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1.
Dissolved and particulate Zn and Ni concentrations were determined at 76 locations along the Yangtze River basin from the headwaters to the estuary during flood and dry seasons. Spatial and temporal variations of Zn and Ni were investigated and six major source zones were identified. The Three Gorges Dam (TGD) blocked most of the suspended loads and extremely low concentration of Zn and Ni were observed downstream of the dam. Dissolved (ranging from 0.062 to 8.0 μg L−1) and particulate (ranging from 12 to 110 mg kg−1) Ni showed similar levels of concentrations during flood and dry seasons, whereas dissolved (ranging from 0.43 to 49 μg L−1) and particulate (ranging from 54 to 1100 mg kg−1) Zn were slightly and much lower in the flood season than dry season, respectively. This was attributed to the increased water discharge during the flood season causing a dilution effect and sediment resuspension. In the flood season, average concentrations of Zn and Ni were higher in the main channel than in tributaries, due to soil erosion and mining activities providing the dominant inputs. The situation was opposite in the dry season, attributed to the contribution of municipal sewage, industrial activities, and waste disposal. During the flood season, dissolved Zn and Ni concentrations were negatively correlated with pH. Water and suspended particulate matter (SPM) from the upper reaches, middle reaches, and lower reaches of the Yangtze River were characterized by their Zn and Ni concentrations. The Panzhihua, Nanling and Tongling mining areas were considered as the most important source zones of particulate Zn and Ni. The Chongqing region, Wuhan region and the Yangtze River Delta provided most of the dissolved Zn and Ni inputs into the river. Annual net flux of Zn (10–72 × 105 kg a−1) and Ni (5.0–19 × 105 kg a−1) in each source zone were estimated according to their respective influent and effluent fluxes. Contributions of the source zones to Zn and Ni transport decreased from the upper reaches to the lower reaches. 相似文献
2.
《Applied Geochemistry》2004,19(8):1255-1293
In order to investigate the mechanism of As release to anoxic ground water in alluvial aquifers, the authors sampled ground waters from 3 piezometer nests, 79 shallow (<45 m) wells, and 6 deep (>80 m) wells, in an area 750 m by 450 m, just north of Barasat, near Kolkata (Calcutta), in southern West Bengal. High concentrations of As (200–1180 μg L−1) are accompanied by high concentrations of Fe (3–13.7 mg L−1) and PO4 (1–6.5 mg L−1). Ground water that is rich in Mn (1–5.3 mg L−1) contains <50 μg L−1 of As. The composition of shallow ground water varies at the 100-m scale laterally and the metre-scale vertically, with vertical gradients in As concentration reaching 200 μg L−1 m−1. The As is supplied by reductive dissolution of FeOOH and release of the sorbed As to solution. The process is driven by natural organic matter in peaty strata both within the aquifer sands and in the overlying confining unit. In well waters, thermo-tolerant coliforms, a proxy for faecal contamination, are not present in high numbers (<10 cfu/100 ml in 85% of wells) showing that faecally-derived organic matter does not enter the aquifer, does not drive reduction of FeOOH, and so does not release As to ground water.Arsenic concentrations are high (≫50 μg L−1) where reduction of FeOOH is complete and its entire load of sorbed As is released to solution, at which point the aquifer sediments become grey in colour as FeOOH vanishes. Where reduction is incomplete, the sediments are brown in colour and resorption of As to residual FeOOH keeps As concentrations below 10 μg L−1 in the presence of dissolved Fe. Sorbed As released by reduction of Mn oxides does not increase As in ground water because the As resorbs to FeOOH. High concentrations of As are common in alluvial aquifers of the Bengal Basin arise because Himalayan erosion supplies immature sediments, with low surface-loadings of FeOOH on mineral grains, to a depositional environment that is rich in organic mater so that complete reduction of FeOOH is common. 相似文献
3.
《Comptes Rendus Geoscience》2014,346(1-2):28-36
There is a lack of studies devoted to coarse particulate matter (CPM) in estuaries, although this fraction can disturb activities that filter large volumes of water, such as industrial or fishery activities. In the macrotidal and highly-turbid Gironde Estuary, a monthly sampling of CPM was performed in 2011 and 2013 at two stations in the Turbidity Maximum Zone (TMZ) to understand its seasonal, tidal and hydrological dynamics. Regardless of the season and station, low quantities of CPM (few g m−3) were observed in comparison with suspended particulate matter (several 103 g m−3). The highest concentrations were consistently recorded in bottom waters and at the upstream station. Whereas there is no clear link between the CPM present in the column water and spring or neap tides, an increase in the CPM size has been identified at the two stations after a flood event, fact potentially critical regarding filtering functioning of estuarine activities. 相似文献
4.
