Freshwater Aquifers Research Articles

Porewater chemistry of Opalinus Clay revisited: Findings from 25 years of data collection at the Mont Terri Rock Laboratory

The characterisation of porewater chemistry in nanoporous clayrocks is a difficult task. Appropriate extraction methods that have been developed fairly recently and the Mont Terri Rock Laboratory (Switzerland) have played a pioneer role in this regard. During the last 25 years high-quality data from the Opalinus Clay have been acquired. Notably, since the early synthesis of Pearson et al. (2003) a considerable number of newer data from borehole waters and waters extracted from drillcores have been generated. In this study, borehole, squeezing, leaching and cation exchange data were critically evaluated in order to derive a consistent porewater chemistry database across the formation. The results underline that the porewater composition is not constant but exhibits a regular change towards the formation boundaries. This is explained by diffusive exchange between the Na–Cl type porewater and the two bounding freshwater aquifers. Furthermore, the porewater is constrained by cation exchange, carbonate mineral and celestite equilibria. Major solute data obtained from borehole waters and squeezed waters are broadly consistent, although the latter exhibit somewhat more scatter. Overall, the knowledge on porewaters at the Mont Terri Rock Laboratory has been significantly improved. In particular, this regards the spatial profiles of major elements besides Cl, and better constraints on exchanger composition and pH/pCO2 conditions.

Performance of dual multistage flashing - recycled brine and solar power plant, in the framework of the water-energy nexus

Water is an essential source for life, and due to rapid growth in the population, the demand for clean water is increasing, while the freshwater reservoirs and aquifers are continuously depleting, creating water scarcity. By using desalination techniques, ocean water can be converted into useable water. In this study, a Multistage flashing- Brine recirculation (MSF-BR) model is used as a technique to produce desalinated water. A mathematical model is developed to investigate the performance ratio of the MSF plant driven by solar energy by using a poly PV array type. This solar power plant can provide 6.52 kg/s superheated steam for the system of thermal desalination. The solar power plant is made up of 72 poly-Si panels with 34 strings each. This facility has a capacity of 30 MW; 15 MW is utilized to produce 6.52 kg/s of superheated steam, which is used to power the MSF-BR desalination plant, while the rest is fed into the grid. The MSF-BR plant is made up of twenty-four stages, twenty-one of which are in the heat recovery section (HRS) and the remaining three in the heat rejection section, which is designed to be the most efficient. The top brine temperature is 110 C, the distilled water is 63.314 k/s, and the blowdown brine salinity concentration is around 69,439.54 ppm, according to the MSF-BR performance. Also, with a heat transfer area of 14,559.8 m2 for HRS and 1,663.8 m2 for the rejection section and a stage length of 1.37 to 2.648 m from the first to the last stage, the optimum gain was achieved.

Hydrothermal bowls in the giant Cretaceous Botucatu paleoerg

Fascinating circular hydrothermal bowls 0.5 m in diameter occur in paleodunes of the 1.2 million km2 Botucatu paleoerg in the Fronteira Oeste of Brazil, Rio Grande do Sul, and were exposed upon erosion of presumed 2,000 m of basalt and rhyodacite cover of the Paraná Volcanic Province (1 million km2) since the Cretaceous (135 Ma). The tops of the paleodunes display low-temperature (150-50°C) hydrothermal structures comparable to those in basalts and rhyodacites. The source beds of sand injectites display evidence of sequential fault-valve action. The bowls represent a new structure in continental paleodunes. They present circular rims sealed by quartz and a flat horizontal bottom with a central sealed vent. The inclined internal rims of the bowls exhibit a radial set of linear fractures filled with quartz, forming prominent, sharp, positive structures. Their origin is ascribed to the work of water vapor originated in the heated freshwater aquifer. The concave ceiling was lifted a few millimeters along circular fractures long enough for quartz to be deposited. Erosional exhumation of the buried Botucatu hyperdry sand sea has revealed the effects, including the new structures described here, of hydrothermalism associated with a major igneous province upon a giant paleoerg turned-aquifer.

