Seawater Ingress Research Articles

Astronomically forcing salinity variations in a marginal-marine environment, Bohai Bay Basin, NE China

Exploring the interdependence between watermass conditions and climate change in marginal marine regions is essential for gaining insights into contemporary environmental challenges arising from global warming. Salinity, a key parameter of watermass conditions in coastal areas, plays a crucial role in influencing nutrient availability, stratification, and the spatial-temporal distribution of redox conditions. Here, we focus on the cyclostratigraphic analysis of gamma-ray (GR) data obtained from Eocene strata in the Luo-69 drillcore from the Bohai Bay Basin (NE China). This analysis establishes a high-resolution astronomical time scale (ATS) for the lower third member of the Shahejie Formation (Es3l), spanning 39.04 Ma to 41.46 million years ago (Ma). Various proxies for watermass conditions, such as salinity, sedimentary structures, mineral content, total organic carbon (TOC), organic carbon isotopes and nitrogen isotopes (δ13Corg and δ15N), exhibit a strong correlation with 405-kyr long orbital eccentricity climate forcing. Notably, spectral analysis of salinity data (represented by the Sr/Ba proxy) reveals a clear astronomical control, with 405-kyr eccentricity cycles that align closely with variations in the GR data. Peaks in paleosalinity, as indicated by Sr/Ba (as well as B/Ga and S/TOC), correspond with maxima in 405-kyr long orbital eccentricity cycles in the GR data. As such, we infer that astronomical forcing regulated long-term changes in watermass conditions, likely through mediation of the East Asia monsoon system. Specifically, during eccentricity maxima, the basin would have experienced a warm and humid climate with pronounced seasonality and a robust summer monsoon. During such periods, increased continental runoff would lead to a rise in lake-levels, facilitating better connections with the ocean, and hence increased salinity. By contrast, during eccentricity minima, cooler and more arid conditions with weaker seasonality would result in lower lake levels which together with a global eustatic lowstand would result in as weakened connection with the open ocean restricting the ingress of seawater into the basin lowering salinity. Our dataset spans the Middle Eocene Climatic Optimum (MECO, ∼40.60–40.10 Ma), identified by elevated GR values and a conspicuous negative excursion in oxygen isotopes. This interval is characterized by a significant decline in salinity, likely attributed to enhanced freshwater runoff driven by an extremely warm and humid climate. The paleosalinity fluctuation recorded by the proxies B/Ga, Sr/Ba, and S/TOC in Bohai Bay Basin demonstrate the sensitivity of marginal-marine environment to subtle changes in climate driven by astronomical forcing. Our results provide new insights into how elemental salinity proxies can be utilized in paleoenvironmental reconstruction studies.

Progressive Strain Localization and Fluid Focusing in Mantle Shear Zones during Rifting: Petrostructural Constraints from the Zabargad Peridotites, Red Sea

Abstract This article documents the evolution of pressure and temperature conditions and the successive influence of hydrous melts and aqueous fluids on the operation of extensional shear zones, which exhumed mantle slivers from deep lithospheric or asthenospheric depths, in a rift-to-drift setting. These results are based on a re-analysis of 40 samples from three peridotite massifs of Zabargad island in the northern Red Sea. By integrating high-resolution mapping of the microstructure by electron backscattered diffraction with recent developments in barometry for plagioclase-bearing peridotites and thermodynamic modelling of peridotitic compositions, this study (1) constrains the temporal and spatial evolution of petrological and tectonic processes in the shallow mantle during rifting and (2) documents the presence of melts or aqueous fluids throughout the activity of the shear zones, unravelling substantial feedback between petrological and tectonic processes. Thermobarometry and thermodynamic modelling, constrained by the microstructural observations, document progressive strain localization associated with shearing under decreasing pressure and temperature, from near solidus conditions at >1 GPa (in the north and central peridotite massifs) or ~ 0.7 GPa (in the southern massif) to <600°C and < 0.3 GPa in all three massifs. The data substantiate local aqueous fluid saturation in the shear zones. This together with higher contents of hydrous minerals in ultramylonites indicate fluid focusing in the shear zones, with seawater ingress extending to >10 km depth. The presence of melts or fluids enabled concurrent dislocation and dissolution–precipitation creep, resulting in weakening of the shear zones. However, fluid supply was spatially heterogeneous and likely intermittent, with equilibrium achieved only locally in the ultramylonites. The present study documents therefore how the feedback between progressive strain localization and fluid focusing in extensional shear zones contributes to thinning and exhumation of the mantle during continental rifting and the rift-to-drift transition.

