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1.
The ability of organic matter as well as carbonate ions to extract rare earth elements (REEs) from sandy sediments of a Coastal Plain aquifer was investigated for unpurified organic matter from different sources (i.e., Mississippi River natural organic matter, Aldrich humic acid, Nordic aquatic fulvic acid, Suwannee River fulvic acid, and Suwannee River natural organic matter) and for extraction solutions containing weak (i.e., CH3COO−) or strong (i.e., ) ligands. The experimental results indicate that, in the absence of strong REE complexing ligands in solution, the amount of REEs released from the sand is small and the fractionation pattern of the released REEs appears to be controlled by the surface stability constants for REE sorption with Fe(III) oxides/oxyhydroxides. In the presence of strong solution complexing ligands, however, the amount and the fractionation pattern of the released REEs reflect the strength and variation of the stability constants of the dominant aqueous REE species across the REE series. The varying amount of REEs extracted by the different organic matter employed in the experiments indicates that organic matter from different sources has different complexing capacity for REEs. However, the fractionation pattern of REEs extracted by the various organic matter used in our experiments is remarkable consistent, being independent of the source and the concentration of organic matter used, as well as solution pH. Because natural aquifer sand and unpurified organic matter were used in our experiments, our experimental conditions are more broadly similar to natural systems than many previous laboratory experiments of REE-humic complexation that employed purified humic substances. Our results suggest that the REE loading effect on REE-humic complexation is negligible in natural waters as more abundant metal cations (e.g., Fe, Al) out-compete REEs for strong binding sites on organic matter. More specifically, our results indicate that REE complexation with organic matter in natural waters is dominated by REE binding to weak sites on dissolved organic matter, which subsequently leads to a middle REE (MREE: Sm-Ho)-enriched fractionation pattern. The experiments also indicate that carbonate ions may effectively compete with fulvic acid in binding with dissolved REEs, but cannot out compete humic acids for REEs. Therefore, in natural waters where low molecular weight (LMW) dissolved organic carbon (DOC) is the predominant form of DOC (e.g., lower Mississippi River water), REEs occur as “truly” dissolved species by complexing with carbonate ions as well as FA, resulting in heavy REE (HREE: Er-Lu)-enriched shale-normalized fractionation patterns. Whereas, in natural terrestrial waters where REE speciation is dominated by organic complexes with high molecular weight DOC (e.g., “colloidal” HA), only MREE-enriched fractionation patterns will be observed because the more abundant, weak sites preferentially complex MREEs relative to HREEs and light REEs (LREEs: La-Nd). 相似文献
2.
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
3.
Donald E. Wilson 《Geochimica et cosmochimica acta》1980,44(9):1311-1317
Montmorillonite, kaolinite, goethite, and particulate and soluble natural organic materials influence the rate of Mn(II) oxidation. While surfaces accelerate the reaction, apparently by bonding Mn2+ in a manner which fulfills the requirements of the transition state, soluble organic materials retard the reaction by complexing the oxidizable species. It is doubtful whether particulate matter would influence the oxidation process under natural loading conditions since 50–500 mg l?1quantities are required to produce measurable changes in the reaction rate. Complexation by humic materials, however, might be expected to reduce the rate of oxidation by an amount proportional to the dissolved organic carbon concentration. Oxidation followed by precipitation is predicted to be an important mechanism for Mn2+ removal in oceanic waters. The situation is less predictable in lake waters. 相似文献
4.