Degradation of Coast and Coastal Habitat in Pakistan- Propose Preventive Measures for Sustainable Development

Coastlines are the interface between the open oceans and the terrestrial environments. Due to their unique habitat and resourcefulness, they provide ecosystem services of all types to the communities. They not only support the life under water but also provide breeding grounds to several bird species. The quality of coastlines and coastal waters is affected by a complex nexus of interrelated ecological, physical, chemical, and biological aspects and stressors. The conditions of coastlines are also an indicator of the changes in climatic patterns. In this century, we have evidenced various spatial and temporal changes occurring in coastal waters globally. The frequency of extreme extremes including Tsunamis and Cyclones increased. The glacial melting has resulted in sea level rise which has affected millions of people globally. Other challenges include intrusion of sea water into freshwater aquifers and land subsidence. Human activities have also contributed to degradation of coastal areas at large and have also contributed towards enhancing these challenges. The coastal areas and the marine resources of Pakistan are not only an integral part of natural capital but also a major contributor in national economy. The coastal cities are serving as industrial hubs, there are international seaports, diversity of habitats and rich fauna including sea creatures, dolphins, turtles, porpoises are the key distinguishing features. Unfortunately, rather than utilizing the full potential of this Blue Economy, we have evidenced degradation of coastal habitats in Pakistan. This calls for policy interventions and advocacy to ensure that the degradation of coastal areas could be stopped and mitigation measures are being adopted. This paper focuses on proposing measures to protect the coastline and coastal habitat of Pakistan from degradation meanwhile capitalizing them to achieve sustainable development. The study plan includes 1) Identification of causes of degradation of coast and coastal habitat of Pakistan, 2) Evaluation of the effects of degradation of coast and coastal habitat on socio-economic and strategic installation of Pakistan, 3) Determining the needs for protection and proposing mitigation measures for sustainable development and 4) Assessment of the future economic potential of the coast of Pakistan.

Dissolved trace elements dynamics during a rich-CO2-water leakage in a near-surface carbonate freshwater aquifer

An experimental leak “simulation” was carried out at the Saint-Emilion experimental site (France). A volume of 200 L of CO2-rich water was injected into the shallow carbonated aquifer during low water table periods. One injection well and seven monitoring wells were equipped with either CO2 probes or multi-parameters probes to follow the plume.After the CO2-rich water injection, dissolved CO2 and electrical conductivity increased as the pH values decreased, highlighting the calcite dissolution. The calcite dissolution and desorption of iron oxides led to the migration of trace elements in the aqueous phase. As, V, Mo Cu, Ga, Co, Fe, and Cd showed a rapid increase in their concentrations. Mn, Sr, Li and Se showed the same evolution but with a temporal offset. The concentrations of some of these elements increased a second time several hours after the injection. Ba and Pb showed a major decrease immediately after injection, but Ba showed two peaks several hours after the injection. Zn and Si seemed to not be affected by the CO2 injection.Only As, Ba, and Se exceeded WHO/UE drinking water standards for a period of few hours. The global return to initial conditions was fast, showing the great resilience and the high buffering capacity of carbonate aquifers.

Joint estimation of groundwater salinity and hydrogeological parameters using variable-density groundwater flow, salt transport modelling and airborne electromagnetic surveys

Freshwater aquifers in low elevation coastal zones are known to be threatened by saltwater intrusion (SWI). As these areas host a significant share of the world's population, an excellent understanding of this phenomenon is required to effectively manage the availability of freshwater. SWI is a dynamic process, therefore saline groundwater distributions can change quickly over time – particularly in stressed areas with anthropogenic drivers. To model these changes, regional 3D variable-density groundwater (3D-VDG) flow and coupled salt transport models are often used to estimate the current (and future distributions) of saline groundwater. Unfortunately, parameterising 3D-VDG models is a challenging task with many uncertainties. Generally, uncertainty is reduced through the addition of observational data – such as Airborne Electromagnetic (AEM) surveys or ground-based information – that offer information about parameters such as salinity and hydraulic head. Recent research has shown the ability of AEM surveys to provide accurate 3D groundwater salinity models across regional scales, as well as highlighting the potential for good survey repeatability. To this end we investigated the novel approach of using repeat AEM surveys (flown over the same area at different points in time) and 3D-VDG models to jointly improve the parameterisation of 3D-VDG models - while simultaneously providing a detailed 3D map of groundwater salinity distributions. Using detailed 3D synthetic models, the results of this study quantitatively highlight the usefulness of this approach, while offering practical information on implementation and further research.