《Applied Geochemistry》2006,21(7):1240-1247
This paper reports the abundance of elemental S in drain sediments associated with acid sulfate soils. The sediments exhibited near-neutral pH (5.97–7.27), high concentrations of pore-water Fe2+ (1.37–15.9 mM) and abundant oxalate-extractable Fe (up to 4300 μmol g−1). Maximum acid-volatile sulfide (AVS) concentrations in each sediment profile were high (118–1019 μmol g−1), with AVS often exceeding pyrite-S. Elemental S occurred at concentrations of 13–396 μmol g−1, with the higher concentrations exceeding previous concentrations reported for other sedimentary systems. Up to 62% of reduced inorganic S near the sediment/water interface was present as elemental S, due to reaction between AVS and oxidants such as O2 and Fe(III). Significant correlation (r = 0.74; P < 0.05) between elemental S and oxalate-extractable Fe(III) is indicative of elemental S formation by in situ oxidation of AVS. The results indicate that AVS oxidation in near-surface sediments is dynamic in acidified coastal floodplain drains, causing elemental S to be a quantitatively important intermediate S fraction. Transformations of elemental S may therefore strongly influence water quality in ASS landscapes. 相似文献
5.
The isotopic composition of water and dissolved Sr as well as other geochemical parameters at the 2516 m deep Outokumpu Deep Drill Hole, Finland were determined. The drill hole is hosted by Palaeoproterozoic turbiditic metasediments, ophiolite-derived altered ultramafic rocks and pegmatitic granitoids. Sodium–Ca–Cl and Ca–Na–Cl-rich waters (total dissolved solids up to ca. 70 g L−1) containing significant amounts of gas, mainly CH4 (up to 32 mmol L−1), N2 (up to 10 mmol L−1), H2 (up to 3.1 mmol L−1) and He (up to 1.1 mmol L−1) discharge from fracture zones into the drill hole. This water is distinct from the shallow fresh groundwater of the area, and has an isotopic composition typical of shield brines that have been modified during long-term water–rock interaction. Based on water stable isotopes and geochemistry, the drill hole water profile can be divided into five water types, each discharging from separate fracture systems and affected by the surrounding rocks. The δ2H varies from −90‰ to −56‰ (VSMOW) and δ18O from −13.5‰ to −10.4‰ (VSMOW), plotting clearly above the Global and Local Meteoric Water Lines on a δ2H vs. δ18O diagram. The 87Sr/86Sr ratios range between 0.72423 and 0.73668. Simple two-component mixing between 2H and 18O rich end-member brine and meteoric water cannot explain the water stable isotopic composition and trends observed. Instead, hydration of silicates by ancient groundwaters recharged under different climatic conditions, warmer than at present, is the most likely mechanism to have caused the variation of the δ2H and δ18O values. Water types correlate with changes in microbial communities implying that different ecosystems occur at different depths. The different water types and microbial populations have remained isolated from each other and from the surface for long periods of time, probably tens of millions of years. 相似文献
6.
《Applied Geochemistry》2005,20(5):961-972
The temperature dependence of the self-diffusion of HTO, 22Na+ and 36Cl− in Opalinus Clay (OPA) was studied using a through-diffusion technique, in which the temperature was gradually increased in the steady state phase of the diffusion. The measurements were done on samples from two different geological locations. The dependence of the effective diffusion coefficient on temperature was found to be of an Arrhenius type in the temperature range between 0 and 70 °C. A slight difference between the two locations could be observed. The average value of the activation energy of the self-diffusion of HTO in OPA was 21.1 ± 1.6 kJ mol−1, and 21.0 ± 3.5 and 19.4 ± 1.5 kJ mol−1 for 22Na+ and 36Cl−, respectively. The measured values for HTO are slightly higher than the values found for the bulk liquid water (HTO: 18.8 ± 0.4 kJ mol−1). This indicates that the structure of the confined water in OPA might be slightly different from that of bulk liquid water. Also for Na+ and Cl−, slightly higher values than in bulk liquid water (Na+: 18.4 kJ mol−1; Cl−: 17.4 kJ mol−1) were observed.The Stokes–Einstein relationship, based on the temperature dependency of the viscosity of bulk water, could not be used to describe the temperature dependence of the diffusion of HTO in OPA. This additionally indicates the slightly different structure of the pore water in OPA. 相似文献
7.
