Browsing by Author "Grice, K"

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    Agriculture and environmental change at Qingpu, Yangtze delta region, China: a biomarker, stable isotope and palynological approach
    (SAGE Publications, 2007-05) Atahan, P; Grice, K; Dodson, JR
    Rice (Oryza sp.) agriculture sustains vast numbers of people and, despite great advancements made in recent years, questions about its origins and spread throughout Asia remain unanswered. This study uses sedimentary biomarker, stable carbon isotope and palynological analyses to investigate early rice agriculture in the Yangtze delta, a region where rice agriculture emerged at least 7000 years ago. Accelerator mass spectrometer (AMS) C-14 dating reveals the age of sedimentary section to be between c. 6000 and 1800 cal. BP. Widespread clearing of forest vegetation c. 2400 cal. BP, is the earliest major human influence detected in the Qingpu record. Following this, rice agriculture probably dominated the Qingpu area. Evidence supporting rice agriculture after c. 2400cal. BP is provided by increased Poaceae and Cereal-type taxa, which occur with high concentrations of plant wax n-alkanes with a dominant C-3 plant origin (C-27-C-31 with odd/even preference, delta C-13 -29.8 parts per thousand to -36.3 parts per thousand). Also, high concentrations of a C-20 highly branched isoprenoid (HBI) thought to be from epiphytic algae associated with rice agriculture occur after c. 2400cal. BP. C-13-depleted diploptene (in high concentrations) and C-13-depleted C-31 3b-methylhopanes of methanotrophic bacterial origin also occur after c. 2400cal. BP. The strong methane cycle detected in the trench sediment may have provided an alternative CO2 source for plants and algae associated with rice agriculture. © 2007, SAGE Publications
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    Early Neolithic diets at Baijia, Wei River valley, China: Stable carbon and nitrogen isotope analysis of human and faunal remains
    (Past Global Changes, 2013-02-13) Atahan, P; Dodson, JR; Li, XQ; Zhou, XY; Hu, S; Chen, L; Bertuch, F; Grice, K
    The first farmers of the Wei River valley belonged to the Laoguantai period (ca. 8500-7000 yr BP) and lived in small settlements that were sparsely distributed in the landscape. Understanding of Laoguantai farming practices is limited as only a small number of archaeological sites are known. Here we present stable carbon and nitrogen isotope values for faunal and human bone collagen from Baijia, a Laoguantai site in the Wei River valley of Shaanxi Province, China. Five of the collagen samples have been AMS 14C dated and have a calibrated age range of ca. 7659-7339 yr BP. Stable isotope results show millet and aquatic foods, such as fish and shellfish, being included in the human diet. Bovid samples, which are tentatively identified as water buffalo, have stable carbon isotope values reflecting some millet consumption. The question of whether these bovids were grazing on millet growing wild, or had diets directly influenced by humans, remains to be answered. Stable isotope results for a single pig reveal a markedly different diet, one dominated by C3 plants which would have dominated natural vegetation of the region. Overall, stable isotope results conform to the current view of Laoguantai people being millet farmers with subsistence strategies that included hunted wild foods.
