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1.
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   

2.
Wetlands are valued for their high biodiversity and for their ecosystem services. However, we still do have a poor understanding of their role in the redox transformation of contaminants such as mercury, particularly in fluvial settings. Seasonal and spatial variations in dissolved gaseous mercury (DGM) distribution and production were studied in the Bay St. François, a wetland in the St. Pierre Lake, a fluvial lake of the St. Lawrence River, in Quebec, Canada. A high spatial resolution for DGM, with samples taken every 10-cm depth, was used in field measurements. Through a series of parallel field and incubation experiments, we assessed the main factors determining Hg(0) transformations as a function of depth, seasons, and presence/absence of macrophyte beds. Besides light penetration in the water column and water temperature, iron and dissolved organic carbon likely stimulated Hg(II) reduction. Inversely, chloride favored Hg(0) oxidation. Macrophytes and associated epiphytes appeared to be important sites of adsorption/absorption of Hg(II) and likely of DGM. It seems however that the effects of macrophytes were restricted to immediately adjacent waters. Near the bottom, under anoxic conditions, the reduction of Hg(II) was highly promoted. In addition, sediments and decomposing macrophytes seemed to release DGM and/or reducible Hg to bottom waters. Overall, differences in DGM between surface and bottom waters tended to be more accentuated than observed differences in DGM between macrophyte beds and sites devoid of plant.  相似文献   

3.
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   

4.
The water, pore water, sediment, and fish samples were collected from the Hongfeng Reservoir in November 2003 and February 2004 in accordance with trace metal protocols. The average concentrations of total mercury （THg）, dissolved mercury （DHg）, reactive mercury, dissolved gaseous mercury, total methylmercury, and dissolved methylmercury in the water columns were 8.00, 5.70, 0.63, 0.05, 0.16, and 0.07 ng/L, respectively. THg and DHg in the water columns, THg in pore water and THg in lake sediments of the Hongfeng Reservoir showed the level of mercury in the Hongfeng Reservoir was higher than in other natural waters in the world due to the loading of a lot of waste water with relatively high concentrations of mercury, whereas methylmercury concentrations in fish （wet weight） varied from 1.73-51.00 ng/g, much lower than in most remote lakes and reservoirs reported in northern Europe and North America. Methylmercury distributions in pore water and sediments showed methylation occurred mainly in the upper several centimeters of sediment cores in the Hongfeng Reservoir. The concentrations of dissolved organic carbon, total suspended particles, total Hg, and methylmercury were higher at Houwu than those at Daba in November 2003. It is suggested that other pollutants such as N and P from fishing farm and other waste water at Houwu, which resulted in deterioration of water quality, affected the concentrations and distributions of mercury species in the reservoir.  相似文献   

5.
Dissolved mercury in estuarine waters from the Mississippi Delta and Florida Everglades is associated with dissolved organic matter which has the properties of fulvic matter found in soils. Ultrafiltration of water samples demonstrated that mercury and dissolved organic carbon are selectively enriched in the < 500 molecular size cut-off fraction. A decrease in high molecular weight dissolved organic matter with increasing salinity in the Everglades exerts a partial control on the mercury content of these estuarine waters.  相似文献   

6.
Pore water samples from seven nearshore areas in Bermuda were obtained under in situ conditions and analyzed for dissolved organic carbon, dissolved carbohydrates, dissolved free amino acids and dissolved humic substances. The concentration of dissolved organic carbon is higher than in the overlying nearshore waters indicating significant diagenetic remobilization of carbon in these recently deposited carbonate sediments. Dissolved carbohydrates decrease with depth due to microbial utilization.  相似文献   

