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1.
A 52-yr record of dissolved oxygen in Chesapeake Bay (1950–2001) and a record of nitrate (NO3 −) loading by the Susquehanna River spanning a longer period (1903, 1945–2001) were assembled to describe the long-term pattern of hypoxia and anoxia in Chesapeake Bay and its relationship to NO3 − loading. The effect of freshwater inflow on NO3 − loading and hypoxia was also examined to characterize its effect at internannual and longer time scales. Year to year variability in river flow accounted for some of the observed changes in hypoxic volume, but the long-term increase was not due to increased river flow. From 1950–2001, the volume of hypoxic water in mid summer increased substantially and at an accelerating rate. Predicted anoxic volume (DO<0.2 mg I−1) at average river flow increased from zero in 1950 to 3.6×109 m3 in 2001. Severe hypoxia (DO<1.0 mg I−1) increased from 1.6×109 to 6.5×109 m3 over the same period, while mild hypoxia (DO<2.0 mg I−1) increased from 3.4×109 to 9.2×109 m3. NO3 − concentrations in the Susquehanna River at Harrisburg, Pennsylvania, increased up to 3-fold from 1945 to a 1989 maximum and declined through 2001. On a decadal average basis, the superposition of changes in river flow on the long-term increase in NO3 − resulted in a 2-fold increase in NO3 − loading from the Susquehanna River during the 1960s to 1970s. Decadal average loads were subsequently stable through the 1990s. Hypoxia was positively correlated with NO3 − loading, but more extensive hypoxia was observed in recent years than would be expected from the observed relationship. The results suggested that the Bay may have become more susceptible to NO3 − loading. To eliminate or greatly reduce anoxia will require reducing average annual total nitrogen loading to the Maryland mainstem Bay to 50×106 kg yr−1, a reduction of 40% from recent levels.  相似文献   

2.
Single-crystal electron paramagnetic resonance (EPR) spectra of a natural citrine quartz without any artificial irradiation, measured at W-band frequencies (∼94 GHz) and temperatures of 77, 110 and 298 K, allow better characterization of three previously-reported Centers (#6, #7 and B) and discovery of three new defects (B′, C′ and G′). The W-band EPR spectra reveal that Centers #6 and #7 do not reside on twofold symmetry axes, contrary to results from a previous X-band EPR study. The W-band spectra also show that the previously reported Center B is a mixture of two defects (B and B′) with similar g matrices but different-sized 27Al hyperfine structures. Center C′ has similar principal g values to the previously reported Center C but is distinct from the latter by a larger 27Al hyperfine structure with splittings from 0.10 to 0.22 mT. Also, Center G′ has a similar g matrix to the previously reported Center G but a different 27Al hyperfine structure with splittings from 0.41 to 0.53 mT. These spin-Hamiltonian parameters, together with observed thermal properties and microwave-power dependence, suggest that Centers #6 and #7 probably represent O23− type defects. Centers B and B′ are probably superoxide radicals (O2−) with the unpaired spin localized on the same pair of oxygen atoms around a missing Si atom but linked to a substitutional Al3+ ion each at different neighboring tetrahedral sites. Similarly, Centers G and G′ are most likely superoxide radicals with the unpaired spin localized on another pair of oxygen atoms around a missing Si atom and linked to a substitutional Al3+ ion each at different neighboring tetrahedral sites. Center C′ is probably an ozonide radical associated with a missing Si atom and linked to a substitutional Al3+ ion at the neighboring tetrahedral site. This study exemplifies the value of  high-frequency EPR for discrimination of  similar defect centers and determination of  small local structural distortions that are often difficult to resolve in conventional  X- and Q-band EPR studies.  相似文献   

3.
This study measured the major element concentrations and compositions of atmospheric dust aerosol samples collected weekly for nearly 2 years at Mt. Muztagata, a remote and high-elevation site (38°17′N, 75°01′E, 4,430 m) in the Eastern Pamirs. Inductively coupled plasma mass spectroscopy (ICP–MS) results show that on the weekly timescale, air at Muztagata contained average element Al concentrations of 842 ng m−3 between June 2004 and December 2005, and 509 ng m−3 between June 2005 and April 2006. The dust load over the Eastern Pamirs appears to be far lower (by more than an order of magnitude) than those in northern China. The Muztagata dust aerosols show Ca/Al ratios (~0.7) and Fe/Al ratios (~0.7) that differ from that in northern China. The general homogeneity exists in the major element compositions, expect Ca/Al ratios which show minor but clear seasonal variations. Element ratios vary with aerosol concentration. Results indicate that concentrations and compositions of Asian dust change significantly between different emission regions, and confirm that major element ratios can be used to efficiently characterize the dust aerosols composition at different sites in northern China.  相似文献   