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    Elucidating stygofaunal trophic web interactions via isotopic ecology
    (PLOS One, 2019-10-16) Saccò, M; Blyth, AJ; Humphreys, WF; Kuhl, A; Mazumder, D; Smith, C; Grice, K
    Subterranean ecosystems host highly adapted aquatic invertebrate biota which play a key role in sustaining groundwater ecological functioning and hydrological dynamics. However, functional biodiversity studies in groundwater environments, the main source of unfrozen freshwater on Earth, are scarce, probably due to the cryptic nature of the systems. To address this, we investigate groundwater trophic ecology via stable isotope analysis, employing δ13C and δ15N in bulk tissues, and amino acids. Specimens were collected from a shallow calcrete aquifer in the arid Yilgarn region of Western Australia: a well-known hot-spot for stygofaunal biodiversity. Sampling campaigns were carried out during dry (low rainfall: LR) and the wet (high rainfall: HR) periods. δ13C values indicate that most of the stygofauna shifted towards more 13C-depleted carbon sources under HR, suggesting a preference for fresher organic matter. Conversion of δ15N values in glutamic acid and phenylalanine to a trophic index showed broadly stable trophic levels with organisms clustering as low-level secondary consumers. However, mixing models indicate that HR conditions trigger changes in dietary preferences, with increasing predation of amphipods by beetle larvae. Overall, stygofauna showed a tendency towards opportunistic and omnivorous habits—typical of an ecologically tolerant community—shaped by bottom-up controls linked with changes in carbon flows. This study provides baseline biochemical and ecological data for stygofaunal trophic interactions in calcretes. Further studies on the carbon inputs and taxa-specific physiology will help refine the interpretation of the energy flows shaping biodiversity in groundwaters. This will aid understanding of groundwater ecosystem functioning and allow modelling of the impact of future climate change factors such as aridification. Subterranean ecosystems host highly adapted aquatic invertebrate biota which play a key role in sustaining groundwater ecological functioning and hydrological dynamics. However, functional biodiversity studies in groundwater environments, the main source of unfrozen freshwater on Earth, are scarce, probably due to the cryptic nature of the systems. To address this, we investigate groundwater trophic ecology via stable isotope analysis, employing δ13C and δ15N in bulk tissues, and amino acids. Specimens were collected from a shallow calcrete aquifer in the arid Yilgarn region of Western Australia: a well-known hot-spot for stygofaunal biodiversity. Sampling campaigns were carried out during dry (low rainfall: LR) and the wet (high rainfall: HR) periods. δ13C values indicate that most of the stygofauna shifted towards more 13C-depleted carbon sources under HR, suggesting a preference for fresher organic matter. Conversion of δ15N values in glutamic acid and phenylalanine to a trophic index showed broadly stable trophic levels with organisms clustering as low-level secondary consumers. However, mixing models indicate that HR conditions trigger changes in dietary preferences, with increasing predation of amphipods by beetle larvae. Overall, stygofauna showed a tendency towards opportunistic and omnivorous habits—typical of an ecologically tolerant community—shaped by bottom-up controls linked with changes in carbon flows. This study provides baseline biochemical and ecological data for stygofaunal trophic interactions in calcretes. Further studies on the carbon inputs and taxa-specific physiology will help refine the interpretation of the energy flows shaping biodiversity in groundwaters. This will aid understanding of groundwater ecosystem functioning and allow modelling of the impact of future climate change factors such as aridification. © 2019 Saccò et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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    Exceptionally well-preserved cutin in extinct seed ferns (carboniferous): are these early angiosperms?
    (2019-09-01) Tripp, M; Rickard, WDA; Whiteside, J; Gadd, PS; Grice, K
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    Glacial and Holocene terrestrial temperature variability in subtropical east Australia as inferred from branched GDGT distributions in a sediment core from Lake McKenzie.
    (Elsevier Inc., 2014-07-01) Woltering, M; Atahan, P; Grice, K; Heijnis, H; Taffs, K; Dodson, JR
    Branched glycerol dialkyl glycerol tetraether (GDGT) distributions observed in a sediment core from Lake McKenzie were utilized to quantitatively reconstruct the pattern of mean annual air temperature (MAAT) from coastal subtropical eastern Australia between 37 and 18.3 cal ka BP and 14.0 cal ka BP to present. Both the reconstructed trend and amplitude of MAAT changes from the top of the sediment core were nearly identical to a local instrumental MAAT record from Fraser Island, providing confidence that in this sediment core branched GDGTs could be used to produce a quantitative record of past MAAT. The reconstructed trend of MAAT during 37 to 183 cal ka BP and timing of the Last Glacial Maximum (LGM) in the Lake McKenzie record were in agreement with previously published nearby marine climate records. The amplitude of lower-than-present MAAT during the LGM potentially provides information on the latitude of separation of the Tasman Front from the East Australian current in the subtropical western Pacific. The Lake McKenzie record shows an earlier onset of near modern day warm temperatures in the early Holocene compared to marine records and the presence of a warmer than present day period during the mid-Holocene. © 2014, Elsevier Inc.
