Conceptual model of a coastal aquifer system in northern Greece and assessment of saline vulnerability due to seawater intrusion conditions

This paper refers to the development of a conceptual model for the management of a coastal aquifer in northern Greece. The research presents the interpretation and analysis of the quantitative (groundwater level recordings and design of piezometric maps) regime and the formation of the upcone within the area of investigation. Additionally it provides the elaboration of the results of chemical analyses of groundwater samples (physicochemical parameters, major chemical constituents and heavy metals and trace elements) of the area which were taken in three successive irrigation periods (July–August 2003, July–August 2004 and July 2005), in order to identify areas of aquifer vulnerability. The study identifies the areas where ion exchange phenomena occur, as well as the parts of the aquifer where the qualitative degradation of the aquifer system is enhanced. The paper, finally, assesses the lack of any scientific groundwater resources management of the area by the local water authorities, as well as the current practices of the existing pumping conditions scheme as applied by groundwater users.An erratum to this article can be found at     

Evaluation of soil physical properties as influenced by various green manuring legumes and phosphorus fertilization under rain fed conditions

A field experiment was conducted under rainfed environment of Pothowar region of Pakistan to assess physical properties of soil as influenced by various green manure legumes (sesbania, cluster bean and rice bean) and different P levels (0, 30, 60, 90 kg P2O5/ha). Highest fresh biomass was observed in sesbania (23 t/ha) followed by cluster bean (19 t/ha) and lowest in rice bean (17 t/ha). Maximum crude protein content was found in sesbania (17%) followed by rice bean (10%) and cluster bean (8%). Green manuring crops, on average reduced soil bulk density (5%), enhanced total porosity (8%), and macropores and large mesopores (28%). Maximum reduction (7%) in soil bulk density, and an increase (11%) in total soil porosity and available water (17%) was observed in plots where sesbania was incorporated as green manuring crop. The order of effectiveness in improving bulk density, macro and mesopores was sesbania > cluster bean > rice bean. Sesbania produced greater number of macro and large mesopores about 41% increase over control followed by cluster bean (29%) and rice bean (16%). Phosphorus application showed meager positive impact on various soil physical properties but did not significantly increased porosity or reduced bulk density. Significant differences in volume fraction in pore space suggest that pore space on a volume basis was much higher in sesbania-amended soil than in other treatments.     

Diffuse instability of granular material under various drainage conditions: discrete element simulation and constitutive modeling

Acta Geotechnica - Diffuse instability is a typical failure mode of sand that occurs before the perfect plastic flow condition is attained. Whereas extensive laboratory experiments have...     

Fluorescence micro-spectrometry of synthetic and natural hydrocarbon fluid inclusions: crude oil chemistry,density and application to petroleum migration

The fluorescence spectra of crude oils, synthesized as hydrocarbon fluid inclusions (hcfi) in NaCI crystals, have been recorded and correlated with crude oil chemical analysis. The crude oils represent a wide range in total hydrocarbons, saturate and aromatic fractions, and resin-asphaltene concentration. The fluorescence properties (Lambda max and Q) of the hydrocarbon fluid inclusions display a systematic red shift to longer wavelengths from 440 nm to 595 nm with increasing aromatic content and increasing concentration of NSO-bearing compounds. A positive correlation also exists between Lmax-Q and the thermal maturity parameters nC17/pristane and nC₁₈/phytane. First order linear regression equations provide a method for constraining the chemical composition of natural hydrocarbon fluid inclusions. Lmax and Q correlate positively with oil density (°API), providing for an indirect method of estimating the API of a natural hydrocarbon fluid inclusion assemblage. Fluorescence spectra of non-biodegraded crude oils from the Upper Devonian Birdbear Formation, Saskatchewan, Canada, have been correlated with regionally widespread hcfi within carbonate carrier beds and reservoir rocks of the same formation. The two most dominant types of hcfi spectra match well with the fluorescence spectra from crude oils within the Birdbear Formation. A third, less common population of very-blue fluorescing hcfi (Lmax=415440 nm, Q ≤ 0.10) also occur within fractures, intercrystalfne cements or in fossil overgrowths. The Lmax-Q-API-chemical correlations establised for the synthetic hcfi suggests that the °API of these inclusions is probably > 45° and the saturate/aromatic ratio ranges from 3.2 to 5.1. Spectra from hcfi within quartz overgrowths and cements, fractures and carbonate cements from sandstone reservoirs in the Jeanne d'Arc Basin offshore Newfoundland, compared with fluorescence spectra of crude oils suggests that some of the reservoirs may have been filled by a relatively low maturity oil and then a higher maturity oil. This is reflected in the intermediate spectra of the crude oils relative to the spectra of two separate hcfi events. Other reservoirs appear to have been charged with a relatively high gravity oil which was later biodegraded. This is marked by a blue region spectra for the hcfi compared with a red-shifted spectra for the crude oil (°API = 19). The API of the original unaltered oil which charged the reservoir is estimated to be between 32 and 38° using the Lmax-Q-API relationship established for the synthetic hcfi.     

