Seawater Infiltration Research Articles

Archaeological deposits and tunnel constructions: Simulations of groundwater head at the Old Wharf of Bergen, Norway

The purpose of this study was to examine the impact of tunnel constructions on the steady-state groundwater head in the archaeological deposits at the Old Wharf (Bryggen) of Bergen. Water infiltration, permeabilities, and boundary conditions were deduced from available data and supplemented by leakage measurements into the existing railway tunnel located upstream of the Bryggen area. The pore water in the deposits at Bryggen has different origins viz. precipitation; leakage from drainage systems; infiltration of seawater; infiltration via the bedrock, and based on these observations, a 2D horizontal – and a 2D vertical numerical model were constructed where the seawater was the boundary at one side of the model and the groundwater divide at the other side. Given estimates of bedrock permeability and steady state infiltration rate, it was possible to calculate groundwater heads in the sediments at Bryggen that were consistent with observations, assuming that all the water percolating into the sediments flow through fractures in the bedrock. By this extreme assumption, a maximum sensitivity of the relation between groundwater flux in the bedrock and the groundwater level in the archaeological deposits was achieved. After simulation of the natural groundwater level (i.e. without any artificial extraction of water in the catchment), the impact of the water leakage into the existing tunnels was calculated. Given the relatively rough estimates of water leakage into the existing tunnels (4 L/day/meter of tunnel), the calculated decline of the groundwater head in the archaeological deposits was less than 1% of the natural groundwater level (<1 cm). If leakage rates were increased to one and two orders of magnitude, the steady state groundwater decline would be from 5% to more than 35% of the reference groundwater level (4–15 cm). The reason for these relatively robust groundwater conditions in the sediments are caused by the boundary conditions: Without any local water extraction in the deposits, the steady-state groundwater head at Bryggen will always be higher than the seawater level. A crucial point for these results was the leakage rates into the existing tunnels. Water discharge into tunnels and other subsurface constructions is the principal risk factor in this study and should be monitored before any new tunnels are constructed.

A TWO-COMPONENT BARRIER SYSTEM TO PROTECT COASTAL REGIONS FROM THE RISING SEA LEVELS

Global warming is expected to result in the rising of sea levels. Should this occur, coastal cities, ports, and wet lands would be threatened with more frequent inundation, increased beach erosion, and saline water encroachment into coastal aquifers. The purpose of this paper is to present one possible mitigation methodology to protect the northern sea shores of Egypt and limit the sea water infiltration into the sand aquifer along the Mediterranean Sea shores. A 2-D finite element model, using Z-Soil finite element analysis program, was used to analyze the proposed underground impervious cut-off wall. Studies were undertaken of the main factors which affect the head losses through the cut-off wall to optimize its dimensions. In case of a 1-m rise in the sea level, the numerical model represented the proposed solution with its two-component protection. PVC sheet pile embedded into as oil-cement-bypass-bentonite(SBPB) cut-off wall provide a two-component barrier system. The proposed solution succeeded in providing a top barrier wall in addition to complete blockage of the subsurface seeping water

Paleo-modeling of coastal saltwater intrusion during the Holocene: an application to the Netherlands

