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1.
《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   

2.
Reactive dissolved Hg (HgR), non-reactive dissolved Hg (HgNR), particulate Hg (HgP), dissolved organic C (DOC), particulate organic C (POC), salinity and other interpretative parameters were determined in water samples collected in the North Channel and in adjacent areas of the Tagus estuary (Portugal). Higher concentrations of both dissolved and particulate Hg in the North Channel indicate a pollution source and raise the possibility of Hg escaping to adjacent areas by tidal action. This transport was confirmed by the increase of HgR with salinity and HgNR with DOC, along a longitudinal axis paralleling the North Channel. Apparently, Hg leaving this channel is progressively complexed by inorganic and organic ligands. Near the mouth of the estuary, values decreased reflecting dilution with seawater. Moreover the HgP:POC ratio also increased seaward, suggesting mixing with Hg enriched particles that escaped the North Channel, or incorporation of dissolved Hg species in river-derived particles. These results suggest that the pathway of anthropogenic Hg in contaminated waters may be identified by their enrichment in organic matter, both in the dissolved and particulate fraction.  相似文献   

3.
Considerable fractions of the Hg content of lake and river systems in Scandinavia are discharged from the soil of the catchments. An important soil type in Scandinavia is the iron–humus podzol. The sorption characteristics of this soil type for inorganic Hg(II) and monomethyl mercury were investigated by batch experiments. The solubility of Hg2+ and CH3Hg+ in the soil horizons containing organic matter increases with increasing pH of the soil solution by favoring the formation of solute organic matter–mercury complexes. While the solubility of Hg2+ is strongly dependent on complexation to dissolved organic matter, the solubility of CH3Hg+ is more dependent on ion exchange. The concentration of solute inorganic Hg(II) increased with increasing temperature probably because of an increase in the concentration of dissolved organic carbon. There was no effect of temperature on the concentration of solute CH3Hg+. At pH values where inorganic mercury–hydroxo complexes are formed, inorganic Hg(II) is efficiently sorbed to the metal oxides of the mineral soil. The soil–water distributions of inorganic Hg(II) in the different soil horizons were described by Freundlich isotherms or linear isotherms for common and contaminated mercury contents in the soils.  相似文献   

4.
The effects of photoirradiation of dissolved organic matter (DOM) on its subsequent adsorption to the Fe(III)oxyhydroxide mineral goethite were investigated at 22°C in 0.10 mol L−1 NaClO4 solutions at pH 3.5 and 5.5, Photoirradiation of DOM decreased the abundance of high molecular-weight components and formed new lower molecular-weight components, including low molecular weight carboxylic acids (i.e., formic, malonic, and acetic acids). Adsorption of non-irradiated DOM decreased from pH 3.5 to 5.5 and was dominated by the intermediate molecular weight (1251-3750 Da) fraction, although the 451-1250 and 3751-11350 Da fractions also contributed to adsorption at pH 3.5. Irradiation resulted in a substantial decrease in DOM adsorption affinity at pH 3.5, primarily due to loss of components in the 1251-3750 and 3751-11350 Da fractions. Irradiation resulted in only a small decrease in DOM adsorption affinity at pH 5.5; the loss of components in the 3751-11350 Da fraction upon irradiation had little effect on adsorption because they played little or no role in the non-irradiated sample at this pH. Irradiation of DOM also affected its interactions with Fe in solution and the solution iron(II)/iron(III) speciation. The combined effects of irradiation followed by adsorption produced DOM that was lower in molecular weight and had a decreased UV-Vis absorptivity than either process, alone. Together, these two processes are likely to have important environmental consequences in terms of UV penetration of surface waters, contaminant mobility, and DOM bioavailability.  相似文献   