4.
A black shale sample collected from the Chimiari site(Tarbela) was analyzed for elemental contents.Inductively coupled plasma-optical emission spectrometry(ICP-OES) was employed to determine major and trace elements in the digests.Precise analysis was accomplished for the black shales,which was better than 2.0%.Result shows that the shales are very rich in Ca(25439 μg·g-1),Fe(13933 μg·g-1),Ti(6932 μg·g-1),Al(5993 μg·g-1) and K(2730 μg·g-1).  相似文献   

5.
The Markandeya River Basin stretches geographically from 15o56′ to 16o08′ N latitude and 74o37′ to 74o58′ E longitude, positioned in the midst of Belgaum district, in the northern part of Karnataka. The groundwater quality of 54 pre-monsoon samples in the Markandeya River Basin was evaluated for its suitability for drinking and irrigation purposes by estimating pH, EC, TDS, hardness and alkalinity besides major cations (Na+, K+, Ca2+, Mg2+) and anions (HCO3–, Cl–, SO42–, PO43-, F-, NO3–), boron, SAR, % Na, RSC, RSBC, chlorinity index, SSP, non-carbonate hardness, Potential Salinity, Permeability Index, Kelley’s ratio, Magnesium hazard and Index of Base Exchange. Negative Index of Base Exchange indicates the chloro-alkaline disequilibrium in the study area and the majority of water samples fall in the rock dominance field based on Gibbs’ ratio. Permeability indices of classes I and II suggest suitability of groundwater for irrigation. Based on Cl, SO4, HCO3 concentrations, water samples can be classified as normal chloride (96.3%) and normal sulfate (94.4%) and normal bicarbonate (44.4%) water types.  相似文献   

6.
Large-scale interaction between the Continental Intercalaire and the Djeffara aquifer systems in the southeast of Tunisia has been investigated with the aid of chemical and isotopic tracers. Two distinct groundwater types have been identified: (1) the Continental Intercalaire groundwater characterized by elevated temperatures (50–61.4°C), low δ18O (−8.4 to−7.87) and δ2H (−67.2 to−59) values and negligible radiocarbon content, both testifying its great age dating from the late Pleistocene period, and (2) the Djeffara groundwater with distinctly heavier isotopic composition (δ18O = −8.31 to −5.80, δ2H = −65.9 to −31.9). The Djeffara groundwaters reveal a distinct changes of physico-chemical and isotopic parameters near El Hamma Faults in the northwestern part of the Djeffara basin. These changes could possibly be explained by a vertical leakage from the Continental Intercalaire aquifer through El Hamma Faults. The mixing proportions inferred from stable isotope mass balance prove that the contribution of the Continental Intercalaire to the recharge of Djeffara aquifer is very significant and may reach 100% in the El Hamma region and in the northern part of Gabes. Isotope tracers strongly suggest that recent recharge to the Djeffara aquifer system is very limited. Its current yield, particularly in its central and northern parts can be maintained only thanks to large-scale underground inflow from the Continental Intercalaire aquifer system, which carries late Pleistocene palaeowater. Consequently, current exploitation of groundwater resources of the Djeffara aquifer has non-sustainable character.  相似文献   

7.
Detailed geological，chronological,mineralogical,petrological and geochemical studies have been conducted of the Chichent gneissic complex in northwestern Hebei province.The gneissic complex is composed mainly of tonalitic-granodioritic rocks according to O'Connor's classification.The zircou U-Pb age of the gneissic complex is 2468-27^+33 Ma.,consistent with that of the rocks in the North Tonalitic-granodioritic Gneiss Belt in the North China Platorm.The Archean Chicheng gneissic complex is part of the belt.No significant difference in composition between early anhedral metasomatic and late semi-euhedral plagiocalases suggests that the gneissic complex is not composed merely of mafic rocks replaced by felsic fiuids.The REE patterns in the complex,in conjunction with major and trace elements data,show that the gneissic complex is the mixture of felsic magma produced by partial melting of FI dacitic granulite and crystallate derived from the magma produced by 50%±partial melting of TH2 tholeiitic granulite and 40%±fractional crystallization of hornblende.  相似文献   