7.
Lakes of the Klutlan moraines originate by down-melting of stagnant ice under a mantle of rock debris and vegetation ranging from scattered herbs and shrubs on the younger moraines to multiple-generation closed spruce forest on the oldest moraines, which are 600–1200 yr old. Lakes on the youngest moraines are temporary, turbid with glacial silt, and marked by unstable ice-cored slopes. On older moraines most lakes have clear water and stable slopes. On the oldest moraines many lakes have brown water caused by dissolved humic materials derived from the thick forest floor, but even here some slopes are unstable because of continued melting of buried ice. Morainic lakes contain bicarbonate waters of moderate alkalinity and conductivity and low levels of nutrients. The highly diverse phytoplankton is dominated by chrysophytes and cryptomonads, with few diatoms. Extremely low values for phytoplankton biomass place most of the lakes in an “ultraoligotrophic” category. Zooplankton is dominated by copepods, which were found even in ice ponds only a few years old, and by the cladoceran Daphnia pulex. Surface-sediment samples contained a total of 16 species of chydorid Cladocera. Of these, Alonella excisa and Alona barbulata are apparently the pioneer species in the youngest lakes. Chydorus sphaericus only appears in lakes of the oldest moraines. A successional pattern is not conspicuous, however, partly because some of the lakes on the older moraines originated by recent collapse over buried ice. Lakes on the upland outside the dead-ice moraines yielded 39 species in the zooplankton. The distinctive assemblage on upland lakes may relate more to different water chemistry than to age.  相似文献   

8.
The role of organic ligands in metal complexing in natural waters has received little attention because of uncertainties regarding both the abundance and nature of dissolved organic carbon compounds. Recent data show that the bulk of dissolved organic matter in natural waters consists of highly oxidized and chemically and biologically stable polymeric compounds closely resembling soil humic substances. Average molar concentrations of these aquatic humics in major U.S. rivers range from 5 × 10?6to 3 × 10?5 moles 1?1. Fractional elution of soil organic matter by meteoric waters may be considered to be the main process contributing to the presence of humic matter in rivers. The aquatic humic polymers participate in complex formation through ionizable functional groups with a range of differential acidities. The stabilities of metal-humic complexes in natural waters are higher than those of the corresponding inorganic metal complexes. Quantitative evaluation of the metal-organic interactions can be approached by applying variable equilibrium functions which take into account the differential physico-chemical characteristics of the active complexing sites on the polymer molecule. Assuming an average humic concentration of 10 mg 1?1, complexation of trace metals can be significant even in the presence of excess concentrations of major cations.  相似文献   

9.
This study discusses the problem of evolution of water chemistry under the influence of acid loadings from copper–nickel smelters of the Kola mining and smelting company (“KGMK”). The natural waters of the Kola Peninsula are characterized by low contents of biogenic substances and mineral salts owing to low water temperatures and low mass transfer rates at high latitudes. Acid precipitation causes water acidification in regions made up by granite gneisses and sandy rocks. Unlike naturally acidic waters with high humic acid contents, these lakes have high-transparency waters. The results show that Cd, Bi, Se, and Re become involved in the transport fluxes irrespective of a natural or anthropogenic source of acidification. Acidified lakes have higher Zn, Pb, As, Bi, and Sb contents compared to neutral lakes. The high coefficient of aqueous migration of Se, Re, Bi, Sb, Cd, and Sn is indicative of the anthropogenically-induced dispersal of these elements.  相似文献   

10.
Contents of rare earth elements in waters and bottom sediments are maximum in the most mineralized soda lakes. It is shown that REE occur in waters mainly as carbonate (LnСО3)+ and oxyhydroxide LnO2H, LnO+, (LnO2)– complexes, whose activity in the La → Lu series changes in opposite directions. It has been determined that increase of mineralization leads mainly to higher concentrations of the dissolved HREE. Prevalence of the absolute values of MREE and HREE is recorded in basins with the development of bacterial processes. Geochemical barrier for the accumulation of LREE in waters can be represented by fluorcarbonates, whose saturation degree in the soda lake waters can be several orders of magnitude higher than the solubility products (SP). Oxidative and reductive settings in lakes are favorable for the formation of Ce(OH)4 and Ce(OH)3, respectively.  相似文献   