5.
《Applied Geochemistry》2004,19(10):1581-1599
The association of dissolved 90Sr, 239,240Pu and 241Am with natural colloids was investigated in surface waters in the Chernobyl nuclear accident area. A 4-step ultrafiltration (UF) study (<1 kilodaltons (Da), 1–10 kDa, 10–100 kDa, 100 kDa<) showed that 49–83% of 239,240Pu and 76% of 241Am are distributed in colloids of the two size fractions larger than 10 kDa (nominal molecular weight limit of the filter, NMWL), while 90Sr was found exclusively (85–88%) in the lowest molecular size fraction below 1 kDa (NMWL) for the Sahan River water at the highly contaminated area close to the Chernobyl Nuclear Power Plant (ChNPP). Consistent results were obtained by 2-step fractionation (larger than and smaller than 10 kDa (NMWL)) for river and lake waters including other locations within about 30 km away from ChNPP. It is likely that Pu and Am isotopes were preferentially associated with dissolved organic matter of high molecular size, as suggested by the fact that (i) only a few inorganic elements (Mg, Ca, Sr, Si, Mn, Al) were found in the colloidal size ranges, and (ii) the positive correlation between dissolved organic C (DOC) concentrations and UV absorbance at 280 nm, a broad absorption peak characteristic of humic substances (HS) was found. A model calculation on the complexation of Pu and Am with HS as an organic ligand suggests that the complexed form could be dominant at a low DOC concentration of 1 mgC L−1, that is commonly encountered as a lower limit in fresh surface water. The present results suggest the general importance of natural organic colloids in dictating the chemical form of actinides in the surface aquatic environment.  相似文献   

6.
This study deals with the weathering processes operating at the scale of a small catchment (Nsimi-Zoetele, Cameroon) and is focused on the role of organic colloids on mineral weathering and transport of elements in natural waters. Samples of river, spring and groundwaters from Nsimi-Zoetele were filtered through membranes of decreasing pore size (0.22 μm, 0.025 μm, or: 300,000 Da, 5000 Da) to separate colloidal fractions from the truly dissolved one. Major and trace elements and dissolved organic carbon (DOC) were analysed in each fraction. Two kinds of waters can be distinguished in the catchment: clear and coloured waters. Clear waters exhibit low concentrations of major and trace elements and DOC. Elements are carried in these solutions in a true dissolved form except Al and rare earth elements (REEs). By contrast, the higher abundances of Al, Fe and trace elements in coloured waters are controlled by the colloidal fraction. Thermodynamic equilibrium calculations show that clear waters are in equilibrium with kaolinite and iron oxi-hydroxide which are major minerals in the weathered soil. For coloured waters, the aqueous speciation of Ca, Mg, Cu, Fe, Al, La and Th was calculated taking into account the complexes with humic acids. Speciation calculations for Cu, Fe, Al, La, Th show a strong complexation with humic acids, in good agreement with the results of the filtration experiments. By contrast, although filtration experiments show a strong control of major cations by organic matter (for example 75% for Ca), speciation calculations reveal that their complexes with humic ligands do not exceed a few percent of total dissolved elements. This discrepancy is explained as an artefact induced by the organic colloids and occurring during the filtration procedure. Finally, both filtration experiments and speciation calculations show that organic matter plays an important role in natural DOC-rich waters. Organic acids increase significantly the dissolution rates of silicates and oxi-hydroxides and thus the amounts of solutes and of complexed elements leaving the catchment.  相似文献   

7.
《Applied Geochemistry》1993,8(5):483-493
Information regarding the origin, composition and transport of natural dissolved organic carbon (DOC) in groundwater is necessary to understand the transport of metals and organic pollutants, as well as for the use of14C in DOC as an isotopic groundwater dating method. Previous research in several groundwater systems has suggested soil organic C is the predominant source of high molecular weight DOC to the subsurface. Through the use of stable isotopes,14C and geochemical analyses, this study shows that significant concentrations of DOC and CH4 in a regional confined aquifer can be generated in situ from subsurface sedimentary organic sources. The DOC and CH4 produced is a combined result of degradation of buried peats and bacterial action, resulting in high DOC concentrations and strongly methanogenic conditions in the aquifer. The DOC and CH4 comprise, on average, nearly 50% of the total dissolved C pool in the central part of the aquifer. Methanogenic conditions complicate isotopic groundwater dating by the conventional dissolved inorganic carbon (DIC) method. Estimates of isotopic groundwater residence time using DOC14C data are proposed by the application of14C isotope and mass balance corrections.  相似文献   