Recent data were summarized on the concentration and mass of inorganic and organic carbon in reservoirs of the Earth’s hydrosphere. We compared carbon masses and accumulation conditions in the surface hydrosphere and waters of the sedimentary shell and proportions between carbonate, dissolved, and suspended particulate organic carbon. It was shown that the total masses of carbon in the surface hydrosphere and in the waters of the sedimentary shell are approximately equal to 80 × 1018 g C at an organic to carbonate carbon ratio of 1 : 36 and 1 : 43, respectively. Three main forms of organic compounds in the ocean (living organisms, suspended particles, and dissolved species) occur in the proportion 1 : 13 : 250 and form the pyramid of masses 4 × 1015 g, 50 × 1015 g, and 1000 × 1015 g Corg. The descending sequence of the organic to carbonate carbon ratio in water, ocean (1 : 36) > glaciers (1 : 8) > lakes (1 : 2) > rivers (1 : 0.6) > wetlands (1 : 0.3), is in general consistent with an increase in the same direction in the mean concentrations of organic matter: 0.77 mg Corg/L in the ocean, 0.7 mg Corg/L in glaciers, 6–30 mg Corg/L in lakes, 15 mg Corg/L in rivers, and 75 mg Corg/L in wetlands. Both the mean concentrations and masses of dissolved organic matter in the pore waters of oceanic sediments and in the waters of the sedimentary shell are similar: 36–37 mg/L and 5 × 1018 and 5.6 × 1018 g, respectively. The mass of carbonate carbon in the pore waters of the ocean, (19–33) × 1018 g, is comparable with its mass in the water column, 38.1 × 1018 g. 相似文献
5.
Complexation of metal ions by organic matter is frequently considered to play a part in metal ion dissolution in natural waters. A field study of a relatively unperturbed stream, high in organics, associates this with the fraction related to soil organic acids (humic acids). The association might have two origins. The first is complexation. However, well known sequences of complexing tendency do not predict the behaviour. A better theory uses the additional factor of the reducing capacity of dissolved organic matter toward Fe(III) and Mn(IV). 相似文献
6.
Many developing countries have regions of high demographic density, where untreated residuary waters from different sources are often discharged into rivers, streams and other water bodies. This paper discusses the reducing action of organic matter of anthropic origin on the mercury redox cycle in the Jundiaí River impacted by discharged wastes, and on the Piraí River, a non-impacted water body. The total mercury concentrations in these locations vary from 1.7 to 32?ng?L?1 in the former and from 0.6 to 10.6?ng?L?1 in the latter. Dissolved organic carbon concentrations of up to 68.3 and 6.5?mg?L?1 were observed, confirming the higher impact on the Jundiaí River. It was found that an inverse correlation between the concentration of dissolved organic carbon and total mercury was stronger in the Jundiaí River, given that it receives higher organic loads, suggesting that organic matter exerts a reducing action on mercury, which is released as gas into the atmosphere. This correlation was not observed in the Piraí River, where the organic matter of natural origin is probably not sufficiently labile to act intensely upon the Hg redox cycle, favoring the metal transport. 相似文献
7.
The stability and structure of aqueous complexes formed by trivalent antimony (SbIII) with carboxylic acids (acetic, adipic, malonic, lactic, oxalic, tartaric, and citric acid), phenols (catechol), and amino acids (glycine) having O- and N-functional groups (carboxyl, alcoholic hydroxyl, phenolic hydroxyl and amine) typical of natural organic matter, were determined at 20 and 60 °C from solubility and X-ray absorption fine structure (XAFS) spectroscopy measurements. In organic-free aqueous solutions and in the presence of acetic, adipic, malonic acids and glycine, both spectroscopic and solubility data are consistent with the dominant formation of SbIII hydroxide species, , at strongly acid, acid-to-neutral and basic pH, respectively, demonstrating negligible complexing with mono-functional organic ligands (acetic) or those having non adjacent carboxylic groups (adipic, malonic). In contrast, in the presence of poly-functional carboxylic and hydroxy-carboxylic acids and catechol, SbIII forms stable 1:1 and 1:2 complexes with the studied organic ligands over a wide pH range typical of natural waters (3 < pH < 9). XAFS spectroscopy measurements show that in these species the central SbIII atom has a distorted pseudo-trigonal pyramidal geometry composed of the lone pair of 5s2 electrons of Sb and four oxygen atoms from two adjacent functional groups of the ligand (OC-OH and/or COH), forming a five-membered bidendate chelate cycle. Stability constants for these species, generated from Sb2O3 (rhomb.) solubility experiments, were used to model Sb complexing with natural humic acids possessing the same functional groups as those investigated in this study. Our predictions show that in an aqueous solution of pH between 2 and 10, containing 1 μg/L of Sb and 5 mg/L of dissolved organic carbon (DOC), up to 35% of total dissolved Sb binds to aqueous organic matter via carboxylic and hydroxy-carboxylic groups. This amount of complexed Sb for typical natural DOC concentrations is in agreement with that estimated from dialysis experiments performed with commercial humic acid in our work and those available in the literature for a range of standardized IHSS humic acids. Our results imply that a significant part of Sb is likely to be bound with humic acids via hydroxy-carboxylic moieties, in the form of bidendate complexes. However, following the strong chemical affinity of SbIII for reduced sulfur, some undefined fraction of SbIII might also be bound to the minor thiol-bearing moieties of humic acids; further studies are required to check this hypothesis. 相似文献
8.
