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1.
The adverse impacts of the inorganic labile monomeric Al (Ali) fraction on aquatic organisms have meant that Al (Altot) determination and even speciation has become a routine part of environmental monitoring and assessment. However, if samples are not filtered prior to analysis then particulate Al (Altot(p)) could influence the determination of Altot, and therefore the determination of the more toxicologically important (Ali), both when it is measured analytically or modelled from Altot. This paper shows that the Al/DOC ratio in unfiltered samples can identify the Altot(p) fraction, and thus improve the speciation of Ali. These findings are based on data from a study in a 67 km2 catchment in northern Sweden during the snowmelt-driven spring flood of two consecutive years. Filtered and unfiltered samples were studied to determine the spatial and temporal patterns in Altot(p). The concentrations of Altot(p) were greatest in larger downstream sites where significant silt deposits are located. The sites with no silt in their drainage area showed a mean difference between filtered (Altot(f)) and unfiltered (Altot(uf)) samples of 6%, while sites with silt deposits had a mean difference of 65%. The difference between filtered and unfiltered samples was greatest at peak flow. Spikes in Altot(p) did not behave consistently during fractionation with a cation exchange column, resulting in increases in either measured Ali(f) or non-labile monomeric Al (Alo(f)). Altot(p) spikes were associated with sharp increases in the Al:DOC ratio. The baseflow Al:DOC ratio could be used to model filtered Altot from DOC with a Spearman rho of 0.75.  相似文献   

2.
Due to the importance of colloids in regulating element transport and mobility in aquifers, As distribution in the colloidal fraction needs to be identified in high As groundwaters. Groundwater samples were filtered in the field through a progressively decreasing pore size (0.45 μm, 100, 30, 10, 5 kDa) using a filtration technique under a N2 atmosphere. Major and trace elements and organic C (OC) were measured in (ultra)filtrates. The studied groundwater samples have typical physio-chemical characteristics of the basin waters. Declines in concentrations of alkali (Na, K), alkaline-earth (Mg, Ca, Sr, Ba) elements, Mo, Si and Se during ultrafiltration are smaller relative to other elements. Arsenic, Cu, Cr, U and V are generally about 30% lower in 5 kDa ultrafiltrates in comparison with 0.45 μm filtrates. Around 50% of Fe, OC and Al are bound to colloids with grain size between 5 kDa and 0.45 μm. Two types of colloids, including large-size Fe colloids and small-size organic colloids, have been identified. Results indicate that As would be more likely to be associated with small-size organic colloids than Fe colloids. SEM images and EDS analysis and synchrotron XRF analyses confirm the association of As with NOM with molecular weights of 5-10 kDa. The better correlation between As(V) and OC in the 5-10 kDa fraction indicates that the small-size organic colloids have a greater affinity for As(V) than As(III). Arsenic associated with organic complexes may not be immobilized by adsorption, and, therefore, easily transported in the aquifer. Thus, the presence of As-containing colloidal complexes in high As groundwaters must be considered in the modeling of As transport in the aquifers.  相似文献   

3.
Lanthanoids were studied in a boreal landscape where an abundance of acid sulfate soils and Histosols provide a unique opportunity to increase the understanding of how these metals behave in acidic soils and waters and interact with soil and aqueous organic matter. In the acid sulfate soils lanthanoids are mobile as reflected in high to very high concentrations in soil water and runoff (typically a few mg l−1 but up to 12 mg l−1) and abundant release by several relatively weak extractants (ammonium acetate EDTA, sodium pyrophosphate, hydroxylamine hydrochloride) applied on bulk soil. Normalisation with the lanthanoid pool in the underlying parent materials (sulphide-bearing sediments deposited in brackish-water) and soil water showed that the extensive release/retention in the acidic soil was accompanied by large, and variable, fractionation trends across the lanthanoid series. In low-order streams draining these soils, the lanthanoid concentrations were high and, as indicated by frontal ultrafiltration and geochemical modelling, largely dissolved (<1 kDa) in the form of the species LnSO4+ and Ln3+. In other moderately acidic stream waters (pH 4.3-4.6), organic complexation was predicted to be important in the <1 kDa fraction (especially for the heavy lanthanoids) and strongly dominating in the colloidal phase (1 kDa-0.45 μm). Along the main stem of a stream in focus (catchment area of 223 km2), lanthanoid concentrations increased downstream, in particular during high flows, caused by a downstream increase in the proportion of acid sulfate soils which are extensively flushed during wet periods. The geochemical models applied to the colloidal Ln-organic phase were not successful in predicting the measured fractionation patterns.  相似文献   

