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1.
Seawater intrusion is a problem in the coastal areas of Korea. Most productive agricultural fields are in the western and southern coastal areas of the country where irrigation predominantly relies on groundwater. Seawater intrusion has affected agricultural productivity. To evaluate progressive encroachment of saline water, the Korean government established a seawater intrusion monitoring well network, especially in the western and southern part of the peninsula. Automatic water levels and EC monitoring and periodic chemical analysis of groundwater help track salinization. Salinization of fresh groundwater is highly associated with groundwater withdrawal. A large proportion of the groundwaters are classified as Na–Cl and Ca–Cl types. The Na–Cl types represent effects of seawater intrusion. The highest EC level was over 1.6 km inland and high Cl values were observed up to 1.2 km inland. Lower ratios of Na/Cl and SO4/Cl than seawater values indicate the seawater encroachment. A linear relation between Na and Cl represents simple mixing of the fresh groundwater with the seawater. The saline Na–Cl typed groundwaters showed Br/Cl ratios similar to or less than seawater values. The Ca–HCO3 type groundwaters had the highest Br/Cl ratios. Substantial proportions of the groundwaters showed potential for salinity and should be better managed for sustainable agriculture.  相似文献   

2.
Sorption of phosphate by Fe(III)- and Al(III)-(hydr)oxide minerals regulates the mobility of this potential water pollutant in the environment. The objective of this research was to determine the molecular configuration of phosphate bound on ferrihydrite at pH 6 by interpreting P K-edge XANES spectra in terms of bonding mode. XANES and UV-visible absorption spectra for aqueous Fe(III)-PO4 solutions (Fe/P molar ratio = 0-2.0) provided experimental trends for energies of P(3p)-O(2p) and Fe(3d)-O(2p) antibonding molecular orbitals. Molecular orbitals for Fe(III)-PO4 or Al(III)-PO4 complexes in idealized monodentate or bidentate bonding mode were generated by conceptual bonding arguments, and Extended-Hückel molecular orbital computations were used to understand and assign XANES spectral features to bound electronic states. The strong white line at the absorption edge in P K-edge XANES spectra for Fe-PO4 or Al-PO4 systems is attributable to an electronic transition from a P 1s atomic orbital into P(3p)-O(2p) or P(3p)-O(2p)-Al(3p) antibonding molecular orbitals, respectively. For Fe-PO4 systems, a XANES peak at 2-5 eV below the edge was assigned to a P 1s electron transition into Fe(4p)-O(2p) antibonding molecular orbitals. Similarly, a shoulder on the low-energy side of the white line for variscite corresponds to a transition into Al(3p)-O(2p) orbitals. In monodentate-bonded phosphate, Fe-O bonding is optimized and P-O bonding is weakened, and the converse is true of bidentate-bonded phosphate. These differences explained an inverse correlation between energies of P(3p)-O(2p) and Fe(3d)-O(2p) antibonding molecular orbitals consistent with a monodentate-to-bidentate transition in aqueous Fe(III)-PO4 solutions. The intensity of the XANES pre-edge feature in Fe(III)-bonded systems increased with increasing number of Fe(III)-O-P bonds. Based on the similarity of intensity and splitting of the pre-edge feature for phosphate sorbed on ferrihydrite at 750 mmol/kg at pH 6 and aqueous Fe-PO4 solutions containing predominantly bidentate complexes, XANES results indicated that phosphate adsorbed on ferrihydrite was predominantly a bidentate-binuclear surface complex.  相似文献   