Cherkasova Elena V. Konyshev Artem A. Soldatova Evgeniya A. Sidkina Evgeniya S. Mironenko Mikhail V. 《Aquatic Geochemistry》2021,27(2):141-158
Equilibrium-kinetic modeling allows investigating metal behavior in the water–rock-organic matter system with time to evaluate anthropogenic effects on the environment. In the article, the interactions of stagnant mine drainage water of the flooded mine “Arsenic” with ore and gangue minerals were simulated using different organic matter incorporation approaches. If the model is closed to humic substances (no additional organic matter input), most fulvic acids are bound in the Fe fulvate complex. While under the removal of Fe fulvate from the model, the Cu fulvate becomes prevalent, the contribution of the fulvate complexes with Zn, Mg, and Ca also increases. This scenario simulates the organo-mineral complexes behavior well and allows identifying the sequence of metal binding to organic ligands as follows Fe?>?Cu?>?Zn?>?Mg?>?Ca. The second scenario imitates the constant input of organic matter to the model (open system regarding humic substances). The dissolved metal concentrations in the model solution are extremely high in comparison to the mine drainage water. This scenario demonstrates that excessive input of organic matter leads to the accumulation of the metals in a dissolved form and blocks the secondary mineral formation despite the faster dissolution of the primary minerals under a more acidic pH than in the first scenario. However, despite the differences between the model solution and the mine drainage water, this scenario is useful to address specific issues associated with changes in natural and anthropogenic conditions. Both scenarios show the importance of organic matter incorporation to the equilibrium-kinetic models.
相似文献9.
Thermodynamic properties of 32 dissolved thorium species and 9 thorium-bearing solid phases have been collected from the literature, critically evaluated and estimated where necessary for 25°C and 1 atm pressure. Although the data are incomplete, especially for thorium minerals and organic complexes, some tentative conclusions can be drawn. Dissolved thorium is almost invariably complexed in natural waters. For example, based on ligand concentrations typical of ground water (ΣCl = 10 ppm, ΣF = 0.3 ppm, ΣSO4 = 100 ppm, andΣPO4 = 0.1 ppm), the predominant thorium species are Th(SO4)02, ThF2+2, and Th(HPO4)20below pH ≈ 4.5; Th(HPO4)2?3 from about pH 4.5 to 7.5; and Th(OH)04 above pH 7.5. Based on stability constants for thorium citrate, oxalate and EDTA complexes, it seems likely that organic complexes predominate over inorganic complexes of thorium in organic-rich stream waters, swamp waters, soil horizons, and waterlogged recent sediments. The thorium dissolved in seawater is probably present in organic complexes and as Th(OH)04. The tendency for thorium to form strong complexes enhances its potential for transport in natural waters by many orders of magnitude below pH 7 in the case of inorganic complexing, and below about pH 8 when organic complexing is important. The existence of complexes in addition to those formed with hydroxyl, is apparent from the fact that measured dissolved thorium in fresh surface waters (pH values generally 5–8) usually ranges from about 0.01 to 1 ppb and in surface seawater (pH = 8.1) is about 0.00064 ppb. This may be contrasted with the computed solubility of thorianite in pure water which is only 0.00001 ppb Th as Th(OH)04 above pH 5. Although complexing increases the solubility of thorium-bearing heavy minerals below pH 8, maximum thorium concentrations in natural waters are probably limited in general by the paucity and slow solution rate of these minerals and by sorption processes, rather than by mineral-solution equilibria. 相似文献
10.