4.
Stream water from a stream network of 15 small boreal catchments (0.03-67 km2) in northern Sweden was analyzed for unfiltered (total) and filtered (<0.4 μm) concentrations of iron (Fetot and Fe<0.4) and manganese (Mntot and Mn<0.4). The purpose was to investigate the temporal and spatial dynamics of Fe, Mn and dissolved organic carbon (DOC) as influenced by snow melt driven spring floods and landscape properties, in particular the proportion of wetland area. During spring flood, concentrations of Fetot, Fe<0.4, Mntot, Mn<0.4 and DOC increased in streams with forested catchments (<2% wetland area). In catchments with high coverage of wetlands (>30% wetland area) the opposite behavior was observed. The hydrogeochemistry of Fe was highly dependent on wetlands as shown by the strong positive correlation of the Fetot/Altot ratio with wetland coverage (r2 = 0.89, p < 0.001). Furthermore, PCA analysis showed that at base flow Fetot and Fe<0.4 were positively associated with wetlands and DOC, whereas they were not associated during peak flow at spring flood. The temporal variation of Fe was likely related to varying hydrological pathways. At peak discharge Fetot was associated with variables like silt coverage, which highlights the importance of particulates during high discharge events. For Mn there was no significant correlation with wetlands, instead, PCA analysis showed that during spring flood Mn was apparently more dependent on the supply of minerogenic particulates from silt deposits on the stream banks of some of the streams. The influence of minerogenic particulates on the concentration of, in particular, Mn was greatest in the larger, lower gradient streams, characterized by silt deposits in the near-stream zone. In the small forested streams underlain by till, DOC was of greater importance for the observed concentrations, as indicated by the positive correlation of both Fetot and Fe<0.4 with DOC (r2 = 0.77 and r2 = 0.76, p < 0.001) at the smallest headwater forest site. In conclusion, wetland area and DOC were important for Fe concentrations in this boreal stream network, whereas silt deposits strongly influenced Mn concentrations. This study highlights the importance of studying stream water chemistry from a landscape perspective in order to address future environmental issues concerning mobility of Fe, Mn and associated trace metals.  相似文献   

5.
A dialysis procedure was used to assess the distribution coefficients of ∼50 major and trace elements (TEs) between colloidal (1 kDa–0.22 μm) and truly dissolved (<1 kDa) phases in Fe- and organic-rich boreal surface waters. These measurements allowed quantification of both TE partitioning coefficients and the proportion of colloidal forms as a function of solution pH (from 3 to 8). Two groups of elements can be distinguished according to their behaviour during dialysis: (i) elements which are strongly associated with colloids and exhibit significant increases of relative proportion of colloidal forms with pH increase (Al, Ba, Cd, Co, Cr, Cu, Fe, Ga, Hf, Mn, Ni, Pb, rare earth elements (REEs), Sr, Th, U, Y, Zn, Zr and dissolved organic C) and (ii) elements that are weakly associated with colloids and whose distribution coefficients between colloidal and truly dissolved phases are not significantly affected by solution pH (As, B, Ca, Cs, Ge, K, Li, Mg, Mo, Na, Nb, Rb, Sb, Si, Sn, Ti, V). Element speciation was assessed using the Visual MINTEQ computer code with an implemented NICA-Donnan humic ion binding model and database. The model reproduces quantitatively the pH-dependence of colloidal form proportion for alkaline-earth (Ba, Ca, Mg, Sr) and most divalent metals (Co, Cd, Mn, Ni, Pb, Zn) implying that the complexation of these metals with low molecular weight organic matter (<1 kDa fraction) is negligible. In contrast, model prediction of colloidal proportion (fraction of 1 kDa–0.22 μm) of Cu2+ and all trivalent and tetravalent metals is much higher than that measured in the experiment. This difference may be explained by (i) the presence of strong metal-binding organic ligands in the <1 kDa fraction whose stability constants are several orders of magnitude higher than those of colloidal humic and fulvic acids and/or (ii) coprecipitation of TE with Fe(Al) oxy(hydr)oxides in the colloidal fraction, whose dissolution and aggregation controls the pH-dependent pattern of TE partitioning. Quantitative modeling of metal – organic ligand complexation and empirical distribution coefficients corroborate the existence of two colloidal pools, formerly reported in boreal surface waters: “classic” fulvic or humic acids binding divalent transition metals and alkaline-earth elements and large-size organo-ferric colloids transporting insoluble trivalent and tetravalent elements.  相似文献   