《Applied Geochemistry》2006,21(10):1760-1780
Sulfide-rich mine tailings in Adak that are exposed to weathering cause acid mine drainage characterized by low pH (2–4) and high SO4 (up to 800 mg L−1). Surface water, sediment and soil samples collected in this study contain higher concentrations of As, Cu, Fe and Zn, compared to the target and/or intervention limits set by international regulatory agencies. In particular, high As concentrations in water (up to 2900 μg L−1) and sediment (up to 900 mg kg−1) are of concern. There is large variability in trace element concentrations, implying that both physical (grain size) and chemical factors (pH, secondary phases as sulfides, Al-oxides or clay minerals) play an important role in their distribution. The low pH keeps the trace elements dissolved, and they are transported farther downstream. Trace element partition coefficients are low (log Kd = 0.3–4.3), and saturation indices calculated with PHREEQC are <0 for common oxide and sulfidic minerals. The sediment and soil samples indicate an enhanced pollution index (up to 17), and high enrichment factors for trace elements (As up to 38,300; Zn up to 800). Finally, leaves collected from different plant types indicate bioaccumulation of several elements (As, Al, Cu, Fe and Zn). However, some of the plants growing in this area (e.g., Salix, Equisétum) are generally resistant to metal toxicity, and hence, liming and phytoremediation could be considered as potential on-site remediation methods. 相似文献
8.
《Applied Geochemistry》2006,21(6):1044-1063
A suite of trace metals was analyzed in water and sediment samples from the Blesbokspruit, a Ramsar certified riparian wetland, to assess the impact of mining on the sediment quality and the fate of trace metals in the environment. Limited mobility of trace metals was observed primarily because of their high partition coefficient in alkaline waters. Nickel was most mobile with a mean Kd of 103.28 L kg−1 whereas Zr was least mobile with a mean Kd of 105.47 L kg−1. The overall trace metal mobility sequence, derived for the Blesbokspruit, in increasing order, is: Zr < Cr < Pb < Ba < V < Cu < Zn < Sr < Mn < U < Mo < Co < Ni. Once removed from the solution, most trace metals were preferentially associated with the carbonate and Fe–Mn oxide fraction followed by the exchangeable fraction of the sediments. Organic C played a limited role in trace metal uptake. Only Cu was primarily associated with the organic fraction whereas Ti and Zr were mostly found in the residual fraction. Compared to their regional background, Au and Ag were most enriched, at times by a factor of 20–400, in the sediments. Significant enrichment of U, Hg, V, Cr, Co, Cu and Zn was also observed in the sediments.The calculated geoaccumulation indices suggest that the sediments are very lightly to lightly polluted with respect to most trace metals and highly polluted with respect to Au and Ag. The metal pollution index (MPI) for the 20 sampled sites varied between 2.9 and 45.7. The highest MPI values were found at sites that were close to tailings dams. Sediment eco-toxicity was quantified by calculating the sediment quality guideline index (SQG-I). The calculated SQG-I values (0.09–0.69) suggest that the sediments at the study area have low to moderate potential for eco-toxicity. 相似文献
9.
The concentration and the role of colloids in the transport of elements in the vicinity of a fossil reactor at Bangombé, Gabon, were assessed. Colloid sampling was conducted in seven boreholes around and in the extinguished natural reactor. The ground waters are of Na–Mg–Ca–HCO3 type, with variable salinities, pH 4.6–6.8 and anaerobic Eh values. Filtered ground water and colloid samples were taken from the reactor and the surroundings. Filtered fluids and colloid samples collected on membranes and resuspended in solution were analysed by ICP-MS and ICP-AES in order to examine the element association in the colloid phase within the size range 3000 to 400 to 50 nm. The colloid concentrations for the size 400 to 50 nm range from 80 to 300 ng ml−1. They consist of silica particles associated with ferrihydrite coated with organics. Trace element results show that metals including Pb, Sc, Y, La, Ce, Pr, Nd, Bi, Th and U are associated to various degrees with the colloid phase. The distribution ratios of these trace elements between the water and the colloid phase (Kp) were experimentally determined. The high Pb distribution ratios of 10+7 ml g−1 are specifically discussed. Values range from 10+6 to 10+5 ml g−1for the trivalent elements (Sc, Y, La, Ce, … , Bi). For uranium, a Kp of the order of 10+5 ml g−1 may be calculated and compared with data gained using the surface complexation model. These Kp values suggest that the uranium is partially sorbed or associated with ground water colloids. Measurements from the reactor zone show that about 2–4% of the uranium is associated with the colloid phase, which contributes partially to the uranium transport. The rather low colloid concentrations are due to the relatively high concentrations of Ca, Mg and Na in these quasi-neutral waters. These soluble elements contribute to the attachment of the colloids, restricting their transport. This indicates that the colloid phase may not be an important transport medium for the radionuclides in the Bangombé system if their association is reversible. The Bangombé colloid results are compared with those studied for other systems. 相似文献
10.