Groundwater, salt and contaminant transport in a coastal aquifer system with a low‐permeability layer in the intertidal zone

AbstractLow‐permeability layer (LPL), formed by natural deposit or artificial reclamation and commonly found below the intertidal zone of coastal groundwater system, can retard the ingress of seawater and contaminants, and shorten the travel time of the land‐sourced contaminant to the marine environment compared with a homogenous sandy coastal aquifer. However, there is limited understanding on how an intertidal LPL, a condition occurred in a coastal aquifer at Moreton Bay, Australia, influences the groundwater and contaminant transport across the shallow beach aquifer system. We characterized the aquifer hydrological parameters, monitored the in situ groundwater heads, and constructed a 2‐D numerical model to analyses the cross‐shore hydrological processes in this stratified system. The calibrated model suggests that in the lower aquifer, the inland‐source fresh groundwater flowed horizontally towards the sea, upwelled along the freshwater–saltwater interface, and exited the aquifer at the shore below the LPL. Whereas in the upper aquifer, the tidally driven seawater circulation formed a barrier that prevented fresh groundwater from horizontal transport and discharge to the beach above the LPL, thereby directing its leakage to the lower aquifer. A contaminant represented by a conservative tracer was ‘released’ the upper aquifer in the model and results showed that the spreading extent of the contaminant plume, the maximum rate of contaminant discharge to the ocean, and its plume length decreased compared with a simulation case in a homogenous sandy aquifer. Sensitivity analysis was also conducted to investigate the characteristics of the LPL, including its continuity and hydraulic conductivity, which were found to vary along the beach at Moreton Bay. The result shows that with a lower hydraulic conductivity and continuous layer of LPL reduced the groundwater exchange and contaminant transport between upper and lower aquifer. The findings from the combined field and modelling investigations on the impact of an intertidal LPL on coastal aquifer systems highlight its significant implications to alter the groundwater and mass transport across the land–ocean interface.

Multi-temporal SAR Interferometry (MTInSAR)-based study of surface subsidence and its impact on Krishna Godavari (KG) basin in India: a support vector approach.

The surface subsidence in the Krishna Godavari (KG) basin in India has increased with the discovery of crude oil and natural gas reserves since 1983. With private players coming up to bag the exploration and refining contracts, there must be timely monitoring of the surface subsidence of the region so that remedial measures for the resettlement of the populations can be taken promptly. Regular monitoring is necessary since the region is fertile and any seawater ingress results in the loss of valuable cultivable land. Multi-temporal SAR Interferometry (MTInSAR) technique has been applied successfully all over the world for the study and regular monitoring of land surface subsidence scenarios. This study utilizes data from Sentinel-1 C-band SAR sensor for MTInSAR-based surface subsidence and RADAR Vegetation Index (RVI)-based vegetation loss for the same season estimation between 2017 and 2022 for the KG basin region. It is inferred from the study that the region has shown surface subsidence of 80mm/year between April 2020 and June 2022. This study uses support vector regressor (SVR) to predict the loss in forest cover in terms of RVI using MTInSAR-based surface subsidence, VH, and VV backscatter as parameters. It is observed that the SVR gave R2-statistics of 0.89 and 0.873 in the training and testing phases with a mean absolute error (MAE) and root mean squared error (RMSE) of 0.08 and 0.02, respectively. It is also observed that the region showed a loss of 3.21 km2 of cultivable land between 2020 and 2022.