3.
Presented here are halogen concentrations (Cl, Br and I) in pore waters and sediments from three deep cores in gas hydrate fields of the Nankai Trough area. The three cores were drilled between 1999 and 2004 in different geologic regions of the northeastern Nankai Trough hydrate zone. Iodine concentrations in all three cores increase rapidly with depth from seawater concentrations (0.00043 mmol/L) to values of up to 0.45 mmol/L. The chemical form of I was identified as I−, in accordance with the anaerobic conditions in marine sediments below the SO4 reduction depth. The increase in I is accompanied by a parallel, although lesser increase in Br concentrations, while Cl concentrations are close to seawater values throughout most of the profiles. Large concentration fluctuations of the three halogens in pore waters were found close to the lower boundary of the hydrate stability zone, related to processes of formation and dissociation of hydrates in this zone. Generally low concentrations of I and Br in sediments and the lack of correlation between sediment and pore water profiles speak against derivation of I and Br from local sediments and suggest transport of halogen rich fluids into the gas hydrate fields. Differences in the concentration profiles between the three cores indicate that modes of transportation shifted from an essentially vertical pattern in a sedimentary basin location to more horizontal patterns in accretionary ridge settings. Because of the close association between organic material and I and the similarity of transport behavior for I− and CH4, the results suggest that the CH4 in the gas hydrates also was transported by aqueous fluids from older sediments into the present layers.  相似文献   

4.
About 150 coastal spring outlets discharging from a karstified carbonate rock aquifer constitute the Azmak streamflow which is slightly brackish with 3000 mg/l of total dissolved solids. In this study, multivariate statistical methods were applied including the use of factor analysis, correlation analysis and cluster analysis to evaluate groundwater quality of Azmak Spring Zone using eight variables (Ca, Mg, Na, K, Cl, SO4, EC25 and B) at 19 water points sampled in the dry and wet seasons. Hydrochemical analysis results revealed that for majority of the sampling points, the abundance of cations and anions were ordered as Na?+?K?>?Mg?>?Ca and Cl?>?SO4?>?HCO3?+?CO3, respectively. Factor analysis results indicated that three factors explain 98% and 91% of the total variance in the dry and wet seasons, respectively. Factor 1 was found to be associated with the seawater, factor 2 indicated the effect of fresh water and factor 3 was defined to reflect the effect of seasonal fresh surface water contribution. Cluster analysis results indicated that two main groups and four subgroups could be defined with respect to the ratio of the seawater contribution. Cluster A (A1 and A2) represents the waters affected by seawater while waters less affected by the seawater intrusion are grouped in cluster B (B1 and B2).  相似文献   

5.
In order to understand the fractionation of Re and Os in marine environments, their removal from artificial seawater to Tokyo Bay sediments is studied using a multitracer technique. The chemical processes of the removal of Re and Os are also estimated based on their speciation analyses by X-ray absorption fine structure (XAFS) spectroscopy. The partitioning experiments, which use the multitracer technique, provide information on Re and Os regarding (i) their distributions between artificial seawater-sediment systems, (ii) their complexation with humic acid, and (iii) their carriers in sediments. In addition, XAFS spectroscopy provides direct information on the chemical states of Re and Os in the sediments.In an artificial seawater-sediment system containing a multitracer, Re is removed from the artificial seawater only under a reducing environment. The speciation of Re by X-ray absorption near-edge structure (XANES) suggests that the majority of Re remains as in the artificial seawater even under highly reducing conditions, during laboratory time scale (about 2 weeks). Moreover, XANES simulation shows that some Re exists at a lower oxidation state, such as ReO2, in the reducing sediment. These results can be explained by the slow kinetics of the reaction which is similar to those suggested by previous geochemical studies.In contrast, Os is readily removed from the artificial seawater into sediments under various redox conditions. Even under oxic conditions, a large fraction of Os is removed from the artificial seawater to sediments without organic matter. Based on the Os XANES study, it is confirmed that the oxidation states of Os incorporated in the reducing sediment and oxic sediment are trivalent and tetravalent, respectively. Sequential extraction suggests that the main carrier of Os in the organic-rich sediment is either ferromanganese oxides or organic matter, and that the Os in these two fractions may correspond to hydrolyzed insoluble Os species and Os species interacting with organic matter, at lower valence, respectively. The results of distribution study of Os in the absence and presence of humic acid (HA) also imply that Os assumes more than one chemical species, and a small fraction of Os may interact with HA in the experimental system. Meanwhile, extended X-ray absorption fine structure (EXAFS) confirms that the first neighboring atom of Os in the reducing sediment is oxygen. If Os(VIII) is the main dissolved species in seawater, as is expected thermodynamically, reductive removal may control the enrichment of Os in the sediment. Osmium, which is removed as Os(IV), is reduced further to Os(III) by a diagenetic process and may be complexed with organic matter in the reducing sediment.The results of the removal behaviors of Re and Os obtained in the current study show that Re can be removed from the artificial seawater only under highly reducing conditions within 2 weeks, but Os removal from the artificial seawater can be found under various redox conditions. Thus, a high 187Re/188Os ratio can occur only in reducing sediments, such as black shales. The high187Re/188Os ratio, in turn, makes black shales suitable for Re-Os dating. In contrast, authigenic sediments (and minerals) under oxic environments can enrich Os, but since Re is not distributed to the sediments under oxic conditions, this will cause a much lower 187Re/188Os ratio than that of seawater. The Os isotope system of these materials can be used as a paleo-marine environmental tracer since the 187Os/188Os ratio cannot grow significantly due to its extremely low 187Re/188Os ratio.  相似文献   