A Review of Well Integrity Based on Field Experience at Carbon Utilization and Storage Sites

Maintaining well integrity is critical to the success of geologic carbon storage (GCS) and carbon dioxide enhanced oil recovery (CO2-EOR) operations. Wells that experience leakage because of integrity issues can potentially become a risk to the environment or human health if they release previously captured CO2 back into the atmosphere or into freshwater aquifers. There are many GCS and CO2-EOR sites in operation around the world. However, well integrity experiences at these sites are not widely documented in the public domain. This study details findings from a survey of well integrity experiences elicited from operators of GCS and CO2-EOR sites. The goal of the survey was to obtain information about site characteristics and operator experiences with well integrity, monitoring methods, and risk assessment of legacy wells. Literature relevant to the survey questions was also reviewed and summarized to provide context for survey responses and identify areas where field experiences with well integrity do and do not align with the current state of research. We highlight the current state-of-practice, identify research needs, and provide context for future interactions between researchers, operators, and regulators on issues related to well integrity.

CO2 Storage Potential Reconnaissance of the Newly Identified Red Beds of Hazlehurst in the Southeastern United States

The states of Georgia and South Carolina emitted ∼100 million tons (Mt) of CO2 in 2019 from point sources. Integration and interpretation of subsurface data enabled identification of a previously unrecognized, regionally extensive, and thick (up to 450 m) sedimentary sequence—the Red beds of Hazlehurst (RbH)—as a potential saline reservoir for CO2 storage in the southeastern United States. Based on the renewed stratigraphic framework and structural interpretation of the RbH interval, we analyzed detailed well logs and the depositional environments to provide reconnaissance-level regional scale estimations of the storage resource. The volumetric results suggest the effective storage area (∼85,000 km2) has a maximum resource potential for 390 gigatons (Gt) of anthropogenic CO2. Petrophysical measurements suggest the permeability of RbH ranges from 0.001 to 48 mD, and the porosity ranges from 11.1 to 18.4%. Residual/capillary trapping and solubility trapping act as the main trapping mechanisms for long term storage and prevent vertical migration of CO2 into the shallow freshwater aquifers. Due to the heterogeneity observed in geophysical logs and the scarcity of well penetrations, future data collection is needed to characterize the storage aquifer and confining aquitards of a site-specific system at this stage.

Arsenic distribution in sediments of multi-tier sedimentary formation of coastal Pondicherry, India – Implications on groundwater quality

In this work, sediments collected from a 150-m deep litho-section of a coastal region and encompassing Quaternary, Tertiary and Cretaceous sedimentary formations were studied for arsenic distribution and other trace and redox sensitive elements. Arsenic concentration in the sediments is found to vary from <0.5 to 30 mg·kg−1 and showed an increasing trend with the depth. The highest As content is observed at a depth of 129–131 m bgl belonging to Cretaceous formation. Though XRD studies do not indicate any arsenic mineral in sediments, positive correlations between As–Fe and S, as well as ESEM-EDS and TXRF studies confirm the presence of As sorbed to FeS mineral. The organic matter and As correlations suggest microbial mediated reduction process, which may pose future risk to water quality of this prolific coastal fresh water aquifer system. The elemental profiles infer that Cretaceous and Tertiary formations demonstrate inner shelf and marginal marine condition respectively.