8.
This study represents the first report on sediment accretion rates using137Cs dating for a southern California salt marsh. Vertical accretion rates ranged from 0.7 to 1.2 cm yr−1, which is at the high end of sediment accretion values for coastal wetlands. This has lead to increases in elevation within the estuary from 18 to 35 cm over the last 35 years. Depth profiles of metal concentrations were converted to time-based profiles using vertical accretion rates. Chronologies for most cores indicate a consistent peak in sediment lead (Pb) concentrations in the early to mid 1980s, corresponding to the historic decline in Pb use, which was completed in the U.S. by the early 1980s, but not begun in Mexico until 1991. Sediment Pb levels ranged from about 6–56 μg g−1. Other metals did not show any consistent trends in sediment chronology, except for a single core from a mid-marsh site (east-mid 2), which showed a 2–3-fold increase in levels of Cu, Ni, and Zn during the past two decades. Sediment levels of copper (Cu), nickel (Ni), and zinc (Zn) ranged from 6–34 μg g−1, 11–27 μg g−1, and 42–122 μg g−1, respectively. Despite rapid industrial development of the watershed, a comparison of the sediment metal concentrations in the Tijuana Estuary to other anthropogenically-impacted estuaries in the United States and Europe, shows that metal levels in sediments of the north arm of the estuary are relatively low.  相似文献   

9.
In order to avoid the pollution of trace metals in marine environment, it is necessary to establish the data and understand the mechanisms influencing the distribution of trace metals in marine environment. The concentration of heavy metals (Fe, Mn, Cr, Cu, Ni, Pb, Zn, Co and Cd) were studied in sediments of Ennore shelf, to understand the metal contamination due to heavily industrialized area of Ennore, south-east coast of India. Concentration of metals shows significant variability and range from 1.7 to 3.7% for Fe, 284–460 μg g−1 for Mn, 148.6–243.2 μg g−1 for Cr, 385–657 μg g−1 for Cu, 19.8–53.4 μg g−1 for Ni, 5.8–11.8 μg g−1 for Co, 24.9–40 μg g−1 for Pb, 71.3–201 μg g−1 for Zn and 4.6–7.5 μg g−1 for Cd. For various metals the contamination factor (CF) and geoaccumulation index (I geo) has been calculated to assess the degree of pollution in sediments. The geoaccumulation index shows that Cd, Cr and Cu moderately to extremely pollute the sediments. This study shows that the major sources of metal contamination in the Ennore shelf are land-based anthropogenic ones, such as discharge of industrial wastewater, municipal sewage and run-off through the Ennore estuary. The intermetallic relationship revealed the identical behavior of metals during its transport in the marine environment.  相似文献   

10.
Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment. A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada, with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88 species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m−2 (ranged from 4,371 to 19,930 ind. m−2), 23.4 species grab−1 and 3.29 grab−1, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth (1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting (σI). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay fraction, σI and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction as the single best-correlated variable.  相似文献   

11.
210Pb geochronologies of Cd, Cu, Hg, and Pb fluxes were obtained from the intertidal mudflat sediments of the coastal lagoons Chiricahueto, Estero de Urías, and Ohuira in the Mexican Pacific. The Cu and Hg sediment concentrations at the three lagoons fell within the ranges of 6–76 μg g−1 and 0.1 to 592 ng g−1, respectively; Chiricahueto and Estero de Urías sediments had comparable Cd and Pb concentrations within the ranges of 0.2–2.1 μg g−1 and 10–67 μg g−1, respectively; whereas in Ohuira lagoon, Cd concentrations were lower (0.1–0.5 μg g−1) and Pb concentrations were higher (115–180 μg g−1) than in the other lagoons. The metal fluxes (μg cm−2 y−1) for the three lagoons fell within the ranges of 0.02–0.15 for Cd, 0.7–6.0 for Cu, 0.001–0.045 for Hg, and 0.7–20 for Pb. The Hg pollution in Estero de Urías was attributed to the exhausts of the thermoelectric plant of Mazatlan and the metal enrichment in Chiricahueto and Ohuira was related to the agrochemical wastes from the croplands surrounding these lagoons.  相似文献   