6.
On-site size fractionation of about 40 major and trace elements (TE) was performed on waters from boreal small rivers and their estuaries in the Karelia region of North-West Russia around the “Vetreny Belt” mountain range and in Paanajärvi National Park (Northern Karelia). Samples were filtered in the field using a progressively decreasing pore size (5 μm, 2.5 (3) μm, 0.22 (0.45) μm, 100 kDa, 10 and 1 kDa) by means of frontal filtration and ultrafiltration (UF) techniques and employing in-situ dialysis with 10 and 1 kDa membranes followed by ICP-MS analysis. For most samples, dialysis yields a systematically higher (factor of 2-3) proportion of colloidal forms compared to UF. Nevertheless, dialysis is able to provide a fast and artefact-free in-situ separation of colloidal and dissolved components.Similar to previous studies in European subarctic zones, poor correlation of iron concentration with that of organic carbon (OC) in (ultra)filtrates and dialysates reflect the presence of two pools of colloids composed of organic-rich and Fe-rich particles. All major anions and silica are present as dissolved species (or solutes) passing through the 1-kDa membrane. Size-separation ultrafiltration experiments show the existence of larger or smaller pools of colloidal particles different for each of the considered elements.The effect of rock lithology (acidic versus basic) on the colloidal speciation of TE is seen solely in the increase of Fe and some accompanying TE concentrations in catchment areas dominated by basic rocks compared to granitic catchments. Neither the ultrafiltration pattern nor the relative proportions of colloidal versus truly dissolved TE are affected by the lithology of the underlying rocks: within ±10% uncertainty, the two colloidal (10 kDa-0.22 μm and 1-10 kDa) and the truly dissolved (<1 kDa) pools show no difference in percentage of TE distribution between two types of bedrock lithology. The same conclusion is held for organic- and Fe-rich waters. In contrast, landscape context analysis demonstrated slight dominance, for most TE affected by UF, of large-size colloids (10 kDa-0.22 μm) in rivers and streams and small-size colloids and truly dissolved fractions in swamp stagnant surface waters. This supports the existence of two pathways of colloids formation: during the plant litter degradation in wetland zones and at the redox front in river riparian zone.  相似文献   

7.
Aluminium has received great attention in the second half of the 20th century, mainly in the context of the acid rain problem mostly in forest soils. In this research the effect of land use and depth of the groundwater on Al, pH and DOC concentration in groundwater under Dutch sandy soils has been studied. Both pH and DOC concentration play a major role in the speciation of Al in solution. Furthermore, the equilibrium with mineral phases like gibbsite, amorphous Al(OH)3 and imogolite, has been considered. Agricultural and natural land use were expected to have different effects on the pH and DOC concentration, which in turn could influence the total Al concentration and the speciation of Al in groundwater at different depths (phreatic, shallow and deep). An extensive dataset (n = 2181) from the national and some provincial monitoring networks on soil and groundwater quality was used. Land use type and groundwater depth did influence the pH, and Al and DOC concentrations in groundwater samples. The Al concentration ranged from <0.4 μmol L−1 at pH > 7 to 1941 μmol L−1 at pH < 4; highest Al concentrations were found for natural-phreatic groundwater. The DOC concentration decreased and the median pH increased with depth of the groundwater. Natural-phreatic groundwater showed lower pH than the agricultural-phreatic groundwater. Highest DOC concentrations were found for the agricultural-phreatic groundwater, induced by the application of organic fertilizers. Besides inorganic complexation, the NICA-Donnan model was used to calculate Al3+ concentrations for complexation with DOC. Below pH 4.5 groundwater samples were mainly in disequilibrium with a mineral phase. This disequilibrium is considered to be the result of kinetic constraints or equilibrium with organic matter. Log K values were derived by linear regression and were close to theoretical values for Al(OH)3 minerals (e.g. gibbsite or amorphous Al(OH)3), except for natural-phreatic groundwater for which lower log K values were found. Complexation of Al with DOC is shown to be an important factor for the Al concentrations, especially at high DOC concentrations as was found for agricultural-phreatic groundwater.  相似文献   