Structure and dynamics of the Ecuador Fracture Zone, Panama Basin

SUMMARYIn this study, multiple geophysical data types are used to investigate the structure and dynamics of the Ecuador Fracture Zone—a complex multistranded strike-slip fault system located in the Panama Basin. Gravity modelling reveals a 25–30-km-wide region of ∼3-km-thick, low-density crust beneath this system and an anomalously low-density region in the uppermost mantle. Along both edges, the transition to the ‘normal’ structure and thickness oceanic crust formed at both the Ecuador and Costa Rica Rifts is abrupt. Within the Ecuador Fracture Zone itself, normal faults bound the median ridges. These faults traverse the entire thickness of accumulated sediment and offset the seabed, while sediment layer geometries document multiple phases of relative uplift, with the most recent phase still ongoing. Active extensional faulting, with an approximately spreading ridge-parallel strike, is also observed in 6–7 Ma Costa Rica Rift crust. The median ridges and the transverse ridge at the eastern edge of the Ecuador Fracture Zone also have contrasting crustal density structures. Both median ridges have a lower density crust than between the intervening valleys, while the transverse ridge crust has an equivalent thickness and density structure to that formed at the Costa Rica Rift. The active median valley basement-cutting normal faults allow seawater ingress and alternation of the crustal footwall, and also flow to mantle depth where, based on gravity modelling, 30–50 per cent serpentinization of mantle peridotite occurs. The resulting serpentinite-driven buoyancy acts as the primary control on the observed median ridge relative vertical tectonism. In contrast, the relative uplift of the transverse ridge results from lithospheric flexure in response to a change in spreading direction between the Ecuador and Costa Rica Rifts. Contrary to the widely accepted assumption that fracture zones are tectonically inactive systems, the Ecuador Fracture Zone provides evidence of extension, serpentinization due to ongoing hydrothermal circulation and relative uplift.

Prior exposure of microbial communities to seawater reduces resilience but increases compositional and functional resistance to flooding events

Storm surges, flooding, and the encroachment of seawater onto agricultural land are predicted to increase with climate change. These flooding events fundamentally alter many soil properties and have knock-on effects on the microbial community composition and its functioning. The hypotheses tested in this study were (1) that the extent of change (resistance) of microbial community functioning and structure during seawater flooding is a factor of pre-adaptation to the stress, and (2) if structure and function are altered, the pre-adaptation will result in communities returning to previous state prior to flooding (resilience) faster than unexposed communities. We chose a naturally occurring saltmarsh-terrestrial pasture gradient from which three elevations were selected to create mesocosms. By selecting these sites, we were able to incorporate the legacy of differing levels of seawater ingress and exposure. Mesocosms were submerged in seawater for 0, 1, 96- and 192-h, with half of the mesocosms sacrificed immediately after flooding, and the other half taken after a 14 day “recovery” period. The following parameters were monitored: 1) changes in soil environmental parameters, 2) prokaryotic community composition, and 3) microbial functioning. Our results indicated that any length of seawater inundation significantly altered the physicochemical properties of all the soils, although a greater change is observed in the pasture site compared to the saltmarsh sites. These changes remained following a recovery period. Interestingly, our results indicated that for community composition, there was a high degree of resistance for the Saltmarsh mesocosms, with the Pasture mesocosm displaying higher resilience. Further, we observed a functional shift in the enzyme activities with labile hemicellulose being preferentially utilised over cellulose, with the effect increasing with longer floods. These results suggest that changing bacterial physiology is more critical to understanding the impact of storm surges on agricultural systems than bulk community change.