Influence of Saltwater Submergence on Geohydraulic Properties of Sand: A Laboratory Investigation

Saline water intrusion into freshwater aquifers is a major geohydraulic problem relevant to coastal environment. Apart from contaminating the fresh groundwater resources, the saltwater intrusion alters the geotechnical properties of the aquifer materials, affecting the coastal water resource planning and management. The present study focuses on an in-depth laboratory investigation of the influence of saltwater submergence on the geohydraulic properties of sand. The fine sand sample was submerged under saline water of specified concentrations for specific periods, and the alteration in their engineering properties has been studied. It is observed that the specific gravity, dry density, and permeability of fine sand is significantly affected by the period of submergence and saline concentration. The specific gravity of sand particles was observed to increase almost linearly with period of submergence and saline concentration. While the sand dry density decreased fairly linearly with the period of submergence, the same is not being affected significantly by saline concentration. The permeability of sand increased nonlinearly with both period of submergence and saline concentration; for a submergence period of 14 days and saline concentration of 30,000 ppm, the permeability increased to a maximum value.

Carbon dynamics driven by seawater recirculation and groundwater discharge along a forest-dune-beach continuum of a high-energy meso-macro-tidal sandy coast

High-energy tidal beaches are exposed to strong physical forcings. The submarine groundwater discharge (SGD) that occurs in intertidal sandy sediments includes both terrestrial, fresh groundwater flow and seawater recirculation, and plays a significant role in regulating biogeochemical cycles in some coastal zones. In this transition zone between land and sea, complex biogeochemical reactions alter the chemical composition of pore waters that discharge to the coastal ocean. Recent studies highlight that SGD can be a significant source of carbon to the coastal ocean but very few have investigated SGD in high-energy environments. We have characterized the dissolved carbon dynamics in such a high-energy environment (Truc Vert Beach, SW France) through pore-water sampling in key compartments of the SGD system. Dissolved organic carbon (DOC), pH, total alkalinity (TA), and the isotopic composition of dissolved inorganic carbon (δ13C-DIC) were measured in pore waters sampled at regular intervals between 2011 and 2014 in the intertidal zone of the beach, the mixing zone of the subterranean estuary (STE), and the freshwater aquifer upstream from the beach. Results reveal that SGD exports dissolved carbon mostly as DIC to the Aquitaine coast, some of which originates from the aerobic respiration of marine organic matter within the beach aquifer. This is highlighted by the reverse spatial trend of DOC, which is consumed, and DIC, which is produced. Saline pore waters expelled from the beach through tidally-driven recirculation of seawater provide about 4400 tons of carbon per year to the coastal zone of the 240-km long Aquitaine sandy coast. Terrestrial groundwater, characterized by high pCO2 values, is also a significant contributor to the DIC flux to the coastal ocean (16,200 tons per year). This flux is abated by CO2 evasion in the upper beach, at the onset of the salinity gradient in the STE, and within the surficial freshwater aquifer along the forest-beach transect below the coastal foredune. Accordingly, the DIC:TA ratio evolves to below 1, suggesting that this SGD increases the buffer capacity of coastal seawater against acidification. This study demonstrates that high-energy beaches are active vectors of DIC from the land to the coastal ocean as well as significant sources of CO2 to the atmosphere, and must therefore be taken into consideration in SGD carbon budgets.

Coupled effect of seawater intrusion on groundwater quality: study of South-West zone of Surat city

Abstract Groundwater quality is a major problem for humanity since it is closely related to human health. The flow of seawater into freshwater aquifers is known as saltwater intrusion, and it can lead to groundwater quality contamination, including drinking water. Due to the extremely severe hydraulic interface between groundwater and seawater, saltwater intrusion can happen naturally in coastal aquifers. The aim of the study is to examine the status of seawater intrusion within the study region of the South-West zone of Surat city, Gujarat. The present study evaluates Groundwater Quality Index using a weighted arithmetic method including various chemical ions. The South-West zone of Surat city is located along the coast; seawater infiltration has a significant impact on the groundwater in the state. The conceptual model will be developed and analyzed using MODFLOW to analyze the effects of seawater intrusion analysis. The model domain is characterized by three hydro-stratographic layers and covers an area of approximately 110 km2 in a 400 m × 400 m grid size. An analytical study with MODFLOW would be carried out for three-dimensional groundwater flows with species of solute transport. This study would help profile the study area regarding groundwater quality.