6.
Sulfur K-edge x-ray absorption spectra (XANES and EXAFS) and L-edge XANES of sphalerite (ZnS), chalcopyrite (CuFeS2) and stannite (Cu2FeSnS4) have been recorded using synchrotron radiation. The K- and L-edge XANES features are interpreted using a qualitative MO/energy band structure model. The densities of unoccupied states at the conduction bands of sphalerite, chalcopyrite and stannite are determined using S K- and L-edge XANES features (up to 15 eV above the edge), combined with published metal K-edge XANES. The SK- and L-edge XANES also indicate that, for sphalerite, the Fe2+ 3d band at the fundamental gap has little or no bonding hybridization with S 3p and S 3s orbitals; for chalcopyrite, the Cu+ 3d and Fe3+ 3d bands have strong mixing with S 3p and S 3s states, while for stannite the Cu+ 3d band strongly hybridizes with S 3p and S 3s orbitals, but the Fe2+ 3d band does not. The post-edge XANES features (15–50 eV above the edge) of sphalerite, chalcopyrite and stannite are similar. These features are related to the tetrahedral coordination of sulfur in all these structures, and interpreted by a multiple scattering model. The resonance energies from both the K-edge and L-edge XANES for these minerals are well correlated with reciprocal interatomic distances and lattice spaces. Sulfur K-edge EXAFS analyses using Fourier transform and curve fitting procedures are presented. Comparison of the structural parameters from EXAFS with x-ray structure data shows that the first shell bond distances (BD) from EXAFS are usually accurate to ±0.02 Å, and that coordination numbers (CN) are generally accurate to ±20 percent. For sphalerite, EXAFS analysis yields the structure parameters for the first three neighbour shells around a sulfur atom; the BD and CN even for the third shell are in close agreement with the x-ray structure, and the Debye-Waller term decreases from the first shell to the third shell. It is shown that sphalerite (ZnS) is a good model compound for EXAFS analysis of sulfur in chalcogenide glasses and metalloproteins.  相似文献   

