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1.
The shallow aquifer beneath the Western Snake River Plain (Idaho, USA) exhibits widespread elevated arsenic concentrations (up to 120 μg L−1). While semi-arid, crop irrigation has increased annual recharge to the aquifer from approximately 1 cm prior to a current rate of >50 cm year−1. The highest aqueous arsenic concentrations are found in proximity to the water table (all values >50 μg L−1 within 50 m) and concentrations decline with depth. Despite strong vertical redox stratification within the aquifer, spatial distribution of aqueous species indicates that redox processes are not primary drivers of arsenic mobilization. Arsenic release and transport occur under oxidizing conditions; groundwater wells containing dissolved arsenic at >50 μg L−1 exhibit elevated concentrations of O2 (average 4 mg L−1) and NO3 (average 8 mg L−1) and low concentrations of dissolved Fe (<20 μg L−1). Sequential extractions and spectroscopic analysis of surficial soils and sediments indicate solid phase arsenic is primarily arsenate and is present at elevated concentrations (4–45 mg kg−1, average: 17 mg kg−1) relative to global sedimentary abundances. The highest concentrations of easily mobilized arsenic (up to 7 mg kg−1) are associated with surficial soils and sediments visibly stained with iron oxides. Batch leaching experiments on these materials using irrigation waters produce pore water arsenic concentrations approximating those observed in the shallow aquifer (up to 152 μg L−1). While As:Cl aqueous phase relationships suggest minor evaporative enrichment, this appears to be a relic of the pre-irrigation environment. Collectively, these data indicate that infiltrating irrigation waters leach arsenic from surficial sediments to the underlying aquifer.  相似文献   

2.
Waters from abandoned Sb-Au mining areas have higher Sb (up to 2138 μg L−1), As (up to 1252 μg L−1) and lower Al, Zn, Li, Ni and Co concentrations than those of waters from the As-Au mining area of Banjas, which only contain up to 64 μg L−1 As. In general, Sb occurs mainly as SbO3− and As H2AsO4−. In general, waters from old Sb-Au mining areas are contaminated in Sb, As, Al, Fe, Cd, Mn, Ni and NO2−, whereas those from the abandoned As-Au mining area are contaminated in Al, Fe, Mn, Ni, Cd and rarely in NO2−. Waters from the latter area, immediately downstream of mine dumps are also contaminated in As. In stream sediments from Sb-Au and As-Au mining areas, Sb (up to 5488 mg kg−1) and As (up to 235 mg kg−1) show a similar behaviour and are mainly associated with the residual fraction. In most stream sediments, the As and Sb are not associated with the oxidizable fraction, while Fe is associated with organic matter, indicating that sulphides (mainly arsenopyrite and pyrite) and sulphosalts containing those metalloids and metal are weathered. Arsenic and Sb are mainly associated with clay minerals (chlorite and mica; vermiculite in stream sediments from old Sb-Au mining areas) and probably also with insoluble Sb phases of stream sediments. In the most contaminated stream sediments, metalloids are also associated with Fe phases (hematite and goethite, and also lepidocrocite in stream sediments from Banjas). Moreover, the most contaminated stream sediments correspond to the most contaminated waters, reflecting the limited capacity of stream sediments to retain metals and metalloids.  相似文献   

3.
The occurrence of mining areas in the vicinities of salt marshes may affect their ecological functions and facilitate the transfer of pollutants into the food chain. The mobilisation of metals in salt marsh soils is controlled by abiotic (pH, redox potential) and biotic (influence of rhizosphere) factors. The effect of the rhizosphere of two plant species (Sarcocornia fruticosa and Phragmites australis) and different flooding regimes on potentially harmful metals and As mobilisation from salt marsh soil polluted by mining activities were investigated (total concentrations: 536 mg kg−1 As, 37 mg kg−1 Cd, 6746 mg kg−1 Pb, 15,320 mg kg−1 Zn). The results show that the changes in redox conditions (from 300 mV to −100 mV) and pH after flooding and rewetting periods may mobilise the contaminant elements into soil solution (e.g., 100 μg L−1 Cd, 30 μg L−1 Pb, 7 mg L−1 Zn), where they are available for plants or may be leached from the soil. Drying periods generated peaks of concentrations in the soil solution (up to 120 μg L−1 Cd and 50 μg L−1 Pb). The risk assessment of As and metal-polluted salt marshes should take into account flood dynamics in order to prevent metal(loid) mobilisation.  相似文献   