Three new microcerberids (Isopoda: Microcerberidae) from subterranean freshwater habitats in Texas, USA

ABSTRACT The stygobiontic genus Texicerberus gen. nov. and the three species T. amistad sp. nov., T. schotteae sp. nov., and T. castilloi sp. nov. are described from freshwater aquifer or hyporheic sites across central and western Texas, USA. The status of the new genus and species is based on morphological characters that distinguish them from all other described Microcerberidae from both marine and freshwater environments. Cephalon without rostral projection, coxae II–IV rounded, medial margin of antenna article 3 angulate but not produced as spine, male pleopod II endopod uniramous, and male pleopod IV biramous are among the characters that distinguish Texicerberus gen. nov. from other genera in the family. Collected from deep karst aquifer wells, karst springs, and the hyporheic zone along the Rio Grande (Rio Bravo del Norte), these three new species represent the first documented occurrences of Microcerberidae in Texas and substantially increase the described diversity in the family in North America and from freshwater environments globally. Additional sampling, especially in the hyporheic zone, is expected to reveal additional diversity in Texas. Future collection and analysis of molecular data will be required to understand the evolutionary relationships among these and other species.

Geophysical Delineation of Freshwater–Saline Water Interfaces in Coastal Area of Southwest Bangladesh

Insufficiency of potable water is acute in southwest (SW) coastal areas of Bangladesh. The local population ignores the depth to saltwater/freshwater interface causing many unsuccessful waters wells drilling. In this context, a combined use of borehole logs, geophysical well logs, vertical electrical soundings (VES), electrical resistivity tomography (ERT) and electrical conductivity (EC) of sampled waters was performed to identify saltwater/freshwater interface depths in this coastal part. The study shows that the depth to freshwater/saltwater interface varies from place to place occurring commonly between 190 to 285 m, and locally as shallow as 146 m. The shallow freshwater/saltwater interface depth is greatly influenced by the upconing of fresh water from the deep aquifer (DA) near the major rivers and coast compared to the landward part and is mixed with more saline waters above. Vertically infiltrated saltwater is the main cause of brackish water in the upper shallow aquifer (USA), which is hydraulically connected with the lower shallow aquifer (LSA), and not directly recharged from the Bay of Bengal in the south. The study will contribute to find out the depth of the potential freshwater aquifer and assess the aquifer vulnerability in the coastal area of SW Bangladesh.

Impact of reservoir parameters and wellbore permeability uncertainties on CO2 and brine leakage potential at the Shenhua CO2 Storage Site, China

This paper describes a system-level risk assessment for the Shenhua CO2 storage site, China, using the National Risk Assessment Partnership Integrated Assessment Model for Carbon Storage (NRAP-IAM-CS). We begin by determining the optimal number of Monte Carlo (MC) simulations to achieve CO2 and brine leakage result convergence. Then, we calculate mass CO2 and brine leakage to the atmosphere and a hypothetical shallow aquifer. Finally, we assess the geochemical impacts in the event of leakage as if there were a shallow freshwater aquifer at the Shenhua site. Simulation results show that leakage results tend to stabilize after 300 Monte Carlo simulations. When the three wells on site are assigned a permeability of 10−11 m2 (representing significantly leaking wells), moderate CO2 and brine leakages occur, and the percentage of CO2 leakage exceeds the threshold value we set based on the Intergovernmental Panel on Climate Change (IPCC). This is, however, unlikely to be the case for the Shenhua site. For all the other scenarios, the CO2 leakage is trivial although there is still the possibility of CO2 leakage into the groundwater aquifer exceeding the 1% threshold over 1000 years, assuming constant legacy wellbore permeability. For the significantly leaking scenario, there is a 10% probability to have a moderate (2.7 × 107 m3) leakage-affected volume in the shallow aquifer with the pH below 6.5, and a large (1.4 × 108 m3) volume with the total dissolved solids (TDS) above 500 ppm, hence pH and TDS may be considered for site monitoring plans. Based on the simulation results, there is a very low probability of significant CO2/brine leakage through the existing wells at the Shenhua CO2 storage site.