8.
Humic Ion-Binding Model V, which focuses on metal complexation with humic and fulvic acids, was modified to assess the role of dissolved natural organic matter in the speciation of rare earth elements (REEs) in natural terrestrial waters. Intrinsic equilibrium constants for cation-proton exchange with humic substances (i.e., pKMHA for type A sites, consisting mainly of carboxylic acids), required by the model for each REE, were initially estimated using linear free-energy relationships between the first hydrolysis constants and stability constants for REE metal complexation with lactic and acetic acid. pKMHA values were further refined by comparison of calculated Model V “fits” to published data sets describing complexation of Eu, Tb, and Dy with humic substances. A subroutine that allows for the simultaneous evaluation of REE complexation with inorganic ligands (e.g., Cl−, F−, OH−, SO42−, CO32−, PO43−), incorporating recently determined stability constants for REE complexes with these ligands, was also linked to Model V. Humic Ion-Binding Model V’s ability to predict REE speciation with natural organic matter in natural waters was evaluated by comparing model results to “speciation” data determined previously with ultrafiltration techniques (i.e., organic acid-rich waters of the Nsimi-Zoetele catchment, Cameroon; dilute, circumneutral-pH waters of the Tamagawa River, Japan, and the Kalix River, northern Sweden). The model predictions compare well with the ultrafiltration studies, especially for the heavy REEs in circumneutral-pH river waters. Subsequent application of the model to world average river water predicts that organic matter complexes are the dominant form of dissolved REEs in bulk river waters draining the continents. Holding major solute, minor solute, and REE concentrations of world average river water constant while varying pH, the model suggests that organic matter complexes would dominate La, Eu, and Lu speciation within the pH ranges of 5.4 to 7.9, 4.8 to 7.3, and 4.9 to 6.9, respectively. For acidic waters, the model predicts that the free metal ion (Ln3+) and sulfate complexes (LnSO4+) dominate, whereas in alkaline waters, carbonate complexes (LnCO3+ + Ln[CO3]2−) are predicted to out-compete humic substances for dissolved REEs. Application of the modified Model V to a “model” groundwater suggests that natural organic matter complexes of REEs are insignificant. However, groundwaters with higher dissolved organic carbon concentrations than the “model” groundwater (i.e., >0.7 mg/L) would exhibit greater fractions of each REE complexed with organic matter. Sensitively analysis indicates that increasing ionic strength can weaken humate-REE interactions, and increasing the concentration of competitive cations such as Fe(III) and Al can lead to a decrease in the amount of REEs bound to dissolved organic matter.  相似文献   