4.
Hydrochemical patterns resulting from differing bedrock geochemistry were ascertained by concurrent streamwater sampling in three small catchments, each underlain by geochemically contrasting silicate rock types in the western Czech Republic, Central Europe in 2001–2010. The catchments are situated 5–7 km apart in the Slavkov Forest and are occupied by Norway spruce (Picea abies) plantations. They have similar altitude, area, topography, mean annual air temperature, and atmospheric deposition fluxes. The amount of base cations oxides (Ca + Mg + Na + K) is markedly different among the three studied rocks (leucogranite 8%, amphibolite 22%, serpentinite 36%). The leucogranite contains a very small amount of MgO, while the serpentinite contains extremely large amounts of MgO. The amphibolite contains an intermediate amount of MgO and elevated CaO. The Lysina, on leucogranite, exhibited very small concentrations of Mg (median 0.4 mg L−1) in streamwater; Pluh?v Bor, on serpentinite, contained extremely high concentrations of streamwater Mg (18 mg L−1). Streamwater in the Na Zeleném catchment, on amphibolite, contained an intermediate amount of Mg and an elevated Ca. Very low pH (4.2), negative alkalinity (−60 μeq L−1) and high inorganic monomeric Al concentrations (0.3 mg L−1) were found in the stream draining leucogranite. Serpentinite streamwater exhibited the highest pH (7.6), alkalinity (+940 μeq L−1) and Ni concentrations (100 μg L−1). Aquatic chemistry reflected the composition of the underlying rocks within the studied catchments. Contrasting streamwater compositions of the studied catchments were generated according to the MAGIC model simulations mainly by differences in chemical weathering rates of base cations (65 meq m−2 a−1 at Lysina, 198 meq m−2 a−1 at Na Zeleném, and 241 meq m−2 a−1 at Pluh?v Bor).  相似文献   

5.
Sixty five urban road dust samples were collected from different land use areas of ∼240 km2 in Xi’an, China. The concentrations of Ag, As, Cr, Cu, Hg, Pb, Sb and Zn were determined to investigate potentially harmful element (PHE) contamination, distribution and possible sources. In addition, the concentrations in different size fractions were measured to assess their potential impact on human health. The highest concentrations were found in the fraction with particle diameters between 80 μm and 101 μm, the finest particles (<63 μm) were not the most important carriers for Ag, As, Cd, Cr, Cu, Hg, Pb and Zn. The percentages of these elements in particles with diameters less than 63 μm (PM63) and less than 101 μm (PM101) were in the range of 7–15%, and 30–55%, respectively. Three main factors influencing element distributions have been identified: (a) industrial activities; (b) prior agricultural land use; and (c) other activities commonly found in urban areas, such as traffic, coal combustion, waste dumping, and building construction/renovation. The highest concentrations were found in industrial areas for As (20 mg kg−1), Cr (853 mg kg−1), Cu (1071 mg kg−1), Pb (3060 mg kg−1) and Zn (2112 mg kg−1), and in previous agricultural areas for Ag and Hg, indicating significant contributions from industrial activities and prior agricultural activities.  相似文献   