Combined effect of seawater and load on methacrylate adhesive

Although the shipbuilding industry is constantly demanding new advanced joining solutions, adhesive technology is not as developed in the marine as compared to other industries. The main reason is the lack of specific knowledge that guarantees the durability of the bonded joints in optimal conditions during the life cycle of a ship. This work simulates in the laboratory a marine-like environment by immersing an adhesive in seawater and subjecting it to constant loading. The objective is to characterize the seawater absorption behavior and its consequences on the mechanical, thermal, and chemical properties of the adhesive after this aging process. Seawater ingress was determined through gravimetric tests at several load conditions of the tensile strength of the adhesive. Besides, absorption process was studied using Fick's Law, determining the diffusion coefficients. The thermal behavior was monitored with differential scanning calorimetry (DSC) and the chemical degradation was analyzed using Fourier transform infrared spectroscopy (FTIR). Also, the mechanical properties were determined by tensile tests. The surface of the adhesive (dried) was studied by Scanning Electron Microscopy (SEM) technique and the porosity was measured by physisorption with a high-performance adsorption analyzer. A numerical simulation was developed using Darcy's Law combined with continuity equation. The results show that application of loads and immersion in seawater until full saturation of seawater improve the mechanical properties of the adhesive, but it affects negatively to the glass transition temperature. This should be considered when designing adhesive bonding joints on ships.

Structural analysis of a fibre-reinforced composite blade for a 1 MW tidal turbine rotor under degradation of seawater

This paper presents a structural performance study of a fibre-reinforced composite blade for a 1 MW tidal turbine rotor blade that was designed for a floating tidal turbine device. The 8-m long blade was manufactured by ÉireComposites Teo and its structural performance was experimentally evaluated under mechanical loading in the Large Structures Research Laboratory at the University of Galway. Composite coupons, applied with an accelerated ageing process, were tested to evaluate the influence of seawater ageing effects on the performance of the materials. The material strength of the composites was found to have a considerable degradation under the seawater ingress. As part of the design stage, a digital twin of the rotor blade was developed, which was a finite-element model based on layered shell elements. The finite-element model was verified to have good accuracy, with a difference of 4% found in the blade tip deflection between the physically measured test results in the laboratory and numerical prediction from the model. By updating the numerical results with the material properties under seawater ageing effects, the structural performance of the tidal turbine blade under the working environment was studied. A negative impact from seawater ingress was found on the blade stiffness, strength and fatigue life. However, the results show that the blade can withstand the maximum design load and guarantee the safe operation of the tidal turbine within its design life under the seawater ingress.

Response of Indian Cultivar of Isabgol on Halopriming under the Saline Condition

Soil salinity is one of the major abiotic stresses that strongly affect seed germination in agriculture. In order to fulfill the need of demand in agriculture, seed priming is one of the promising techniques that enhance seed germination and uniformity. Isabgol, one of India’s important medicinal crops, has a low germination rate. In Gujarat state, Isabgol has considered a cash crop, serving as a source of income to the farmers. Gujarat state faces many challenges, and seawater ingress is one of the major issues creating salinity in the soil, affecting seed germination. This research was carried out to study the effects of seed priming on seed germination behavior of Gujarat Isabgol variety 4. The method where KNO3 was used for priming with two different salinity levels, 0 dS/m, and 5.3 dS/m. The experiment was a completely randomized design. In this experiment, germination traits like germination percentage, Mean Germination Time, plumule length, radicle length, seed vigour, and fresh weight were measured. Data were analyzed by using SPSS software. The present study shows that halopriming with KNO3 at a lower concentration was quite an effective treatment since it significantly increased some of the germination traits of Gujarat Isabgol variety 4.