9.
Mercury is a global contaminant of concern due to its transformation by microorganisms to form methylmercury, a toxic species that accumulates in biological tissues. The effect of dissolved organic matter (DOM) isolated from natural waters on reactions between mercury(II) (Hg) and sulfide (S(-II)) to form HgS(s) nanoparticles across a range of Hg and S(-II) concentrations was investigated. Hg was equilibrated with DOM, after which S(-II) was added. Dissolved Hg (Hgaq) was periodically quantified using ultracentrifugation and chemical analysis following the addition of S(-II). Particle size and identity were determined using dynamic light scattering and X-ray absorption spectroscopy. S(-II) reacts with Hg to form 20 to 200 nm aggregates consisting of 1-2 nm HgS(s) subunits that are more structurally disordered than metacinnabar in the presence of 2 × 10−9 to 8 × 10−6 M Hg and 10 (mg C) L−1 DOM. Some of the HgS(s) nanoparticle aggregates are subsequently dissolved by DOM and (re)precipitated by S(-II) over periods of hours to days. At least three fractions of Hg-DOM species were observed with respect to reactivity toward S(-II): 0.3 μmol reactive Hg per mmol C (60 percent), 0.1 μmol per mmol C (20 percent) that are kinetically hindered, and another 0.1 μmol Hg per mmol C (20 percent) that are inert to reaction with S(-II). Following an initial S(-II)-driven precipitation of HgS(s), HgS(s) was dissolved by DOM or organic sulfur compounds. HgS(s) formation during this second phase was counterintuitively favored by lower S(-II) concentrations, suggesting surface association of DOM moieties that are less capable of dissolving HgS(s). DOM partially inhibits HgS(s) formation and mediates reactions between Hg and S(-II) such that HgS(s) is susceptible to dissolution. These findings indicate that Hg accessibility to microorganisms could be controlled by kinetic (intermediate) species in the presence of S(-II) and DOM, undermining the premise that equilibrium Hg species distributions should correlate to the extent or rate of Hg methylation in soils and sediments.  相似文献   

10.
We combined synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy and binding affinity studies to determine the coordination, geometry, and strength of methyl mercury, CH3Hg (II), bonding in soil and stream organic matter. Samples of organic soil (OS), potentially soluble organic substances (PSOS) from the soil, and organic substances from a stream (SOS) draining the soil were taken along a short “hydrological transect.” We determined the sum of concentrations of highly reduced organic S groups (designated Org-SRED), such as thiol (RSH), disulfane (RSSH), sulfide (RSR), and disulfide (RSSR), using sulfur K-edge XANES. Org-SRED varied between 27% and 64% of total S in our samples. Hg LIII-edge EXAFS analysis were determined on samples added CH3Hg (II) to yield CH3Hg (II)/Org-SRED ratios in the range 0.01-1.62. At low ratios, Hg was associated to one C atom (the methyl group) at an average distance of 2.03 ± 0.02 Å and to one S atom at an average distance of 2.34 ± 0.03 Å, in the first coordination shell. At calculated CH3Hg(II)/Org-SRED ratios above 0.37 in OS, 0.32 in PSOS, and 0.24 in SOS, the organic S sites were saturated by CH3Hg+, and O (and/or N) atoms were found in the first coordination shell of Hg at an average distance of 2.09 ± 0.01 Å. Based on the assumption that RSH (and possibly RSSH) groups take part in the complexation of CH3Hg+, whereas RSSR and RSR groups do not, approximately 17% of total organic S consisted of RSH (+ RSSH) functionalities in the organic soil. Corresponding figures for samples PSOS and SOS were 14% and 9%, respectively. Competitive complexation of CH3Hg+ by halide ions was used to determine the average binding strength of native concentrations of CH3Hg (II) in the OS sample. Using data for Org-SRED, calculated surface complexation constants were in the range from 1016.3 to 1016.7 for a model RSH site having an acidity constant of mercaptoacetic acid. These values compare favorably with identically defined stability constants (log K1) for the binding of methyl mercury to thiol groups in well-defined organic compounds.  相似文献   