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    Late quaternary environmental change at Lake McKenzie, in subtropical eastern Australia: evidence from sedimentary carbon, nitrogen and biomarkers
    (Past Global Changes, 2013-02-13) Atahan, P; Heijnis, H; Le Métayer, P; Grice, K; Taffs, K; Hembrow, SC; Dodson, JR
    Fraser Island is part of a large sand mass that extends along the subtropical coastline of south-eastern Queensland. The island is a World Heritage site, listed for its unique natural environment that includes numerous perched oligotrophic dune lakes and a diverse suite of coastal and subtropical vegetation communities. Here we present geochemical and microfossil information for a sediment core collected from Lake McKenzie, in the island’s centre. AMS 14C and 210Pb dating has been conducted and indicates a basal age of ca. 37,000 cal. BP. A hiatus in the sedimentary record is apparent at around 25 cm depth and spans the time period from ca. 18,280 to 13,990 cal yr BP. Elemental and stable isotope measurements of carbon and nitrogen in bulk organic matter, along with biomarker and compound specific carbon isotope analyses, show a clear shift in lake conditions appearing with the re-commencement of sediment accumulation following this hiatus. A marked decline in the abundance of microfossils of the green colonial algae Botryococcus, coincides with a distinct change in composition of Botryococcus derived lipids and a shift to more negative δ13C values of long chain odd n-alkane compounds. An increase in lake size around 13,990 cal yr BP is suggested by the recommencement of sediment accumulation at the site, and is presumably in response to increased effective precipitation. The lake McKenzie record provides a long-term perspective on changing environmental conditions in central Fraser Island.
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    Late quaternary environmental change at Lake McKenzie, Southeast Queensland: evidence from microfossils, biomarkers and stable isotope analysis
    (University of Western Australia, 2013-07-10) Atahan, P; Heijnis, H; Dodson, JR; Grice, K; Le Métayer, P; Taffs, K; Hembrow, SC; Woltering, M; Zawadzki, A
    Unravelling links between climate change and vegetation response during the Quaternary is a research priority, and needed if the climate-environment interactions of modern systems are to be fully understood. Using a sediment core from Lake McKenzie, Fraser Island, we reconstruct changes in the lake ecosystem and surrounding vegetation over the last ca. 36.9 cal kyr BP. Evidence is drawn from multiple sources, including pollen, micro-charcoal, biomarker and stable isotope (C and N) analyses, and is used to improve understanding about the timing and spatial scale of past changes that have occurred locally and in the southeast Queensland region. The glacial period of the record, from ca. 36.9-18.3 cal kyr BP, is characterised by lower lake water levels and increased abundance of, or closer proximity to, plants of the aquatic and littoral zone. High abundance of biomarkers and microfossils of the colonial green alga Botryococcus occur at this time and include high variation in individual botryococcene 13C values. A distinct period of dry or ephemeral conditions at the site is detected during deglaciation, causing a hiatus in the sedimentary record covering the time period from ca. 18.3-14.0 cal kyr BP. The recommencement of sediment accumulation around 14.0 cal kyr BP occurs with evidence of lower fire activity in the area and reduced abundance of terrestrial herbs in the surrounding sclerophyll vegetation. The Lake McKenzie record conforms to existing records from Fraser Island by containing evidence for a mid-Holocene dry period, spanning the time period from ca. 6.1-2.5 cal kyr BP. © The Authors
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    Lipid abundance and stable isotopic composition of photosynthetic microbial mats in hypersaline embayments at Shark Bay, Western Australia
    (Australasian Environmental Isotope Conference, 2009-12-03) Ertefai, T; Jahnert, R; Grice, K; Dodson, JR; Collins, L
    Photosynthetic microbial mats and living stromatolites/microbialites in hypersaline embayments at Shark Bay, Western Australia are significant microbial niches. Cyanobacteria together with a consortium of microbes form microbialites/stromatolites. These organisms are important as it is believed they evolved some 3.5 billion years ago. In this study, modern analogues of the fossilised counterparts (Pilbara, WA) are being investigated to provide clues to the origin of life on early Earth. The distribution and growth of different microbial mats across the hypersaline coastal plain of Shark Bay is thought to be attributed to a complex network of physicochemical factors [1]. The relationship of internal mat structures (lithification), geochemical conditions and microbial community structure, are not well understood. A complex interplay of different metabolic pathways, microbial physiologies (including of cyanobacteria, sulphur