The distribution of saline groundwater and its relation to the hydraulic conditions of aquifers and aquitards: examples from Israel

The effect of separation by aquitard layers on the distribution of saline groundwater in coastal aquifers has been demonstrated in two Israeli coastal aquifers: the Mediterranean and the Dead Sea aquifers. There is vertical separation in the Dead Sea area, even where the clayey aquitard layers are <1?m thick, exhibited by large differences in hydraulic head (2?C5?m), salinity (TDS of 50?C340?g/L) and chemical composition (e.g. Na/Cl range 0.28?C0.55). Similar features are found in the Mediterranean coastal aquifer, where the separating aquitard layers are thicker (??5?C10?m). Here, the different subaquifers host fresh and saline groundwater of different ages (tritium and ¹⁴C ages range from tens to thousands of years), as well as different chemical compositions. This high resolution of results can be obtained only by drilling without fluids; otherwise, the spatial information may lead to incorrect representation of the studied aquifer. This is especially important in saline systems where only partial flushing occurs and, thus, large variations in salinity and chemical composition are expected. The main factors controlling the salinity of groundwater in subaquifers in coastal aquifers are their connection to the sea or saline lakes, existence of brines, salinization and flushing rates, and separation by aquitard layers.     

Distribution of bacterial and archaeal ether lipids in soils and surface sediments of Tibetan lakes: Implications for GDGT-based proxies in saline high mountain lakes

Bacterial and archaeal lipids, such as glycerol dialkyl glycerol tetraethers (GDGTs) and dialkyl glycerol diethers, are increasingly used as proxies for specific environmental parameters, such as air temperature and soil pH in lacustrine environments. Little is known, however, about the distribution and applicability of bacterial and archaeal lipids on the Tibetan Plateau. We investigated nine different watersheds across the plateau by way of sediments from lakes and rivers, as well as the surrounding soils. Our transect study included a salinity gradient and focused on saline lakes, which are rarely examined. We analyzed archaeal isoprenoid (i) and bacterial branched (b) GDGTs, as well as archaeol to trace their sources and environmental factors, influencing their distributions. We could show that iGDGTs were produced in situ and bGDGTs were primarily soil-derived although we could not exclude in situ production of bGDGTs in the lakes. The most important environmental variables correlating with GDGT distributions were temperature and salinity. Bacterial GDGT distributions correlated mainly with salinity, while archaeal lipid distributions correlated with temperature. Based on the correlation of methylation (MBT′) and cyclisation (CBT) indices of bGDGTs with pH and mean annual air temperature (MAAT), we established local calibrations for the Tibetan lakes. TEX₈₆ could also be applied to reconstruct temperature, which was strongly biased towards measured summer lake water temperature, indicating enhanced production of iGDGTs in the summer months. Existing proxies show, therefore, potential for palaeoclimate reconstruction on the Tibetan Plateau if local calibrations are applied.     

Inactive supply wells as conduits for flow and contaminant migration: conditions of occurrence and suggestions for management

Water supply wells can act as conduits for vertical flow and contaminant migration between water-bearing strata under common hydrogeologic and well construction conditions. While recognized by some for decades, there is little published data on the magnitude of flows and extent of resulting water quality impacts. Consequently, the issue may not be acknowledged widely enough and the need for better management persists. This is especially true for unconsolidated alluvial groundwater basins that are hydrologically stressed by agricultural activities. Theoretical and practical considerations indicate that significant water volumes can migrate vertically through wells. The flow is often downward, with shallow groundwater, usually poorer in quality, migrating through conduit wells to degrade deeper water quality. Field data from locations in California, USA, are presented in combination with modeling results to illustrate both the prevalence of conditions conducive to intraborehole flow and the resulting impacts to water quality. Suggestions for management of planned wells include better enforcement of current regulations and more detailed consideration of hydrogeologic conditions during design and installation. A potentially greater management challenge is presented by the large number of existing wells. Monitoring for evidence of conduit flow and solute transport in areas of high well density is recommended to identify wells that pose greater risks to water quality. Conduit wells that are discovered may be addressed through approaches that include structural modification and changes in operations.     

