Multi-site proton interactions with natural organic matter

Water samples from various locations in Norway were used to isolate natural organic matter (NOM). The NOM was isolated using both reverse osmosis and low-pressure low-temperature evaporation for each sample site. These samples were titrated from −log[H⁺] 3 to 11 at 0.1 unit intervals. The data were analyzed using the Discrete Site Analysis (DISI) technique for pK_a intervals of 0.2. The acidity constants are grouped into four classes: strong (pK_a < 5), intermediate strong (5.1 < pK_a < 7.5), intermediate weak (7.6 < pK_a < 9.2), and weak (pK_a > 9.3). All samples, regardless of isolation method, were found to contain strong and weak ligands, along with some intermediate ligands. For the same sample site, the concentration of these ligands were found to be dependent on isolation method and titration direction (acid then base vs. base then acid). In addition, the concentration and classes of ligands present were found to vary between sample sites. Suwannee River fulvic acid was analyzed as a reference sample, and was qualitatively similar to the NOM samples but quantitatively different. Overall, the differences in pKa spectra due to isolation method and/or titration direction are almost as significant as differences between sample location, but there are no consistent trends in effects of isolation method or titration direction on characterization of NOM.     

Monitoring natural organic matter in water with scanning spectrophotometer

This study uses scanning ultraviolet-visible (UV-Vis) spectrophotometer to monitor natural organic matter (NOM) in water. The results showed that the area under the UV-Vis spectra is a good surrogate to monitor the concentration of the aqueous NOM. No apparent difference was found between the spectra of the three commercially available humic acids used in this study. The use of the scanning spectra compensates the potential random error in the absorbance determined at single wavelength due to the heterogeneous NOM compositions. The major interference of the proposed method comes from the formazine turbidity and nitrate nitrogen (NO3- -N). Although filtration with a 0.45-microm filter can remove most of the interference from formazine, some interference is still present at a wavelength less than 250 nm. Also it is found that the presence of the NO3- -N greatly affect the spectra of the NOM. In order to monitor the NOM in water with minimized interference, it is recommended that the area under the spectra between 250 and 350 nm should be used as a surrogate for concentration of NOM in water.     

Characterization of natural organic matter by pyrolysis/GC-MS

Natural organic matter (NOM) in nine water samples selected for the NOM typing project were characterized by pyrolysis in conjunction with gas chromatography and mass spectrometry (GC-MS). NOM samples both isolated by reverse osmosis and evaporation techniques were subjected to high temperature pyrolysis and the products obtained were assigned to one of the four main types: biopolymers carbohydrates, proteinaceous materials, N-acetylamino sugars, and polyhydroxy aromatics. These biopolymers in the water samples were quantified and the quantities were used in characterization. Principal component analysis was employed in revealing the similarities and differences between the samples and between the separation techniques. The results indicate that there are little differences between the samples, and the NOM separated by evaporation preserves most of the organic material compared to the reverse osmosis technique.     

Fluorescence analysis for multi-site aluminum binding to natural organic matter

Natural organic matter (NOM) samples isolated from different water sources in Norway were compared using their fluorescence properties. Fluorescence surfaces were observed at pH 4.36 and deconvoluted using SIMPLISMA (Windig and Guilment 1991). There were a total of seven different fluorophores observed for these samples and each sampling site had between four and six of the fluorescent components. These components were observed to bind Al during titrations at the same pH. Multiresponse titration curves were fit using the method of Smith and Kramer (1998) and most of the binding strengths are similar to values for Suwannee River fulvic acid (logK' between 4.8 and 5.5), but there are strong sites (logK' = 7) and weak sites (logK' between 3 and 4) also observed. Results depended on the isolation method used; reverse osmosis and low pressure evaporation yielded different values but with no consistent trends.     