6.
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7.
Despite reduced anthropogenic deposition during the last decades, deposition sulphate may still play an important role in the biogeochemical cycles of S and many catchments may act as net sources of S that may remain for several decades. The aim of this study is to elucidate the temporal and spatial dynamics of both SO42− and δ34SSO4 in stream water from catchments with varying percentage of wetland and forest coverage and to determine their relative importance for catchment losses of S. Stream water samples were collected from 15 subcatchments ranging in size from 3 to 6780 ha, in a boreal stream network, northern Sweden. In forested catchments (<2% wetland cover) S-SO42− concentrations in stream water averaged 1.7 mg L−1 whereas in wetland dominated catchments (>30% wetland cover) the concentrations averaged 0.3 mg L−1. A significant negative relationship was observed between S-SO42− and percentage wetland coverage (r2 = 0.77, p < 0.001) and the annual export of stream water SO42− and wetland coverage (r2 = 0.76, p < 0.001). The percentage forest coverage was on the other hand positively related to stream water SO42− concentrations and the annual export of stream water SO42− (r2 = 0.77 and r2 = 0.79, respectively). The annual average δ34SSO4 value in wetland dominated streams was +7.6‰ and in streams of forested catchments +6.7‰. At spring flood the δ34SSO4 values decreased in all streams by 1‰ to 5‰. The δ34SSO4 values in all streams were higher than the δ34SSO4 value of +4.7‰ in precipitation (snow). The export of S ranged from 0.5 kg S ha−1 yr−1 (wetland headwater stream) to 3.8 kg S ha−1 yr−1 (forested headwater stream). With an average S deposition in open field of 1.3 kg S ha−1 yr−1 (2002-2006) the mass balance results in a net export of S from all catchments, except in catchments with >30% wetland. The high temporal and spatial resolution of this study demonstrates that the reducing environments of wetlands play a key role for the biogeochemistry of S in boreal landscapes and are net sinks of S. Forested areas, on the other hand were net sources of S.  相似文献   

8.
Industrialization, urbanization, and agricultural practices are 3 of the most important sources of metal accumulations in soils. Concentrations of Cr, Mn, Ni, Cu, Pb, Zn and Cd were determined in surface soils collected under different land uses, including urban (UR), industrial (IN-1 and IN-2), agricultural (AG), abandoned unused (AB), and natural (NA) sites to examine the influence of anthropogenic activities on metals in soils formed in a typical Mediterranean environment. The highest concentrations of Cr, Cd, and Pb observed in the NW industrial area (IN-2) were 63.7, 3.34 and 2330 mg metal kg−1 soil, for each metal, respectively. The SW industrial area (IN-1) contained the highest Zn content at 135 mg kg−1. However, soils with the highest concentrations of Ni and Cu were located in AG sites at 30.9 and 64.9 mg kg−1 soil, respectively. Sampling locations with the highest concentrations of Mn were identified in AB sites. Using the concentrations of metals at the NA sites as the baseline levels, soils collected from all other land uses in the study area exhibited significantly higher total contents of Zn, Mn, Cr and Ni. Metal enrichment was attributed to fertilizer and pesticide applications, industrial activities, and metal deposition from a high volume of vehicular traffic (for Pb and Cd). High concentrations of Mn in some samples were attributed to parent materials. The study demonstrated that anthropogenic activities associated with various land uses contribute to metal accumulation in soils and indicated a need to closely monitor land management practices to reduce human and ecological risks from environmental pollution.  相似文献   

9.
The availability of dissolved O2 can limit biodegradation of organic compounds in aquifers. Where O2 is depleted, biodegradation proceeds via anaerobic processes, including NO3-, Mn(IV)-, Fe(III)- and SO4-reduction and fermentation/methanogenesis. The environmental controls on these anaerobic processes must be understood to support implementation of management strategies such as monitored natural attenuation (MNA). In this study stable isotope analysis is used to show that the relative significance of two key anaerobic biodegradation processes (bacterial SO4 reduction (BSR) and methanogenesis) in a phenol-contaminated sandstone aquifer is sensitive to spatial and temporal changes in total dissolved phenols concentration (TPC) (= phenol + cresols + dimethylphenols) over a 5-a period. In general, 34SO4-enrichment (characteristic of bacterial SO4 reduction) is restricted spatially to locations where TPC < 2000 mg L−1. In contrast, 13C-depleted CH4 and 13C-enriched CO2 isotope compositions (characteristic of methanogenesis) were measured at TPC up to 8000 mg L−1. This is consistent with previous studies that demonstrate suppression of BSR at TPC of >500 mg L−1, and suggests that methanogenic microorganisms may have a higher tolerance for TPC in this contaminant plume. It is concluded that isotopic enrichment trends can be used to identify conditions under which in situ biodegradation may be limited by the properties of the biodegradation substrate (in this case TPC). Such data may be used to deduce the performance of MNA for contaminated groundwater in similar settings.  相似文献   