Groundwater recharge dams in arid areas as tools for aquifer replenishment and mitigating seawater intrusion: example of AlKhod, Oman

Groundwater depletion and seawater intrusion constitute major challenges along coastal aquifers in arid areas. This paper assesses the role of groundwater recharge dams constructed to replenish aquifers and fight seawater intrusion with reference to AlKhod dam, Oman, sited 7 km from the coast on a gravely unconfined aquifer. Water table rise in piezometers located downstream from the dam shows regular patterns correlating with magnitude of wadi flow, whereas upstream piezometers show irregular patterns. Controlled release of water captured by the dam optimizes water percolation and enhances artificial recharge which was estimated in the wet years 1997, 2003 and 2005 as 15, 22 and 27 Mm³, respectively, using water table fluctuation method. Recharge contributed 40–60 % of the total annual abstraction. Groundwater salinity increased in the 1980s and 1990s and the saline/freshwater interface advanced inland, but has receded partially after 1997 (highest rainfall) and completely after 2005 indicated by reduction in electrical conductivity and thickening of freshwater lens. The recession is attributed to the dam’s induced recharge and reduction of pumping in 2004 following the commissioning of Barka desalination plant. Integrating artificial recharge with groundwater resources management is therefore an effective measure to replenish aquifers in arid areas and mitigate seawater intrusion along the coasts.     

Multi‐species diffusion analysis in porous media under various dry density and temperature conditions: molecular dynamics simulation,homogenization analysis,and finite element method

In porous media, chemical species that dissolve in pore water can be transported via diffusion mechanisms or advective fluxes, close to or far away from where precipitation occurs. In the case of a high‐level radioactive waste disposal system, compacted bentonite is used in a buffer material in an engineering barrier system to minimize the amount of specific nuclides that breach into the surrounding host rock. To minimize breaching, it is very important to understand the transport mechanism of multiple chemical species in porous media. In the following research, we introduced FEM analysis methods using the results of the molecular dynamics simulation and homogenization analysis (MD/HA) method. First, the diffusion coefficients of ions (Cl^?, I^?, and Na⁺) in different water layers of Na‐beidellite were calculated using the MD/HA procedure under various dry density (1.2, 1.6, and 2.0 Mg/m³) and temperature (293, 323, and 363 K) conditions. Next, using FEM analysis that used the MD/HA results as input parameters, the diffusion behaviors of ions in porous media were calculated. The results indicate that the diffusion coefficients of the interlayer water in Na‐beidellite are different from the diffusion coefficients under dry density conditions. Further, the concentration profiles (C_t/C₀) of iodine and chloride are proportional to temperature but inversely proportional to dry density. Copyright © 2014 John Wiley & Sons, Ltd.     

Dissolution of Columbia River Basalt under mildly acidic conditions as a function of temperature: Experimental results relevant to the geological sequestration of carbon dioxide

Increasing attention is being focused on the rapid rise of CO₂ levels in the atmosphere, which many believe to be the major contributing factor to global climate change. Sequestering CO₂ in deep geological formations has been proposed as a long-term solution to help stabilize CO₂ levels. However, before such technology can be developed and implemented, a basic understanding of H₂O–CO₂ systems and the chemical interactions of these fluids with the host formation must be obtained. Important issues concerning mineral stability, reaction rates, and carbonate formation are all controlled or at least significantly impacted by the kinetics of rock–water reactions in mildly acidic, CO₂-saturated solutions. Basalt has recently been identified as a potentially important host formation for geological sequestration. Dissolution kinetics of the Columbia River Basalt (CRB) were measured for a range of temperatures (25–90 °C) under mildly acidic to neutral pH conditions using the single-pass flow-through test method. Under anaerobic conditions, the normalized dissolution rates for CRB decrease with increasing pH (3 ? pH ? 7) with a slope, η, of −0.15 ± 0.01. Activation energy, E_a, has been estimated at 32.0 ± 2.4 kJ mol⁻¹. Dissolution kinetics measurements like these are essential for modeling the rate at which CO₂-saturated fluids react with basalt and ultimately drive conversion rates to carbonate minerals in situ.     