11.
Aquatic geochemistry of small lakes: Effects of environment changes   总被引：1，自引：0，他引：1  
This paper reports the results of an extensive investigation of water chemistry in the small lakes of European Russia and Western Siberia along a climatic gradient. It was demonstrated that small lakes unaffected by any direct contamination can be used as indicators of natural geochemical conditions of water formation, as well as global and regional fluxes of airborne pollution and climate warming. A novel concept was developed for within- and between-zone variability in water chemistry over vast areas of tundra, taiga, forest, and steppe, and contributions of natural and anthropogenic factors to its formation under present-day conditions were estimated. A proposed predictive scenario showed that climate warming will result in an increase in water salinity in southern regions and ubiquitous phosphorus enrichment in terrestrial waters; the hydrologic and geochemical conditions of water formation in northern Siberia will change significantly in response to permafrost thawing. Zonal features in the development of anthropogenically-induced processes in terrestrial surface waters (acidification, eutrophication, and metal enrichment) were determined. It was demonstrated that, in addition to naturally acidified lakes with high contents of humic acids, acid lakes of anthropogenic origin occur over the whole humid region discussed here, and acidification processes were characterized for each subregion. The trophic status of lakes and limitation of their bioproductivity with respect to nutrients were estimated. The concentrations and distribution of trace elements were analyzed in terrestrial waters from various climatic zones of European Russia and Western Siberia, and the first estimates were obtained for the mean concentrations and coefficients of migration of a wide range of elements in terrestrial freshwaters. We distinguished a group of metal (Mo, As, U, Bi, Sb, Cd, Ag, Se, Re, Pb, Cd, W, etc.) the enrichment of which in natural waters results from their global dispersion in the environment. Experimental results and natural observations are presented on the processes of metal ion complexation with humus substances, and sequences of their increasing activity in competing for organic ligands were derived. Data are presented on the speciation of metals depending on natural water chemistry in the tundra, taiga, and steppe zones. The pioneering investigations on the geochemistry of natural waters allowed us to substantiate new regional norms for water quality.  相似文献   

12.
In order to find out whether Aha Lake was polluted by the acid mining waste water or not, the concentration and distribution of different mercuryspecies in the water columns and sediment profile collected from Aha Lake were investigated. It was found that discernible seasonal variation of different mercury species in water body were obtained in the Aha Reservoir. With regards to the whole sampling periods, the concentrations of HgP in the Aha Reservoir water body were evidently correlated to the concentrations of total mercury, showing that total mercury was mostly associated with particle mercury. The concentrations of methylmercury in water body were also evidently correlated to the concentrations of dissolved mercury. The dissolved mercury evidently affects the distribution and transportation of methylmercury. However, there is no correlation between methylmercury and total mercury. The dissolved mercury, reactive mercury, dissolved methylmercury levels in the water body of high flow period were much higher than those in low flow period. The distribution, speciation and levels of mercury within the Aha Reservoir water body were governed by several factors, such as the output of river, the release of sediment . Discernible seasonal variation of total mercury and methylmercury in porewater was described during the sampling periods, with the concentrations in high flow period generally higher than those in low flow period. The methylmercury in pore water column was evidently correlated to that of the sediment. The results indicated that highly elevated MeHgD concentrations in the porewater were produced at the depths from 2 to 5 cm in the sediment profile, and decreased sharply with depth. A positive correlation has been found between MeHgD formation and sulfate reducing bacterial activity. These highly elevated concentrations of MeHgD at the intersurface between waters and sediments suggest a favorable methylation condition. Moreover,  相似文献   