10.
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11.
Lignin phenol concentrations and compositions were determined on dissolved organic carbon (DOC) extracts (XAD resins) within the Sacramento-San Joaquin River Delta (the Delta), the tidal freshwater portion of the San Francisco Bay Estuary, located in central California, USA. Fourteen stations were sampled, including the following habitats and land-use types: wetland, riverine, channelized waterway, open water, and island drains. Stations were sampled approximately seasonally from December, 1999 through May, 2001. DOC concentrations ranged from 1.3 mg L−1 within the Sacramento River to 39.9 mg L−1 at the outfall from an island drain (median 3.0 mg L−1), while lignin concentrations ranged from 3.0 μg L−1 within the Sacramento River to 111 μg L−1 at the outfall from an island drain (median 11.6 μg L−1). Both DOC and lignin concentrations varied significantly among habitat/land-use types and among sampling stations. Carbon-normalized lignin yields ranged from 0.07 mg (100 mg OC)−1 at an island drain to 0.84 mg (100 mg OC)−1 for a wetland (median 0.36 mg (100 mg OC)−1), and also varied significantly among habitat/land-use types. A simple mass balance model indicated that the Delta acted as a source of lignin during late autumn through spring (10-83% increase) and a sink for lignin during summer and autumn (13-39% decrease). Endmember mixing models using S:V and C:V signatures of landscape scale features indicated strong temporal variation in sources of DOC export from the Delta, with riverine source signatures responsible for 50% of DOC in summer and winter, wetland signatures responsible for 40% of DOC in summer, winter, and late autumn, and island drains responsible for 40% of exported DOC in late autumn. A significant negative correlation was observed between carbon-normalized lignin yields and DOC bioavailability in two of the 14 sampling stations. This study is, to our knowledge, the first to describe organic vascular plant DOC sources at the level of localized landscape features, and is also the first to indicate a significant negative correlation between lignin and DOC bioavailability within environmental samples. Based upon observed trends: (1) Delta features exhibit significant spatial variability in organic chemical composition, and (2) localized Delta features appear to exert strong controls on terrigenous DOC as it passes through the Delta and is exported into the Pacific Ocean.  相似文献   

12.
Anomalous concentrations of Cr(VI) occur in groundwaters of the Adamantina Aquifer, in a large region in the western state of São Paulo, sometimes exceeding the potability limit (0.05 mg L−1). To identify the possible geochemical reactions responsible for the occurrence of Cr in groundwater in Urânia, borehole rock samples were collected in order to carry out mineralogical and chemical analyses. In addition, multilevel monitoring wells were installed and groundwater samples were analyzed. Analyses of the borehole rock samples show the occurrence of a geochemical anomaly of Cr in the quartzose sandstones (average concentrations of 221 ppm). Chrome-diopside is one of the main minerals contributing to this anomaly, having an average Cr content of 1505 ppm. Sequential extraction experiments indicated weakly adsorbed Cr in the order of 0.54 ppm, and this quantity is enough to provide the Cr concentrations observed in groundwater. Groundwaters from the monitoring wells proved to be stratified, with the highest concentrations of Cr(VI) (0.13 mg L−1) being associated with high redox and pH values (over 10) and high concentrations of Na. Geochemical reactions that may explain the release of Cr from the solid phase to groundwater involve the release of Cr(III) from minerals (like chrome-diopside and Cr-Fe hydroxide), followed by oxidation of Cr(III) to Cr(VI), probably related to the reduction of Mn oxides present in the aquifer. Then cation exchange occurs and dissolution of carbonates which increases the pH of groundwater, resulting in the desorption and mobilization of Cr(VI) into groundwater.  相似文献   