Abstract. Coastal groundwater reserves often reflect a complex evolution of marine transgressions and regressions, and are only rarely in equilibrium with current boundary conditions. Understanding and managing the present-day distribution and future development of these reserves and their hydrochemical characteristics therefore requires insight into their complex evolution history. In this paper, we construct a paleo-hydrogeological model, together with groundwater age and origin calculations, to simulate, study and evaluate the evolution of groundwater salinity in the coastal area of the Netherlands throughout the last 8.5 kyr of the Holocene. While intended as a conceptual tool, confidence in our model results is warranted by a good correspondence with a hydrochemical characterization of groundwater origin. Throughout the modeled period, coastal groundwater distribution never reached equilibrium with contemporaneous boundary conditions. This result highlights the importance of historically changing boundary conditions in shaping the present-day distribution of groundwater and its chemical composition. As such, it acts as a warning against the common use of a steady-state situation given present-day boundary conditions to initialize groundwater transport modeling in complex coastal aquifers or, more general, against explaining existing groundwater composition patterns from the currently existing flow situation. The importance of historical boundary conditions not only holds true for the effects of the large-scale marine transgression around 5 kyr BC that thoroughly reworked groundwater composition, but also for the more local effects of a temporary gaining river system still recognizable today. Model results further attest to the impact of groundwater density differences on coastal groundwater flow on millennial timescales and highlight their importance in shaping today's groundwater salinity distribution. We found free convection to drive large-scale fingered infiltration of seawater to depths of 200 m within decades after a marine transgression, displacing the originally present groundwater upwards. Subsequent infiltration of fresh meteoric water was, in contrast, hampered by the existing density gradient. We observed discontinuous aquitards to exert a significant control on infiltration patterns and the resulting evolution of groundwater salinity. Finally, adding to a long-term scientific debate on the origins of groundwater salinity in Dutch coastal aquifers, our modeling results suggest a more significant role of pre-Holocene groundwater in the present-day groundwater salinity distribution in the Netherlands than previously recognized. Though conceptual, comprehensively modeling the Holocene evolution of groundwater salinity, age and origin offered a unique view on the complex processes shaping groundwater in coastal aquifers over millennial timescales.

The Marsili Volcanic Seamount (Southern Tyrrhenian Sea): A Potential Offshore Geothermal Resource

Italy has a strong geothermal potential for power generation, although, at present, the only two geothermal fields being exploited are Larderello-Travale/Radicondoli and Mt. Amiata in the Tyrrhenian pre-Apennine volcanic district of Southern Tuscany. A new target for geothermal exploration and exploitation in Italy is represented by the Southern Tyrrhenian submarine volcanic district, a geologically young basin (Upper Pliocene-Pleistocene) characterised by tectonic extension where many seamounts have developed. Heat-flow data from that area show significant anomalies comparable to those of onshore geothermal fields. Fractured basaltic rocks facilitate seawater infiltration and circulation of hot water chemically altered by rock/water interactions, as shown by the widespread presence of hydrothermal deposits. The persistence of active hydrothermal activity is consistently shown by many different sources of evidence, including: heat-flow data, gravity and magnetic anomalies, widespread presence of hydrothermal-derived gases (CO2, CO, CH4), 3He/4He isotopic ratios, as well as broadband OBS/H seismological information, which demonstrates persistence of volcano-tectonic events and High Frequency Tremor (HFT). The Marsili and Tyrrhenian seamounts are thus an important—and likely long-lasting-renewable energy resource. This raises the possibility of future development of the world’s first offshore geothermal power plant.

Contrasting subduction structures within the Philippine Sea plate: Hydrous oceanic crust and anhydrous volcanic arc crust

AbstractWe show contrasting subduction structures within the Philippine Sea plate inferred from active‐source wide‐angle reflection data. Previous studies showed that large‐amplitude reflections from the slab are observed in southwest Japan and indicated that a thin low‐velocity layer with a high fluid content is formed along the top of the subducting oceanic crust. On the contrary, we found that the slab reflections have smaller amplitudes in the Izu collision zone, central Japan, where the Izu‐Bonin volcanic arc has been colliding/subducting, suggesting that such a low‐velocity layer does not exist beneath the collision zone. This structural difference is also supported by P‐wave and S‐wave velocity anomalies by passive‐source tomography and electrical conductivity, and correlates with the regional distribution of deep tremors and intraslab earthquakes, both of which are induced by dehydration processes within the downgoing slab. Based on these comparisons, we suggest that the original structure of the incoming plate controls the contrasting subducting systems: typical oceanic plate absorbs water by hydrothermal circulation at spreading centers and/or seawater infiltration at outer rises, whereas volcanic arc crust consumes a large amount of hydrous minerals for melt production and metamorphoses to more stable, anhydrous forms before subduction.