Assessment of groundwater vulnerability using the GIS approach-based GOD method in Surat district of Gujarat state, India

Abstract There are different sources of groundwater pollution among them industrial water disposal, seawater ingress, usage of pesticides and fertilizers in agricultural fields, and municipal and residential wastewater disposal. The aim of the study is to assess groundwater vulnerability in terms of quality using the GOD method using the Geographical Investigation System approach for Surat and its surroundings. Groundwater confinement, overlying strata and depth to water table are the three parameters that are used in the assessment of groundwater vulnerability. In this study, all three parameters are given by the conventional weights which are suggested by Foster 1987. Based on the study Mahuva, Mandvi, Umarpada and some parts of the Bardoli talukas lie in very high-vulnerability zones whereas another part of the study area lies in a high-vulnerability zone. Almost 35.98% of the area of the district lies in the higher-vulnerability zone. Depth to the water table and the overlying strata are very important parameters that effectively cause groundwater vulnerability. This study may help in groundwater quality management, and watershed management as well as it is very much useful for the policymakers and local authorities as well as the government.

Assessment of seawater ingress in the coastal aquifers of south Andaman Island, India

Seawater ingress is a widespread environmental issue posing threat to the fresh groundwater reserves of the coastal aquifers of Andaman and Nicobar Islands (ANI) particularly after the great Indian Ocean Tsunami 2004, and the comprehensive investigations of seawater ingress in this region are relatively uncommon. In this context, the spatial distribution and vertical movement of seawater ingress in the coastal and catchment areas were mapped using geo-spatial techniques and the extensive geoelectrical resistivity surveys (96 vertical electric soundings (VES) and profiling) along and across the identified and affected coastlines. The geoelectrical surveys unravels very low resistivity formations (≤10 Ω m) at varying depths interpreted as the lateral and vertical intrusion of seawater. The hydro-chemical and other physical analyses of groundwater samples reveal critical concentrations of the different major elements and other physical parameters like TDS, pH as well the EC above its permissible limit for drinking water standards. The integrated approach allows to delineate the site specific hydrogeological setting including the saline/fresh aquifer geometry (transition zone) and stratigraphic−geomorphological reconstruction of coastal aquifers. Further, various assessment parameters including very low formation resistivity, surface manifestation of salt tolerant plants, high chloride concentration, low formation factor and high ionic strength were employed to infer the various levels of contamination. The present study show that impact of seawater intrusion is intense in sedimentary formations than Ophiolite suite and needs site specific mitigation measure to prevent further deterioration of aquifer health.

Depth Profiles of Re-Os Geochemistry in Drill Cores from Hole U1530A in Brothers Volcano Hydrothermal Field, Kermadec Arc: Mobilization and Extreme Enrichment of Os by Volcanic Gas

AbstractBetter understanding metallogenesis in oceanic crust depends on costly sea-floor drilling projects in areas where metal-bearing deposits, such as sea-floor massive sulfide deposits, are currently forming. In 2018, International Ocean Discovery Program (IODP) Expedition 376 recovered drill cores from an active hydrothermal field at Brothers volcano, in the Kermadec arc. These provide insight into the formation of mineral deposits along arcs, the structure and permeability of hydrothermal sites, and the relationship between the discharge of magmatic fluids and the deep biosphere. We report whole-rock major and trace element compositions and the Re-Os isotope geochemistry of hydrothermally altered volcanic rocks in a core from Hole U1530A, extending 453 m beneath the sea floor, and unaltered volcanic rocks in cores from four other drilling sites and interpret these data to better understand subseafloor mixing of hydrothermal fluids and ambient seawater. The core exhibits more radiogenic 187Os/188Os values than typical basal values in four intervals. We propose two causal mechanisms of these radiogenic values: (1) mixing between seawater and hydrothermal fluid, associated with abundant deposition of sulfide or sulfate minerals; and (2) ingress of seawater with radiogenic 187Os/188Os values, associated with abundant chlorite and high porosity. Extreme Os enrichments up to 61.5 ppb are interpreted as the result of mobilization of Os as OsO4 or OsF6 and transport by volcanic gas, which also affected the Re-Os geochemistry of the rocks from the other Expedition 376 holes. Mobilization and transport of Os by volcanic gas may be an appreciable factor in the influx of unradiogenic Os into the ocean.