12.
In order to investigate the distribution characteristics of stable carbon isotope ratios (δ 13C) in the desert plant Reaumuria soongorica, the δ 13C values of leaves were measured in 407 individuals of 21 populations. Soil physicochemical properties including soil water content, soil total dissolved solids, soil total nitrogen, soil total phosphorus and soil organic content were also analyzed in order to survey the major factors influencing δ 13C values on spatial variation. Leaves and soil samples were simultaneously collected from the ten major distribution areas in Northwest China at altitudes from 394 m to 1 987 m above sea level, at latitudes from 36°10′N to 44°33′N, and at longitudes from 81°43′E to 106°37′E. These ten areas include Shihezi, Baicheng, Yiwu areas in Xinjiang Uygur Autonomous Region; Anxi, Zhangye, Baiyin, Lanzhou areas in Gansu Province; Shapotou, Yinchuan areas in Ningxia Hui Autonomous Region; and Alashan County in Inner Mongolia Autonomous Region. The results show that the δ 13C value of R. soongorica ranges from −22.77‰ to −29.85‰ with an average of −26.52‰. Foliar d13C values in R. soongorica are not significantly correlated with altitude, latitude or longitude, and a spatial distribution trend of d13C values of R. soongorica is not obvious on a large scale. However, when d13C values of two R. soongorica populations under the same climate conditions are compared, δ 13C values increase obviously from east to west and from north to south. As none of the soil total dissolved solids, soil total nitrogen, soil total phosphorus, and soil organic content shows a uniform trend from east to west and from north to south, we suppose that the small-scaled spatial distribution pattern of δ 13C values of R. soongorica is mainly controlled by the soil water content. Translated from Quaternary Sciences, 2006, 26(6): 947–954 [译自: 第四纪研究]  相似文献   

13.
This study aims to explore the condensation and fractionation trends of persistent organic pollutants (POPs) in the karst soils. The tiankeng is a karst surface expression that can act as a focal point for introduction of contaminants to a karst aquifer, which may serve both as condenser for vapor phase POPs and as barrier/sink for particulate associated less volatile POPs. The fractionation of POPs in soils from the upper rim and floor of tiankeng is of interest in understanding the role of tiankeng in the long-distance transport of POPs. In the present study, polycyclic aromatic hydrocarbons (PAHs) in the surface soils from the upper rim and floor of Dashiwei tiankeng in Southern China were analyzed. The total PAH concentrations in soils were 23.40–190 ng g−1, with phenanthrene being the most abundant. The distribution patterns of PAH compounds in the soil samples matched well with their properties. It indicated the heavy PAHs were susceptible to retention by the floor soils of tiankeng than light PAHs. A plot of Cfloor/Crim against PAH molecular weight gave a good positive relationship in the molecular weight range of 152–276. It is suggested that the floor soils can be focal points of more concentrated PAH and deserve attention. The concentrations of total PAHs in the floor soils (43.40–190 ng g−1, mean 87.76 ng g−1) were higher than those in the upper rim (23.40–88.94 ng g−1, mean 57.74 ng g−1). In addition, there was a shift in compound pattern with an increase in the proportion of light PAHs (2–3 rings), a decrease in heavy PAHs (5–6 rings) and a relatively stable content of 4-ring PAHs. A combination of particulate scavenging and cold condensation is proposed as the major mechanism for the compositional fractionation of PAHs in the soils from the upper rim and floor of tiankeng.  相似文献   