Palaeobotanical, chemical and physical investigation of the content of an ancient wine amphora from the northern Tyrrhenian sea in Italy

Elemental, isotopic and archaeobotanical analysis were performed on the contents of an intact Dressel 1B amphora from a Roman navis oneraria shipwreck dating back to 100–90 BC, discovered at a depth of 42 m near Albenga (Italy). Analysis aimed at assessing the origin and nature of the samples was carried out. The chemical characterisation, in particular lead content, was consistent with an oenological product produced using ancient techniques. The organic matrix was observed and shown to have deteriorated seriously, with infiltration of sea water and migration from the clay vessel. Isotope ratio mass spectrometry (IRMS) analysis confirmed that the residue was wine, excluding the possibility of the sediment coming from the sea or the clay of the amphora. As regards palynological analysis, the pollen components were useful for diagnosing and characterising the oenological nature and geographical origin of the sample from Albenga. The extremely high percentage of grape pollen suggested that the liquid traded was must or wine subjected to little decantation. Finally, the presence of pollen from certain arboreal species widespread in central-southern Italy is in accordance with the opinion of archaeologists, who have suggested that the cargo originated in the centre-south of the Tyrrhenian area.

Assessment of water qualities and evidence of seawater intrusion in a deep confined aquifer: case of the coastal Djeffara aquifer (Southern Tunisia)

Research Article| October 07 2013 Assessment of water qualities and evidence of seawater intrusion in a deep confined aquifer: case of the coastal Djeffara aquifer (Southern Tunisia) Adel Kharroubi; Adel Kharroubi 1Higher Institute of Water Sciences and Techniques, University of Gabes, Tunisia, Cité Erryadh 6072, Gabes, Tunisia Search for other works by this author on: This Site PubMed Google Scholar Soumaya Farhat; Soumaya Farhat 1Higher Institute of Water Sciences and Techniques, University of Gabes, Tunisia, Cité Erryadh 6072, Gabes, Tunisia Search for other works by this author on: This Site PubMed Google Scholar Belgacem Agoubi; Belgacem Agoubi 1Higher Institute of Water Sciences and Techniques, University of Gabes, Tunisia, Cité Erryadh 6072, Gabes, Tunisia E-mail: Belgacem.Agoubi@isstegb.rnu.tn Search for other works by this author on: This Site PubMed Google Scholar Zouhir Lakhbir Zouhir Lakhbir 2Société Nationale d'Exploitation et de Distribution d'Eau (SONEDE), Direction Production, Jerba, Tunisia Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2014) 63 (1): 76–84. https://doi.org/10.2166/aqua.2013.105 Article history Received: September 20 2012 Accepted: August 08 2013 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Adel Kharroubi, Soumaya Farhat, Belgacem Agoubi, Zouhir Lakhbir; Assessment of water qualities and evidence of seawater intrusion in a deep confined aquifer: case of the coastal Djeffara aquifer (Southern Tunisia). Journal of Water Supply: Research and Technology-Aqua 1 February 2014; 63 (1): 76–84. doi: https://doi.org/10.2166/aqua.2013.105 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Geochemical analyses of groundwater samples from the Djeffara confined aquifer (Southern Tunisia) were performed. The distribution of saline waters was investigated to identify the origin of the groundwater contamination. The aquifer was shown to be affected by an abnormal increase in groundwater salinity. Near the recharge zone, the groundwater salinity does not exceed 2.5 g l−1 but reaches 7 g l−1 in the northeast of the study area. Due to over pumping, groundwater level decline is so important that it disturbs the equilibrium between fresh and saline waters. The salinity distribution coupled with the structure and geology of the Djeffara aquifer suggest current seawater intrusion is possible through the deep fault systems affecting the zone. The groundwater level was shown to be highly correlated with the sea level fluctuation in the area near the fault systems, suggesting a communication between the sea and the confined aquifer. Groundwater salinization is probably related to infiltration of seawater through the faults. However, an intrusion on the side of the discharge area of the aquifer may also be possible. The bromide and chlorine analyses coupled with the SO4/Cl ratio confirmed that the mixing between fresh and saline waters is the main origin of groundwater salinization. aquifer, fault systems, groundwater, seawater intrusion This content is only available as a PDF. © IWA Publishing 2014 You do not currently have access to this content.