13.
Willow Slough, a seasonally irrigated agricultural watershed in the Sacramento River valley, California, was sampled weekly in 2006 in order to investigate seasonal concentrations and compositions of dissolved organic carbon (DOC). Average DOC concentrations nearly doubled from winter baseflow (2.75 mg L−1) to summer irrigation (5.14 mg L−1), while a concomitant increase in carbon-normalized vanillyl phenols (0.11 mg 100 mg OC−1 increasing to 0.31 mg 100 mg OC−1, on average) indicates that this additional carbon is likely vascular plant-derived. A strong linear relationship between lignin concentration and total suspended sediments (r2 = 0.79) demonstrates that agricultural management practices that mobilize sediments will likely have a direct and significant impact on DOC composition. The original source of vascular plant-derived DOC to Willow Slough appears to be the same throughout the year as evidenced by similar syringyl to vanillyl and cinnamyl to vanillyl ratios. However, differing diagenetic pathways during winter baseflow as compared to the rest of the year are evident in acid to aldehyde ratios of both vanillyl and syringyl phenols. The chromophoric dissolved organic matter (CDOM) absorption coefficient at 350 nm showed a strong correlation with lignin concentration (r2 = 0.83). Other CDOM measurements related to aromaticity and molecular weight also showed correlations with carbon-normalized yields (e.g. specific UV absorbance at 254 nm (r2 = 0.57) and spectral slope (r2 = 0.54)). Our overall findings suggest that irrigated agricultural watersheds like Willow Slough can potentially have a significant impact on mainstem DOC concentration and composition when scaled to the entire watershed of the main tributary.  相似文献   

14.
Complete hydrochemical data are rarely reported for coal-mine discharges (CMD). This report summarizes major and trace-element concentrations and loadings for CMD at 140 abandoned mines in the Anthracite and Bituminous Coalfields of Pennsylvania. Clean-sampling and low-level analytical methods were used in 1999 to collect data that could be useful to determine potential environmental effects, remediation strategies, and quantities of valuable constituents. A subset of 10 sites was resampled in 2003 to analyze both the CMD and associated ochreous precipitates; the hydrochemical data were similar in 2003 and 1999. In 1999, the flow at the 140 CMD sites ranged from 0.028 to 2210 L s−1, with a median of 18.4 L s−1. The pH ranged from 2.7 to 7.3; concentrations (range in mg/L) of dissolved (0.45-μm pore-size filter) SO4 (34–2000), Fe (0.046–512), Mn (0.019–74), and Al (0.007–108) varied widely. Predominant metalloid elements were Si (2.7–31.3 mg L−1), B (<1–260 μg L−1), Ge (<0.01–0.57 μg L−1), and As (<0.03–64 μg L−1). The most abundant trace metals, in order of median concentrations (range in μg/L), were Zn (0.6–10,000), Ni (2.6–3200), Co (0.27–3100), Ti (0.65–28), Cu (0.4–190), Cr (<0.5–72), Pb (<0.05–11) and Cd (<0.01–16). Gold was detected at concentrations greater than 0.0005 μg L−1 in 97% of the samples, with a maximum of 0.0175 μg L−1. No samples had detectable concentrations of Hg, Os or Pt, and less than half of the samples had detectable Pd, Ag, Ru, Ta, Nb, Re or Sn. Predominant rare-earth elements, in order of median concentrations (range in μg/L), were Y (0.11–530), Ce (0.01–370), Sc (1.0–36), Nd (0.006–260), La (0.005–140), Gd (0.005–110), Dy (0.002–99) and Sm (<0.005–79). Although dissolved Fe was not correlated with pH, concentrations of Al, Mn, most trace metals, and rare earths were negatively correlated with pH, consistent with solubility or sorption controls. In contrast, As was positively correlated with pH.  相似文献   

