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.
Palaeotemperature proxies based on glycerol dialkyl glycerol tetraethers (GDGTs) lipids have been established for marine and lacustrine environments, but there has been relatively little study of ...their application in speleothems. In this study we analyse the GDGT content of 33 speleothem samples from 16 different sites around the globe, and test whether proxies based on isoprenoid tetraethers (TEX86) or branched tetraethers (MBT/CBT) are correlated with measured surface and cave mean annual air temperature (MAT). The results show that the TEX86 has a strong relationship with measured temperature (r2=0.78, standard error of the estimate 2.3°C, when calibrated with surface MAT). Furthermore, the MBT/CBT also showed a significant relationship with temperature (r2=0.73, standard error of the estimate 2.7°C, when calibrated with surface MAT). Some issues remain requiring future work, in particular the development of a larger calibration sample set with measured cave temperature data, and the investigation of controls other than temperature on GDGT distribution, but overall the results indicate that GDGT based proxies derived from speleothems may be highly viable new methods for reconstructing continental palaeotemperatures.
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.
The Hexabathynella genus is the only genus of the family Parabathynellidae that has supposedly a worldwide distribution. Currently, there are 23 species described from five continents. In Australia, ...only two Hexabathynella species have been named from the eastern coast, however, a few taxa have been collected from Western Australia during stygofauna sampling as part of research studies and legislated compliance-based Environmental Impact Assessments. One of these areas includes Rottnest Island (Wadjemup), located offshore of Perth in Western Australia. Unpublished data on stygofaunal communities inhabiting the groundwater of the island refer to discrete abundances of copepods and syncarids, but no species description has been carried out. In this study, we describe two new species: Hexabathynella quokkai and H. bisetosa, expanding the characterization of the subterranean aquatic community at Rottnest Island, and using a COI, 18S and 12S sequence-based phylogeny to test the monophyletic status of the genus. Our findings shed new light on the distribution of Hexabathynella and its reported cosmopolitan distribution.
http://zoobank.org/urn:lsid:zoobank.org:act:03634EAD-4D27-4446-AE53-4248303D5020
http://zoobank.org/urn:lsid:zoobank.org:act:1B325914-90FD-471E-AC03-20741C7C925A
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.
Lignin has been analysed as a proxy for vegetation change in the Quaternary science literature since the early 1990s in archives such as peat, lakes, and intertidal and marine sediment cores. ...Historically, it has been regarded as comparatively resistant to various types of degradation in comparison to other plant components. However, studies of modern biogeochemical processes affecting organic carbon have demonstrated significant degradation and alteration of lignin as it is transported through the terrestrial biosphere, including phase changes from particulate to dissolved organic matter, mineral binding and decay due to biotic and abiotic processes. The literature of such topics is vast, however it is not particularly useful to Quaternary research without a comprehensive review to link our understanding of modern processes involving lignin to Quaternary environments. This review will outline the current state of the art in lignin phenol research that is relevant to the Quaternary scientist, and highlight the potential future applications for this important biomarker for vegetation change and terrestrial organic carbon cycling.
•Quaternary science has regarded lignin as comparatively resistant to degradation.•Studies of modern biogeochemical processes demonstrate this is a simplification.•This review outlines lignin phenol research relevant to the Quaternary scientist.
Coastal aquifers are vital water sources for humanity. Their quality and the ecosystem services they provide depend on the integrity of their subterranean biota. However, current anthropogenic ...impacts such as climate change effects and coastal population growth place enormous pressure on the sustainability of these environments.
Despite the significance of subterranean biota to ecosystem function and the delivery of ecosystem services, stygofauna—groundwater‐dwelling aquatic animals—have until recently been largely ignored in aquifer monitoring and management. This issue is of importance in both coastal and inland zones. Common threats in inland and coastal areas are water extraction, reduced recharge caused by aridification, and pollution, while, in coastal zones, additional complications arise from sea‐level change and salt water ingress.