The influence of Zn speciation on Zn transport by drainage from different soils to surface water is examined in a stream catchment
in an agricultural area. Drainage waters were collected from two types of soils, a mineral soil (MS) and a soil rich in organic
matter (OS) by means of artificial drainage pipes. The speciation of dissolved Zn in the stream and the drainage waters was
determined using ligand-exchange and voltammetry. About 50–95% of dissolved Zn is bound in strong complexes, and the free
Zn2+ ion concentration is in the range of 1–16% of dissolved Zn. A substantial part of Zn is present in weaker organic or inorganic
complexes. The simulated Zn speciation using the WHAM VI model is compared to the determined speciation. Free Zn2+ concentrations predicted by the WHAM VI model are generally higher than the analytically determined free Zn2+, but are mostly within the same order of magnitude. Effects of different soil organic matter content on Zn speciation and
transport are discussed. Zn speciation in the drainage at the OS site is influenced by the distribution of organic matter
between the solid and solution phase. The abundant organic Zn complexes in solution contribute to facilitate Zn transport
from soil into surface waters, through the drainage at the OS site. Drainage from the OS site contributes about twice as much
Zn input to the receiving water as the MS soil, as related to specific area. The mineral soil contains much lower organic
matter, and a part of Zn bound with inorganic phases can hardly be released by dissolved organic ligands, leading to much
higher Zn retention at the MS site. 相似文献
11.
《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
12.
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
13.
Kaelin M. Cawley Youhei Yamashita Nagamitsu Maie Rudolf Jaffé 《Estuaries and Coasts》2014,37(2):399-410
Dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) optical properties were analyzed along two estuarine river transects during the wet and dry seasons to better understand DOM dynamics and quantify mangrove inputs. A tidal study was performed to assess the impacts of tidal pumping on DOM transport. DOM in the estuaries showed non-conservative mixing indicative of mangrove-derived inputs. Similarly, fluorescence data suggest that some terrestrial humic-like components showed non-conservative behavior. An Everglades freshwater-derived fluorescent component, which is associated with soil inputs from the Northern Everglades, behaved conservatively. During the dry season, a protein-like component behaved conservatively until the mid-salinity range when non-conservative behavior due to degradation and/or loss was observed. The tidal study data suggests mangrove porewater inputs to the rivers following low tide. The differences in quantity of DOM exported by the Shark and Harney Rivers imply that geomorphology and tidal hydrology may be a dominant factor controlling the amount of DOM exported from the mangrove ecotone, where up to 21 % of the DOC is mangrove-derived. Additionally, nutrient concentrations and other temporal factors may control DOM export from the mangroves, particularly for the microbially derived fluorescent components, contributing to the seasonal differences. The wet and dry season fluxes of mangrove DOM from the Shark River is estimated as 0.27?×?109 mg C d?1 and 0.075?×?109 mg C d?1, respectively, and the Harney River is estimated as 1.9?×?109 mg C d?1 and 0.20?×?109 mg C d?1. 相似文献
14.