cycling organisms and Archaea) may play a role in the differentiation of the lithifying vs. non-lithifying mats [2]. In this study, we have applied a variety of different analytical techniques to address the biological, geochemical and geological makeup of microbial mats from four embayments differing in salinity levels. We wish to link the different morphotypes of microbial mats with their biology and chemistry to understand the regional occurrence and enhance our geological interpretation. Biomarker abundances determined by both, liquid chromatography (LC), gas chromatography (GC) and mass spectrometry (MS) provide clues to the microbial community structure. Here we report for first time the presence of intact polar lipids (IPLs) and bacteriohopanepolyols (BHPs) by LC-MS specific to cyanobacteria and other microbes. Compound-specific isotope analysis (CSIA) of carbon and hydrogen reflects the metabolic pathways and the hydrologic conditions (including salinity). Hydro Pyrolysis (HyPy) experiments of the non-extractable organics reveal biomarkers similar to those reported in the rock record. The IPLs of microbial mats collected at the internal pond of Garden Point (salinity ~40-80‰, depending on season and tide) shows a complex distribution of different glyco- and phospholipids (Fig. 1). These IPLs can be attributed to different groups of microorganisms. Phospholipids, and specifically PG, are present in all phototrophic bacteria [3]. The presence of ornithine lipids and the sulpholipid SQ-DAG has been described in oxygenic and anoxygenic phototrophs, such as cyanobacteria and purple (non-) sulphur bacteria [3, 4]. Latter group uses sulphur, sulphide or hydrogen as an electron donor which do not evolve oxygen as a byproduct, and causes mat colouration. With the analysis of carbon and hydrogen stable isotopes of the hydrolysed biolipids, we can gain further insights into the biogeochemical conditions and biochemical pathways. We especially focus on the domain Archaea, as their role in the Shark Bay microbialites are poorly understood [e.g. 2]. The role of methane cycling Archaea is being investigated via labelling experiments using 13C-enriched bicarbonate and methane. Hydrogenotrophic methanogenesis and methanotrophy will be quantified via solvent extraction of biolipids and the uptake of labelled substrates into their specific biolipids by CSIA.
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    Millet agriculture in north-central China: evidence from human remains
    (Australasian Quaternary Association, 2010-07-16) Atahan, P; Dodson, JR; Li, XQ; Zhou, XY; Chen, L; Grice, K
    Not available - Powerpoint slides only.
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    New insights into the origin of perylene in geological samples.
    (Elsevier, 2009-11-01) Grice, K; Lu, H; Atahan, P; Asif, M; Hallmann, C; Greenwood, P; Maslen, E; Tulipani, S; Williford, K; Dodson, JR
    The origin of the polycyclic aromatic hydrocarbon (PAH) perylene in sediments and petroleum has been a matter of continued debate. Reported to occur in Phanerozoic organic matter (OM), fossil crinoids and tropical termite mounds, its mechanism of formation remains unclear. While a combustion source can be excluded, structural similarities to perylene quinone-like components present in e.g. fungi, plants, crinoids and insects, potentially suggest a product–precursor relationship. Here, we report perylene concentrations, 13C/12C, and D/H ratios from a Holocene sediment profile from the Qingpu trench, Yangtze Delta region, China. Perylene concentrations differ from those of pyrogenic PAHs, and rise to prominence in a stratigraphic interval that was dominated by woody vegetation as determined by palynology including fungal spores. In this zone, perylene concentrations exhibit an inverse relationship to the lignin marker guaiacol, D/H ratios between −284‰ and −317‰, similar to the methoxy groups in lignin, as well as co-variation with spores from wood-degrading fungi. 13C/12C of perylene differs from that of land plant wax alkanes and falls in the fractionation range expected for saprophytic fungi that utilise lignin, which is isotopically lighter than cellulose and whole wood. During progressive lignin degradation, the relative carbon isotopic ratio of the perylene decreases. We therefore hypothesise a relationship of perylene to the activity of wood-degrading fungi. To support our hypothesis, we analysed a wide range of Phanerozoic sediments and oils, and found perylene to generally be present in subordinate amounts before the evolutionary rise of vascular plants, and to be generally absent from marine-sourced oils, few exceptions being attributed perhaps to a contribution of marine and/or terrestrial-derived fungi, anoxia (especially under marine conditions) and/or contamination of core material by fungi. A series of low-molecular-weight aromatic quinones bearing the perylene-backbone were detected in Devonian and Cretaceous sediments, potentially representing precursor components to perylene. © 2009, Elsevier Ltd.