11.
The δ13C values of dissolved HCO3? in 75 water samples from 15 oil and gas fields (San Joaquin Valley, Calif., and the Houston-Galveston and Corpus Christi areas of Texas) were determined to study the sources of CO2 of the dissolved species and carbonate cements that modify the porosity and permeability of many petroleum reservoir rocks. The reservoir rocks are sandstones which range in age from Eocene through Miocene. The δ13C values of total HCO3? indicate that the carbon in the dissolved carbonate species and carbonate cements is mainly of organic origin.The range of δ13C values for the HCO3? of these waters is ?20–28 per mil relative to PDB. This wide range of δ13C values is explained by three mechanisms. Microbiological degradation of organic matter appears to be the dominant process controlling the extremely low and high δ13C values of HCO3? in the shallow production zones where the subsurface temperatures are less than 80°C. The extremely low δ13C values (< ?10 per mil) are obtained in waters where concentrations of SO42? are more than 25 mg/l and probably result from the degradation of organic acid anions by sulfate-reducing bacteria (SO42? + CH3COO? → 2HCO3? + HS?). The high δ13C values probably result from the degradation of these anions by methanogenic bacteria (CH3COO? + H2OaiHCO3? + CH4).Thermal decarboxylation of short-chain aliphatic acid anions (principally acetate) to produce CO2 and CH4 is probably the major source of CO2 for production zones with subsurface temperatures greater than 80°C. The δ13C values of HCO3? for waters from zones with temperatures greater than 100°C result from isotopic equilibration between CO2 and CH4. At these high temperatures, δ13C values of HCO3? decrease with increasing temperatures and decreasing concentrations of these acid anions.  相似文献   

12.
A geochemical survey, in shallow aquifers and soils, has been carried out to evaluate the feasibility of natural gas (CH4) storage in a deep saline aquifer at Rivara (MO), Northern Italy. This paper discusses the areal distribution of CO2 and CH4 fluxes and CO2, CH4, Rn, He, H2 concentrations both in soils and shallow aquifers above the proposed storage reservoir. The distribution of pathfinder elements such as 222Rn, He and H2 has been studied in order to identify potential faults and/or fractures related to preferential migration pathways and the possible interactions between the reservoir and surface. A geochemical and isotopic characterization of the ground waters circulating in the first 200 m has allowed to investigation of (i) the origin of the circulating fluids, (ii) the gas–water–rock interaction processes, (iii) the amount of dissolved gases and/or their saturation status. In the first 200 m, the presence of CH4-rich reducing waters are probably related to organic matter (peat) bearing strata which generate shallow-derived CH4, as elsewhere in the Po Plain. On the basis of isotopic analysis, no hints of thermogenic CH4 gas leakage from a deeper reservoir have been shown. The δ13C(CO2) both in ground waters and free gases suggests a prevalent shallow origin of CO2 (i.e. organic and/or soil-derived). The acquisition of pre-injection data is strategic for the natural gas storage development project and as a baseline for future monitoring during the gas injection/withdrawing period. Such a geochemical approach is considered as a methodological reference model for future CO2/CH4 storage projects.  相似文献   

13.
Membrane filtration technique was applied to study the distribution of iodine and some other chemical elements (iron, manganese, aluminum, and silicon) in natural waters between different sized fractions (>0.45, 0.45–0.22, 0.22–0.1, and <0.1 μm). The paper presents analysis of factors able to modify the proportions of the adsorbed and dissolved species of the elements in waters. It is proved that up to 90% of the total amount of the iodine ion occurs in aquatic environments in the form of dissolved species (according to the current standard, in the fraction < 0.45 μm), with approximately 49% of the total concentration corresponding to the fraction of <0.10 μm. An increase in the acidity of the waters and their enrichment in finely divided organic and mineral material, and also an increase in Fe and Mn concentrations, may increase in the concentrations of the trace element in the particulate matter (up to 26% of the total iodide concentration). The greatest variations in iodine distribution between different fractions are found in the surface waters.  相似文献   

14.
Chemical analyses of pore waters from recent marine carbonate sediments, Devil's Hole, Harrington Sound, Bermuda, have been obtained at intervals over a four year period. Interstitial waters were systematically analyzed for pH, titration alkalinity, dissolved sulfides, NH4+, Ca2+, Mg2+ and Na+ or Cl?. Additional analyses on some cores included SO42?, PO43?, dissolved CH4 and N2, and C:N:H ratios in the detrital organic material. The following general trends with depth (to ～ 1 m) are observed: (1) major cations show little or no change; (2) pH decreases; (3) alkalinity, sulfides, NH4+ and PO43? increase; (4) dissolved CH4 is consistently low. The chemical changes with depth can be modelled theoretically and are consistent with experimental data.Significant seasonal changes in pore water chemistry are observed. The data suggest an annual exchange between the pore waters (to a depth of ～ 1 m) and the overlying water of Harrington Sound; the exchange occurs between August and January. The nutrient flux out of the sediments during this process may be a major factor in the plankton ecology of Harrington Sound.  相似文献   