7.
Pollution of groundwater by seawater intrusion poses a threat to sustainable agriculture in the coastal areas of Korea. Therefore, seawater intrusion monitoring stations were installed in eastern, western, and southern coastal areas and have been operated since 1998. In this study, groundwater chemistry data obtained from the seawater intrusion monitoring stations during the period from 2007 to 2009 were analyzed and evaluated. Groundwater was classified into fresh (<1,500 μS/cm), brackish (1,500–3,000 μS/cm), and saline (>3,000 μS/cm) according to EC levels. Among groundwater samples (n = 233), 56, 7, and 37% were classified as the fresh, brackish, and saline, respectively. The major dissolved components of the brackish and saline groundwaters were enriched compared with those of the fresh groundwater. The enrichment of Na+ and Cl− was especially noticeable due to seawater intrusion. Thus, the brackish and saline groundwaters were classified as Ca–Cl and Na–Cl types, while the fresh groundwater was classified as Na–HCO3 and Ca–HCO3 types. The groundwater included in the Na–Cl types indicated the effects of seawater mixing. Ca2+, Mg2+, Na+, K+, SO4 2−, and Br− showed good correlations with Cl− of over r = 0.624. Of these components, the strong correlations of Mg2+, SO4 2−, and Br− with Cl− (r ≥ 0.823) indicated a distinct mixing between fresh groundwater and seawater. The Ca/Cl and HCO3/Cl ratios of the groundwaters gradually decreased and approached those of seawater. The Mg/Cl, Na/Cl, K/Cl, SO4/Cl, and Br/Cl ratios of the groundwaters gradually decreased, and were similar to or lower than those of seawater, indicating that Mg2+, Na+, K+, SO4 2−, and Br−, as well as Cl− in the saline groundwater can be enriched by seawater mixing, while Ca2+ and HCO3 − are mainly released by weathering processes. The influence of seawater intrusion was evaluated using threshold values of Cl− and Br−, which were estimated as 80.5 and 0.54 mg/L, respectively. According to these criteria, 41–50% of the groundwaters were affected by seawater mixing.  相似文献   

8.
The main carrying phases of mercury (Hg) were analyzed in a 120 cm sediment core taken at the Laguna del Plata (LP), a small lake connected to the main water body of Laguna Mar Chiquita (LMC) during highstands. LMC is considered to be one of the largest saline lakes in the world representing a sensitive climatic indicator due to its frequent lake level variations at millennial and interdecadal scale like the last ones that started early in the 1970s and after 2004. Total particulate Hg (HgTP) concentrations vary between ∼13 and ∼131 μg kg−1 indicating a system with low pollution. Selective extractions with ascorbate, HCl and H2O2 were performed in the sediments and they revealed that Hg is associated mainly to reactive sulphides in the base of the core, while in the middle and upper part the organic matter seems to be the main Hg-bearing phase. The highest and most important peak was found in sediments accumulated between 1991 and 1995. More than a punctual source of pollution, this peak is likely related to two eruptive events occurred in the Andean Cordillera in this period: the eruption of Hudson volcano in southern Patagonia that occurred in 1991 and the one of the Láscar volcano in northern Chile that occurred in 1993. In both cases, the respective ash plumes were documented to have reached the Laguna del Plata region.  相似文献   

9.
Silicon K-edge x-ray absorption near-edge structure (XANES) spectra of a selection of silicate and aluminosilicate minerals have been measured using synchrotron radiation (SR). The spectra are qualitatively interpreted based on MO calculation of the tetrahedral SiO 4 4? cluster. The Si K-edge generally shifts to higher energy with increased polymerization of silicates by about 1.3 eV, but with considerable overlap for silicates of different polymerization types. The substitution of Al for Si shifts the Si K-edge to lower energy. The chemical shift of Si K-edge is also sensitive to cations in more distant atom shells; for example, the Si K-edge shifts to lower energy with the substitution of Al for Mg in octahedral sites. The shifts of the Si K-edge show weak correlation with average Si-O bond distance (dSi-O), Si-O bond valence (sSi-O) and distortion of SiO4 tetrahedra, due to the crystal structure complexity of silicate minerals and multiple factors effecting the x-ray absorption processes.  相似文献   