15.
Our ability to adapt to changes in groundwater quality, arising from a changing climate and/or local pressures, is dependent on comprehension of the governing controls of spatial variation in groundwater chemistry. This paper presents results of an assessment of dominant hydro-geochemical processes controlling groundwater chemical composition, using an integrated application of hierarchical cluster analysis (HCA) and principal component analysis (PCA) of a major ion dataset of groundwater from lower Shire River valley, Malawi. The area is in the southernmost part of the western section of the East African Rift System (EARS) and has localised occurrence of saline groundwater. HCA classified samples into three main clusters (C1-C3) according to their dominant chemical composition: C1 (dominant composition: Na-Cl; median TDS: 3436 mg L−1), C2 (dominant composition: Na-HCO3; median TDS: 966 mg L−1) and C3 (dominant composition: alkali earths-HCO3; median TDS: 528 mg L−1). These clusters were in turn described by the principal components PC1, PC3 and PC2, respectively, resulting from the PCA. The results of the PCA and geochemical interpretation suggest that the spatial variation of groundwater quality in the area is influenced by the following processes: C3 samples result mainly from H2CO3 weathering of aluminosilicate minerals by percolating water supersaturated with CO2. In addition to aluminosilicate weathering, C2 samples are influenced by the processes of cation exchange of Ca2+ and Mg2+ in the water for Na+ on clay minerals, and carbonate precipitation. The increase in ionic strength of C2 samples is attributed to mixing with high TDS groundwater in proximity with C2 samples. The saline/brackish C1 groundwater results from the processes of evaporation (for samples with high water table close to the Shire marshes) and dissolution of Cl− and SO4-evaporative salts followed by mineralised seep from sedimentary Karoo and Cretaceous Lupata sandstones.  相似文献   

16.
We report seawater boron concentration (mg kg−1) and chlorinity (‰) values measured in seawater samples (n = 139) collected at various depths in the North Pacific and North Atlantic oceans and the East/Japan Sea (located in the western temperate North Pacific). Our results indicate that variations in seawater boron concentration are strongly coupled to variations in chlorinity (and salinity), yielding a mean boron to chlorinity ratio of 0.2414 ± 0.0009 mg kg−1 ‰−1 (boron to salinity ratio = 0.1336 ± 0.0005 mg kg−1 ‰−1). This ratio was surprisingly universal throughout the water column in the three marine basins and across widely different ocean surface regimes, but differs from the generally accepted ratio of 0.232 ± 0.005 mg kg−1 ‰−1 determined by Uppström (1974), which was based on only 20 measurements at four sites in the tropical Pacific Ocean. In converting total alkalinity to carbonate alkalinity (and vice versa) for thermodynamic calculations, the difference between these two ratios leads to a difference of 5 μmol kg−1 in estimates for ocean surface waters, where the contribution of borate to total alkalinity is typically greatest. We suggest the use of the new boron to chlorinity ratio for predicting seawater boron concentrations using chlorinity (or salinity) data.  相似文献   

17.
Partitioning of Ni in calcite, CaCO3, was evaluated with the aim of collecting data on partition and distribution coefficients and to enhance understanding about the interaction of Ni with the calcite surface and further incorporation into the bulk. This information will aid in the interpretation of geological processes for safety assessment of waste repositories and contamination of groundwater. Coprecipitation experiments were carried out by the constant addition method at 25 °C and pCO2 = 1 and 10−3.5 atm. Ni was moderately partitioned from solution into calcite. For dilute solid solutions (XNi < 0.001), Ni partition coefficients were estimated to be ∼1 and found to be weakly dependent on calcite precipitation rate in the range of 3-230 nmol m−2 s−1. Ni molar fraction in the solid is directly proportional to Ni concentration in the solution. The fit of the data to such a model is good evidence that Ni is taken up as a true solid solution, not simply by physical trapping.  相似文献   

