Thermal groundwaters of the UK: geochemical indications of flow, vulnerability and possible threat to the shallow hydrosphere

Three types of thermal groundwater are known from the UK: warm springs (≤45°C), mine inflows (≤50°C) and deep basin waters (≤80°C). The warm springs depend on Carboniferous Limestone conveying water to sufficient depth (600–3000 m) to acquire a significantly higher temperature. The springs have residence times of a few thousand years, but also contain ≤5% modern groundwater. Their water quality is little threat to the environment; the main danger to the springs is construction activity near the emergences. Mine inflows significantly >20°C are known only from Cornish granite. High dissolved 4He has been interpreted as indicating long residence of the thermal component, but there is also modern water in the system, leading to uncertainty in the mean age. Unpredictable fracturing could hinder development of this resource, while the seawater-like salinity, combined with the presence of toxic metals, would require treatment or re-injection of the spent water to protect the near-surface environment. Mesozoic sedimentary basin brines reach temperatures >60°C, suitable for district heating. This resource is large and effectively invulnerable. However, these waters are generally more saline than seawater and, while disposal of spent brine could take place into the sea under favourable conditions, re-injection would be necessary for inland sites

Inferring energy-composition relationships with Bayesian optimization enhances exploration of inorganic materials

Computational exploration of the compositional spaces of materials can provide guidance for synthetic research and thus accelerate the discovery of novel materials. Most approaches employ high-throughput sampling and focus on reducing the time for energy evaluation for individual compositions, often at the cost of accuracy. Here, we present an alternative approach focusing on effective sampling of the compositional space. The learning algorithm PhaseBO optimizes the stoichiometry of the potential target material while improving the probability of and accelerating its discovery without compromising the accuracy of energy evaluation

Structure of the semiquinone form of flavodoxin from Clostridium MP : Extension of 1.8 A resolution and some comparisons with the oxidized state

As part of a series of comparisons of the structures of the three oxidation states of flavodoxin from Clostridium MP, phases for the semiquinono form were determined to 2.0 A resolution by isomorphous replacement (m > = 0.725). Subsequently, the structure was refined at 1.8 A resolution by a combination of difference Fourier, real space and reciprocal space methods. After refining to an R of 0.194, we explored the conformation of the FMN binding site by real space refinement versus maps with Fourier coefficients of the form (2|Fo|- |Fc|) exp (i[alpha]c). To minimize bias in the fitting, groups of atoms were systematically omitted from the structure factors used in computation of the (2|Fo - |Fc|) maps.One-electron reduction of oxidized flavodoxin is accompanied by several changes at the FMN binding site: the conformation of residues in the reverse bend formed by Met56-Gly57-Asp58-Glu59 differs in the crystal structures of the oxidized and semiquinone species; further, backbone atoms in residues 55 and 89 shift by more than 0.5 A and the indole ring of Trp90 undergoes a significant displacement. The orientation of the peptide unit connecting Gly57 and Asp58 is consistent with the presence of a hydrogen bond between the carbonyl oxygen of Gly57 and the flavin N(5) in flavodoxin semiquinone. No equivalent bond is found in oxidized flavodoxin. In both the oxidized and semiquinone species of clostridial flavodoxin, the isoalloxazine ring is essentially planar : the bending angles about N(5)---N(10) are ~2.5 [deg] for the semiquinone structure and ~0 [deg] in oxidized flavodoxin.The intensity changes resulting from the oxidized agsemiquinone conversion (RI = 0.33) arise in part from changes in molecular packing. Intermolecular contacts, including neighbors of the prosthetic group, are altered in the repacking. Maps or models of the two oxidation states can be brought into approximate coincidence by a rigid body motion. The required transformation, determined for the isomorphous replacement maps by the method of Cox (1967), is equivalent to a screw motion with a rotation of 1.18 [deg] and a translation of -0.34 A. The molecular structures of oxidized and semiquinone flavodoxins have been compared after superposition of models with idealized co-ordinates and discrepancy indices Rox = 0.213 and Rsq = 0.200. The root-mean-square distance between 523 backbone atoms (excluding sequences 56 to 59 and 89 to 91) is 0.308 A.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22809/1/0000366.pd

Groundwater recharge and flow on Montserrat, West Indies: insights from groundwater dating