10.
《Applied Geochemistry》1999,14(6):735-745
In the Lower Andarax river basin 3 aquifer units have been defined, namely the Carbonate Aquifer, the Deep Aquifer and the Detrital Aquifer, which between them contain a wide variety of water types. Identification of hydrogeochemical processes has been performed by studying a series of ionic ratios, comprising the principal constituents together with B and Li (Cl vs SO4, Cl vs Mg, Cl vs Li, B vs Li). Among the processes detected, the circulation of groundwaters with high concentrations of SO4 was found to have significant effects. Moreover, in the coastal region, naturally occurring processes related to the flushing of saline waters from sediments of marine origin occur in conjunction with others, clearly of human origin, that are related to saltwater intrusion. A further factor is the entry, from overlying deposits, of waters with a high saline content; this salinity is related to the flushing of sediments of marine origin. The use of B and Li together enables waters in which salinity is related to seawater to be distinguished from others in which salinity is related to evaporitic layers or to thermal areas. The concentration of Li is directly related to water temperature, while that of B is greater in the most saline sectors, of gypsiferous and/or seawater origin.  相似文献   

11.
An experiment has been performed reacting seawater with fresh peridotite (80% olivine, Fo90 and ～- 15% enstatitic orthopyroxene En95 and minor clinopyroxene and spinel) at 300°C, 500 bars and water/rock mass ratio of 20. The duration of the experiment was approximately 1500 hr.Seawater chemistry was appreciably modified during the experiment. Mg, Ca, Sr, SO4 and H2O were removed, while H2S(aq), Fe, Mn and Zn were added. H2S(aq) resulted from the inorganic reduction of seawater SO4. pH was initially acid (2.8), but then rose slowly to a value of 5.2. The aqueous concentrations of Na, K, Cl and boron (B) changed little from that in seawater prior to reaction. However, as the solution was cooled to room temperature at the end of the experiment, the B concentration decreased. This suggests that the B content of oceanic serpentinites may be the result of retrograde reactions between a previously serpentinized body and ‘cold’ seawater.The primary minerals in the peridotite were replaced to varying degrees by serpentine (lizardite), magnetite. Mg-hydroxysulfate, anhydrite and possibly pyrite and sphalerite. Mg-hydroxysulfate and much anhydrite dissolved on quench.The alteration mineral assemblage generated during this experiment is consistent with that predicted from equilibrium phase relations and is similar in chemical composition, mineralogy and paragenesis to that reported for oceanic serpentinites.  相似文献   

12.
A hydrochemical study has been carried out on the fresh groundwater resources of Potharlanka, Krishna Delta, India. Groundwater samples were collected at 58 sites and analyzed in June and December 2001. The groundwater is mildly alkaline with a pH of 7.2–8.2, electrical conductivity (EC) varies from 645–4,700 µS/cm in June 2001 (pre-monsoon) and from 605–5,770 µS/cm in December 2001 (post-monsoon). More than 75% of the samples have >1000 mg/l TDS which is higher than the maximum permissible limit for potable water. Na and Cl are the dominating cations and these are directly proportional to TDS. Extremely low HCO 3/Cl and variable high Mg/Ca (molar ratios) indicated the transformation of the fresh groundwater aquifer systems to saline. Groundwater of this island is classified as Na–Cl, Na–Ca–Cl–HCO 3, Na–Mg–Cl–SO 4 and mixed types. A high percentage of mixed water types indicates the possibility of simultaneous fresh groundwater dilution activity along with a seawater ingression/intrusion process. Low rainfall and excessive withdrawal of groundwater has caused the increase of saline water intrusion.  相似文献   

13.
The conversion of undisturbed coastal regions to commercial and suburban developments may pose a threat to surface and groundwater quality by introducing nitrate-nitrogen (NO3 ?-N) from runoff of land-applied wastewater and fertilizers. Microbial denitrification is an important NO3 ?-N removal mechanism in coastal sediments. The objective of this study was to compare denitrification and nitrate conversion rates in coastal sediments from a golf course, suburban site, undeveloped marsh, and nonmarsh area near rapidly developing Hilton Head Island, South Carolina. Nitrous oxide was measured using gas chromatography and nitrate and ammonium concentrations were measured using a flow injection autoanalyzer in microcosms spiked, with 50 μg NO3 ?-N gdw?1. The two marsh sites had the greatest ammonium production, which was correlated with fine sediment particle size and higher background sediment nitrate and surface water sulfate concentrations. The golf course swale had greatest denitrification rates, which were correlated with higher total carbon and organic nitrogen in sediments. Nitrate was consumed in golf course sediments to a greater extent than in the undeveloped marsh and upland freshwater sites, suggesting that the undeveloped sites and receiving estuaries may be more susceptible to nitrate contamination than the golf course swale and marsh under nonstorm conditions. Construction of swales and vegetated buffers using sediments with high organic carbon content as best management practices may aid in removing nitrate and other contaminants from runoff prior to its transport to the receiving marsh and estuary.  相似文献   