This study investigated the distribution and sources of Cd in soils from a Cd-rich area in the Three Gorges region, China. The results showed that in the study area arable soils contain 0.42–42 mg kg−1 Cd with 0.12–8.5 mg kg−1 in the natural soils, corresponding to high amounts of Cd (0.22–42 mg kg−1) in outcropping sedimentary rocks in the area. Both lognormal distribution and enrichment factor (EF) plots were applied in an attempt to distinguish between geogenic and anthropogenic origins of Cd in the local soils. The lognormal distribution plots illustrated that geogenic sources dominated in soils with low and moderate Cd concentrations (<8.5 mg kg−1), whereas anthropogenic sources (agricultural activities, coal mining) significantly elevated Cd contents in some arable soils (>8.5 mg kg−1). The enrichment factor plots illustrated that the majority of the soil samples had EF values of <5, pointing to a geogenic origin of Cd in the soils, whereas some arable soils had EF values >5, pointing to an additional anthropogenic input of Cd to the soils. Sequential extraction results showed that Cd soluble in water and weak acid (water-soluble, exchangeable and carbonate fraction of the soil) accounts for an average of 31% of the total soil Cd, which indicates high potential for Cd mobility and bioavailability. The findings point to a potential health risk from Cd in areas with high geogenic background concentrations of this metal. 相似文献
11.
《Applied Geochemistry》2006,21(11):1837-1854
Total dissolved and total particulate Hg mass balances were estimated during one hydrological period (July 2001–June 2002) in the Thur River basin, which is heavily polluted by chlor-alkali industrial activity. The seasonal variations of the Hg dynamics in the aquatic environment were assessed using total Hg concentrations in bottom sediment and suspended matter, and total and reactive dissolved Hg concentrations in the water. The impact of the chlor-alkali plant (CAP) remains the largest concern for Hg contamination of this river system. Upstream from the CAP, the Hg partitioning between dissolved and particulate phases was principally controlled by the dissolved fraction due to snow melting during spring high flow, while during low flow, Hg was primarily adsorbed onto particulates. Downstream from the CAP, the Hg partitioning is controlled by the concentration of dissolved organic and inorganic ligands and by the total suspended sediment (TSS) concentrations. Nevertheless, the particulate fluxes were five times higher than the dissolved ones. Most of the total annual flux of Hg supplied by the CAP to the river is transported to the outlet of the catchment (total Hg flux: 70 μg m−2 a−1). Downstream from the CAP, the bottom sediment, mainly composed of coarse sediment (>63 μm) and depleted in organic matter, has a weak capacity to trap Hg in the river channel and the stock of Hg is low (4 mg m−2) showing that the residence time of Hg in this river is short. 相似文献
12.
《Chemie der Erde / Geochemistry》2015,75(4):465-474
Drip water, collected above three actively forming stalagmites, has been analyzed and the results discussed using a calcite saturation index versus equilibrium carbon dioxide partial pressure theoretical relationship. Percolating water appears to have been originated from a parent solution in equilibrium with a carbon dioxide rich gas phase having a minimum concentration varying between 15,000 ppmv and 26,000 ppmv while large part of the variability recorded in the cave can be explained by different stage of degassing. Similarly, analyses performed at several cave pools confirm that drip water rapidly achieves equilibrium with the cave atmosphere after impact on the stalagmite apex, while oversaturation is retained longer. Using these boundary conditions, the changes in inorganic carbon concentration in the percolating water have been calculated and converted into fluxes using an average effective infiltration flow estimated from the annual water balance.The predicted flux of carbon dioxide degassing from drip water is in the range of 0.03–0.06 μmol m−2 s−1. This flux has been found to be one of the major sources of carbon dioxide in the cave atmosphere during low ventilation periods. 相似文献
13.