15.
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   

16.
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   

17.
We estimated CO2 and CH4 emissions from mangrove-associated waters of the Andaman Islands by sampling hourly over 24 h in two tidal mangrove creeks (Wright Myo; Kalighat) and during transects in contiguous shallow inshore waters, immediately following the northeast monsoons (dry season) and during the peak of the southwest monsoons (wet season) of 2005 and 2006. Tidal height correlated positively with dissolved O2 and negatively with pCO2, CH4, total alkalinity (TAlk) and dissolved inorganic carbon (DIC), and pCO2 and CH4 were always highly supersaturated (330–1,627 % CO2; 339–26,930 % CH4). These data are consistent with a tidal pumping response to hydrostatic pressure change. There were no seasonal trends in dissolved CH4 but pCO2 was around twice as high during the 2005 wet season than at other times, in both the tidal surveys and the inshore transects. Fourfold higher turbidity during the wet season is consistent with elevated net benthic and/or water column heterotrophy via enhanced organic matter inputs from adjacent mangrove forest and/or the flushing of CO2-enriched soil waters, which may explain these CO2 data. TAlk/DIC relationships in the tidally pumped waters were most consistent with a diagenetic origin of CO2 primarily via sulphate reduction, with additional inputs via aerobic respiration. A decrease with salinity for pCO2, CH4, TAlk and DIC during the inshore transects reflected offshore transport of tidally pumped waters. Estimated mean tidal creek emissions were ～23–173 mmol m?2 day?1 CO2 and ～0.11–0.47 mmol m?2 day?1 CH4. The CO2 emissions are typical of mangrove-associated waters globally, while the CH4 emissions fall at the low end of the published range. Scaling to the creek open water area (2,700 km2) gave total annual creek water emissions ～3.6–9.2?×?1010 mol CO2 and 3.7–34?×?107 mol CH4. We estimated emissions from contiguous inshore waters at ～1.5?×?1011 mol CO2?year?1 and 2.6?×?108 mol CH4?year?1, giving total emissions of ～1.9?×?1011 mol CO2?year?1 and ～3.0?×?108 mol CH4?year?1 from a total area of mangrove-influenced water of ～3?×?104 km2. Evaluating such emissions in a range of mangrove environments is important to resolving the greenhouse gas balance of mangrove ecosystems globally. Future such studies should be integral to wider quantitative process studies of the mangrove carbon balance.  相似文献   

18.
Aqueous production and water-air exchange of elemental mercury (Hg0) are important features of the environmental cycling of Hg. We investigated Hg0 cycling in ten Arctic Alaskan lakes that spanned a wide range in physicochemical characteristics. Dissolved gaseous Hg (DGM, dominated by Hg0) varied from 40 to 430 fM and averaged 200 fM. All surface waters were supersaturated relative to the atmosphere. DGM averaged 3 ± 2% of dissolved (i.e., filter passing) dissolved total mercury (DTM) and 15 ± 6% of dissolved labile Hg (DLM). In-lake DGM profiles generally followed the vertical distribution of light, indicating photoreduction of Hg(II) complexes as a source of Hg0. Additionally, DGM correlated linearly with DLM (r2 = 0.82, p < 0.0001) in the lake surface, signifying that Hg complexes (mostly organic Hg associations) in dissolved phase are photoreducible and contribute to production of DGM. Further, a positive relation between DGM/DTM and both Ka (light attenuation coefficient; r2 = 0.73, p < 0.02) and DOC (r2 = 0.60, p = 0.02) suggests that solar radiation and dissolved organic matter control DGM production and its cycling. An average rate of DGM formation (0.6 ± 0.2% of DTM d−1; range, 0.20.8) was estimated by assuming steady state with the evasional rate. In-lake DGM formation occurs at lower rates in waters with greater suspended particulate matter and dissolved organic carbon (DOC), pointing to the significant role of organic matter plays in controlling DGM formation in these aquatic systems. Estimated evasional fluxes of Hg0 (average, 140 ± 50 pmol m−2 d−1; range, 60-200) were comparable to those of temperate lakes (e.g., Wisconsin, Michigan). In arctic lakes, the rate of evasion during ice-free periods (7 ± 3 nmol m−2 yr−1) is similar to the atmospheric input of Hg (wet + dry) to the lakes based on levels in summertime precipitation but not including additional sources, e.g., springtime depletion.  相似文献   