An implementation of differential evolution algorithm for inversion of geoelectrical data

Abstract Differential evolution (DE), a population-based evolutionary algorithm (EA) has been implemented to invert self-potential (SP) and vertical electrical sounding (VES) data sets. The algorithm uses three operators including mutation, crossover and selection similar to genetic algorithm (GA). Mutation is the most important operator for the success of DE. Three commonly used mutation strategies including DE/best/1 (strategy 1), DE/rand/1 (strategy 2) and DE/rand-to-best/1 (strategy 3) were applied together with a binomial type crossover. Evolution cycle of DE was realized without boundary constraints. For the test studies performed with SP data, in addition to both noise-free and noisy synthetic data sets two field data sets observed over the sulfide ore body in the Malachite mine (Colorado) and over the ore bodies in the Neem-Ka Thana cooper belt (India) were considered. VES test studies were carried out using synthetically produced resistivity data representing a three-layered earth model and a field data set example from Gokceada (Turkey), which displays a seawater infiltration problem. Mutation strategies mentioned above were also extensively tested on both synthetic and field data sets in consideration. Of these, strategy 1 was found to be the most effective strategy for the parameter estimation by providing less computational cost together with a good accuracy. The solutions obtained by DE for the synthetic cases of SP were quite consistent with particle swarm optimization (PSO) which is a more widely used population-based optimization algorithm than DE in geophysics. Estimated parameters of SP and VES data were also compared with those obtained from Metropolis–Hastings (M–H) sampling algorithm based on simulated annealing (SA) without cooling to clarify uncertainties in the solutions. Comparison to the M–H algorithm shows that DE performs a fast approximate posterior sampling for the case of low-dimensional inverse geophysical problems.

CHARACTERISTIC OF LITORAL SEDIMENT ON SINDULANG SATU COASTAL

Coastal area is defined as the interface point where sea and land meet. To the land the area is limited to the area influenced by the sea factors (wind, tide, and sea water infiltration), while to the sea is limited to the area influenced by the land factors. Special concern need to be addressed in regarding to the use of coastal area. As part of the coastal area, littoral zone is very dynamics due to factors of oceanography and human activities. The same fact is experienced by the littoral zone in Sindulang Satu. Physical change has been the fact in this littoral zone. In relation to the change, it is considered of importance to describe and analysis the characteristics of the sediment and related oceanography factors. Result of observation indicated that sediment in the littoral zone consist of fine sand, medium sand, very fine sand, coarse sand and pebbles. Silt and boulder were also found. Distribution of sediment granulometry showed that the littoral zone was dominated by fine sand material, bad sorted, asymetrical to small size and symmetrical granulometry, and mesokurtic. Tidal current is the type of current working in the littoral zone and it plays importance role in the sediment.

CHARACTERISTIC OF LITORAL SEDIMENT ON SINDULANG SATU COASTAL

Coastal area is defined as the interface point where sea and land meet. To the land the area is limited to the area influenced by the sea factors (wind, tide, and sea water infiltration), while to the sea is limited to the area influenced by the land factors. Special concern need to be addressed in regarding to the use of coastal area. As part of the coastal area, littoral zone is very dynamics due to factors of oceanography and human activities. The same fact is experienced by the littoral zone in Sindulang Satu. Physical change has been the fact in this littoral zone. In relation to the change, it is considered of importance to describe and analysis the characteristics of the sediment and related oceanography factors. Result of observation indicated that sediment in the littoral zone consist of fine sand, medium sand, very fine sand, coarse sand and pebbles. Silt and boulder were also found. Distribution of sediment granulometry showed that the littoral zone was dominated by fine sand material, bad sorted, asymetrical to small size and symmetrical granulometry, and mesokurtic. Tidal current is the type of current working in the littoral zone and it plays importance role in the sediment.