《Chemie der Erde / Geochemistry》2015,75(3):323-334
The current study was designed to investigate the extent and severity of contamination as well as the fractionation of potentially toxic elements (As, Cd, Cr, Cu, Pb, Zn, Ni) in minesoils and agricultural soils around a Pb–Zn mine in central Iran. For this purpose, 20 agricultural soils and eight minesoils were geochemically characterized. Results showed that minesoils contained elevated concentrations of As (12.9–254 mg kg−1), Cd (1.2–55.1 mg kg−1), Pb (137–6239 mg kg−1) and Zn (516–48,889 mg kg−1). The agricultural soils were also polluted by As (5.5–57.1 mg kg−1), Cd (0.2–8.5 mg kg−1), Pb (22–3451 mg kg−1) and Zn (94–9907 mg kg−1). The highest recorded concentrations for these elements were in soils influenced directly by tailing ponds. Chromium, Cu and Ni content in agricultural soils (with average value of 74.1, 34.6 and 50.7 mg kg−1, respectively) were slightly higher than the minesoils (with average value of 54.5, 33.1 and 43.4 mg kg−1, respectively). Sequential extraction data indicated that there were some differences between the speciation of PTEs in soil samples. In the agricultural soils, Zn and Cd were mainly associated with carbonate bound fraction, As and Pb with reducible fraction, Cu with oxidisable fraction and Cr and Ni with residual phase. With respect to mobility factor values, Zn and Cd in the agricultural soils have been found to be the most mobile while As mobility is negligible. Also, the mobility factor of As, Cd and Pb in agricultural soils adjoining tailing ponds was high. In minesoil sample Cd was most abundant in the carbonate form, whereas other studied elements were mainly present in the reducible and residual fractions; therefore, despite the high total concentrations of As, Pb and Zn in the minesoils, the environmental risk of these elements was low. Based on the obtained data, a portion of Cu, Cr and Ni input was from agricultural activities. 相似文献
14.
《Applied Geochemistry》2005,20(3):627-638
Concentrations of total Hg and methylmercury (MMHg) in riparian soil, mine-waste calcine, sediment, and moss samples collected from abandoned Hg mines in Wanshan district, Guizhou province, China, were measured to show regional dispersion of Hg-contamination. High total Hg and MMHg concentrations obtained in riparian soils from mined areas, ranged from 5.1 to 790 mg kg−1 and 0.13 to 15 ng g−1, respectively. However, total Hg and MMHg concentrations in the soils collected from control sites were significantly lower varying from 0.1 to 1.2 mg kg−1 and 0.10 to 1.6 ng g−1, respectively. Total Hg and MMHg concentrations in sediments varied from 90 to 930 mg kg−1 and 3.0 to 20 ng g−1, respectively. Total Hg concentrations in mine-waste calcines were highly elevated ranging from 5.7 to 4400 mg kg−1, but MMHg concentrations were generally low ranging from 0.17 to 1.1 ng g−1. Similar to the high Hg concentrations in soil and sediments, moss samples collected from rocks ranged from 1.0 to 95 mg kg−1 in total Hg and from 0.21 to 20 ng g−1 in MMHg. Elevated Hg concentrations in mosses suggest that atmospheric deposition might be an important pathway of Hg to the local terrestrial system. Moreover, the spatial distribution patterns of Hg contamination in the local environment suggest derivation from historic Hg mining sites in the Wanshan area. 相似文献
15.