8.
Fluorescence characterization of dissolved organic matter (DOM) and measurements of Cr-reducible sulfide (CRS) are presented for 72 coastal marine and estuarine water samples obtained from the USA and Canada. Each sample is identified according to source: terrigenous, autochthonous, wastewater or mixed. Fluorescence data are resolved into contributions from humic, fulvic, tyrosine and tryptophan-like fluorophores. Humic and fulvic-like fluorophores correlate well with dissolved organic C (DOC) (r2 = 0.73 and 0.71, respectively) but tyrosine and tryptophan-like fluorophores show no correlation with DOC. Quality factors are identified by normalization of fluorescence contributions to DOC. Humic and fulvic components show no statistical differences between sources but the amino acid-like fluorescence quality factors show significant variations between source, with highest values for autochthonous sources (0.07 ± 0.01 arbitrary fluorescence units per mg of C) versus low values (0.015 ± 0.005) for terrigenous source waters. CRS concentrations are highly variable from 0.07 ± 0.01 to 7703 ± 98 nM and do no correlate with DOC except when terrigenous source waters (n = 13) are separated out from the total sample set (r2 = 0.55). There is an open question in the literature; does DOC source matter in terms of protective effects towards metal toxicity? Here is shown that DOC molecular-level quality does vary and that this variation is mostly in terms of the contributions of amino acids to total fluorescence.  相似文献   

9.
The Stockholm Humic Model (SHM) and Humic Ion-Binding Models V and VI were compared for their ability to predict the role of dissolved organic matter (DOM) in the speciation of rare earth elements (REE) in natural waters. Unlike Models V and VI, SHM is part of a speciation code that also allows us to consider dissolution/precipitation, sorption/desorption and oxidation/reduction reactions. In this context, it is particularly interesting to test the performance of SHM. The REE specific equilibrium constants required by the speciation models were estimated using linear free-energy relationships (LFER) between the first hydrolysis constants and the stability constants for REE complexation with lactic and acetic acid. Three datasets were used for the purpose of comparison: (i) World Average River Water (Dissolved Organic Carbon (DOC) = 5 mg L−1), previously investigated using Model V, was reinvestigated using SHM and Model VI; (ii) two natural organic-rich waters (DOC = 18-24 mg L−1), whose REE speciation has already been determined with both Model V and ultrafiltration studies, were also reinvestigated using SHM and Model VI; finally, (iii) new ultrafiltration experiments were carried out on samples of circumneutral-pH (pH 6.2-7.1), organic-rich (DOC = 7-20 mg L−1) groundwaters from the Kervidy-Naizin and Petit-Hermitage catchments, western France. The results were then compared with speciation predictions provided by Model VI and SHM, successively. When applied to World Average River Water, both Model VI and SHM yield comparable results, confirming the earlier finding that a large fraction of the dissolved REE in rivers occurs as organic complexes This implies that the two models are equally valid for calculating REE speciation in low-DOC waters at circumneutral-pH. The two models also successfully reproduced ultrafiltration results obtained for DOC-rich acidic groundwaters and river waters. By contrast, the two models yielded different results when compared to newly obtained ultrafiltration results for DOC-rich (DOC > 7 mg L−1) groundwaters at circumneutral-pH, with Model VI predictions being closer to the ultrafiltration data than SHM. Sensitivity analysis indicates that the “active DOM parameter” (i.e., the proportion of DOC that can effectively complex with REE) is a key parameter for both Model VI and SHM. However, a survey of ultrafiltration results allows the “active DOM parameter” to be precisely determined for the newly ultrafiltered waters studied here. Thus, the observed discrepancy between SHM predictions and ultrafiltration results cannot be explained by the use of inappropriate “active DOM parameter” values in this model. Save this unexplained discrepancy, the results presented in this study demonstrate that both Model VI and SHM can provide reliable estimates of REE speciation in organic-rich waters. However, it is essential to know the proportion of DOM that can actively complex REE before running these two speciation models.  相似文献   