This review examines stygofaunal diversity, impacts, and future conservation challenges in coastal aquifers. Focussing on Australia, we provide a summary of the available data on stygofaunal communities and distributions; identify and describe potential threats to these communities across the diverse coastal regions of the continent; and propose future research priorities with the goal of facilitating the long‐term preservation of these ecosystems on the Australian continent. While we focus this review on Australia, the threats and management issues discussed are relevant globally.
Recent subterranean studies in Australia have been primarily undertaken in inland areas, and while coastal data exist, ecological assessment of coastal subterranean ecosystems is incomplete, compromising the efficacy of conservation plans. This review indicates that the Australian continent hosts five major coastal stygofaunal biodiversity areas characterised by heterogeneous community assemblages, involving a total of 17 taxonomic groups spanning microscopic aquatic invertebrates to vertebrates. The most relevant impacts and threats identified were aquifer size reduction, intrusion of seawater, land clearing, contamination, and mining.
Given the projections of increasing coastal development and subsequent loss or degradation of habitat during coming decades, it is important to improve our limited understanding of the ecology of coastal aquifers. Future research should include the refinement of biological assessment tools for coastal systems, functional and ecotoxicological studies, and faunal surveys of urban coastal aquifers. The recommendations and guidelines outlined in this review are applicable globally and provide a further step toward the sustainable use of coastal groundwater resources and the maintenance of healthy groundwater ecosystems.
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.
Understanding of cryptic ecosystems is enabled by multi‐factor models and interdisciplinary research.
Groundwater biota are crucial for the ecological functioning of subterranean ecosystems. However, while knowledge of the taxonomic diversity of groundwater invertebrates (stygofauna) is increasing, ...functional ecological information is still limited. Here, we investigate seldom empirically tested assumptions around stygofaunal trophic plasticity in coping with oligotrophic habitats. We focus on Barrow Island (Western Australia), an ideal natural laboratory due to the occurrence of natural oil seeps in association with aquifers. The trophic position and food source use of the endemic atyid shrimp
(Holthuis, 1960) were assessed
C and
N stable isotope analysis (SIA). Background information on the environmental conditions was gathered through hydrochemical data and
C SIA combined with
C data from dissolved inorganic/organic carbon and particulate organic carbon from groundwater samples. Our results indicate carbon enrichment in proximity to the natural oil seepage coupled with changes in trophic positions of
from higher consumers/predators to biofilm grazers/decomposers. These results are consistent with an increased involvement of hydrocarbon seeps and associated microbial communities in the carbon flows and confirm potential for the trophic flexibility in stygofauna. Further investigations involving other trophic groups will help elucidate the functioning of the ecosystems at a community level.
•Comparison of GDGT composition in soils and speleothems carried out.•Clear evidence of in situ production in cave environments.•Increased cyclisation in speleothem samples independent of measured ...pH.
Glycerol dialkyl glycerol tetraethers (GDGTs) preserved in speleothems can form useful records of terrestrial palaeotemperature. However, understanding of the sources of these compounds in caves is limited, particularly whether or not they should be considered as an in situ signal derived from microbial communities in the cave or vadose zone, a transported soil signal, or a mixture of the two. We have analysed speleothem samples and related soils from five cave sites and demonstrate that clear differences were apparent between soils and speleothems in GDGT distributions. Speleothems were primarily, but not uniformly, dominated by crenarchaeol, reflected in the branched and isoprenoid tetraether (BIT) index values, and had a lower relative abundance of the crenarchaeol regioisomer than soils. The most distinct differences were in the bacterially derived branched GDGTs, where no relationship was seen between speleothems and soils for the cyclisation of branched tetraethers (CBT) index, with speleothems in four out of five caves showing a greater degree of cyclisation in GDGT structures than could be explained by measured pH values. Differences in speleothem GDGT composition between sites were also seen. We suggest that the speleothem GDGT record is distinct from the GDGT distribution produced in soils, and is primarily derived from in situ microbial communities within the cave or vadose zone. Variation within these communities or in the cave microenvironment also acts to produce site-specific differences.
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