《Applied Geochemistry》2005,20(5):989-1016
Groundwater from the Quaternary loess aquifer of La Pampa, central Argentina, has significant problems with high concentrations of As (up to 5300 μg L−1) as well as other potentially toxic trace elements such as F, B, Mo, U, Se and V. Total As concentrations in 45 loess samples collected from the aquifer have a range of 3–18 mg kg−1 with a mean of 8 mg kg−1. These values are comparable to world-average sediment As concentrations. Five samples of rhyolitic ash from the area have As concentrations of 7–12 mg kg−1. Chemical analysis included loess sediments and extracted porewaters from two specially cored boreholes. Results reveal a large range of porewater As concentrations, being generally higher in the horizons with highest sediment As concentrations. The displaced porewaters have As concentrations ranging up to 7500 μg L−1 as well as exceptionally high concentrations of some other oxyanion species, including V up to 12 mg L−1. The highest concentrations are found in a borehole located in a topographic depression, which is a zone of likely groundwater discharge and enhanced residence time. Comparison of sediment and porewater data does not reveal unequivocally the sources of the As, but selective extract data (acid-ammonium oxalate and hydroxylamine hydrochloride) suggest that much of the As (and V) is associated with Fe oxides. Primary oxides such as magnetite and ilmenite may be partial sources but given the weathered nature of many of the sediments, secondary oxide minerals are probably more important. Extract compositions also suggest that Mn oxide may be an As source. The groundwaters of the region are oxidising, with dissolved O2, NO3 and SO4 normally present and As(V) usually the dominant dissolved As species. Under such conditions, the solubility of Fe and Mn oxides is low and As mobilisation is strongly controlled by sorption–desorption reactions. Desorption may be facilitated by the relatively high-pH conditions of the groundwaters in the region (7.0–8.8) and high concentrations of potential competitors (e.g. V, P, HCO3). PHREEQC modelling suggests that the presence of V at the concentrations observed in the Pampean porewaters can suppress the sorption of As to hydrous Fe(III) oxide (HFO) by up to an order of magnitude. Bicarbonate had a comparatively small competitive effect. Oxalate extract concentrations have been used to provide an upper estimate of the amount of labile As in the sediments. A near-linear correlation between oxalate-extractable and porewater As in one of the cored boreholes investigated has been used to estimate an approximate Kd value for the sediments of 0.94 L kg−1. This low value indicates that the sediments have an unusually low affinity for As. 相似文献
16.
A field experiment is being carried out at the Diavik diamond mine in northern Canada to investigate the influence of unsaturated flow behavior on the quality of drainage from mine waste rock piles in a region of continuous permafrost. This paper is part of a series describing processes affecting the weathering of waste rock and transport of reaction products at this site; here the focus is on unsaturated water flow and its role in mass loading. Two 15 m-high instrumented test piles have been built on 60 m by 50 m collection systems, each consisting of lysimeters and a large impermeable high-density polyethylene (HDPE) liner. Collection lysimeters are installed nearby to investigate infiltration in the upper 2 m of the waste rock. Porosity, water retention curves, and hydraulic conductivity functions are estimated from field measurements and for samples ranging in size from 200 cm3 to 16 m3. Net infiltration in 2007 is estimated to have been 37% of the rainfall for mean annual rainfall conditions. Early-season infiltration freezes and is remobilized as the waste rock thaws. Wetting fronts migrate at rates of 0.2–0.4 m d−1 in response to common rainfall events and up to 5 m d−1 in response to intense rainfall. Pore water and non-reactive solutes travel at rates of <10−2 to 3 × 10−2 m d−1 in response to common rainfall events and up to 0.7 m d−1 in response to intense rainfall. Time-varying SO4 mass loading from the base of the test piles is dictated primarily by the flow behavior, rather than by changes in solute concentrations. 相似文献
17.
《Chemie der Erde / Geochemistry》2015,75(2):261-270
The aim of this study was to investigate the accumulation of arsenic (As) in and on roots of Zea mays (maize) and Helianthus annuus (sunflower) by means of synchrotron-based micro-focused X-ray fluorescence imaging (μ-XRF). Plant and soil samples were collected from two field sites in the Hetao Plain (Inner Mongolia, China) which have been regularly irrigated with As-rich groundwater. Detailed μ-XRF element distribution maps were generated at the Fluo-beamline of the Anka synchrotron facility (Karlsruhe Institute of Technology) to assess the spatial distribution of As in thin sections of plant roots and soil particles. The results showed that average As concentrations in the roots (14.5–27.4 mg kg−1) covered a similar range as in the surrounding soil, but local maximum root As concentrations reached up to 424 mg kg−1 (H. annuus) and 1280 mg kg−1 (Z. mays), respectively. Importantly, the results revealed that As had mainly accumulated at the outer rhizodermis along with iron (Fe). We therefore conclude that thin crusts of Fe-(hydr)oxides cover the roots and act as an effective barrier to As, similar to the formation of Fe plaque in rice roots. In contrast to permanently flooded rice paddy fields, regular flood irrigation results in variable redox conditions within the silty and loamy soils at our study site and fosters the formation of Fe-(hydr)oxide plaque on the root surfaces. 相似文献
18.