Capillary zone electrophoretic studies on Norwegian surface water natural organic matter

Capillary zone electrophoresis (CZE) is a useful tool for the analysis of the electrophoretic behavior of anionic polyelectrolytes like humic substances. CZE was used to compare natural organic matter (NOM) with high ash content obtained by reverse osmosis (RO) and low temperature, low pressure evaporation (Ev.) from different Norwegian surface water sources. The quantitative relation between the resulting electrophoretic signals (peak height and area) and the carbon amount of the injected NOM samples was found linear. The NOM gave homogeneous signals in CZE, with a distribution of the detection signals around an average electrophoretic mobility (AEM) corresponding to the charge density distribution of the NOM, governed by the distribution of their molecular sizes and acidities. Like humic substances, NOM only appears as anions in capillary electrophoresis (CE), but the high ash content of these samples and the presence of metals strongly influenced their mobilities at lower pH. CZE could be used as a tool for the rapid evaluation of the average net charge and the molecular radius of the NOM at pH 5.1.     

Biological vs. chemical properties of natural organic matter isolated from selected Norwegian lakes

Relationships among different spectroscopic, chemical, and biological properties of dissolved natural organic matter (NOM) were investigated. NOM samples were isolated by means of reverse osmosis from eight Norwegian lakes. Elemental composition, absorption spectra (UV, VIS, IR), the influence on algal growth, and accumulation rates of metals by mussels in the presence of NOM were measured. Linear regression and principal components analyses were utilised to assess relationships between the biological and chemical properties. It was concluded that the content of organic matter in the isolates and the aromaticity of NOM, as characterised by UV and VIS spectra, are best correlated with the biological properties.     

Characterization of natural organic matter from eight Norwegian surface waters: Proton and copper binding

As a part of the International NOM-Typing Project, proton and copper binding studies were conducted on ultrafiltered (>1000 dal.) and dialysed (>100 dal.) natural organic matter (NOM) samples from eight Norwegian Lakes. The NOM samples were similar with respect to proton and copper binding, although minor differences were observed among the samples of different origin. Slight variations occurred for seasonal changes and lime additions. The proton binding pK_a values grouped in three distinct classes: pK_a1 = 4.20–4.28; pK_a2 = 6.61–6.87; and pK_a3 = 9.27–9.8. The average total proton binding site concentration of the NOM samples was: 12.7 meq/g total organic carbon (TOC). Two binding sites were established for copper with average log K1 = 4.84 and log K2 = 7.17. The average site concentration for samples isolated by reverse osmosis (RO) was 0.56 μmol/mg C. Copper binding characteristics appear to be influenced by the method of sample isolation. For NOM isolated by low pressure evaporation (evap), binding site concentrations are smaller, conditional stability constants are higher, variability of the copper complexation capacity is smaller, and correlation with elemental composition (C, N, H) is better than in the case of NOM isolated by RO.     

Characterization of Norwegian natural organic matter: Size,diffusion coefficients,and electrophoretic mobilities

Eighteen Norwegian NOM samples were analyzed by AFM, TEM, FCS, and CE. The TEM and AFM gave complementary, but not identical, information regarding the conformation of the NOM. A large majority of the material in all samples appeared as points with a size of approximately 2 nm or less. FCS gave values for diffusion coefficients which were in the range 2.1–3.0 × 10⁻¹⁰ m² s⁻¹. This corresponds to molecular diameters of between 1.6 and 2.0 nm, in reasonable agreement with both TEM and AFM. Electropherograms, using absorbance at 200 nm, were all dissimilar except for the Gjerstad and Hellerudmyra sample pairs, for which no major differences were observed. CE was also carried out using both fluorescence (excitation at 325, 457, and 488 nm) and UV-absorbance (200, 210, 254, and 288 nm) detection on three of the NOM samples. The different modes of detection and wavelengths gave qualitatively similar electropherograms. Calculated EPMs of the major sample components were in the range -2.0 to -5.0 10⁻⁸ m² s⁻¹ V⁻¹.     