Crushing and embedment of proppant packs under cyclic loading:An insigh to enhanced unconventional oil/gas recovery

Crushing and embedment are two critical downhole proppant degradation mechanisms that lead to a significant drop in production outputs in unconventional oil/gas stimulation projects.These persistent production drops due to the non-linear responses of proppants under reservoir conditions put the future utilization of such advanced stimulation techniques in unconventional energy extraction in doubt.The aim of this study is to address these issues by conducting a comprehensive experimental approach.According to the results,whatever the type of proppant,all proppant packs tend to undergo significant plastic deformation under the first loading cycle.Moreover,the utilization of ceramic proppants(which retain proppant pack porosity up to 75％),larger proppant sizes(which retain proppant pack porosity up to 15.2％)and higher proppant concentrations(which retain proppant pack porosity up to 29.5％)in the fracturing stimulations with higher in-situ stresses are recommended to de-escalate the critical consequences of crushing associated issues.Similarly,the selection of resin-coated proppants over ceramic and sand proppants may benefit in terms of obtaining reduced proppant embedment.In addition,selection of smaller proppant sizes and higher proppant concentrations are suggested for stimulation projects at depth with sedimentary formations and lower in-situ stresses where proppant embedment pre-dominates.Furthermore,correlation between proppant embedment with repetitive loading cycles was studied.Importantly,microstructural analysis of the proppant-embedded siltstone rock samples revealed that the initiation of secondary induced fractures.Finally,the findings of this study can greatly contribute to accurately select optimum proppant properties(proppant type,size and concentration)depending on the oil/gas reservoir char-acteristics to minimize proppant crushing and embedment effects.     

Earthquake-induced reactivation of landslides under variable hydrostatic conditions: evaluation at regional scale and implications for risk assessment

Landslides - Earthquake-induced landslides represent a significant seismic hazard since they can largely increase the damage and losses due to a seismic event, an issue that must be considered in...     

Ordovician low- to intermediate-Mg calcite marine cements from Sweden: marine alteration and implications for oxygen isotopes in Ordovician seawater

Petrography demonstrates the presence of three types of fibrous calcite cement in buildup deposits of the Kullsberg Limestone (middle Caradoc), central Sweden. Translucent fibrous calcite has intrinsic blue luminescence (CL) indicative of pure calcite. This cement has 2–5 mol% MgCO₃, low Mn and Fe (≤ 100 p.p.m.), and is considered to be slightly altered to unaltered, primary low- to intermediate-Mg calcite. Grey turbid fibrous calcite has variable but generally low MgCO₃ content (most analyses <2 mol%) and variable CL response, with Mn and Fe concentrations up to 1200 and 500 p.p.m., respectively. The heterogeneous characteristics of this variety of fibrous calcite are caused by diagenetic alteration of a translucent fibrous calcite precursor. Light-brown turbid fibrous calcite has low MgCO₃ (near 1 mol%) and variable Mn (up to 800 p.p.m.) and Fe (up to 500 p.p.m.) concentrations, with an abundance of bright luminescent patches, which formed during alteration caused by reducing diagenetic fluids. The δ¹³C and δ¹⁸O values of all fibrous calcite form a tight field (δ¹³C=1·7 to 3·1‰ PDB, δ¹⁸O= ? 2·6 to ? 4·1‰ PDB) compared with fibrous calcite isotope values from other units. Fibrous calcite δ¹⁸O values are larger than adjacent meteoric or burial cements, which have δ¹⁸O δ ? 8‰ PDB. Consequently, most diagenetic alteration of Kullsberg fibrous calcite is interpreted to have occurred in the marine diagenetic realm. First-generation equant and bladed calcite cements, which pre-date fibrous calcite, are interpreted as unaltered, low-Mg calcite marine cements based on δ¹³C and δ¹⁸O data (δ¹³C = 2·3 to 2·7‰ PDB, δ¹⁸O= ? 2·8 to ? 3·5‰ PDB). Unlike fibrous cement, which reflects global sea water chemistry, first-generation equant and bladed calcite are indicators of localized modification of seawater chemistry in restricted settings. Kullsberg abiotic marine cements have larger δ¹⁸O values than most Caradoc marine precipitates from equatorial Laurentia. Positive Kullsberg δ¹⁸O values are attributed to lower seawater temperatures and/or slightly elevated salinity on the Baltic platform relative to seawater from which other marine precipitates formed.