Systematic changes in the incoming plate structure at the Kuril trench

Recent seismic structural studies in trench‐outer rise regions have shown that Vp within the incoming oceanic plate systematically decreases toward the trench, probably owing to bending and fracturing of the plate. To understand the mechanisms acting to reduce Vp, Vs is critical because the Vp/Vs ratio is a sensitive indicator of lithology, porosity, and the presence of fluid. In the outer rise region of the Kuril trench, we conducted an extensive seismic refraction and reflection survey that revealed systematic changes in Vp, Vs, and Vp/Vs. Our results suggest that water content within the incoming oceanic plate increases toward the trench accompanied by the development of bending‐related fractures at the top of the oceanic crust, consistent with the seawater percolation. Our results support the idea that plate bending and fracturing during the bending in the outer rise of the trench play an important role in the water cycle of subduction zones.

Outer rise seismicity related to the Maule, Chile 2010 mega-thrust earthquake and hydration of the incoming oceanic lithosphere

Most of the recent published geodetic models of the 2010 Maule, Chile mega-thrust earthquake (Mw=8.8) show a pronounced slip maximum of 15-20 m offshore Iloca (~35°S), indicating that co-seismic slip was largest north of the epicenter of the earthquake rupture area. A secondary slip maximum 8-10 m appears south of the epicenter west of the Arauco Peninsula. During the first weeks following the main shock and seaward of the main slip maximum, an outer rise seismic cluster of >450 events, mainly extensional, with magnitudes Mw=4-6 was formed. In contrast, the outer rise located seaward of the secondary slip maximum presents little seismicity. This observation suggests that outer rise seismicity following the Maule earthquake is strongly correlated with the heterogeneous coseismic slip distribution of the main megathrust event. In particular, the formation of the outer-rise seismic cluster in the north, which spatially correlates with the main maximum slip, is likely linked to strong extensional stresses transfered from the large slip of the subducting oceanic plate. In addition, high resolution bathymetric data reveals that bending-related faulting is more intense seaward of the main maximum slip, where well developed extensional faults strike parallel to the trench axis. Also published seismic constraints reveal reduced P-wave velocities in the uppermost mantle at the trench-outer rise region (7.5-7.8 km/s), which suggest serpentinization of the uppermost mantle. Seawater percolation up to mantle depths is likely driven by bending related-faulting at the outer rise. Water percolation into the upper mantle is expected to be more efficient during the co-seismic and early post-seismic periods of large megathrust earthquakes when intense extensional faulting of the oceanic lithosphere facilitates water infiltration seaward of the trench.

Geochemical behaviour of Radium isotopes and Radon in a coastal thermal system (Balaruc-les-Bains, South of France)

The behaviour of the four Ra isotopes (measured by gamma spectrometry) and 222Rn (measured with an AlphaGUARD ionisation chamber) has been investigated in NaCl-rich thermal waters of Balaruc-les-Bains on the Mediterranean coast (South of France). This study allows identification of the deep thermal water signature and reveals the influence of seawater or karst water inflows on Ra isotopes and 222Rn. The deep thermal water has 226Ra and 222Rn activities of 840 and 1900mBq/l, respectively, a (228Ra/226Ra) activity ratio of 0.59, and low (224Ra/228Ra) and (223Ra/226Ra) ratios of 0.67 and 0.025, respectively. Several arguments suggest a dominant role of radioactive decay for short-lived Ra isotopes and Rn during the relatively rapid ascent of thermal water through wide open fractures and drains. The low (223Ra/226Ra) ratio constrains the maximum ascent velocity of thermal water to 8–10m/h. Seawater inflow into the hydrothermal system results in an enrichment in short-lived Ra isotopes and 222Rn. The high (223Ra/226Ra) ratio (0.23) suggests that 223Ra, 224Ra and 222Rn produced by alpha-recoil in the upper-Jurassic limestone are entrained by seawater percolation through the coastal basement, due to active pumping in one of the near shore production well. This process would be enhanced by a low water/rock ratio (i.e. in a low-porosity, micro-fractured limestone). Mixing of this enriched seawater with thermal water induces barite precipitation with co-precipitation of a large fraction of Ra. Short-lived Ra isotopes may thus be useful tracers of seawater flux towards the continent. Conversely, the inflow and mixing of karst groundwater result in a general dilution of all dissolved elements, only a small enrichment in 224Ra and 223Ra, but a large enrichment in 222Rn (up to 26Bq/l). The combination of Ra isotopes and 222Rn data provides a good way to trace the dynamics of different water masses along coastal areas.