Radiocarbon and stable carbon isotope compositions of chemically fractionated soil organic matter in a temperate-zone forest

To better understand the role of soil organic matter in terrestrial carbon cycle, carbon isotope compositions in soil samples from a temperate-zone forest were measured for bulk, acid-insoluble and base-insoluble organic matter fractions separated by a chemical fractionation method. The measurements also made it possible to estimate indirectly radiocarbon ((14)C) abundances of acid- and base-soluble organic matter fractions, through a mass balance of carbon among the fractions. The depth profiles of (14)C abundances showed that (1) bomb-derived (14)C has penetrated the first 16cm mineral soil at least; (2) Delta(14)C values of acid-soluble organic matter fraction are considerably higher than those of other fractions; and (3) a significant amount of the bomb-derived (14)C has been preserved as the base-soluble organic matter around litter-mineral soil boundary. In contrast, no or little bomb-derived (14)C was observed for the base-insoluble fraction in all sampling depths, indicating that this recalcitrant fraction, accounting for approximately 15% of total carbon in this temperate-zone forest soil, plays a role as a long-term sink in the carbon cycle. These results suggest that bulk soil organic matter cannot provide a representative indicator as a source or a sink of carbon in soil, particularly on annual to decadal timescales.     

Sorption of metals onto natural organic matter as a function of complexation and adsorbent-adsorbate contact mode

The effect of complexing anion and adsorbate-adsorbent contact mode (static equilibrium or dynamic non-equilibrium) on binding and partition of Cu(2+), Cd(2+) and Zn(2+) onto organic matter (exemplified in a low-moor peat) was studied. The study comprised comparative batch and column flow-through sorption experiments on monometallic solutions of Me-Cl and Me-SO(4) salts, at pH 4.0, and sequential fractionation of sorbed metals with respect to binding strength. Both the presence of an anion having complexing properties (Cl(-)) as well as a contact mode was found to quantitatively and qualitatively affect the sorption capacity and binding strength of organic matter (peat) for metal ions. Complexing effect of Cl(-) on metal ions resulted mostly in reduction of metal ability to form strongly bound metal-organic compounds, in accordance with the order of stability constant of complex ions log K: Cd>Zn>Cu. Flow-through (dynamic) contact mode, which is the most appropriate to simulate environmental conditions, appeared to strongly attenuate the complexing effect of chloride ions on Cd and Zn sorption, and significantly enhance sorption capacity also in the absence of complexing ions. For Cd, it was mainly due to the enrichment in the strongly bound "insoluble organic" fraction, while for Zn the quantitative increase of sorption capacity did not alter significantly its partitioning. Neither a quantitative nor qualitative effect of contact mode on Cu binding was observed. Complex and diverse effects of different environmental parameters on metal sorption capacity and binding strength onto organic matter, which strongly influence metal mobility, leads to the conclusion that the correct simulation of these parameters for ecotoxicological testing is crucial for the reliable predicting of metal bioavailability under actual terrestrial environmental conditions.     

Depth profiles of radiocarbon and carbon isotopic compositions of organic matter and CO2 in a forest soil

Depth profiles of the specific activities of (14)C and carbon isotopic compositions (Delta(14)C, delta(13)C) in soil organic matter and soil CO(2) in a Japanese larch forest were determined. For investigating the transport of CO(2) in soil, specific activities of (14)C, Delta(14)C and delta(13)C in the organic layer, and atmospheric CO(2) in the same forest area were also determined. The specific activity of (14)C and Delta(14)C in the soil organic matter decreased with the increase in depth of 0-60cm, while that of soil CO(2) did not vary greatly at a soil depth of 13-73cm and was more prevalent than that of atmospheric CO(2). Peaks of specific activities of (14)C appeared at the depth of 0-4cm and Delta(14)C values were positive in the depth range from 0 to 15cm. These results suggest that the present soil at a depth of 0-4cm had been produced from the mid-1950s up until 1963, and the bomb C had reached the depth of 15cm in the objective soil area. The delta(13)C in the soil organic matter increased at the depth of 0-55cm, while that of soil CO(2) collected on 8 November 2004 decreased rapidly at the depth of 0-13cm and only slightly at the depth of 53-73cm. By combining the Delta(14)C and delta(13)C of the respective components and using the Keeling plot approach it was made clear that the entering of atmospheric CO(2) showed a large contribution to soil CO(2) at the depth of 0-13cm and a negligible contribution at the depth of 53-73cm for soil air collected on 8 November 2004. Respiration of live roots was presumed to be the main source of soil CO(2) at the depth of 53-73cm on 8 November 2004.     