18.
Methane microseepage is the result of natural gas migration from subsurface hydrocarbon accumulations to the Earth’s surface, and it is quite common in commercial petroleum fields. While the role of microseepage as a pathfinder in petroleum exploration has been known for about 80 a, its significance as an atmospheric CH4 source has only recently been studied, and flux data are currently available only in the USA and Europe. With the aim of increasing the global data-set and better understanding flux magnitudes and variabilities, microseepage is now being extensively studied in China. A static flux chamber method was recently applied to study microseepage emissions into the atmosphere in four different sectors of the Yakela condensed gas field in Tarim Basin, Xinjiang, China, and specifically in: (a) a faulted sector, across the Luntai fault systems; (b) an oil–water interface sector, at the northern margin of the field; (c) an oil–gas interface sector, in the middle of the field; (d) an external area, outside the northern gas field boundaries. The results show that positive CH4 fluxes are pervasive in all sectors and therefore, only part of the CH4 migrating from the deep oil–gas reservoirs is consumed in the soil by methanotrophic oxidation. The intensity of gas seepage seems to be controlled by subsurface geologic settings and lateral variabilities of natural gas pressure in the condensed gas field. The highest CH4 fluxes, up to ∼14 mg m−2 d−1 (mean of 7.55 mg m−2 d−1) with higher spatial variability (standard deviation, σ: 2.58 mg m−2 d−1), occur in the Luntai fault sector. Merhane flux was lower in the oil–water area (mean of 0.53 mg m−2 d−1) and the external area (mean of 1.55 mg m−2 d−1), and at the intermediate level in the gas–oil sector (mean of 2.89 mg m−2 d−1). These values are consistent with microseepage data reported for petroleum basins in the USA and Europe. The build-up of methane concentration in the flux chambers is always coupled with an enrichment of 13C, from δ13C1 of −46‰ to −42.5‰ (VPDB), which demonstrates that seeping methane is thermogenic, as that occurring in the deep Yakela reservoir. Daily variations of microseepage are very low, with minima in the afternoon, corresponding to higher soil temperature (and higher methanotrophic consumption), and maxima in the early morning (when soil temperatures are lowest). A preliminary and rough estimate of the total amount of CH4 exhaled from the Yakela field is in the order of 102 tonnes a−1.  相似文献   

19.
The Xunyang Hg mine (XMM) situated in Shaanxi Province is an active Hg mine in China. Gaseous elemental Hg (GEM) concentrations in ambient air were determined to evaluate its distribution pattern as a consequence of the active mining and retorting in the region. Total Hg (HgT) and methylmercury (MeHg) concentrations in riparian soil, sediment and rice grain samples (polished) as well as Hg speciation in surface water samples were measured to show local dispersion of Hg contamination. As expected, elevated concentrations of GEM were found, ranging from 7.4 to 410 ng m−3. High concentrations of HgT and MeHg were also obtained in riparian soils, ranged from 5.4 to 120 mg kg−1 and 1.2 to 11 μg kg−1, respectively. Concentrations of HgT and MeHg in sediment samples varied widely from 0.048 to 1600 mg kg−1 and 1.0 to 39 μg kg−1, respectively. Surface water samples showed elevated HgT concentrations, ranging from 6.2 to 23,500 ng L−1, but low MeHg concentrations, ranging from 0.022 to 3.7 ng L−1. Rice samples exhibited high concentrations of 50–200 μg kg−1 in HgT and of 8.2–80 μg kg−1 in MeHg. The spatial distribution patterns of Hg speciation in the local environmental compartments suggest that the XMM is the source of Hg contaminations in the study area.  相似文献   

20.
The influence of soil organisms on metal mobility and bioavailability in soils is not currently fully understood. We conducted experiments to determine whether calcium carbonate granules secreted by the earthworm Lumbricus terrestris could incorporate and immobilise lead in lead- and calcium-amended artificial soils. Soil lead concentrations were up to 2000 mg kg−1 and lead:calcium ratios by mass were 0.5-8. Average granule production rates of 0.39 ± 0.04 mgcalcite earthworm−1 day−1 did not vary with soil lead concentration. The lead:calcium ratio in granules increased significantly with that of the soil (r2 = 0.81, p = 0.015) with lead concentrations in granules reaching 1577 mg kg−1. X-ray diffraction detected calcite and aragonite in the granules with indications that lead was incorporated into the calcite at the surface of the granules. In addition to the presence of calcite and aragonite X-ray absorption spectroscopy indicated that lead was present in the granules mainly as complexes sorbed to the surface but with traces of lead-bearing calcite and cerussite. The impact that lead-incorporation into earthworm calcite granules has on lead mobility at lead-contaminated sites will depend on the fraction of total soil lead that would be otherwise mobile.  相似文献   

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