last 105 years, exist from floodplains and cave speleothems, as well as evidence from lakes and their associated lunettes. More recently, historical climate records show major changes in relation to El Niño–Southern Oscillation cycles and decadal shifts in rainfall regimes. A considerable body of research currently exists on the past climates of southeastern Australia but, this has not been collated and validated over large spatial scales. It is clear that a number of knowledge gaps still exist, and there is a pressing need for the establishment of new paleoclimatic research within the MDB catchment and within adjacent, sensitive catchments if past climate science is to fulfil its potential to provide policy-relevant information to natural-resource management into the future. © 2013, Taylor & Francis.
Paleoclimate studies and natural-resource management in the Murray-Darling Basin II: unravelling human impacts and climate variability
(Taylor and Francis Group, 2013-08-09) Mills, K; Gell, PA; Gergis, J; Baker, PJ; Finlayson, CM; Hesse, PP; Jones, R; Kershaw, P; Pearson, S; Treble, PC; Barr, C; Brookhouse, MT; Drysdale, RN; McDonald, J; Haberle, SG; Reid, M; Thoms, M; Tibby, J
The management of the water resources of the Murray-Darling Basin (MDB) has long been contested, and the effects of the recent Millennium drought and subsequent flooding events have generated acute contests over the appropriate allocation of water supplies to agricultural, domestic and environmental uses. This water-availability crisis has driven demand for improved knowledge of climate change trends, cycles of variability, the range of historical climates experienced by natural systems and the ecological health of the system relative to a past benchmark. A considerable volume of research on the past climates of southeastern Australia has been produced over recent decades, but much of this work has focused on longer geological time-scales, and is of low temporal resolution. Less evidence has been generated of recent climate change at the level of resolution that accesses the cycles of change relevant to management. Intra-decadal and near-annual resolution (high-resolution) records do exist and provide evidence of climate change and variability, and of human impact on systems, relevant to natural-resource management. There exist now many research groups using a range of proxy indicators of climate that will rapidly escalate our knowledge of management-relevant, climate change and variability. This review assembles available climate and catchment change research within, and in the vicinity of, the MDB and portrays the research activities that are responding to the knowledge need. It also discusses how paleoclimate scientists may better integrate their pursuits into the resource-management realm to enhance the utility of the science, the effectiveness of the management measures and the outcomes for the end users. © 2020 Informa UK Limited
Paleolimological investigation of the use of stable isotopes of carbon and nitrogen in bulk sediment and cladoceran zooplankton to reveal ecosystem changes in Kings Billaong Northwest Victoria, Australia
(University of Western Australia, 2013-07-10) Kattel, G; Gell, PA; Zawadzki, A; Barry, LA
Northwest Victoria hosts a large number of shallow floodplain wetlands along the Murray River system. One of these, Kings Billabong, is known for its high conservation values. However, the naturally occurring flood pulses, which maintain ecological connectivity between river and wetlands, have been altered impacting the ecology of Kings Billabong. The human-induced river regulation in the Murray River following the arrival of Europeans, and increased farming activities around Mildura for irrigation, has switched Kings Billabong to a permanent water regime resulting in accelerated sedimentation rates and changed sources of carbon and, subsequently, altered ecological character. This study focuses on a 90 cm long sediment core taken from Kings Billabong in 2011, where the 210Pb dating detected sediments at c. 60 cm depth to be c. 65 years old. Around this time (c. 1940-1945 AD), a systemic change occurred in the billabong. The enrichment of carbon substantially declined, while, in the meantime, nitrogen enrichment increased. Coincidently, the subfossil cladoceran zooplankton assemblages revealed changes in the limnological conditions of the wetland ecosystem. Among the littoral species, the Chydorus sphaericus group, which prefers eutrophic water, became dominant. Since the early 2000s, the abundance of Biapertura affinis, a pioneer plant dwelling species, has declined. Before the assemblage of B. affinis began to decline, a large number of cladoceran ephippia were recorded in sediment samples indicating the elevated stress in the wetland. This study suggests that paleolimnological investigations, together with the use of stable isotopes of carbon and nitrogen in sediment samples, provides an opportunity to reveal the impacts of anthropogenic disturbances on the floodplain wetlands of the Murray River system across northwest Victoria, and potentially more widely across Australia. © The Authors.

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