14.
Twenty-four brine samples from the Heletz-Kokhav oilfield, Israel, have been analyzed for chemical composition and Li isotope ratios. The chemical composition of the brines, together with geological evidence, suggests derivation from (Messinian) seawater by evaporation that proceeded well into the gypsum stability field but failed to reach the stage of halite crystallization. The present salinity of the samples (18-47 g Cl/L) was achieved by dilution of the original evaporitic brine by local fresh waters. Like brines from other sedimentary basins, the Li/Cl ratios in the Heletz-Kokhav samples show a prominent Li enrichment (five-fold to eight-fold) relative to modern seawater. The isotopic ratios of Li, expressed in the δ 6Li notation, vary from −26.3 to −17.9‰, all values being significantly higher than that of modern seawater (−32‰) irrespective of their corresponding Li concentration (1.0-2.3 mg/L). The isotopic composition of Li and the Li/Cl ratio in the oilfield brines were acquired in two stages: (a) The original evaporated seawater gained isotopically light Li during the diagenetic interaction between the interstitial Messinian brine and the basin sediments. A parent brine with an elevated Li/Cl ratio was formed. The brine was later diluted in the oilfields. (b) The δ 6Li values of the final brines were determined during epigenetic interaction with the Heletz-Kokhav aquifer rocks. At the same time, the Li/Cl ratio inherited from stage (a) remained largely unchanged. This work represents the first use of lithium isotopic composition to elucidate the origin and evolution of formation waters in sedimentary basins.  相似文献   

15.
Microthermometry and Raman spectroscopy techniques are routinely use to constrain ore-fluids δ18O and molar proportions of anhydrous gas species (CO2, CH4, N2). However, these methods remain imprecise concerning the ore-fluids composition and source. Synchrotron radiation X-ray fluorescence allows access to major and trace element concentrations (Cl, Br and K, Ca, Fe, Cu, Zn, As, Rb, Sr) of single fluid inclusion. In this paper, we present the results of the combination of these routine and newly developed techniques in order to document the fluids composition and source associated with a Mesoarchaean lode gold deposit (Warrawoona Syncline, Western Australia). Fluid inclusion analyses show that quartz veins preserved records of three fluid inclusion populations. Early fluids inclusions, related to quartz veins precipitation, are characterized by a moderate to high Br/Cl ratio relative to modern seawater, CO2 ± CH4 ± N2, low to moderate salinities and significant base metal (Fe, Cu, Zn) and metalloid (As) concentrations. Late fluid inclusions trapped in secondary aqueous fluid inclusions are divided into two populations with distinct compositions. The first population consists of moderately saline aqueous brines, with a Br/Cl ratio close to modern seawater and a low concentration of base metals and metalloids. The second population is a fluid of low to moderate salinity, with a low Br/Cl ratio relative to modern seawater and significant enrichment in Fe, Zn, Sr and Rb. These three fluid inclusion populations point to three contrasting sources: (1) a carbonic fluid of mixed metamorphic and magmatic origin associated with the gold-bearing quartz precipitation; (2) a secondary aqueous fluid with seawater affinity; and (3) a surface-derived secondary aqueous fluid modified through interaction with felsic lithologies, before being flushed into the syncline. Primary carbonic fluids present similar characteristics than those ascribed to Mesoarchaean lode gold deposits. This suggests similar mineralization processes for mid- and Mesoarchaean lode gold deposits despite contrasting fluid–rock interaction histories. However, in regard to the protracted history documented in the Warrawoona Syncline, we question the robustness of the epigenetic crustal continuum model, as ore-fluid characteristics equally support an epigenetic or a polyphased mineralization process.  相似文献   