10.
Drying induced pH changes were quantified on the surface of Na+, Ca2+, Mg2+ and Al3+ saturated smectite and kaolinite clays. This was achieved using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to measure real time changes to a pH indicator, sorbed to the clay mineral surface, during wetting and drying events. Using this technique it was possible to measure how low the pH of the surface drops during dehydration, the critical water content at which acidification of the surface begins and lastly how reversible the pH decrease is. The results show that only Al3+-smectite shows acidification below pH 4.8 with drying. The pH starts to decrease on the Al3+-smectite surface even when significantly hydrated (gravimetric water content ∼ 125 mg/m2), and falls to between 1.2 and 1.4 when completely air dry. The drying induced pH decrease is completely reversible on rewetting, suggesting large pH oscillations may occur on smectite surfaces with appreciable exchangeable Al3+. Aluminium saturated kaolinite did not show significant acidification in response to drying (pH > 3.5), however, a 0.1 M AlCl3 solution evaporated to a final pH of 2.8. The enhanced acidification observed on an Al-smectite clay compared to a solution containing free Al3+ ions highlights the role of highly charged surfaces in the hydrolysis reaction that occurs within the hydration shell of exchangeable Al3+ ions.  相似文献   

11.
The contents of different organic matter components and dissolved organic matter (DOM) release kinetics of the sediments from the middle and lower reaches of the Yangtze River region were investigated, and their relationships discussed. The results show that organic C (OC) ranged from 8.14 to 43.65 g kg−1, dissolved organic C (DOC) from 0.38 to 1.38 g kg−1, active organic C (AOC) from 1.12 to 4.45 g kg−1, heavy fraction organic C (HFOC) from 6.86 to 39.08 g kg−1, accounting for 2.42-9.34%, 8.66-29.72% and 84.29-93.18% of OC, respectively. With increasing of OC content the ratios of DOC to OC and AOC to OC decreased. The contents of AOC, DOC, light fraction organic C (LFOC) and their contribution ratios to OC in studied sediments were higher than those reported in soils. The DOM release process of the studied sediments includes rapid and slow stages, and the rapid release occurred within 30 min, mainly in 5 min. The DOM release kinetic data in this investigation can be best fitted by the Power Function model. The correlations between total N (TN), total P (TP), OC, DOC, AOC, LFOC, HFOC and the DOM release kinetic parameters (k, c, a, b, rate30) of the sediments were significant. There were also significant correlations between TN, TP, OC, DOC, LFOC and HFOC in sediments. So the DOM release from sediment was not only related to the OC content, but also related to the organic matter composition characteristics, especially the contents of DOC, AOC and LFOC.  相似文献   

12.
The distribution, partition and speciation of mercury (Hg) were studied along the redox gradient of an anthropogenically perturbed tropical estuary, the Sinnamary Estuary in French Guiana. This system is a partially mixed estuary characterized by an anoxic freshwater end-member, while the marine end-member consists of the Amazon Plume.The set up of an artificial oxygenation system in the anoxic freshwater end-member generates sharp gradients of major chemical species (iron, sulfides, etc.) coupled with intense organic matter (OM) turnover. The coexistence of oxygenated waters and dissolved sulfides in an organic rich environment depicts the Upper Sinnamary Estuary (USE: part of Sinnamary Estuary under the tidal influence but upstream of the salt intrusion) as a potential site for Hg methylation. The concentrations of all mercury compounds (HgT) in the unfiltered samples (HgTUNF), in the dissolved (HgTD) and particulate (HgTP) phases of the USE average 11 ± 3, 6 ± 2 and 5 ± 3 (i.e. 600 ± 200 pmol g−1) pmol L−1, respectively. Average concentrations of monomethylmercury (MMHg) in the unfiltered (MMHgUNF), dissolved (MMHgD) and particulate (MMHgP) phases were 3.7 ± 1.0, 2.0 ± 0.9 and 1.8 ± 1.2 (i.e. 220 ± 130 pmol g−1) pmol L−1, respectively. Water oxygenation and sulfides concentrations emerged to play a critical role in controlling MMHg levels. Additionally, iron cycling, acid-base mechanisms, and redox-dependent processes were involved in the MMHg partitioning between phases.Overall, the USE constitutes a biogeochemical reactor that gathers partitioning and methylation processes. The permanent MMHg inputs from the anoxic freshwater end-member combined with the intense endogenous Hg methylation ensures high-MMHg levels in both dissolved and particulate phases. To illustrate, the USE exports 60 ± 20% more MMHgUNF than it imports: 5.5 ± 0.7 vs. 3.5 ± 1.2 kg year−1.  相似文献   