19.
Due to the widespread contamination of groundwater resources with arsenic (As), controls on As mobility have to be identified. In this study we focused on the distribution of As in the dissolved, colloidal and particulate size fraction of experimental solutions rich in ferric iron, dissolved organic matter (DOM) and As(V). Size fractions between <5 kDa and >0.2 μm were separated by filtration and their elemental composition was analyzed. A steady-state particle size distribution with stable element concentration in the different size classes was attained within 24 h. The presence of DOM partly inhibited the formation of large Fe-(oxy)hydroxide aggregates, thus stabilized Fe in complexed and colloidal form, when initially adjusted molar Fe/C ratios in solution were <0.1. Dissolved As concentrations and the quantity of As bound to colloids (<0.2 μm) increased in the presence of DOM as well. At intermediate Fe/C ratios of 0.02-0.1, a strong correlation between As and Fe concentration occurred in all size fractions (R2 = 0.989). At Fe/C ratios <0.02, As was mainly present in the dissolved size fraction. These observations indicate that As mobility increased in the presence of DOM due to (I) competition between As and organic molecules for sorption sites on Fe particles; and (II) due to a higher amount of As bound to more abundant Fe colloids or complexes <0.2 μm in size. The amount of As contained in the colloidal size fractions also depended strongly on the initial size of the humic substance, which was larger for purified humic acids than for natural river or soil porewater samples. Arsenic in the particle size fraction >0.2 μm additionally decreased in the order of pH 4 ? 6 > 8. The presence of DOM likely increases the mobility of As in iron rich waters undergoing oxidation, a finding that has to be considered in the investigation of organic-rich terrestrial and aquatic environments.  相似文献   

20.
Studies were conducted in conjunction with the Integrated Lake-Watershed Acidification Study (ILWAS) to examine the chemistry and leaching patterns of soluble humic substances in forested watersheds of the Adirondack region. During the summer growing season, mean dissolved organic carbon (DOC) concentrations in the ILWAS watersheds ranged from 21–32 mg C l?1 in O/A horizon leachates, from 5–7 mg C l?1 in B horizon leachates, from 2–4 mg C l?1 in groundwater solutions, from 6–8 mg C l?1 in first order streams, from 3–8 mg C l?1 in lake inlets, and from 2–7 mg C l?1 in lake outlets. During the winter, mean DOC concentrations dropped significantly in the upper soil profile. Soil solutions from mixed and coniferous stands contained as much as twice the DOC concentration of lysimeter samples from hardwood stands. Results of DOC fractionation analysis showed that hydrophobia and hydrophilic acids dominate the organic solute composition of natural waters in these watersheds. Charge balance and titration results indicated that the general acid-base characteristics of the dissolved humic mixture in these natural waters can be accounted for by a model organic acid having an averagepKa of 3.85, an average charge density of 4–5 μeq mg?1 C at ambient pH, and a total of 6–7 meq COOH per gram carbon.  相似文献   

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