16.
In the coastal region of Bangladesh, groundwater is mainly used for domestic and agricultural purposes, but salinization of many groundwater resources limits its suitability for human consumption and practical application. This paper reports the results of a study that has mapped the salinity distribution in different aquifer layers up to a depth of 300 m in a region bordering the Bay of Bengal based on the main hydrochemistry and has investigated the origin of the salinity using Cl/Br ratios of the samples. The subsurface consists of a sequence of deltaic sediments with an alternation of more sandy and clayey sections in which several aquifer layers can be recognized. The main hydrochemistry shows different main water types in the different aquifers, indicating varying stages of freshening or salinization processes. The most freshwater, soft NaHCO3-type water with Cl concentrations mostly below 100 mg/l, is found in the deepest aquifer at 200–300 m below ground level (b.g.l.), in which the fresh/saltwater interface is pushed far to the south. Salinity is a main problem in the shallow aquifer systems, where Cl concentrations rise to nearly 8000 mg/l and the groundwater is mostly brackish NaCl water. Investigation of the Cl/Br ratios has shown that the source of the salinity in the deep aquifer is mixing with old connate seawater and that the saline waters in the more shallow aquifers do not originate from old connate water or direct seawater intrusion, but are derived from the dissolution of evaporite salts. These must have been formed in a tidal flat under influence of a strong seasonal precipitation pattern. Long dry seasons with high evaporation rates have evaporated seawater from inundated gullies and depressions, leading to salt precipitation, while subsequent heavy monsoon rains have dissolved the formed salts, and the solution has infiltrated in the subsoil, recharging groundwater.  相似文献   

17.
The need for more agricultural or residential land has encouraged reclamation at the coastal areas of Korea since 1200 ad (approximately). The groundwaters of these reclaimed areas could be expected to reveal hydrogeochemical properties different from those of areas directly affected by seawater intrusion. The purpose of this study, therefore, was to examine the salinization of shallow groundwater in a coastal reclaimed area and to identify the effect of land reclamation on groundwater quality. Major cations and anions, iodide, total organic carbon, δD, δ 18O and δ 13C were measured to assist the hydrogeochemical analysis. Chloride, δD and δ 18O data clearly show that the Na–Cl type water results from mixing of groundwater with seawater. In particular, the δD and δ 18O of Ca+Mg–Cl+NO3 type groundwaters are close to the meteoric water line, but Na–Cl type waters enriched in chloride are 18O-enriched with respect to the meteoric water line. Meanwhile, carbon isotopic data and I/Cl ratios strongly suggest that there are various sources of salinity. The δ 13C values of Na–Cl type groundwaters are generally similar to those of Ca+Mg–Cl+NO3 type waters, which are depleted in 13C with respect to seawater. I/Cl ratios of Na–Cl type groundwater are 10–100 times higher than that of seawater. Because the reclamation has incorporated a large amount of organic matter, it provides optimum conditions for the occurrence of redox processes in the groundwater system. Therefore, the salinization of groundwater in the study area seems to be controlled not only by saltwater intrusion but also by other effects, such as those caused by residual salts and organic matter in the reclaimed sediments.  相似文献   