13.
Volcanogenic sediments are typically rich in Fe and Mn-bearing minerals that undergo substantial alteration during early marine diagenesis, however their impact on the global biogeochemical cycling of Fe and Mn has not been widely addressed. This study compares the near surface (0-20 cm below sea floor [cmbsf]) aqueous (<0.02 μm) and aqueous + colloidal here in after ‘dissolved’ (<0.2 μm) pore water Fe and Mn distributions, and ancillary O2(aq), and solid-phase reactive Fe distributions, between two volcanogenic sediment settings: [1] a deep sea tephra-rich deposit neighbouring the volcanically active island of Montserrat and [2] mixed biosiliceous-volcanogenic sediments from abyssal depths near the volcanically inactive Crozet Islands archipelago. Shallow penetration of O2(aq) into Montserrat sediments was observed (<1 cmbsf), and inferred to partially reflect oxidation of fine grained Fe(II) minerals, whereas penetration of O2(aq) into abyssal Crozet sediments was >5 cmbsf and largely controlled by the oxidation of organic matter. Dissolved Fe and Mn distributions in Montserrat pore waters were lowest in the surface oxic-layer (0.3 μM Fe; 32 μM Mn), with maxima (20 μM Fe; 200 μM Mn) in the upper 1-15 cmbsf. Unlike Montserrat, Fe and Mn in Crozet pore waters were ubiquitously partitioned between 0.2 μm and 0.02 μm filtrations, indicating that the pore water distributions of Fe and Mn in the (traditionally termed) ‘dissolved’ size fraction are dominated by colloids, with respective mean abundances of 80% and 61%. Plausible mechanisms for the origin and composition of pore water colloids are discussed, and include prolonged exposure of Crozet surface sediments to early diagenesis compared to Montserrat, favouring nano-particulate goethite formation, and the elevated dissolved Si concentrations, which are shown to encourage fine-grained smectite formation. In addition, organic matter may stabilise authigenic Fe and Mn in the Crozet pore waters. We conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water, which may impact significantly on deep ocean biogeochemistry. Diffusive flux estimates from Montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved Mn to the bottom waters, and therefore a source for the widespread hydrogenous MnOx deposits found in the Caribbean region.  相似文献   

14.
Brazil has extensive sugar cane monocultures, which significantly alter hydrogeochemical material fluxes. We studied dissolved organic matter (OM) fluxes in the Manguaba lagoon-estuary system, which drains a sugar cane monoculture-dominated hinterland and discharges into the Atlantic coastal ocean. The OM fluxes into the lagoon originate from baseflow, field runoff and sugar cane factory effluents. In the study, dissolved organic carbon (DOC) concentration, δ13C DOC and UV absorbance were analysed along a freshwater-seawater salinity gradient that encompasses river (DOC 9-11 mg l−1, δ13C −22.2‰ to −25.5‰); lagoon (4-11 mg l−1, −20.5‰ to −24.8‰); estuary (3-9 mg l−1, −22.6‰ to −25.3‰) and coastal waters (1.64 mg l−1, −21‰) with different intra-seasonal runoff conditions. We used the carbon isotope data to quantify the sugar cane derived DOC. Where river water meets brackish lagoon water, substantial loss of DOC occurs during rainy conditions, when suspended sediment from eroded fields in the river is very high. During dry weather, at much lower suspension levels, DOC increases, however, presumably from addition of photolysed resuspended sedimentary OM. In the estuary, mixing of DOC is strictly conservative. Ca. 1/3 of riverine DOM discharged into the lagoon has a sugar cane source. Within the lagoon on avg. 20% of the bulk DOM is comprised of sugar cane DOM, whereas during heavy rainfall the amount increases to 31%, due to intensified drainage flow and soil erosion. In the estuary, 14-26% is of sugar cane origin. The sugar cane-derived component follows the mixing patterns of bulk DOM.  相似文献   