The terminal lakes of the Murray River, Australia, were predominantly fresh before large-scale upstream water abstraction: Evidence from sedimentary diatoms and hydrodynamical modelling

The Murray River is Australia's longest river, draining the continent's largest exoreic catchment. The river is Australia's most economically valuable, but is highly degraded by water extraction. The Murray River's terminal lakes, Lakes Alexandrina and Albert, formed following the mid-Holocene marine transgression. These lakes are part of one of the most ecologically important wetland ecosystems on the Australian continent and are recognised as internationally significant by the Ramsar Convention. As a result of upstream water extraction, the Lower Lakes are threatened by rising salinity. To combat this threat, water is allocated to maintain the Lower Lakes as freshwater ecosystems. This practice is part of the Murray-Darling Basin Plan, one of the largest environmental water allocation plans in the world. The water allocations and the natural history of the Lower Lakes are the subject of academic and public debate, since the water would otherwise be used for consumptive purposes, particularly irrigated agriculture, upstream. Recent modelling postulated that the lakes were saline for much of the period between 8500 and 5000 years ago. However, using new sedimentary diatom and hydrodynamic modelling evidence, we demonstrate that the Lower Lakes were fresh for most of this time, particularly after 7200 years ago. Elevated Murray River discharge between 7200 and 6600 years ago prevented sea water ingress, despite sea levels +1 m higher than present. After 6600 years ago, the lakes remained predominately fresh. Current management is, therefore, consistent with the lakes' history before European colonisation.

Dynamic Analysis of A Subsea Suspended Manifold Going Through Splash Zone During Installation

The subsea suspended manifold designed to replace the traditional foundation structure with the buoys is a new generation subsea production system that can be suspended at a certain height from the seafloor and rapidly recycled by its own buoyancy. Due to complex environmental conditions, its hydrodynamic performance in the splash zone is extremely important for the safety of the whole installation process. In this paper, the mathematical model for the dynamic analysis of the seawater ingress process of the single-layer pre-set horizontal cabin is proposed based on the different center of gravity positions of the buoy. Meanwhile, the theoretical analysis of fiber cable is divided into infinite differential units by the discretization method, and the formulae of the horizontal displacement of the subsea suspended manifold are presented. In addition, the simulations are carried out to verify the rules of the dynamic responses on the subsea suspended manifold system with the consideration of the environmental conditions in the South China Sea. Comparing with the calculated value of the mathematical model of the cabin water ingress, the error of the simulation result by use of FLUENT is about 5.47%. Furthermore, the wave height is greater than the current impact on the lowering manifold system and the azimuth angle of the installation vessel is aligned with the direction of the environmental load.

Assessment of Groundwater Flow Dynamics Using MODFLOW in Shallow Aquifer System of Mahanadi Delta (East Coast), India

Despite being a biodiversity hotspot, the Mahanadi delta is facing groundwater salinization as one of the main environmental threats in the recent past. Hence, this study attempts to understand the dynamics of groundwater and its sustainable management options through numerical simulation in the Jagatsinghpur deltaic region. The result shows that groundwater in the study area is extensively abstracted for agricultural activities, which also causes the depletion of groundwater levels. The hydraulic head value varies from 0.7 to 15 m above mean sea level (MSL) with an average head of 6 m in this low-lying coastal region. The horizontal hydraulic conductivity and the specific yield values in the area are found to vary from 40 to 45 m/day and 0.05 to 0.07, respectively. The study area has been calibrated for two years (2004–2005) by using these parameters, followed by the validation of four years (2006–2009). The calibrated numerical model is used to evaluate the net recharge and groundwater balance in this study area. The interaction between the river and coastal unconfined aquifer system responds differently in different seasons. The net groundwater recharge to the coastal aquifer has been estimated and varies from 247.89 to 262.63 million cubic meters (MCM) in the year 2006–2007. The model further indicates a net outflow of 8.92–9.64 MCM of groundwater into the Bay of Bengal. Further, the outflow to the sea is preventing the seawater ingress into the shallow coastal aquifer system.