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    New light in the dark - a proposed multidisciplinary framework for studying functional ecology of groundwater fauna
    (Elsevier, 2019-04-20) Saccò, M; Blyth, AJ; Bateman, PW; Hua, Q; Mazumder, D; White, NE; Humphreys, WF; Laini, A; Griebler, C; Grice, K
    Groundwaters provide the vast majority of unfrozen freshwater resources on the planet, but our knowledge of subsurface ecosystems is surprisingly limited. Stygofauna, or stygobionts -subterranean obligate aquatic animals - provide ecosystem services such as grazing biofilms and maintaining water quality, but we know little about how their ecosystems function. The cryptic nature of groundwaters, together with the high degree of local endemism and stygofaunal site-specific adaptations, represent major obstacles for the field. To overcome these challenges, and integrate biodiversity and ecosystem function, requires a holistic design drawing on classical ecology, taxonomy, molecular ecology and geochemistry. This study presents an approach based on the integration of existing concepts in groundwater ecology with three more novel scientific techniques: compound specific stable isotope analysis (CSIA) of amino acids, radiocarbon analysis (14C) and DNA analyses of environmental samples, stygofauna and gut contents. The combination of these techniques allows elucidation of aspects of ecosystem function that are often obscured in small invertebrates and cryptic systems. Carbon (δ13C) and nitrogen (δ15N) CSIA provides a linkage between biogeochemical patterns and ecological dynamics. It allows the identification of stygofaunal food web structures and energy flows based on the metabolic pathway of specific amino groups. Concurrently, 14C provides complementary data on the carbon recycling and incorporation within the stygobiotic trophic webs. Changes in groundwater environmental conditions (e.g. aquifer recharge), and subsequent community adaptations, can be pinpointed via the measurement of the radiocarbon fingerprint of water, sediment and specimens. DNA analyses are a rapidly expanding approach in ecology. eDNA is mainly employed as a biomonitoring tool, while metabarcoding of individuals and/or gut contents provides insight into diet regimes. In all cases, the application of the approaches in combination provides more powerful data than any one alone. By combining quantitative (CSIA and 14C) and qualitative (eDNA and DNA metabarcoding) approaches via Bayesian Mixing Models (BMM), linkages can be made between community composition, energy and nutrient sources in the system, and trophic function. This suggested multidisciplinary design will contribute to a more thorough comprehension of the biogeochemical and ecological patterns within these undervalued but essential ecosystems. © 2019 Elsevier B.V.
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    Pollen, biomarker and stable isotope evidence of late quaternary environmental change at Lake McKenzie, southeast Queensland
    (Springer, 2014-10-30) Atahan, P; Heijnis, H; Dodson, JR; Grice, K; Le Métayer, P; Taffs, K; Hembrow, SC; Woltering, M; Zawadzki, A
    Unravelling links between climate change and vegetation response during the Quaternary is important if the climate–environment interactions of modern systems are to be fully understood. Using a sediment core from Lake McKenzie, Fraser Island, we reconstruct changes in the lake ecosystem and surrounding vegetation over the last ca. 36.9 cal kyr. Evidence is drawn from multiple sources, including pollen, micro-charcoal, biomarker and stable isotope (C and N) analyses, and is used to gain a better understanding of the nature and timing of past ecological changes that have occurred at the site. The glacial period of the record, from ca. 36.9 to 18.3 cal kyr BP, is characterised by an increased abundance of plants of the aquatic and littoral zone, indicating lower lake water levels. High abundance of biomarkers and microfossils of the colonial green alga Botryococcus occurred at this time and included large variation in individual botryococcene δ13C values. A slowing or ceasing of sediment accumulation occurred during the time period from ca. 18.3 to 14.0 cal kyr BP. By around 14.0 cal kyr BP fire activity in the area was reduced, as was abundance of littoral plants and terrestrial herbs, suggesting wetter conditions from that time. The Lake McKenzie pollen record conforms to existing records from Fraser Island by containing evidence of a period of reduced effective precipitation that commenced in the mid-Holocene. © Springer Science+Business Media Dordrecht 2014