15.
Forward dissolution rates of Na-Montmorillonite (Wyoming) SWy-2 smectite (Ca0.06Na0.56)[Al3.08Fe(III)0.38Mg0.54] [Si7.93 Al0.07]O20(OH)4 were measured at 25 °C in a mixed-flow reactor equipped with interior dialysis compartment (6-8 kDa membrane) as a function of pH (1-12), dissolved carbonate (0.5-10 mM), phosphate (10−5 to 0.03 M), and nine organic ligands (acetate, oxalate, citrate, EDTA, alginate, glucuronic acid, 3,4-dihydroxybenzoic acid, gluconate, and glucosamine) in the concentration range from 10−5 to 0.03 M. In organic-free solutions, the Si-based rates decrease with increasing pH at 1 ? pH ? 8 with a slope close to −0.2. At 9 ? pH ? 12, the Si-based rates increase with a slope of ∼0.3. In contrast, non-stoichiometric Mg release weakly depends on pH at 1 ? pH ? 12 and decreases with increasing pH. The empirical expression describing Si-release rates [R, mol/cm2/s] obtained in the present study at 25 °C, I = 0.01 M is given by
  相似文献   

16.
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   

17.
Arsenic and Sb are common mine-water pollutants and their toxicity and fate are strongly influenced by redox processes. In this study, simultaneous Fe(II), As(III) and Sb(III) oxidation experiments were conducted to obtain rates under laboratory conditions similar to those found in the field for mine waters of both low and circumneutral pH. Additional experiments were performed under abiotic sterile conditions to determine the biotic and abiotic contributions to the oxidation processes. The results showed that under abiotic conditions in aerated Fe(III)–H2SO4 solutions, Sb(III) oxidizes slightly faster than As(III). The oxidation rates of both elements were accelerated by increasing As(III), Sb(III), Fe(III), and Cl− concentrations in the presence of light. For unfiltered circumneutral water from the Giant Mine (Yellowknife, NWT, Canada), As(III) oxidized at 15–78 μmol/L/h whereas Sb(III) oxidized at 0.03–0.05 μmol/L/h during microbial exponential growth. In contrast, As(III) and Sb(III) oxidation rates of 0.01–0.03 and 0.01–0.02 μmol/L/h, respectively, were obtained in experiments performed with acid unfiltered mine waters from the Iberian Pyritic Belt (SW Spain). These results suggest that the Fe(III) formed from microbial oxidation abiotically oxidized As(III) and Sb(III). After sterile filtration of both mine water samples, neither As(III), Sb(III), nor Fe(II) oxidation was observed. Hence, under the experimental conditions, bacteria were catalyzing As and Sb oxidation in the Giant Mine waters and Fe oxidation in the acid waters of the Iberian Pyrite Belt.  相似文献   