Study region Montserrat, Lesser Antilles, Caribbean. Study focus Analysis of δ2H and δ18O isotopes, and chlorofluorocarbon (CFC) anthropogenic tracers in Montserrat groundwater provides insights into the age and provenance of the spring waters. New hydrological insights δ2H and δ18O analysis indicates uniform recharge elevations for groundwaters on Montserrat. CFC-11 and CFC-12 analysis reveals age differences between isotopically similar, high elevation springs and low elevation aquifer waters. Low CFC concentrations within a confined low elevation aquifer suggest water ages of ∼45 years. High CFC concentrations in the northern and western springs are explained by rapid infiltration of cool (high CFC concentration) rainfall into saturated compartments, with flow through the vadose zone to the phreatic zone dominated by compartment flow. Lower CFC concentrations in a number of aligned warmer springs suggest a contribution from older, warmer waters from depth. Temperatures and CFC concentrations indicate older component supply rates of up to 8 L/s to the highest yielding spring on Centre Hills, with contributions of up to 75% in the warmest spring waters

Testing tritium-helium groundwater dating in the Chalk aquifer of the Berkshire Downs, UK

The tritium-helium (3H/3He) dating method has been applied to the Chalk (fractured microporous limestone) aquifer in the UK for the first time. An evaluation of the results from diffusion cell versus pumped tube sampling showed generally good agreement between the two techniques. Measurements of noble gas (Ne, Ar, Kr and Xe) concentrations revealed typically low amounts of excess air in the aquifer, with little variation around a mean of 1.3 ccSTP/kg suggesting the predominance of steady recharge via the microporosity rather than via the fracture network. Chalk boreholes are generally unlined, with discrete inflows from a few fracture-related flow horizons. Despite this, attempts to detect age layering in the water column by suspension of diffusion samplers or by slow-pumping were unsuccessful. However, when shortscreen piezometers were used, better evidence for an age-depth relationship was obtained. Assuming a piston-flow model of water movement, a vertical flow rate of ~3.3 m/yr was indicated. However, a more complex picture of movement was obtained by comparing total 3H activity (including the 3He decay equivalent) against SF6 concentration, which suggested the existence of various modes of mixing. This would be consistent with the high degree of fracturing that exists in the Chalk

Using environmental tracers to evaluate the preservation of palaeoclimate signals in aquifers of the London Basin, UK

The concept of aquifer basins as palaeoclimate archives has existed for some decades, yet few detailed studies comparing aquifer types have been carried out. To assess the potential of a particular aquifer as an archive, its hydrogeochemical characteristics must be thoroughly investigated, ideally in comparison to an adjacent aquifer which can be shown to substantially preserve its ice-age endowment at depth. The London Basin (UK) presents such an opportunity, containing two main aquifers of contrasting type: the Chalk, a fractured microporous limestone, and the Lower Greensand, a porous sandstone. Despite intensive exploitation of both, evidence for Devensian (late-glacial) water remains at depth, though this differs between aquifer type. To understand the reasons for this, a suite of environmental tracers has been applied. In addition to hydrochemistry, stable isotopes (δ18O, δ2H), carbon isotopes (δ13C-DIC, 14C-DIC) and noble gases (He, Ne, Ar, Kr and Xe), two tracers new to the basin (CFCs and 14C-DOC) have been used. In effect the Lower Greensand appears to be the ‘reference aquifer’, preserving recharge from prior to the Last Glacial Maximum (LGM), while the Chalk contains mixed water, with no remaining trace of the undiluted pre-LGM end member even at depth in remote parts of the confined basin. Whereas both aquifers had in the past given maximum 14C-DIC model ages ≥ 30 kyr (the effective limit of that method), in the present study the use of 14C-DOC has reduced this to 23.4 kyr (Lower Greensand) and 17.2 kyr (Chalk). Similar contrasts in maximum stable isotope depletions (−8.2 ‰ and −7.8 ‰ δ18O) and noble-gas-derived recharge temperature minima (2.6° and 4.1 °C) were also observed. CFCs were found at all Chalk sites, with traces detectable even at 40 km from outcrop, so some climate signal degradation appears inevitable throughout the Chalk aquifer of the basin. A correlation between 14C activity and excess 4He suggests that deep saline water in the Lower Greensand could be ≥ 50 kyr old. The use of 14C-DOC in particular appears to be key to understanding how reliable these individual aquifers are as palaeoarchives

Monitoring of methane in groundwater from the Vale of Pickering, UK: temporal variability and source discrimination