13.
The quantity and quality of dissolved organic matters have been widely characterized by fluorescence spectroscopy, yet the relationship between the fluorescence properties of dissolved organic matters and its molecular composition remains poorly described in the literature. Here, we measured the fluorescence excitation–emission matrix of 17 well-characterized humic substance standards to determine a range of fluorescence parameters, including classical fluorescence indices (e.g., fluorescence index, biological index and humification index) and parameters derived from parallel factor analysis (e.g., component contribution). Relationships between humic substance’s fluorescence and compositional parameters were then statistically examined using canonical correspondence and simple correlation analyses. The canonical correspondence analysis generally suggested that most fluorescence parameters determined here are highly associated with the amount of aliphatic and aromatic compounds in humic substances. However, the correlation analysis between single molecular and fluorescence parameters indicated that the fluorescence properties of humic substances including the parallel factor analysis component contribution also significantly correlate well with several aspects of the molecular composition of humic substances, such as elemental composition, carbon species, acidic functional group and iron complexation. Overall, our results suggest that measurement of humic substance’s fluorescence is beneficial in understanding the molecular composition and environmental functions of dissolved organic matters in natural and engineered waters.  相似文献   

14.
Concentrations of Ca, Cd, Cu, Fe, and Pb and binding capacities for Cd, Cu, and Pb were determined for water samples collected from 12 lakes in southwestern Maine using atomic absorption and ion-selective electrodes, respectively. Surface waters in this area are soft and characterized by low pH. Some lakes were highly colored with refractory organics, whereas others had very low organic carbon concentrations. Both Cu and Pb concentrations were positively correlated with organic carbon content. Copper and Pb binding capacities were significantly correlated with organic carbon content, whereas Cd binding capacity was positively correlated with pH, but not with organic carbon. Surface water binding capacity for Pb was greater than that for Cu or Cd. More than 99% of the Ca from all waters studied was removed onto cationic exchange resins. Less than 1% of the total Cu existed as cationic species in highly humic waters, whereas as much as 65% existed as cationic species in less huic waters. Conversely, more than 99% of the Cd present in humic waters existed as cationic species, whereas as little as 50% existed as cationic species in less humic, more alkaline waters. These correlative studies indicate that binding by organic carbon is important for both Cu and Pb in this area and must be considered in models of trace metal speciation. However, Cd binding in the same waters is not correlated with organic carbon, which does not need to be considered in speciation models for Cd.  相似文献   

15.
A new technique is suggested for evaluating the pH buffer capacity of natural aquatic systems (as exemplified by small lakes in western Siberia) with regard for the pH values of the lake waters and the concentrations of the hydrocarbonate ion and anions of humic acids,. The acid-neutralizing capacity evaluated for small lakes in western Siberia by conventionally used techniques (which was suggested by Norwegian researchers) is compared with evaluations by the technique suggested by the authors. Criteria are suggested for quantifying the immunity of natural waters to acidification in various natural climatic zones in western Siberia.  相似文献   

16.
We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM??representative of particle-associated and filter-passing Hg, respectively??together predicted 94?% of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, 2005?C2006. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particle-associated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes.  相似文献   

17.
A year-long study of incident and underwater light transmittance (400–800 nm) in the Rhode River, Maryland, a tidal tributary to Chesapeake Bay, indicated that light transmittance responded in both intensity and spectral quality to changes in the amount and type of dissolved and suspended materials in the water. At times of relatively clear water, transmittance was similar to that previously reported in the literature for coastal waters. With high concentrations of suspended and dissolved materials in the water, attenuation of irradiance was high in the upper part of the water column and different for the various wave bands, depending on the type of material present. At such times, attenuation was higher in the upper part of the water column under sunny, clear skies than on cloudy days. We believe this to be due to higher concentrations of pigments and suspended particles in the water on sunny days, increasing the scattering and adsorption. A second factor was a lower average cosine on cloudy days, decreasing the effect of scattering on the average path length per meter of depth. High attenuation coefficients in the middle of the spectrum are attributed to accessory pigments. Regression of the diffuse attenuation coefficient on eight water-quality parameters explained up to 93% of the variance in the attenuation coefficient. Chlorophylls a and c and mineral suspensates were the three most important variables for data taken under clear skies. In contrast, under cloudy skies, the three most important variables were different for different wavelengths. Models of irradiance attenuation in turbid estuarine waters require the use of more variables than models for open ocean waters.  相似文献   