THE SEAWATER AND FRESHWATER INFLUENCE ON EXPANSIVITY BEHAVIORS OF CLAY MINERALS

Semarang City is characterized by an intercalating of loam-silt and clayey units. The behavior of the clay materials in terms of its expansivity changes in the volumetric parameter when it contacts the water. Some problems in the presence of tidal flooding appears when the seawater ingress to the shoreland that causes severe damage to infrastructures. This research attempts to reveal the influence of both seawater and freshwater on the expansivity behaviors of the clayey materials based on its mineral composition. Some tests are performed to observe the volumetric changes in the clay samples after being soaked in seawater and freshwater for twenty-four hours. The X-Ray Diffraction (XRD) tests are conducted on some selected samples by using the bulk method to determine the mineral composition of the samples. The ANOVA test is also introduced in the analysis to distinguish whether the certain mineral types and its composition influencing the clay expansivity behaviors at a confidence level of about ninety-five percent and alpha (α) of about five percent. The result of this research has proven that the presence of montmorilonite minerals is the most influencing factor on the clayey expansivity behaviors when immersed in seawater and freshwater than kaolinite and illite minerals.

Modelling the removal of an earth bund to maximise seawater ingress into a coastal wetland

Weed infestation is a critical management issue for maintaining the natural values of coastal wetlands across the world. Widespread use of herbicides to control weeds has resulted in environmental issues in the past and has led to the search for more natural control methods such as using saline water. This study investigates management options to restore the natural flow regimes between freshwater wetlands and seawater by removing a bund which was built to grow ponded pasture. The study was carried out in the Mungalla wetland in Queensland, which is an important Nywaigi aboriginal community asset for recreation, cultural and economic activities. The study used modelling and monitoring methods to (a) assess how effective the earth bund was in excluding seawater and (b) the extent to which seawater could enter the wetland without the bund. Eleven scenarios were investigated to estimate seawater ingress under different tide, onshore wind, low atmospheric pressure and sea level rise (SLR) conditions. Results show that removal of the bund reinstated periodic tidal ingress into the wetland. Seawater intrusion was also shown to increase when there were onshore winds and/or low atmospheric pressure associated with cyclones. The greatest impact was under future SLR, where large increases in the inundation frequency and extent are likely to cause a shift in the wetland vegetation towards native salt tolerant species. Findings of this study are useful for examining the potential impact of various management interventions that are being considered for wetland system repair. For example, the removal or height adjustment of tidal barriers, dredging of silted streams, removal of weeds from choked streams and reintroduction of tidal flows to control weed infestation, improve water quality and restore natural values to the wetlands.

Construction of the Tuen Mun–Chek Lap Kok Link Sub-sea Tunnels in Hong Kong

The entire Tuen Mun–Chek Lap Kok Link (TM-CLKL) was commissioned on 27 December 2020 and comprises a 9 km dual twolane carriageway between Tuen Mun and North Lantau, Hong Kong. The challenges for the construction of the TM-CLKL tunnels included sub-sea tunnelling up to 55 m below sea level in mixed ground geology that required replacement of tunnel boring machine (TBM) cutting tools at hyperbaric pressure up to 5.8 bars; replacement of worn TBM cutting tools in complicated ground conditions; construction of approach tunnels in newly reclaimed land subject to long-term consolidation; and construction of cross passages at 100-metre intervals between the two sub-sea tunnels with a risk of sea water ingress at 5.5 bars. This project has deployed sophisticated techniques to surmount the challenges encountered during construction of the five-kilometre-long sub-sea tunnels. These included the use of the world’s largest slurry-type Mixshield TBM, 17.63 m in diameter, for the construction of the northern approach tunnel, followed by two 14 m diameter slurry-type Mixshield TBMs for the construction of the sub-sea tunnels; use of saturation diving techniques for TBM cutterhead interventions up to 5.8 bars which was the first such works in Hong Kong and one of only a few uses of saturation diving in tunnelling worldwide; use of ground freezing techniques in complicated ground conditions for TBM interventions to change worn cutting tools at the TBM cutterhead; TBM tunnelling in newly reclaimed land at the northern landfall and the southern landfall; and the construction of cross passages by mini-TBM using pipe jacking methods between the two main tunnel tubes which was the first such works ever undertaken anywhere in the world. This paper introduces the successful implementation of these techniques for the satisfactory completion of the TM-CLKL sub-sea tunnels.