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    Preservation of terrestrial microorganisms and organics within alteration products of chondritic meteorites from the Nullarbor Plain, Australia
    (Mary Ann Liebert, Inc., 2022-04-13) Tait, AW; Wilson, SA; Tomkins, AG; Hamilton, JL; Gagen, EJ; Holman, AI; Grice, K; Preston, LJ; Paterson, DJ; Southam, G
    Meteorites that fall to Earth quickly become contaminated with terrestrial microorganisms. These meteorites are out of chemical equilibrium in the environments where they fall, and equilibration promotes formation of low-temperature alteration minerals that can entomb contaminant microorganisms and thus preserve them as microfossils. Given the well-understood chemistry of meteorites and their recent discovery on Mars by rovers, a similarly weathered meteorite on Mars could preserve organic and fossil evidence of a putative past biosphere at the martian surface. Here, we used several techniques to assess the potential of alteration minerals to preserve microfossils and biogenic organics in terrestrially weathered ordinary chondrites from the Nullarbor Plain, Australia. We used acid etching of ordinary chondrites to reveal entombed fungal hyphae, modern biofilms, and diatoms within alteration minerals. We employed synchrotron X-ray fluorescence microscopy of alteration mineral veins to map the distribution of redox-sensitive elements of relevance to chemolithotrophic organisms, such as Mn-cycling bacteria. We assessed the biogenicity of fungal hyphae within alteration veins using a combination of Fourier-transform infrared spectroscopy and pyrolysis gas chromatography-mass spectrometry, which showed that alteration minerals sequester and preserve organic molecules at various levels of decomposition. Our combined analyses results show that fossil microorganisms and the organic molecules they produce are preserved within calcite–gypsum admixtures in meteorites. Furthermore, the distributions of redox-sensitive elements (e.g., Mn) within alteration minerals are localized, which qualitatively suggests that climatically or microbially facilitated element mobilization occurred during the meteorite's residency on Earth. If returned as part of a sample suite from the martian surface, ordinary chondrites could preserve similar, recognizable evidence of putative past life and/or environmental change. © 2022 Mary Ann Liebert, Inc
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    Rainfall as a trigger of ecological cascade effects in an Australian groundwater ecosystem
    (Springer Nature Limited, 2021-02-12) Saccò, M; Blyth, AJ; Humphreys, WF; Cooper, SJB; White, NE; Mousavi-Derazmahalleh, M; Hua, Q; Mazumder, D; Smith, C; Griebler, C; Grice, K
    Groundwaters host vital resources playing a key role in the near future. Subterranean fauna and microbes are crucial in regulating organic cycles in environments characterized by low energy and scarce carbon availability. However, our knowledge about the functioning of groundwater ecosystems is limited, despite being increasingly exposed to anthropic impacts and climate change-related processes. In this work we apply novel biochemical and genetic techniques to investigate the ecological dynamics of an Australian calcrete under two contrasting rainfall periods (LR—low rainfall and HR—high rainfall). Our results indicate that the microbial gut community of copepods and amphipods experienced a shift in taxonomic diversity and predicted organic functional metabolic pathways during HR. The HR regime triggered a cascade effect driven by microbes (OM processors) and exploited by copepods and amphipods (primary and secondary consumers), which was finally transferred to the aquatic beetles (top predators). Our findings highlight that rainfall triggers ecological shifts towards more deterministic dynamics, revealing a complex web of interactions in seemingly simple environmental settings. Here we show how a combined isotopic-molecular approach can untangle the mechanisms shaping a calcrete community. This design will help manage and preserve one of the most vital but underrated ecosystems worldwide. © 2021 The Authors Open Access This article is licensed under a Creative Commons Attribution 4.0 International Licence.