14.
A sediment core from Guanabara Bay (Brazil) was analyzed for 210Pb dating, grain size, total organic carbon (TOC) and total nitrogen, carbon stable isotope ratio (δ13C), nitrogen stable isotope ratio (δ15N) and the metals Fe, Mn, Ni, Co, Cu, Pb, V and Zn, to assess the influence of land use changes on the aquatic system in a region for which large industrial and urban development is expected in the next few decades. To obtain baseline data for improving the monitoring of the expected increase in anthropogenic impacts from surrounding drainage basins, a multivariate analysis of data from different sediment layers was carried out to evaluate the dated sediment record. The geochemical data suggested three different sedimentary phases along the last 200 years. Before the 1880s, the highest clay and TOC contents were observed, where the C/N ratios and the δ13C values suggested a mixture of algal and terrestrial organic matter and the lowest concentrations of Co, Cu, Pb, V and Zn, for which background levels were estimated (4.6, 2.7, 14.9, 24.3 and 70.2 mg kg−1, respectively). From the 1880s to the 1950s, the metal concentrations and sand particles increased, but no change in organic matter quality was observed, reflecting a period of land use change, still without significant sewage input. After the 1950s, the sedimentation rate increased from 0.42 to 0.77 cm year−1 and increasing urban sewage input was evidenced by lower C/N ratios, higher δ15N, decrease of Fe and Mn concentrations and increased fluxes of metals and TOC, which showed a good relationship with population growth data.  相似文献   

15.
Summary The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are pyrite, chalcopyrite ± fahlore (As/(As + Sb): 0.06−0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As + Sb): 0.21−0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at.%, occurs interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up to 1.96 at.% As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid inclusion microthermometry shows homogenization temperatures between 130 and 352 °C and salinities between 1.6 and 6.9 wt.% NaCl eq. Isotope data for quartz, ankerite and phyllosilicates and estimated temperatures show that δ18O and δD for the hydrothermal fluids were between 3 and 10‰ and between −95 and −75‰, respectively. These results suggest the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed for the formation of the El Dorado deposit. Author’s present address: J. Carrillo-Rosúa, Dpto. de Didáctica de las Ciencias Experimentales, Universidad de Granada, Campus de Cartuja, 18071, Granada, Spain  相似文献   

16.
In southern California, USA, wildfires may be an important source of mercury (Hg) to local watersheds. Hg levels and Hg accumulation rates were investigated in dated sediment cores from two southern California lakes, Big Bear Lake and Crystal Lake, located approximately 40-km apart. Between 1895 and 2006, fires were routinely minimized or suppressed around Big Bear Lake, while fires regularly subsumed the forest surrounding Crystal Lake. Mean Hg concentrations and mean Hg accumulation rates were significantly higher in Crystal Lake sediments compared to Big Bear Lake sediments (Hg levels: Crystal Lake 220 ± 93 ng g−1, Big Bear Lake 92 ± 26 ng g−1; Hg accumulation: Crystal Lake 790 ± 1,200 μg m−2 year−1, Big Bear 240 ± 54 μg m−2 year−1). In Crystal Lake, the ratio between post-1965 and pre-1865 Hg concentrations was 1.1, and several spikes in Hg levels occurred between 1910 and 1985. Given the remote location of the lake, the proximity of fires, and the lack of point sources within the region, these results suggested wildfires (rather than industrial sources) were a continuous source of Hg to Crystal Lake over the last 150 years.  相似文献   

17.
A high resolution quantitative granulometric record for site Uchediya [21°43′2.22″ N, 73° 6′26.22″ E; 10 m a. s. l.] gives understanding towards accretion history of the late Holocene flood plain in the lower reaches of Narmada River. Two sediment facies (sandy and muddy) and seven subfacies (sandy subfacies: StMS+FS+CS, SmFS+MS, SlFS+VFS, and StMS + CS; muddy subfacies: FmSILT+VFS+FS, FmSILT+VFS (O) and FmSILT+VFS (T)) are identified based on cluster analysis supplemented with sedimentary structures observed in field and other laboratory data. Changes in hydrodynamics are further deduced based on various sedimentological parameters and their ratios leading to arrive at a depositional model.  相似文献   

