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Oxygen-18 is an important indicator determining groundwater origin, recharge sources, and age. However, compared to basic geochemical parameters such as major ion composition, oxygen-18 is measured significantly less. This study aims to develop a machine learning (ML) model to successfully predict oxygen-18 values based on ionic composition (Na + , K + , Mg 2+ , Ca 2+ , Cl − , SO 4 2− , HCO 3 − ), coordinates, well depth as input variables for the whole Baltic Artesian Basin (BAB). A dataset of 567 distinct sample entries was developed from previous research and databases of Lithuania, Latvia, and Estonia. Twelve individual ML models were tested in this research. The prediction results of each model were evaluated using three performance metrics, r-square (R 2 ), mean absolute error (MAE), and root mean square error (RMSE). Overfitting was also evaluated by considering the error metric results of train and test sets and correlation plots of oxygen-18 predicted vs. actual values. The best-performing models—Gradient Boosting, Random Forest, and K-neighbors regressors—achieved R 2 values greater than 0.8. However, overfitting is observed during the ML of Gradient Boosting and Random Forest models. Hyperparameter tuning helped to increase the accuracy of K-neighbors’ regressor performance without creating overfitting. The study results show that the tuned K-neighbors regressor performance is the best fit: R 2 0.82–0.84, MAE 0.98–0.99‰, RMSE 1.67–1.74‰. This study demonstrates that machine learning can be successfully applied to predict oxygen-18 values in groundwater across a basinal scale.

Background This study demonstrates the use of reduced-representation genotyping to provide preliminary identifications for thermophilic bacterial isolates. The approach combines restriction enzyme digestion and PCR with next-generation sequencing to provide thousands of short-read sequences from across the bacterial genomes. Isolates were obtained from compost, hot water systems, and artesian bores of the Great Artesian Basin. Genomic DNA was double-digested with two combinations of restriction enzymes followed by PCR amplification, using a commercial provider of DArTseq™, Diversity Arrays Technology Pty Ltd. (Canberra, Australia). The resulting fragments which formed a reduced-representation of approximately 2.3% of the genome were sequenced. The sequence tags obtained were aligned against all available RefSeq bacterial genome assemblies by BLASTn to identify the nearest reference genome. Results Based on the preliminary identifications, a total of 99 bacterial isolates were identified to species level, from which 8 isolates were selected for whole-genome sequencing to assess the identification results. Novel species and strains were discovered within this set of isolates. The preliminary identifications obtained by reduced-representation genotyping, as well as identifications obtained by BLASTn alignment of the 16S rRNA gene sequence, were compared with those derived from the whole-genome sequence data, using the same RefSeq sequence database for the three methods. Identifications obtained with reduced-representation sequencing agreed with the identifications provided by whole-genome sequencing in 100% of cases. The identifications produced by BLASTn alignment of 16S rRNA gene sequence to the same database differed from those provided by whole-genome sequencing in 37.5% of cases, and produced ambiguous identifications in 50% of cases. Conclusions Previously, this method has been successfully demonstrated for use in bacterial identification for medical microbiology. This study demonstrates the first successful use of DArTseq™ for preliminary identification of thermophilic bacterial isolates, providing results in complete agreement with those obtained from whole-genome sequencing of the same isolates. The growing database of bacterial genome sequences provides an excellent resource for alignment of reduced-representation sequence data for identification purposes, and as the available sequenced genomes continue to grow, the technique will become more effective.

The influence of climate change and anthropogenic activities (e.g., water withdrawals) on groundwater basins has gained attention recently across the globe. However, the understanding of hydrological stores (e.g., groundwater storage) in one of the largest and deepest artesian basins, the Great Artesian Basin (GAB) is limited due to the poor distribution of groundwater monitoring bores. In this study, Gravity Recovery and Climate Experiment (GRACE) satellite and ancillary data from observations and models (soil moisture, rainfall, and evapotranspiration (ET)) were used to assess changes in terrestrial water storage and groundwater storage (GWS) variations across the GAB and its sub-basins (Carpentaria, Surat, Western Eromanga, and Central Eromanga). Results show that there is strong relationship of GWS variation with rainfall (r = 0.9) and ET (r = 0.9 to 1) in the Surat and some parts of the Carpentaria sub-basin in the GAB (2002–2017). Using multi-variate methods, we found that variation in GWS is primarily driven by rainfall in the Carpentaria sub-basin. While changes in rainfall account for much of the observed spatio-temporal distribution of water storage changes in Carpentaria and some parts of the Surat sub-basin (r = 0.90 at 0–2 months lag), the relationship of GWS with rainfall and ET in Central Eromanga sub-basin (r = 0.10–0.30 at more than 12 months lag) suggest the effects of human water extraction in the GAB.