Service Life Prediction of Reactive Powder Concrete due to Seawater Infiltration

Reactive powder concrete (RPC) has a higher strengths, as well as excellent durability and corrosion resistance. So, it is expected to be increasingly used in marine engineering. In this study, After the RPC samples had been subjected to gradually increased high-pressure seawater for 30 days, the chloride contents in the samples along with the infiltration direction were calibrated on an energy dispersive spectrometer. On the basis of second Fick’s law, the chloride ion diffusion model and service life prediction model of reactive powder concrete in sea water are established. The service life of an actual reactive powder concrete structure could be predicted.

Mobilization and Transport of Naturally Occurring Enterococci in Beach Sands Subject to Transient Infiltration of Seawater

This study explores the transport of enterococci (ENT) from naturally contaminated beach sands to the groundwater table via infiltrating seawater using field, laboratory, and modeling experiments. ENT were readily mobilized and transported through the unsaturated zone during infiltration events in both the field and laboratory column experiments. Detachment mechanisms were investigated using a modified version of HYDRUS-1D. Three models for detachment kinetics were tested. Detachment kinetics that are first order with respect to the rate of change in the water content and attached surface bacterial concentrations were found to provide a best fit between predicted and observed data. From these experimental and model results we conclude that detachment mechanisms associated with the rapid increases in pore water content such as air-water interface scouring and thin film expansion are likely drivers of ENT mobilization in the investigated system. These findings suggest that through-beach transport of ENT may be an important pathway through which ENT from beach sands are transported to beach groundwater where they may be discharged to coastal waters via submarine groundwater discharge.

潮位の周期的変動に対する汀線位置の応答特性

The responses of the shoreline change to cyclic tidal changes were investigated by the spectral analysis using FFT method and a multivariate autoregressive model. The shoreline data set were obtained for 25 years at Hazaki Oceanographical Research Station (HORS) facing the Pacific Ocean. The power spectrum densities showed shoreline changes with a period of 14.76 days, which is the spring-neap cycle of the tide. The relative power contribution analysis showed the tidal range affects the shoreline change rate as the main factor of 14.76 days cyclic variability, and it was indicated the mechanisms are due to the effects of the seawater percolation and the groundwater effluent by the difference between the water table and the tidal level.

Microbial Community Composition and Dynamics of Moving Bed Biofilm Reactor Systems Treating Municipal Sewage

Moving bed biofilm reactor (MBBR) systems are increasingly used for municipal and industrial wastewater treatment, yet in contrast to activated sludge (AS) systems, little is known about their constituent microbial communities. This study investigated the community composition of two municipal MBBR wastewater treatment plants (WWTPs) in Wellington, New Zealand. Monthly samples comprising biofilm and suspended biomass were collected over a 12-month period. Bacterial and archaeal community composition was determined using a full-cycle community approach, including analysis of 16S rRNA gene libraries, fluorescence in situ hybridization (FISH) and automated ribosomal intergenic spacer analysis (ARISA). Differences in microbial community structure and abundance were observed between the two WWTPs and between biofilm and suspended biomass. Biofilms from both plants were dominated by Clostridia and sulfate-reducing members of the Deltaproteobacteria (SRBs). FISH analyses indicated morphological differences in the Deltaproteobacteria detected at the two plants and also revealed distinctive clustering between SRBs and members of the Methanosarcinales, which were the only Archaea detected and were present in low abundance (<5%). Biovolume estimates of the SRBs were higher in biofilm samples from one of the WWTPs which receives both domestic and industrial waste and is influenced by seawater infiltration. The suspended communities from both plants were diverse and dominated by aerobic members of the Gammaproteobacteria and Betaproteobacteria. This study represents the first detailed analysis of microbial communities in full-scale MBBR systems and indicates that this process selects for distinctive biofilm and planktonic communities, both of which differ from those found in conventional AS systems.