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    Refining trophic dynamics through multi-factor Bayesian mixing models: a case study of subterranean beetles
    (John Wiley & Sons, Inc, 2020-07-20) Saccò, M; Blyth, AJ; Humphreys, WF; Cooper, SJB; Austin, AD; Hyde, J; Mazumder, D; Hua, Q; White, NE; Grice, K
    Food web dynamics are vital in shaping the functional ecology of ecosystems. However, trophic ecology is still in its infancy in groundwater ecosystems due to the cryptic nature of these environments. To unravel trophic interactions between subterranean biota, we applied an interdisciplinary Bayesian mixing model design (multi-factor BMM) based on the integration of faunal C and N bulk tissue stable isotope data (δ13C and δ15N) with radiocarbon data (Δ14C), and prior information from metagenomic analyses. We further compared outcomes from multi-factor BMM with a conventional isotope double proxy mixing model (SIA BMM), triple proxy (δ13C, δ15N, and Δ14C, multi-proxy BMM), and double proxy combined with DNA prior information (SIA + DNA BMM) designs. Three species of subterranean beetles (Paroster macrosturtensis, Paroster mesosturtensis, and Paroster microsturtensis) and their main prey items Chiltoniidae amphipods (AM1: Scutachiltonia axfordi and AM2: Yilgarniella sturtensis), cyclopoids and harpacticoids from a calcrete in Western Australia were targeted. Diet estimations from stable isotope only models (SIA BMM) indicated homogeneous patterns with modest preferences for amphipods as prey items. Multi-proxy BMM suggested increased—and species-specific—predatory pressures on amphipods coupled with high rates of scavenging/predation on sister species. SIA + DNA BMM showed marked preferences for amphipods AM1 and AM2, and reduced interspecific scavenging/predation on Paroster species. Multi-factorial BMM revealed the most precise estimations (lower overall SD and very marginal beetles' interspecific interactions), indicating consistent preferences for amphipods AM1 in all the beetles' diets. Incorporation of genetic priors allowed crucial refining of the feeding preferences, while integration of more expensive radiocarbon data as a third proxy (when combined with genetic data) produced more precise outcomes but close dietary reconstruction to that from SIA + DNA BMM. Further multidisciplinary modeling from other groundwater environments will help elucidate the potential behind these designs and bring light to the feeding ecology of one the most vital ecosystems worldwide. © 2020 The Authors, published by John Wiley & Sons Ltd.
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    Stygofaunal community trends along varied rainfall conditions: deciphering ecological niche dynamics of a shallow calcrete in Western Australia
    (John Wiley & Sons, Inc, 2019-09-16) Saccò, M; Blyth, AJ; Humphreys, WF; Karasiewicz, S; Meredith, KT; Laini, A; Cooper, SJB; Bateman, PW; Grice, K
    Groundwaters host highly adapted fauna, known as stygofauna, which play a key role in maintaining the functional integrity of subterranean ecosystems. Stygofaunal niche studies provide insights into the ecological dynamics shaping the delicate balance between the hydrological conditions and community diversity patterns. This work aims to unravel the ecological trends of a calcrete stygofaunal community, with special focus on niche dynamics through the Outlying Mean Index analysis (OMI) and additional calculation of Within Outlying Mean Indexes (WitOMI), under three rainfall regimes. Temperature and pH changed significantly among different rainfall conditions (P < .001), and together with salinity were the most influential drivers in shaping stygofaunal assemblages. These environmental conditions, linked with nutrient fluctuations in the groundwater, constrained changes in niche occupation for water mites, two species of beetles and juvenile amphipods (OMI analysis, P < .05). The WitOMI analysis revealed differential subniche breadths linked with taxa-specific adaptations after different rainfall conditions. Our results indicate that stygofaunal niches are closely linked to the hydrodynamic conditions influenced by different rainfall regimes. Further long-term investigations, incorporating broader ecological perspectives, will help to understand the impacts associated with climate change and anthropogenic pressures on one of the most threatened ecosystems in the world. © 2019 John Wiley & Sons, Ltd.