Development of an Embedded UHF-RFID Corrosion Sensor for Monitoring Corrosion of Steel in Concrete

Corrosion of reinforcing steel is the leading cause of deterioration in concrete and impacts strongly the safety and durability of civil infrastructures. It occurs in marine environment with the presence of chloride which breaks the thin oxide film passivation layer leading to dissolution. This research proposes an innovative embedded sensor in concrete for the detection of corrosion of steel. The autonomous UHF RFID (Ultra High Frequency Radio Frequency Identification) sensor is based on the coupling between the antenna of a dipolar RFID tag and a layer of steel exposed to chloride in concrete. Variation of the RSSI (Received Signal Strength Indication) measured by the reader localized in air has two origins, namely the degree of moisture of concrete and the presence of the steel layer. By minimizing the impact of seawater ingress on the antenna property, the presence of metallic films of few micrometers thickness can be detected. This authorizes the development of the proposed method for monitoring mass loss of steel in concrete.

Evaporative loss of moderately volatile metals from the superheated 1849 Ma Sudbury impact melt sheet inferred from stable Zn isotopes

The retention of moderately volatile elements on the growing Earth remains a major uncertainty in models of terrestrial accretion. Large impactors were the main carriers of accreted material but their mutual energetic collisions and impacts onto the Earth also caused chemical fractionation for which limited experimental data exist. The objective of this work was to study several moderately volatile elements in the third-largest impact basin preserved on Earth at Sudbury, Ontario. We conducted a new chemostratigraphic transect (n=41) of Zn isotope ratios and concentrations by analysing melt sheet and basin fill samples. The data were compared to common Pb, Cs, Cd and Sb concentration systematics. Within the crystallised melt sheet there are strong trends in the extent of moderately volatile element deficits, Zn isotope composition (δ66/64ZnJMC-L from 0.18 to 0.47‰) and initial Pb isotope composition. The combined evidence suggests that these trends reflect footwall contamination of a melt sheet that had experienced evaporative Zn-loss of up to 75–80%. Accounting for plausible isotopic signatures of target rocks, the maximum mass-dependent Zn isotope fractionation ε was 0.29 ± 0.04‰ (1 s.d.), which translates to modest fractionation factors α=0.99986 to 0.99975. This is comparable to melt fallout-glass and fused sands from nuclear detonation sites. We attribute the observed Zn loss and isotope fractionation to the formation of the impact melt. The rapid formation of a solid lid of breccias upon seawater ingress may have prevented stronger evaporative loss and isotope fractionation. Within the crater fill, there is an up-stratigraphy increase in Zn isotope variability (δ66/64ZnJMC-L from 0.29 to 1.05‰). Combined with evidence for biogenic reduced C, this suggests sedimentation of authigenic particulates within an enclosed crater sea.In the melt sheet, the Zn-Pb and Rb-Cs pairs experienced different extents of maximum evaporative loss (Pb up to 98.4% vs. Zn 78%; and Cs ∼90% vs. Rb ∼30%). The relative loss pattern could reflect evaporation from superheated silicate melt at ∼1,450°C and 1 atm. Loss from super-liquidus melts formed by bolide impacts could have been a significant process shaping the Earth's volatile and moderately volatile inventory.