Sustainable saltwater intrusion management in coastal aquifers under climatic changes for humid and hyper-arid regions

Saltwater Intrusion (SWI) in many coastal areas is accelerated by freshwater boundary changes due to over-pumping and decreasing aquifer recharge and sea-level rise. This study aims to control SWI due to the rise in sea levels in three climate regions: (i) humid and wet regions using storage dams at different heads and recharge ponds, (ii) hyper-arid and arid regions using physical barriers and wastewater treatment aquifer, brackish water abstraction, and desalination (TRAD) method, and (iii) semi-arid and semi-humid regions using a combination of flooding water recharge well-field and cut-off wall. The study was developed using the world benchmark problem of Henry's problem and Biscayne aquifer in the Cutler Ridge area near Deering Estate, Florida, USA. The finite-difference code SEAWAT was used in numerical simulations. The numerical results indicated that increasing the artificial recharge lake capacity minimizes the SWI in humid and wet regions with a high level of flooding. Moreover, the intrusion is mitigated using physical barriers and the TRAD method for hyper-arid and arid regions. Combining physical barriers during dry seasons and recharge wells for wet seasons resulted in suitable measures to managed the SWI in semi-arid and semi-humid regions. Finally, the best strategy to mitigate the SWI and minimize the desalination costs depends on the precipitation rates. Therefore, the methodology applied to this study represents a valuable tool in order to select the best method based on the climate conditions and particularly the precipitation intensity to increase the water budget in freshwater aquifers.

Classification of Aquifer Vulnerability by Using the DRASTIC Index and Geo-Electrical Techniques

Vulnerability analysis in areas vulnerable to anthropogenic pollution has become a key element of sensible resource management and land use planning. This study is intended to estimate aquifer vulnerability using the DRASTIC model and using the vertical electrical sounding (VES) and electrical conductivity (EC) outcomes. The model allows for the identification of hydrogeological environments within the scope of the research, based on a composite definition of each environment’s main geological, geoelectrical, and hydrogeological factors. The results from the DRASTIC model were divided into four equal intervals, high, medium, low, and very low drastic index values. The SW area and NE area depict drastic index values from medium to very high, making it the most vulnerable zone in the study area, while the NW and SW areas show low to very low drastic index values. In addition, the results from the VES and EC the freshwater aquifer in the NE area and brackish water in the SE area, while the rest of the area falls into the category of brackish water. Overall, it can be concluded that areas having freshwater assemblages are on the verge of becoming contaminated in the future while the rest of the NW and SW areas constitute less vulnerable zones. The validation conducted for DRASTIC and EC shows a nearly positive correlation. Wastewater treatment policies must be developed throughout the studied region to prevent contamination of the remaining groundwater.

Cool deltas: Sedimentological, geomorphological and geophysical characterization of ice‐contact deltas and implications for their reservoir properties (Salpausselkä, Finland)

AbstractSediments deposited by glacial meltwaters (for example, ice‐contact delta deposits) form permeable packages in the subsurface that can act as reservoirs for both water and hydrocarbons. They are also an important source of aggregate for the construction industry. As reservoirs they are challenging to characterize in terms of their structure, flow and storage properties due to their complex depositional history. In this study, ice‐contact deltas of Salpausselkä I and II end moraines in Southern Finland are studied using a combination of geomorphological mapping, sedimentological studies and near surface geophysical methods. Sedimentary logs from isolated outcrops were correlated to ground penetrating radar (GPR) profiles to unravel the internal structure and depositional history of these ice‐contact deltas. Subsequently, electrical resistivity tomography (ERT) and gravity data were analysed to estimate the depth to bedrock and to model porosity distribution within the sediments. Results of the study suggest that the delta deposits have a broad range of porosities (10 to 42%) with lowest values found in the bottomset beds. The most variable porosities are in the subaqueous ice‐contact–fan zone, and consistently high porosities occur in delta foreset/topset facies. Detailed sedimentary logging linked to the GPR data shows heterogeneities such as mud drapes on foresets and kettle holes which are below the resolution of ERT and gravity methods but significantly affect reservoir properties of the deltas. Moreover, oscillation of the ice‐margin may have introduced larger heterogeneities (for example, buried ice marginal ridges, or eskers) into the sedimentary sequence which are atypical for other Gilbert‐type deltas. Finally, subglacially sculpted, highly variable bedrock topography exerts a major control on sediment distribution within the delta making reservoir volume and quality less predictable. This work has implications for present‐day freshwater aquifers and low enthalpy geothermal energy in southern Finland and other deglaciated regions, as well as hydrocarbon exploration of analogous deposits in the subsurface from Pleistocene and pre‐Pleistocene glaciogenic sequences.