Klaus Kaiser 《Organic Geochemistry》1998,28(12):849-854
The purpose of the study was to evaluate the influence of polyvalent cations known to form complexes with natural organic substances on the operational fractionation of dissolved organic matter (DOM) using XAD-8 adsorber resin. Dissolved organic matter solutions from a forest floor were treated with increasing concentrations of polyvalent metal cations (Ca2+, Al3+, Fe3+) at different pH levels. Then the concentrations of total dissolved organic carbon (DOC) and the distribution between hydrophilic and hydrophobic DOC were determined. The concentrations of total DOC decreased slightly when the C/metal ratio was less than 10, especially for Al and Fe. Hydrophilic DOC increased and hydrophobic DOC decreased with increasing concentrations of metal cations. Effects increased in the order Ca<Al<Fe and were more pronounced at low DOC concentrations and high pH values. The reason for the reduction of the DOC concentrations seemed to be the formation of insoluble metal–DOM complexes, while soluble metal–DOM complexes may induce an alteration of the distribution between hydrophilic and hydrophobic DOC. Thus, the polyvalent cations and their concentration need to be considered when DOM fraction distributions, determined with XAD-8 resin, of different waters are compared, especially at low DOC contents and high pH. 相似文献
15.
Seasonal and Annual Fluxes of Nutrients and Organic Matter from Large Rivers to the Arctic Ocean and Surrounding Seas 总被引：3，自引：0，他引：3
Robert Max Holmes James W. McClelland Bruce J. Peterson Suzanne E. Tank Ekaterina Bulygina Timothy I. Eglinton Viacheslav V. Gordeev Tatiana Y. Gurtovaya Peter A. Raymond Daniel J. Repeta Robin Staples Robert G. Striegl Alexander V. Zhulidov Sergey A. Zimov 《Estuaries and Coasts》2012,35(2):369-382
River inputs of nutrients and organic matter impact the biogeochemistry of arctic estuaries and the Arctic Ocean as a whole, yet there is considerable uncertainty about the magnitude of fluvial fluxes at the pan-Arctic scale. Samples from the six largest arctic rivers, with a combined watershed area of 11.3?×?106?km2, have revealed strong seasonal variations in constituent concentrations and fluxes within rivers as well as large differences among the rivers. Specifically, we investigate fluxes of dissolved organic carbon, dissolved organic nitrogen, total dissolved phosphorus, dissolved inorganic nitrogen, nitrate, and silica. This is the first time that seasonal and annual constituent fluxes have been determined using consistent sampling and analytical methods at the pan-Arctic scale and consequently provide the best available estimates for constituent flux from land to the Arctic Ocean and surrounding seas. Given the large inputs of river water to the relatively small Arctic Ocean and the dramatic impacts that climate change is having in the Arctic, it is particularly urgent that we establish the contemporary river fluxes so that we will be able to detect future changes and evaluate the impact of the changes on the biogeochemistry of the receiving coastal and ocean systems. 相似文献
16.
O. G. Savichev A. K. Mazurov I. I. Pipko V. I. Sergienko I. P. Semiletov 《Doklady Earth Sciences》2016,466(1):59-63
The discharge of major cations and dissolved organic carbon (Corg) with water of the Ob River and its tributaries along the natural zones within the Ob River basin was calculated, and the contribution of the underground component to the volumes of total discharge of the Ob River basin was estimated. It was demonstrated that the total chemical composition of river water and the geochemical discharge in the Ob River basin were consistent with the zoned hydroclimatic conditions controlling the character and duration of interaction in the water–rock system. It was established that the average ionic discharge of the Ob River increased from 6–7 × 106 t/year near Barnaul to 46–47 × 106 t/year near Salekhard; the discharge of dissolved Corg increased from 0.1 × 106 to 3.8 × 106 t/year. Multiple enrichment of underground waters of the Ob River in dissolved organic matter from the upper to the lower reaches was revealed. 相似文献
17.