18.
Porewater samples were obtained on five occasions during spring, summer and fall by in situ dialysis from three sites of a large freshwater wetland situated along the St. Lawrence River. These samples were analysed for total dissolved mercury ([Hg]T) and methylmercury ([MeHg]) concentrations and for complementary variables including dissolved sulfate, sulfide and elemental sulfur concentrations. Sediment cores were obtained on three occasions from one of these sites for the determination of total mercury ({Hg}T) and methylmercury ({MeHg}) concentration as well as mercury methyltransferase (HgMT) activity profiles. {MeHg} and HgMT activity varied with time and sediment depth. The porewater [Hg]T and [MeHg] depth profiles varied with time and among sites. Modeling the porewater [MeHg] profiles with a one-dimensional reaction-transport equation allowed identification of the sediment depths where MeHg is produced or consumed, as well as an estimate of the net in situ MeHg production rates in the sediments. The model-predicted depths of MeHg production, as well as the sulfate concentration and the HgMT activity depth distributions are all consistent with the involvement of sulfate reducing bacteria in the production of MeHg.  相似文献   

19.
Shu Tao 《GeoJournal》1996,40(1-2):213-217
Total organic carbon in unpolluted water from Yinluan River, Tianjin, China was fractionated into five operational defined fractions of particulate organic carbon, hydrophobic compounds, humic substances, non-humic anions, and other hydrophilic compounds using a multi-step filtration and adsorption scheme. The organic carbon contents and the trihalomethane formation potential of these fractions were determined. It was demonstrated that about half of the dissolved organic carbon in the sample is humic substances which is quite active in term of chlorination reaction. Particulate organic carbon is also an important precursor of the volatile halogenated hydrocarbons. All other fractions, which account for another half of the dissolved organic carbon, contribute to a relatively small percentage of the trihalomethanes produced during the chlorination experiment. It was concluded that humic substances, dissolved or suspended, are the most important precursor of halogenated hydrocarbons during chlorination, owing to their high abundance and trihalomethane formation potential.This study was supported by the National Excellent Young Scientist Fund of China.  相似文献   

20.
The high molecular weight fraction of dissolved organic matter in a suite of lakes, rivers, seawater, and marine sediment interstitial water samples was collected by ultrafiltration and characterized by molecular level and spectroscopic techniques. Proton nuclear magnetic resonance spectra of all samples show a high degree of similarity, with major contributions from carbohydrates, bound acetate, and lipids. Molecular level analyses of neutral sugars show seven monosaccharides, rhamnose, fucose, arabinose, xylose, mannose, glucose, and galactose, to be abundant, and to occur in comparable relative amounts in each sample. Previous studies have emphasized the distinctive composition of dissolved humic substances in fresh and marine waters, and have attributed these differences to sources and transformations of organic matter unique to each environment. In contrast we find a large fraction of freshwater high molecular weight dissolved organic matter (HMWDOM; > 1kD) to be indistinguishable from marine HMWDOM in bulk and molecular-level chemical properties. Aquatic HMWDOM is similar in chemical composition to biologically derived acylated heteropolysaccharides isolated from marine algal cultures, suggesting a biological source for some fraction of persistent HMWDOM. High molecular weight DOC contributes 51 ± 26% of the total DOC, and monosaccharides 18 ± 8% of the total HMWDOC in our freshwater samples. These contributions are on average higher and more variable, but not significantly different than for surface seawater (30% and 16% respectively). Biogeochemical processes that produce, accumulate, and recycle DOM may therefore share important similarities and be broadly comparable across a range of environmental settings.  相似文献   

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