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    Tracking down carbon inputs underground from an arid zone Australian calcrete
    (Public Library of Science (PLOS), 2020-08-28) Saccò, M; Blyth, AJ; Humphreys, WF; Middleton, JA; White, NE; Campbell, M; Mousavi-Derazmahalleh, M; Laini, A; Hua, Q; Meredith, KT; Cooper, SJB; Griebler, C; Allard, S; Grierson, P; Grice, K
    Freshwater ecosystems play a key role in shaping the global carbon cycle and maintaining the ecological balance that sustains biodiversity worldwide. Surficial water bodies are often interconnected with groundwater, forming a physical continuum, and their interaction has been reported as a crucial driver for organic matter (OM) inputs in groundwater systems. However, despite the growing concerns related to increasing anthropogenic pressure and effects of global change to groundwater environments, our understanding of the dynamics regulating subterranean carbon flows is still sparse. We traced carbon composition and transformations in an arid zone calcrete aquifer using a novel multidisciplinary approach that combined isotopic analyses of dissolved organic carbon (DOC) and inorganic carbon (DIC) (δ13CDOC, δ13CDIC, 14CDOC and 14CDIC) with fluorescence spectroscopy (Chromophoric Dissolved OM (CDOM) characterisation) and metabarcoding analyses (taxonomic and functional genomics on bacterial 16S rRNA). To compare dynamics linked to potential aquifer recharge processes, water samples were collected from two boreholes under contrasting rainfall: low rainfall ((LR), dry season) and high rainfall ((HR), wet season). Our isotopic results indicate limited changes and dominance of modern terrestrial carbon in the upper part (northeast) of the bore field, but correlation between HR and increased old and 13C-enriched DOC in the lower area (southwest). CDOM results show a shift from terrestrially to microbially derived compounds after rainfall in the same lower field bore, which was also sampled for microbial genetics. Functional genomic results showed increased genes coding for degradative pathways—dominated by those related to aromatic compound metabolisms—during HR. Our results indicate that rainfall leads to different responses in different parts of the bore field, with an increase in old carbon sources and microbial processing in the lower part of the field. We hypothesise that this may be due to increasing salinity, either due to mobilisation of Cl- from the soil, or infiltration from the downstream salt lake during HR. This study is the first to use a multi-technique assessment using stable and radioactive isotopes together with functional genomics to probe the principal organic biogeochemical pathways regulating an arid zone calcrete system. Further investigations involving extensive sampling from diverse groundwater ecosystems will allow better understanding of the microbiological pathways sustaining the ecological functioning of subterranean biota. © 2020 Saccò et al
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    What’s going on down (under) there? Unravelling biochemical flows under differential rainfall periods in a Western Australian calcrete
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-24) Saccò, M; Blyth, AJ; Meredith, KT; Smith, C; Hua, Q; Mazumder, D; Humphreys, WF; White, N; Grice, K
    Groundwater is a vital resource. It contains 97% of unfrozen water on the planet, playing a key role in present and future water needs for humanity. However, our knowledge about the ecosystem functioning is very poor, and groundwater environments are increasingly exposed to anthropic impacts and climate change-related processes. Novel biochemical (e.g. isotopic ecology) and genetic (e.g. eDNA) techniques, widely employed in fresh surface water studies, have the potential to unravel the complex dynamics shaping subsurface ecosystems, providing new insights to the small but quickly growing field of groundwater ecology. Stygofauna, together with microbes, are crucial actors in shaping and maintaining the organic matter (OM) cycles in environments characterized by low energy and scarce carbon availability. In order to understand groundwater ecological patterns, we investigate calcrete stygofaunal shifts linked with contrasting rainfall periods (low rainfall (LR), dry season; high rainfall (HR), wet season), through an interdisciplinary design composed of hydrology, isotopic ecology and genetics. Our results indicate that the inflow of rainfall under HR is responsible for increased nutrient concentrations in the system and dissolved organic carbon (DOC) pulses from the surface. Both the meiofaunal and stygofaunal communities’ benefit from these organic inflows, with gamma and proteobacteria the biota that fuels carbon and nutrients to the higher levels of the trophic web. The HR regime - and its subsequent terrestrial carbon incorporation - triggers a cascade effect driven by microbes (OM processors) and amphipods (biofilm grazers), which is finally transferred to the aquatic beetles (top predators). Overall, and in line with other work in the same research area, the inflow of rainfall triggered shifts towards more deterministic dynamics, revealing a complex web of interactions in a seemingly simple environmental setting. This study provides a preliminary untangling of the biochemical flows driven by rainfall in a calcrete aquifer. More investigations involving multidisciplinary approaches on other subsurface ecosystems, i.e. alluvial aquifers, will help to understand present ecological patterns and predict future scenarios in groundwaters. © The Authors