The Brunhes/Matuyama boundary and magnetic parameters related to climatic changes in Quaternary sediments of Argentina 总被引：1，自引：0，他引：1
《Journal of South American Earth Sciences》2007,23(1):17-29
Rock magnetic properties have been measured in a loess–paleosol sequence in the Gorina Quarry, which previously have been suggested to contain records of the Brunhes and part of the Matuyama polarity chrons. Lowest susceptibility values (below 50 × 10−8 m3/kg) are generally related to intensive weathered horizons, whereas highest values are obtained in loess layers (250 × 10−8 m3/kg) as a result of the greater ferromagnetic content in the parent material. The frequency-dependent part of susceptibility ranges between 0.5% and 6.8%; the higher value was obtained in B horizons of paleosols, which can be attributed to superparamagnetic contributions. Hysteresis loops indicate that the differences in ferrimagnetic and paramagnetic content in the sequence reflect the degree of pedogenesis. The same conclusion can be drawn with isothermal remanent magnetization. This point is relevant for determining past climatic changes because the wind-blown titanomagnetites from Cordillera de Los Andes during glacial periods were altered during interglacial periods. The mode of pedogenesis appears not only to control such alterations but also to produce other magnetic minerals. 相似文献
19.
《Applied Geochemistry》2007,22(4):821-836
High-resolution sampling (every 3 h) of SPM was performed during a major flood event in a heterogeneous, medium scale watershed of the Garonne-Gironde fluvial-estuarine system (the Lot River; A = 10,700 km2; Q = 151 m3/s). Particulate metal and metalloid (Cd, Zn, Pb, Co, Cr, Ni, Mo, V, U, As, Sb, Th) concentrations were compared with monthly data of the same site (Temple site) obtained during 1999–2002. During the flood event, suspended particulate matter (SPM) concentrations closely followed river discharge with a maximum value (1530 mg/L) coinciding with the discharge peak (2970 m3/s). Trace metal/metalloid concentrations showed significant temporal variations and very contrasted responses. Particulate concentrations were similar to baseline values at the beginning of the flood and mostly increased during the event, showing anticlockwise and complex shape hystereses. Comparison of SPM yield (440,000 t) and particulate metal/metalloid fluxes during the flood with annual fluxes (1999–2002) highlights the great importance of major flood events in fluvial transport. Adequate sampling frequency during floods is necessary for reliable annual flux estimates and provides geochemical signals that may greatly improve our understanding of fluvial transport processes. The scenario of SPM and metal and metalloid transport during the flood are reconstructed by combining variations of Zn, Cd and Sb concentrations, concentration ratios (e.g. Zn/Cd, As/Th, Cd/Th) and hysteresis loops. Changes in SPM and metal/metalloid transport during distinct key stages of the flood were attributed to successive dominance of different water masses transporting material from different sources (e.g. industrial point source, bed sediment from reservoirs, plain erosion). Flood management (dam flushing) clearly enhanced the remobilization of up to 30-a old polluted sediment from reservoir lakes. Sediment remobilization accounted for ∼185,000 t of SPM (i.e. 42% of the total SPM fluxes during the flood) and strongly contributed to particulate metal/metalloid transport for Cd (90%), Zn (83%) and Pb (61%). Therefore, flood management needs to be taken into consideration in future models for erosion and pollutant transport. 相似文献
20.
Temporal changes of As concentration in surface waters were observed in some areas of the Czech Republic. Mobilized As originates from past atmospheric deposition. To understand the factors influencing As aqueous concentration and mobility the chemistry and runoff generation of a number of brooks, springs and rivers in the central part of the Elbe River catchment, Czech Republic, were monitored. Seasonal variations of As (from 0.5 to 10.5 μg L−1), Fe (from 0.05 to 3.9 mg L−1) and DOC (dissolved organic C – from 1.2 to 17.5 mg L−1) were observed in monitored stream waters with maximum values of As and Fe in the summer months at pH values 7.6–7.8. The concentration of As in particles with a diameter < 60 μm correlates with the Fe concentration. There is no correlation between Fe and As in filtered samples (<0.45 μm). The As concentration in stream water colloids depends on an increase in DOC concentration and a decrease in ionic strength. The DOC stabilizes As in solution and reduces its re-adsorption on Fe colloids and consequently As concentration in the stream increases. 相似文献