Distribution of tritium in estuarine waters: the role of organic matter

Tritium is an important environmental radionuclide whose reactivity with ligands and solids in aquatic systems is assumed to be limited. We studied the fractionation and sorption of tritium (added as tritiated water) in river water and seawater, and found that its distribution appears to be influenced by its affinity for organic matter. Tritium rapidly equilibrates with dissolved organic ligands that are retained by a reverse-phase C18 column, and with suspended sediment particles. Significantly, a measurable fraction of sorbed tritium associates with proteinaceous material that is potentially available to sediment-feeding organisms. These characteristics have not been reported previously and cannot be accounted for solely by isotopic exchange with hydrogen. Nevertheless, they are in qualitative agreement with available measurements of tritium in estuarine and coastal waters where its principal discharge is as tritiated water. Further research into the estuarine biogeochemical behaviour of tritium is required and radiological distribution coefficients and concentration factors that are assumed for this radionuclide may require reconsideration.     

Possible role of organic matter in radiocaesium adsorption in soils

The aim of this review is to examine the hypothesis that organic matter decreases the adsorption of radiocaesium on clay minerals. The factors that determine radiocaesium mobility and bioavailability in soil are briefly outlined to show why a relationship between soil organic matter content and enhanced Cs bioavailability is paradoxical. In all the investigations reviewed the ionic compositions of both the solid and the solution phases have been strictly controlled. We show that the addition of organic matter to reference clay minerals causes decreases of up to an order of magnitude in the distribution coefficient of radiocaesium. Similarly, the chemical removal of organic matter from the clay-sized fraction of soil usually leads to an increase in Cs adsorption. We suggest that the nature of the organic matter and its interaction with mineral surfaces are as important as the amount present.     

Modelling organic matter dynamics in New Zealand soils.

To ensure the sustainability of land systems in terms of nutrient cycling and maintenance of soil physical conditions, there is a need to understand soil organic matter (SOM) and its dynamics. It has been suggested that soil-carbon (C) models developed internationally do not perform well under New Zealand's unique climatic and soil mineralogical conditions. To test this hypothesis, we conducted 14C-labelled ryegrass decomposition studies and assessed the influence of abiotic factors on decomposition rates. These factors were characterized by estimating system mean residence times (MRTs) from estimates of first-order rate coefficients in a simple, three-compartment model. A range of MRTs obtained for decomposition was related to climatic conditions and soil properties. We summarise this work and extend this study to apply the Rothamsted soil-C turnover model, a five-compartment model, to our data with the view of testing both the model projections and the decomposability factors assumed in the model.     