Groundwater abstracted from aquifers in the Vale of Pickering, North Yorkshire, UK and monitored over the period 2015–2022, shows evidence of variable but commonly high concentrations of dissolved CH4. Sampled groundwater from the Jurassic organic-rich Kimmeridge Clay Formation (boreholes up to 180 m depth) has concentrations up to 57 mg/L, and concentrations up to 59 mg/L are found in groundwater from underlying confined Corallian Group limestone (borehole depths 50–227 m). The high concentrations are mainly from boreholes in the central parts of the vale. Small concentrations of ethane (C2H6, up to 800 μg/L) have been found in the Kimmeridge Clay and confined Corallian groundwaters, and of propane (C3H8, up to 160 μg/L) in deeper boreholes (110–180 m) from these formations. The concentrations are typically higher in groundwater from the deeper boreholes and vary with hydrostatic pressure, reflecting the pressure control on CH4 solubility. The occurrences contrast with groundwater from shallow Quaternary superficial deposits which have low CH4 concentrations (up to 0.39 mg/L), and with the unconfined and semi-confined sections of the Corallian aquifer (up to 0.7 mg/L) around the margins of the vale. Groundwater from the Quaternary, Kimmeridge Clay formations and to a small extent the confined Corallian aquifer, supports local private-water supplies, that from the peripheral unconfined sections of Corallian also supports public supply for towns and villages across the region. Dissolved methane/ethane (C1/C2) ratios and stable-isotopic compositions (δ13C-CH4, δ2H-CH4 and δ13C-CO2) suggest that the high-CH4 groundwater from both the Kimmeridge Clay and confined Corallian formations derives overwhelmingly from biogenic reactions, the methanogenesis pathway by CO2 reduction. A small minority of groundwater samples shows a more enriched δ13C-CH4 composition (−50 to −44 ‰) which has been interpreted as due to anaerobic or aerobic methylotrophic oxidation in situ or post-sampling oxidation, rather than derivation by a thermogenic route. Few of the existing groundwater sites are proximal to abandoned or disused conventional hydrocarbon wells that exist in the region, and little evidence has been found for an influence on groundwater dissolved gases from these sites. The Vale of Pickering has also been under recent consideration for development of an unconventional hydrocarbon (shale-gas) resource. In this context, the monitoring of dissolved gases has been an important step in establishing the high-CH4 baseline of groundwaters from Jurassic deposits in the region and in apportioning their sources and mechanisms of genesis

Groundwater-glacier meltwater interaction in proglacial aquifers

Groundwater plays a significant role in glacial hydrology and can buffer changes to the timing and magnitude of meltwater flows. However, proglacial aquifer characteristics or groundwater dynamics in glacial catchments are rarely studied directly. We provide direct evidence of proglacial groundwater storage, and quantify multi-year groundwater-meltwater dynamics, through intensive and high resolution monitoring of the proglacial system of a rapidly retreating glacier, Virkisjökull, in SE Iceland. Proglacial unconsolidated glaciofluvial sediments comprise a highly permeable aquifer in which groundwater flow in the shallowest 20–40 m of the aquifer is equivalent to 4.5 % (2.6–5.8 %) of mean annual meltwater river flow, and 9.7 % (5.8–12.3 %) of winter flow. Groundwater flow through the entire aquifer thickness represents 9.8 % (3.6–21 %) of annual meltwater flow. Groundwater in the aquifer is actively recharged by local precipitation, both rainfall and snowmelt, and strongly influenced by individual precipitation events. Significant glacial meltwater influence on groundwater within the aquifer occurs in a 50–500 m river zone within which there are complex groundwater / meltwater exchanges. Stable isotopes, groundwater dynamics and temperature data demonstrate active recharge from river losses, especially in the summer melt season, with more than 25 % of groundwater in this part of the aquifer sourced from meltwater. Such proglacial aquifers are common globally, and future changes in glacier coverage and precipitation are likely to increase the significance of groundwater storage within them. The scale of proglacial groundwater flow and storage has important implications for measuring meltwater flux, for predicting future river flows, and for providing strategic water supplies in de-glaciating catchments

Professor W Mike Edmunds: a pioneer in applied hydrogeochemistry and champion of international collaboration

Mike Edmunds was a pioneer in modern applied hydrogeochemistry, helping to develop geochemical tools and their application to managing water resources. In a career span- ning almost 50 years, Mike made major contributions to water resource science as well as pro moting the role of chemistry in solving groundwater problems and championing the need to incorporate science into policy. There can be few hydrogeologists who travelled so extensively in order to study the vast range of groundwater environments of the world. Mike ’ s contribution to water scie nce was recognised through the many accolades he received including the Whitaker Medal in 1999, the O.E. Meinzer Award in 2009, and the Vernadsky Medal in 2010

Discovery of a Low Thermal Conductivity Oxide Guided by Probe Structure Prediction and Machine Learning

International audienceWe report the aperiodic titanate Ba10Y6Ti4O27 with a room-temperature thermal conductivity that equals the lowest reported for an oxide. The structure is characterised by discontinuous occupancy modulation of each of the sites and can be considered as a quasicrystal. The resulting localisation of lattice vibrations suppresses phonon transport of heat. This new lead material for low-thermal-conductivity oxides is metastable and located within a quaternary phase field that has been previously explored. Its isolation thus requires a precisely defined synthetic protocol. The necessary narrowing of the search space for experimental investigation was achieved by evaluation of titanate crystal chemistry, prediction of unexplored structural motifs that would favour synthetically accessible new compositions, and assessment of their properties with machine-learning models