The Great Artesian Basin of Australia represents one of the largest and deepest basins of freshwater on Earth. Thousands of springs fed by the Basin are scattered across Australia’s arid zone, often representing the sole sources of freshwater for thousands of kilometers. As “islands” in the desert, the springs support endemic fauna and flora that have undergone millions of years of evolution in almost total isolation. Here, we review the current body of knowledge surrounding Great Artesian Basin springs and their significance from ecological, evolutionary, and cultural perspectives using South Australian spring wetlands as a case study. We begin by identifying the status of these springs as critical sources of groundwater, the unique biodiversity they support, and their cultural significance to the Arabana people as Traditional Custodians of the land. We then summarize known threats to the springs and their biota, both exogenous and endogenous, and the potential impacts of such processes. Finally, considering the status of these at-risk habitats as time capsules of biodiversity, we discuss lessons that can be learnt from current conservation and management practices in South Australia. We propose key recommendations for improved biodiversity assessment and monitoring of Great Artesian Basin springs nationwide, including 1) enhanced legal protections for spring biota; 2) increased taxonomic funding and capacity; 3) improved biodiversity monitoring methods, and 4) opportunities for reciprocal knowledge-sharing with Aboriginal peoples when conducting biodiversity research.

Aim: We investigate the phylogeographical history and determine the time-scale of population divergence of hydrobiid freshwater snails (genus Trochidrobia) inhabiting groundwater springs in the Australian desert. We test the hypothesis that divergence between geographically distinct snail populations occurred simultaneously due to their isolation in hydrologically discrete spring systems, i.e. 'trapped in desert springs'. Location: Groundwater springs of the Great Artesian Basin (GAB) in central Australia. Methods: DNA sequence data from the mitochondrial cytochrome c oxidase subunit I gene and the nuclear 28S and internal transcribed spacer rRNA genes were used to reconstruct phylogenetic relationships within and among three species of Trochidrobia (Hydrobiidae): T. punicea (13 spring groups, n = 90), T. smithi (12 spring groups, n = 62) and T. minuta (2 spring groups, n = 4). Bayesian relaxed molecular clock analyses and approximate Bayesian computation were used to date lineage divergence and distinguish between alternative biogeographical scenarios. Results: The diversification of the three Trochidrobia species probably occurred between 2.54 and 9.3 Ma, prior to the formation of the springs c. 1 Ma. Intraspecific divergences within the two widespread species occurred after the formation and colonization of the springs. Coalescent modelling and molecular clock analyses supported a simultaneous radiation of five allopatric intraspecific snail lineages within T. punicea (two lineages) and T. smithi (three lineages) across the GAB springs examined. Main conclusions: The analyses support the 'trapped in desert springs' hypothesis for the diversification of intraspecific lineages within the species T. punicea and T. smithi. This hypothesis suggests that the formation of deserts around Lake Eyre in the early Pleistocene led to the hydrological isolation of spring complexes in the GAB, resulting in significant molecular divergence, but no morphological divergence, of Trochidrobia snail populations.

We review our current understanding of groundwater flow history in the northern part of the Baltic Artesian Basin (BAB) from the end of the Late Pleistocene to current conditions based on the hydrogeological studies carried out in 2012–2020 by the Department of Geology, Tallinn University of Technology and its partners. Hydrogeochemical data and various numerical models are combined in order to understand the link between glaciations and groundwater flow. The results of our earlier research and published literature on groundwater flow history in the BAB are also taken into account. The reconstruction of groundwater flow history is based on the database of the isotopic, chemical and dissolved gas composition of groundwater. The database contains data on 1155 groundwater samples collected during 1974–2017. We find that groundwater in the BAB is controlled by the mixing of three distinct water masses: interglacial/modern meteoric water (δ18O ≈ –11‰), glacial meltwater (δ18O ≤ –18‰) and an older syngenetic end-member (δ18O ≥–4.5‰). The numerical modelling has suggested that the preservation of meltwater in the northern part of the BAB is controlled by confining layers and the proximity to the outcrop areas of aquifers. Aquifers containing groundwater of glacial origin are in a transient state with respect to modern topographically-driven groundwater flow conditions. The most important topics for future research that can address gaps in our current knowledge are also reviewed.