Connectivity, not short-range endemism, characterises the groundwater biota of a northern Australian karst system

Groundwater ecosystems have a diverse and unique fauna, often dominated by Crustacea and generally characterised by short range endemics confined to single aquifers. Much of this knowledge has come from studies conducted either in fractured rock aquifers or alluvial aquifers. Karstic subterranean environments are present in the Cambrian Limestone Aquifer (CLA) in the Northern Territory, Australia, a freshwater aquifer which spans an area of ~28,000 km2. The presence of underground caverns and channels potentially allows extensive connectivity within this groundwater system. The emerging shale gas industry in the Beetaloo region, which underlies the CLA, provided the impetus to undertake the first survey of the potential existence of a stygofaunal community. Twenty-six groundwater wells (bores) and two springs were sampled in August and October 2019, across a distance of ~500 km, from the sub-tropical Mataranka region in the north to the semi-arid Barkly Tablelands in the south. Plankton nets and motorised pumps were used to collect water samples and conventional microscope-based morphological examinations in conjunction with environmental DNA (eDNA) were used to determine the presence of stygofauna. COI barcoding and 16S rRNA regions were also used for phylogenetic analysis. All stygofaunal communities were dominated by crustaceans, namely shrimps, amphipods, ostracods, copepods and syncarids. This fauna showed little affinity with the stygofauna recorded from more extensively sampled aquifers in north-western Australia, with new genera and species present in the CLA. eDNA analysis showed the presence of diverse biota at sites where direct water sampling for intact animals was difficult. COI and 16S analysis confirmed that a species of blind shrimp, Parisia unguis, occurred extensively throughout the aquifer, over a distance of at least ~300 km. The presence of Pa. unguis at widely separated sites across the CLA is consistent with substantial connectivity within the aquifer. This connectivity indicates that the risk of groundwater contamination from fracking chemicals needs to be adequately mitigated to prevent widespread effects.

Delineating the characteristics of saline water intrusion in the coastal aquifers of Tamil Nadu, India by analysing the Dar-Zarrouk parameters

Tuticorin, located in the southeastern part of Tamil Nadu, is a coastal aquifer on which Vertical Electrical Sounding (VES) was conducted, thereby analysing the interpreted subsurface resistivity layer parameters covering around 112 km2 area of the study region. VES is an essential tool for investigating hard rock terrains of coastal aquifers and perceive an idea about the groundwater quality. In this study, Dar-Zarrouk (D-Z) parameters like longitudinal conductance (Sc), transverse resistance (Tr) and anisotropy (λ) are analysed as these are well-established parameters in delineating the occurrence and distribution of both fresh and saline water aquifers. These parameters are also very persuasive in investigating complex subsurface parameters (resistivity and conductivity) within saline water intruded coastal region environment. After conducting a thorough survey, the resistivity results reflect that the sediments are enriched with saltwater, clay with moderate freshwater and freshwater-bearing formations. The analysis shows that the D-Z parameters offer a helpful and assured answer in demarcating the saline, moderate fresh, and freshwater aquifers. Therefore, the behaviour and patterns of the D-Z parameters in space established the existence of saline water and freshwater aquifer structures in the coastal aquifers over a vast area.