Uranium and barium cycling in a salt wedge subterranean estuary: The influence of tidal pumping

The contribution of submarine groundwater discharge (SGD) to oceanic metal budgets is only beginning to be explored. Here, we demonstrate that biogeochemical processes in a northern Florida subterranean estuary (STE) significantly alter U and Ba concentrations entering the coastal ocean via SGD. Tidal pumping controlled the distribution of dissolved metals in shallow beach groundwater. Hourly observations of intertidal groundwaters revealed high U and low Ba concentrations at high tide as a result of seawater infiltration into the coastal aquifer. During ebb tide, U decreased and Ba increased due to freshwater dilution and, more importantly, biogeochemical reactions that removed U and added Ba to solution. U removal was apparently a result of precipitation following the reduction of U(VI) to U(IV). A significant correlation between Ba and dissolved organic carbon (DOC) in shallow beach groundwaters implied a common source, likely the mineralization of marine particulate organic matter driven into the beach face by tidal pumping. In deeper groundwaters, where the labile organic matter had been depleted, Ba correlated with Mn. We estimate that net SGD fluxes were − 163 and + 1660 μmol m − 1 d − 1 for U and Ba, respectively (or − 1 and + 8 μmol m − 2 d − 1 if a 200-m wide seepage area is considered). Our results support the emerging concept that subterranean estuaries are natural biogeochemical reactors where metal concentrations are altered relative to conservative mixing between terrestrial and marine endmembers. These deviations from conservative mixing significantly influence SGD-derived trace metal fluxes.

Developmental ecology of the American horseshoe crab Limulus polyphemus

Abstract During spawning events, horseshoe crab eggs are released from the female's oviducts, and fertilized by one or more males. Eggs are shaped by the female into discrete clutches deposited in nests at depths of 10-20 cm on intertidal estuarine beaches. Distinguishing between fresh eggs and the early developmental stages is obfuscated by the large amount of dense, opaque yolk. The first unambiguous confirmation of development is the formation of the rudimentary prosomatic appendages at the "limb bud" stage. Several days thereafter, the outer chorion is shed and the developing embryo expands and undergoes a series of molts within the clear inner egg membrane. The trilobite (first instar) stage thus attained may remain within the beach sediments for several more weeks, until hatching is facilitated by environmental factors such as hydration, agitation, and osmotic shock that accompany the infiltration of seawater into the nests. Trilobites exhibit endogenous circatidal swimming rhythms that are entrained by mechanical agitation, suggesting that peaks in larval swimming are timed to coincide with periods of high water and the inundation of the nests. Larval swimming is limited and does not appear to result in long-distance dispersal. The limited dispersal of the larvae has important implications for the population dynamics of relatively isolated populations. The rate of larval development is highly plastic and is influenced by temperature, salinity, dissolved oxygen, and the presence of pollutants. The broad environmental tolerances of horseshoe crab embryos and larvae are important in understanding their current geographic distribution and their evolutionary persistence.

Nature of serpentinization of ultramafic rocks from Hero Fracture Zone, Antarctic: Constraints from stable isotopes

Serpentinites from the Hero Fracture Zone, Drake Passage, Antarctica, contain serpentine, amphibole, talc, chlorite, and magnetite as well as relict olivine, pyroxene, and spinel from a spinel peridotite precursor. Two episodes of serpentinization are recognized. The first event produced lizardite and antigorite, whereas the second produced only lizardite. The initial and subsequent serpentinization events occurred at about 178–283 °C and 170–298 °C, respectively. Calculated water/rock ratios of the serpentinization events are less than 5 for the initial event and greater than 5 for the subsequent event. A model involving deep seawater infiltration in the fracture zone, followed by serpentinization of mantle peridotite and buoyancy-driven uplift controlled by relatively small-scale faults and not by a large-scale detachment fault, is invoked to explain the emplacement of serpentinite on the surface.