Acid-base characteristics of organic carbon in the HUMEX lake Skjervatjern

The Humic Lake Acidification Experiment (HUMEX) was launched in 1988 to study the role of humic substances in the acidification of surface waters and the impacts of acidic deposition on the chemical and biological properties of humic substances. This subproject was designed to determine the contribution of organic acids to the acidity of Lake Skjervatjern (the HUMEX Lake) and the impacts of the acidification on the characteristics of organic carbon. In order to get an empirical measure for organic acidity, dissolved organic carbon (DOC) was fractionated, isolated, and base-titrated from each half of Lake Skjervatjern. Hydrophobic acids were the dominant organic carbon fraction; the total organic acid content was generally greater than 80% of the DOC. The reliability of the fractionation procedure was tested with synthetic acids and the Nordic Fulvic acid. The DOC fractions did not show high variation over the 1.5-y acidification period. Hydrophilic acids had consistently greater exchange acidities compared to hydrophobic acids, averaging 12.9 μeq/mg DOC vs. 10.9 μeq/mg DOC, respectively. The dissociation of organic acids during acid-base titrations clearly increased with increasing pH. The high organic anion contribution to the ion balances indicates that humic matter is an important acidity source in Lake Skjervatjern. There are slight signs that the contribution of organic acids to overall lake acidity has decreased since acidification was initiated.     

Fluxes of dissolved organic matter in larch forests in the cryolithozone of central Siberia

Fluxes of dissolved organic matter (DOM) in larch biogeocenoses and its export from the drainage basin have been studied in the zone of continuous permafrost. A comparative assessment of DOM input into the soil has been made on slopes of northern and southern exposures (as variants reflecting the current state and warming). The dynamics of DOM export in a creek depending on the increasing depth of the active soil horizon in the drainage area have been revealed. It is concluded that an increase in the depth of the seasonally thawing layer induced by global warming will not have any significant effect on the amount of annual DOM export. Reduction of DOM export may be expected upon a decrease in litter stocks under the effect of their mineralization and forest fires.     

Arsenic mobilization from iron oxyhydroxides is regulated by organic matter carbon to nitrogen (C:N) ratio

Arsenic (As) is mobilized from delta and floodplain aquifer sediments throughout S.E. Asia via reductive dissolution of As bound to iron (Fe) oxyhydroxides. The reductive driving force is organic carbon, but its source and constitution is uncertain. Here batch incubation experiments were conducted to investigate the role of organic matter (OM) carbon:nitrogen (C:N) ratio on the mobilization of arsenic, Fe and N from As dosed, Fe oxyhydroxide coated sands. As mobilization into pore waters from the sand was strongly regulated by the C:N ratio of the OM, and also the concentration of OM present. The lower the C:N, the more As released. Fe and ammonium release were similarly dependent on the quality and quantity of OM, but Fe mobilization was more rapid and ammonium release slower than As suggesting that the mobilization of these 3 moieties although interdependent, were not directly linked. It was concluded that low C:N ratios for OM responsible for reducing aquifers were As in groundwater is observed were likely.     

Efficiency of natural reproduction of sturgeons in the lower Volga under current conditions

The results are presented that have been obtained during long-term studies (1991–2009) on the efficiency of natural reproduction of the beluga, Russian sturgeon, stellate sturgeon, and sterlet in different spawning zones of the Volga. The influence of major environmental factors on the formation of the offspring of these fishes is analyzed. It is shown that the productivity of Volga spawning grounds varies depending on the river flow volume during spring floods and the abundance of active spawners. Practical recommendations are proposed for enhancing sturgeon reproduction in the Volga.     

Characterization of natural organic matter from eight Norwegian surface waters: The effect of ash on molecular size distributions and CHN content

Natural organic matter (NOM) was isolated by reverse osmosis (RO) from eight surface waters in southern Norway. The freeze-dried samples were reconstituted in deionized water and part of the sample was dialysed against HCl. Samples of both the dialysed and non-dialysed materials were then ultrafiltered to give fractions: >50 000 dal., <50 000 but >10 000 dal. and <10 000 dal. nominal molecular weights (NMW). Dialysis against acid reduced the ash content of the samples by 68±14%. Non-dialysed NOM has a preponderance of carbon in the largest fraction (52.7±30%), while after dialysis, the smallest fraction of NOM has the greatest carbon content (52.2±9.7%). In addition to altering the overall apparent size distributions of the NOM fractions, dialysis generally reduces the amount of nitrogen relative to carbon in the NOM samples. The latter observation appears to be the result of losses of small molecular size organic matter that is enriched in nitrogen.