Aim: Spring wetlands in arid regions of Australia provide habitat for many highly endemic organisms, including fish, molluscs, crustaceans and plants, but these unique ecosystems have been under pressure since the arrival of Europeans about 250 years ago. Arguments over whether particular plant species are long-term spring inhabitants or recent immigrants are confounding efforts to conserve spring flora. One such example is the swamp foxtail, Cenchrus purpurascens, a grass that is variably listed in the literature as being native to Australian wetlands or as being an introduced weedy species from Asia. Location: Australia, China and Korea. Methods: We use DNA sequences of the nuclear ITS and the chloroplast DNA regions trnL-F and matK, complemented with newly designed simple sequence repeat (SSR) markers, to assess the native status of C. purpurascens in Australia and determine whether there is genetic differentiation among spring populations. Results: We find that, although there has been gene flow between Asia and Australia in the geological past, the populations are now strongly differentiated: C. purpurascens has probably been present in Australia through the Pleistocene. In Australia, there is also strong genetic differentiation among populations from different springs, and between springs and non-springs populations, indicating long-term occupancy of some springs sites. Main conclusions: Cenchrus purpurascens was present in Australia well before European colonization of the continent. The level of genetic differentiation among populations enhances the existing conservation values of Elizabeth Springs, Edgbaston, Doongmabulla and Carnarvon Gorge springs complexes within the Great Artesian Basin.

Aim: Great Artesian Basin (GAB) springs in central Australia support several plant species otherwise not found in the arid zone. Evolutionary theory predicts that isolated populations will experience reductions in gene flow and genetic diversity, and higher levels of inbreeding. Our aim was to test this prediction by comparing the genetic structure of cutting grass, Gahnia trifida, (Cyperaceae) on disjunct GAB springs with coastal populations that have experienced recent fragmentation. Location: Naturally isolated GAB springs near Lake Eyre, central Australia, and coastal sites in southern Australia. Methods: We used 13 microsatellite markers to genotype 267 samples from six GAB spring and four coastal G. trifida populations. These data were used to estimate population genetic statistics and contemporary and historical measures of gene flow in the two regions. Results: GAB spring populations display lower levels of genetic diversity compared with coastal populations. Furthermore, GAB spring populations displayed much higher levels of genetic differentiation (F ST = 0.52) than populations at coastal sites (F ST = 0.22). Several coastal populations exhibited historical genetic connectivity, whereas analysis of molecular variation (AMOVA) and contemporary migration rate estimates indicate that populations from GAB spring groups are demographically independent. Main conclusions: Divergence estimates based on microsatellite data suggest restriction of central Australian G. trifida populations to refugial spring habitats since at least 15—28 ka, a period that spans the Last Glacial Maximum. Dispersal amongst spring groups is insufficient to counteract the effect of genetic drift, leading to a loss of genetic diversity. Species persisting in isolated or fragmented habitats are likely to suffer adverse effects on genetic traits, potentially increasing their risk of extinction.

The Great Artesian Basin is an aquifer system that underlies a large area of north-eastern Australia. The spring wetlands in the Great Artesian Basin are of conservation significance because they provide habitat for endemic species including fish, invertebrates and plants. Since European settlement massive quantities of water have been artificially extracted through bores, reducing spring-flows. Records of the springs of the Queensland section of the Great Artesian Basin (excluding Cape York Peninsula) were compiled from a range of historical sources. Most remaining active springs were visited and surveyed, the physical attributes of the springs described and their current status determined. Recharge springs occur in areas where the evidence suggests the basin is recharged by rainfall and 93% of the original 245 spring-groups in these areas are still active. Discharge springs occur in sections of the Basin down-gradient of the recharge areas and only 36% of the original 300 spring-groups in these areas have at least some springs that are still active. The capping of bores could provide a partial restoration of artesian pressure and enhance spring flows. Of the active spring-groups surveyed 26% have suffered major or total damage as a result of excavation of the wetlands. An emerging threat is the use of exotic grasses as ponded pastures, which have the ability to dominate the habitat of spring wetlands. The potential impacts of other threats including those associated with stock, exotic animals and fire are also discussed. Mitigating these threats requires a conservation strategy that seeks to protect remaining springs with high conservation values.