18.
This study is an attempt to quantify the geochemical processes and the timescale of seawater intrusion into a coastal aquifer from changes in the major ionic composition of the water and the natural distribution of the cosmogenic isotopes 14C and 3H. For that purpose, we sampled saline and brackish groundwaters from the Israeli coastal aquifer. A multilayer sampler (MLS) was used to obtain very high resolution (10 cm) profiles across the fresh-saline water interface (FSI).The chemical and stable isotope data revealed three distinct water types (end members) that are located in different zones on the route to the coastal aquifer: (1) slightly modified Mediterranean seawater (SWS); (2) slightly diluted (with up to 20% fresh groundwater) saline groundwater (SDS); and (3) fresh groundwater (FGW).The SWS samples generally show an excess of total alkalinity and total dissolved inorganic carbon (DIC), and a depletion of 13CDIC and 14CDIC with respect to normal seawater indicating that anaerobic oxidation of organic matter is the first diagenetic reaction that affects seawater during its penetration into the bottom sediments. SDS waters appear when SWS is slightly diluted, gain Ca2+ and Sr2+, and is depleted in K+, suggesting that the main processes that transform SWS into SDS are slight dilution with fresh groundwater and cation exchange. At the fresh-saline water interface, SDS generally shows conservative mixing with FGW.Inspection of chemical data from coastal aquifers around the world indicates that intensive ion exchange in slightly diluted saline groundwater is a globally important phenomenon of seawater intrusion. Most of our saline groundwater samples contain substantial amounts of 3H suggesting that penetration of Mediterranean seawater and its inland travel to a distance of 50-100 m onshore occurred 15-30 yr ago. This is supported by the 14CDIC mass balance that explains the relatively low 14CDIC activities in the SDS as influenced by diagenesis and not by simple radioactive decay.  相似文献   

19.
《Applied Geochemistry》2006,21(10):1715-1731
Three “copper ruby red” (or “flashed”) glasses from the St Gatien cathedral in Tours (windows from the XIII century) were investigated at the Cu K-edge by synchrotron X-ray fluorescence microscopy and μ-XANES/EXAFS spectroscopies. The spectra are compared to XANES/EXAFS spectra collected for modern glasses synthesized at various O2 fugacities. Two main types of red glasses are present in Tours, which show a distinct Cu speciation. In the first type (“plaqués”), Cu is present as sub-micron metallic nucleates, which coexist with monovalent Cu linear moieties (30:70 at.%). In contrast, the glasses of the other type (“feuilletés”) show mostly monovalent Cu (together with some evidence for metallic Cu in the edge region of the XANES).The plaqués glasses appear to have been synthesized at lower O2 fugacity and higher temperatures to promote homogeneous nucleation of metallic Cu. A relative enrichment in Al (provided by the addition of orthoclase in the melt) greatly enhances the glass durability by decreasing the melt peralkalinity by a factor of ∼4. In contrast, the feuilletés were equilibrated at much higher O2 fugacities. Hence, metallic Cu, despite being scarce in that glass, is not at equilibrium and could have well been added on purpose during the melt cooling. It is proposed that a technique called ‘tourage’ could have been used to help create the micron scale greenish and red layers. The feuilleté glasses are also weathered at their surface, promoting the formation of amorphous Cu(II) species related to a Cu sulphate.  相似文献   

20.
Records of stable carbon isotopes (δ13C) are presented from cores collected from four San Francisco Bay marshes and used as a proxy for changes in estuary salinity. The δ13C value of organic marsh sediments are a reflection of the relative proportion of C3 vs. C4 plants occupying the surface, and can thus be used as a proxy for vegetation change on the marsh surface. The four marshes included in this study are located along a natural salinity gradient that exists in the San Francisco Bay, and records of vegetation change at all four sites can be used to infer changes in overall estuary paleosalinity. The δ13C values complement pollen data from the same marsh sites producing a paleoclimate record for the late Holocene period in the San Francisco Bay estuary. The data indicate that there have been periods of higher-than-average salinity in the Bay estuary (reduced fresh water inflow), including 1600-1300 cal yr B.P., 1000-800 cal yr B.P., 300-200 cal yr B.P., and ca. A.D. 1950 to the present. Periods of lower-than-average salinity (increased fresh water inflow) occurred before 2000 cal yr B.P., from 1300 to 1200 cal yr B.P. and ca. 150 cal yr B.P. to A.D. 1950. A comparison of the timing of these events with records from the California coast, watershed, and beyond the larger drainage of the Bay reveals that the paleosalinity variations reflected regional precipitation.  相似文献   

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