18.
Variation of vegetation coverage and canopy height may reflect the complex spatial heterogeneity of nutrient storage and supply capacity, soil moisture, and surface hydrology in the karst terrains suffering from severe land degradation. To assess the patterns of nutrient limitation under different vegetation covers in the subtropical karst ecosystems from Guizhou province, southwestern China, topsoil and leaf samples of dominant tree species were collected in forest stand (FO), shrub stand (SH) and shrub-grass stand (SG), respectively. Nutrient concentrations of both soil and leaf were determined, and ratios of N to P and vegetation nutrient reuse capacity (VNR) calculated as well as vegetation coverage, vegetation canopy height and tree density measured across the three stands. Mean leaf N/P ratio was lowest (16.1 ± 1.4) in FO and highest (33.5 ± 3.2) in SG. Vegetation nutrient reuse increased with the decline in N and P availability in soils for these three stands. VNR of N and P ranged from 8.5 to 25.2 mg N g−1 and from 0.4 to 1.1 mg P g−1, respectively, and appeared lowest in SG (10.4 mg N g−1 and 0.5 P mg g−1 on average, respectively) and highest in FO (22.4 mg N g−1 and 0.9 mg P g−1 on average, respectively). Although there was no substantial difference in phosphorus reuse efficiencies between plant species and vegetation stands, concentrations of N and P of senesced leaves (SLs) were, respectively, found in positive correlation with the concentrations of mature leaves. The variation of VNR with elements indicated that P is cycled within vegetation much more efficiently than N across the stands. This study demonstrated that the karst vegetations were generally at P-limited or N- and P- co-limited stresses and that N/P ratio could be an effective indictor for nutrient limitation in the karst ecosystems at vegetation community level rather than at tree species level. It is proposed that phosphorus reuse by mature leaves could be an adaptation strategy by the dominant species to the low P availability in the karst soil.  相似文献   

19.
Among several salt lakes in the Thar Desert of western India, the Sambhar is the largest lake producing about 2 × 105 tons of salt (NaCl) annually. The “lake system” (lake waters, inflowing river waters, and sub-surface brines) provides a unique setting to study the geo-chemical behavior of uranium isotopes (238U, 234U) in conjunction with the evolution of brines over the annual wetting and evaporation cycles. The concentration of 238U and the total dissolved solids (TDS) in lake water increase from ~8 μg L−1 and ~8 g L−1 in monsoon to ~1,400 μg L−1 and 370 g L−1, respectively, during summer time. The U/TDS ratio (~1 μg g−1 salt) and the 234U/238U activity ratio (1.65 ± 0.05), however, remain almost unchanged throughout the year, except when U/TDS ratio approaches to 3.8 at/or beyond halite crystallization. These observations suggest that uranium behaves conservatively in the lake waters during the annual cycle of evaporation. Also, uranium and salt content (TDS) are intimately coupled, which has been used to infer the origin and source of salt in the lake basin. Furthermore, near uniform ratios in evaporating lake waters, when compared to the ratio in seawater (~0.1 μg g−1 salt and 1.14 ± 0.02, respectively), imply that aeolian transport of marine salts is unlikely to be significant source of salt to the lake in the present-day hydrologic conditions. This inference is further consistent with the chemical composition of wet-precipitation occurring in and around the Sambhar lake. The seasonal streams feeding the lake and groundwaters (within the lake’s periphery) have distinctly different ratios of U/TDS (2–69 μg g−1 salt) and 234U/238U (1.15–2.26) compared to those in the lake. The average U/TDS ratio of ~1 μg g−1 salt in lake waters and ~19 μg g−1 salt in river waters suggest dilution of the uranium content by the recycled salt and/or removal processes presently operating in the lake during the extraction of salt for commercial use. Based on mass-balance calculations, a conservative estimate of "uranium sink" (in the form of bittern crust) accounts for ~5 tons year−1 from the lake basin, an estimate similar to its input flux from rivers, i.e., 4.4 tons year−1.  相似文献   

20.
Three undisturbed sediment samples were collected from the intertidal zone of the Jiaojiang Estuary of Zhejiang Province, China. The sediments were found to contain remarkably low concentrations of organic carbon (<0.6%) and acid volatile sulfide (AVS) (<30 μmol g−1). The availability of these two substrates likely constrained sulfate reduction and pyritization of several trace metals, respectively. This was especially true at one station where AVS concentrations in the upper 20 cm averaged less than 0.05 μmol g−1. Although the depth dependence of the degree of trace metal pyritization was generally consistent with expectations based on redox conditions, depth profiles of reactive-metal and pyrite-metal concentrations in several cases revealed more complex behavior and a positive correlation between reactive-metal concentrations and pore water metal concentrations.  相似文献   

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