18.
The distribution and speciation of mercury (Hg) in the water column, the inputs (wet deposition and tributaries) and the outputs (atmospheric evasion and outlet) of an artificial partially anoxic tropical lake (Petit-Saut reservoir, French Guiana) were investigated on a seasonal basis in order to appraise the cycling and transformations of this metal. The total mercury (HgT) concentrations in the oxygenated epilimnetic waters averaged 5 ± 3 pmol L−1 in the unfiltered samples (HgTUNF) and 4 ± 2 pmol L−1 in the dissolved (HgTD) phase (<0.45 μm). On average, the monomethylmercury (MMHg) constituted 8%, 40% and 18% of the HgT in the dissolved phase, the particulate suspended matter and in the unfiltered samples, respectively. Covariant elevated concentrations of particulate MMHg and chlorophyll a in the epilimnion suggest that phytoplankton is an active component for the MMHg transfer in the lake. In the anoxic hypolimnion the HgTUNF averages 13 ± 6 pmol L−1 and the HgTD 8 ± 4 pmol L−1. The averages of MMHgP and MMHgD in hypolimnetic waters were two and three times the corresponding values of the epilimnion, 170 ± 90 pmol g−1 and 0.9 ± 0.5 pmol L−1, respectively. In the long dry and wet seasons, at the flooded forest and upstream dam sampling stations, the vertical profiles of MMHgD concentrations accounted for two distinct maxima: one just below the oxycline and the other near the benthic interface. Direct wet atmospheric deposition accounted for 14 moles yr−1 HgTUNF, with 0.7 moles yr−1 as MMHgUNF, while circa 76 moles yr−1 of HgTUNF, with 4.7 moles yr−1 as MMHgUNF, coming from tributaries. Circa 78 moles (∼17% as MMHg) are annually exported through the dam, while 23 moles yr−1 of Hg0 evolve in the atmosphere. A mass balance calculation suggests that the endogenic production of MMHgUNF attained 8.1 moles yr−1, corresponding to a methylation rate of 0.06% d−1. As a result, the Petit-Saut reservoir is a large man-made reactor that has extensively altered mercury speciation in favor of methylated species.  相似文献   

19.
《Applied Geochemistry》2004,19(1):153-162
In aquatic systems, the bioavailability of an element to microorganisms is greatly influenced by its chemical speciation. The goal of this work was to assess metal toxicity to a green algae (Pseudokirchneriella subcapitata) and a bacterium (Vibrio fisheri) as a function of size fractionation and chemical speciation (using the program MINTEQA2) in contaminated water of the Upper Vistula River. Water samples were collected at 1 reference site, 4 polluted sites and one polluted site on the Vistula's main tributary, the Przemsza River. Toxicity measurements were performed on unfiltered samples and, total dissolved (<1.2 μm), and truly dissolved (<1 kDa) fractions. Trace metal (Cd, Co, Cr, Cu, Mn, Pb, Zn) concentrations were measured in these samples and also in the colloidal fraction (1 kDa–1.2 μm). At the reference site, the low metal concentrations were in agreement with the absence of measurable toxicity. In the polluted section of the river, free metal concentrations were largely below the potential toxic levels for bacteria, which was in agreement with the absence of toxicity. Although Zn2+ was at potentially toxic-level concentrations in total dissolved and truly dissolved fractions in the polluted riverine section, toxicity for algae was observed, only in truly dissolved fractions from two stations. The absence of toxicity in most samples was related to metal association with particles and with low molecular weight ligands as well as the presence of organic ligands (phenol). The reason for toxic effects in two ultrafiltered samples is not clear, but may be related to the elimination of the colloidal organic fraction and thus the eradication of its protective effect occurring in natural samples.  相似文献   

20.
《Applied Geochemistry》1999,14(3):395-407
An ultrafiltration procedure has been developed to study the interaction between organic C and Hg species in natural waters, and a pilot study was conducted in the surface waters of the Florida Everglades. Compared to total Hg, CH3Hg shows different distribution patterns in the suspended particulate, colloidal, and truly dissolved phases. Colloidal forms (0.22 μm, 3 kDa) contain the majority of the total dissolved Hg, while the amount found in the truly dissolved fraction (<3 kDa) is small (about 10%). However, CH3Hg, which shows strong binding capability with low molecular-weight dissolved organic C, is present almost entirely in the lower molecular-weight fraction of the colloids and in the truly dissolved fraction. Quantitative CH3Hg data correlate well with those for dissolved organic C, an indication that the organic matter present in the system plays an important role in the fate and transport of organomercury. Distribution coefficients between water and the different-sized fractions of the dissolved organic C were determined for both total Hg and CH3Hg. Results for total Hg were in general agreement with other reports resulting from studies of molecular size distributions of total Hg in freshwater systems. This is, to the best of our knowledge, the first report of such distribution profiles for CH3Hg between different-sized fractions of dissolved organic C in natural waters.  相似文献   

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