Neetha Linto J. Barnes Ramesh Ramachandran Jennifer Divia Purvaja Ramachandran R. C. Upstill-Goddard 《Estuaries and Coasts》2014,37(2):381-398
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.
《Applied Geochemistry》1996,11(3):387-402
Naturally occurring organics in groundwaters of the Whiteshell Research Area (WRA) of southern Manitoba were investigated to assess their potential role in radionuclide transport within granite fractures of the Canadian Shield. A survey of dissolved organic carbon concentrations, carried out to determine the variability in the organic content of these groundwaters, showed average concentrations of 0.8 ± 0.1 mg/L for Fracture Zone 2, 0.8 ± 0.4 mg/L for near-vertical fractures and 2.3 ± 0.8 mg/L for deeper saline groundwater. The dissolved organic carbon consisted mainly of hydrophilic neutral compounds (60 to 75%), and hydrophobic and hydrophilic acids (23 to 39%), along with very small amounts of hydrophobic bases and neutrals, and hydrophilic bases. Significant contamination from drilling operations and plastics, mostly in the form of hydrophobic neutrals, was observed in some samples. These compounds would not contribute to radionuclide migration in a natural system and are not included in the assessment of the organic complexing capacity of these groundwaters.Based on groundwater concentrations of hydrophobic and hydrophilic acids and on the measured car☐ylic functional group content of these acids, the average complexing capacity of natural organics in Whiteshell Research Area groundwaters was calculated to be 2.9 × 10−6 eq/L. The ability of these organics to complex radionuclides was tested using conditional stability constants from the literature for humic complex formation with Am(III), Th(IV), and U(VI). The chemistry of U(VI) was predicted to be dominated by inorganic complexes and not significantly affected by organics. The literature contains a wide range in values of stability constants for Am(III) and Th(IV) complexes with humics. The aqueous chemistry of Am(III) and Th(VI) could be affected by complexation with natural organics if the higher stability constant values are valid for WRA groundwaters. 相似文献
19.
Mercury Redox Chemistry in the Negro River Basin, Amazon: The Role of Organic Matter and Solar Light
Wilson F. Jardim Márcia Cristina Bisinoti Pedro Sérgio Fadini Gilmar Silvério da Silva 《Aquatic Geochemistry》2010,16(2):267-278
Pristine water bodies in the Negro River basin, Brazilian Amazon, show relatively high concentrations of mercury. These waters are characterized by acidic pH, low concentrations of suspended solids, and high amounts of dissolved organic matter and are exposed to intense solar radiation throughout the year. This unique environment creates a very dynamic redox chemistry affecting the mobility of mercury due to the formation of the dissolved elemental species (Hg0). It has been shown that in this so-called black water, labile organic matter from flooded forest is the major scavenger of photogenerated H2O2. In the absence of hydrogen peroxide, these black waters lose their ability to oxidize Hg0 to Hg2+, thus increasing Hg0 evasion across the water/atmosphere interface, with average night time values of 3.80 pmol m?2 h?1. When the dry period starts, labile organic matter inputs gradually diminish, allowing the increasing concentration of H2O2 to re-establish oxidative water conditions, inhibiting the metal flux across the water/atmosphere interface and contributing to mercury accumulation in the water column. 相似文献
20.
O. Yu. Drozdova N. A. Anokhina V. V. Demin S. A. Lapitskiy 《Moscow University Geology Bulletin》2018,73(5):467-471
The photodegradation of organo-mineral complexes in natural conditions was studied using samples of soil and swamp waters to study the effect of sunlight on the composition and properties of organic matter and metal forms dissolved in natural waters. The total contents of certain aliphatic and aromatic carboxylic acids increased in the samples after irradiation. Photodegradation of organic matter of the natural waters with the high Fe content is accompanied by the formation of colloidal particles (Fe hydroxides). The number of negatively-charged complexes of Ni, Cu, Zn, and Cd increased under insolation in swamp waters and decreased in soil waters. 相似文献