Fractionation of dissolved organic matter affected by polyvalent metal cations

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.     

Dissolved organic matter fluorescence spectroscopy as a tool to estimate biological activity in a coastal zone submitted to anthropogenic inputs

Here we report on an investigation of the three-dimensional excitation-emission-matrix (EEM) fluorescence spectra of unconcentrated water samples collected in 1996, 1998 and 1999 at a site particularly propitious for macro-algae development. The degradation of these macro-algae was studied to determine the influence of their exudates on natural water EEM fluorescence spectra. This work demonstrates that biological activity is one of the major factors involved in the formation of the blue-shifted fluorescence band observed in marine waters (β component Ex/Em=310–320 nm/380–410 nm); our study also shows that fluorescence can be used to evaluate the biological activity both quantitatively and to determine its different phases.     

Sources and composition of organic matter for bacterial growth in a large European river floodplain system (Danube, Austria)

Dissolved and particulate organic matter (DOM and POM) distribution, lignin phenol signatures, bulk elemental compositions, fluorescence indices and microbial plankton (algae, bacteria, viruses) in a temperate river floodplain system were monitored from January to November 2003. We aimed to elucidate the sources and compositions of allochthonous and autochthonous organic matter (OM) in the main channel and a representative backwater in relation to the hydrological regime. Additionally, bacterial secondary production was measured to evaluate the impact of organic carbon source on heterotrophic prokaryotic productivity. OM properties in the backwater tended to diverge from those in the main channel during phases without surface water connectivity; this was likely enhanced due to the exceptionally low river discharge in 2003. The terrestrial OM in this river floodplain system was largely derived from angiosperm leaves and grasses, as indicated by the lignin phenol composition. The lignin signatures exhibited significant seasonal changes, comparable to the seasonality of plankton-derived material. Microbially-derived material contributed significantly to POM and DOM, especially during periods of low discharge. High rates of bacterial secondary production (up to 135 μg C L(-1) d(-1)) followed algal blooms and suggested that autochthonous OM significantly supported heterotrophic microbial productivity.     

Role of organic matter in the accumulation of platinum in oceanic ferromanganese deposits

In order to elucidate possible processes leading to platinum accumulation in ferromanganese deposits, we analyzed published data on the interaction of dissolved platinum species in different valence states with iron and manganese oxyhydroxides under oceanic conditions and experimentally studied the kinetics of sorption of inorganic and organic complexes of platinum (II) and platinum (IV) on synthetic iron and manganese oxyhydroxides and natural materials (marine colloids, and ferromanganese crust samples). The role of dissolved and suspended particulate aquatic organic matter in the sorption accumulation of platinum was evaluated. Possible reasons for the preferential (compared with other noble metals) accumulation of platinum in oceanic ferromanganese deposits were discussed.     

Origin and composition of organic matter in tidal flat sediments from the German Wadden Sea

Two sediment cores of up to 550 cm length from an intertidal flat of the German Wadden Sea near the island of Spiekeroog were investigated for the quantity and composition of fossil organic matter (OM). The lowermost parts of the cores are dominated by grey mud of a salt marsh facies containing mainly terrestrial OM estimated to account for 60–75% of the total OM, based on δ¹³C values and the ratio of short to long chain n-alkanols. The terrigenous origin of the dominant fraction is indicated, among others, by high proportions of C₂₉ sterols and long chain n-alkanes typical of plant waxes. Coarse shell beds overlying the grey mud at 2–2.5 m depth represent a flooding and erosion event possibly related to heavy storm floods in the Middle Ages. Within the intertidal sand-dominated sediments in the upper parts of the cores total organic carbon (TOC) contents are generally low, ranging from 0.1% to 0.5%, and correlate well with the amount of mud fraction (r² 0.90). At the surface, marine OM has not undergone intense diagenetic alteration and so is the dominant fraction. Eroded peat particles are common throughout most of the sequence and values of the Phragmites peat indicator (PPI) > 5 indicate an origin from reed peat due to a high relative abundance of the n-C₂₄ alkane. Changes in the composition of microbial communities over the depth interval investigated are documented by varying compositions of unsaturated fatty acids with 16 and 18 carbons. Eicosapentaenoic acid (EPA) was detected along the entire cores and indicates the presence of EPA-producing bacterial strains.     

Microanalysis of carbon isotope composition in organic matter by secondary ion mass spectrometry

An analytical procedure has been developed for the in situ measurement of carbon isotope composition of organic matter, with a spatial resolution of 20-30 μm, using a Cameca IMS 1270 ion microprobe. Instrumental mass fractionation (IMF) of carbon isotopes was observed to be independent of primary ion beam intensity and sputtering time, but did depend on vacuum conditions and on the chemical composition of the sample. To evaluate such “matrix effects”, a set of 9 standards representative of the natural chemical variability of organic matter was prepared, with H/C atomic ratios and organic carbon contents (C_org) ranging between 0.04 and 1.74 and between 41 and 100 wt.%, respectively. Under the analytical conditions tested, IMF was not found to be influenced by the presence of silicate mineral impurities in the organic matter, but variations in IMF up to 5‰ were observed over the set of standards with the magnitude of IMF negatively correlated to the H/C ratios of samples. Aliphaticity ratios determined using Fourier transform infrared microspectroscopy provided an in situ estimation of H/C ratios with a spatial resolution barely exceeding that of the ion microprobe and permit a correction for matrix effects with a standard error of ± 0.2‰ (1σ). Taking into account all sources of uncertainty, ion microprobe δ¹³C were accurately determined with a ± 0.7‰ (1σ) total uncertainty. The mechanism for the matrix effect of H/C ratios upon IMF is still to be determined but it is likely related to the difference in proportion of atomic vs. molecular carbon ions observed between samples of different H/C ratios.     

有机质在铀成矿过程中作用的实验模拟研究

沉积型铀矿的形成与有机质存在密切联系。实验模拟研究表明:芳香有机酸在弱酸到弱碱性条件下很容易和铀酰根离子发生配位反应,它能通过羧基上的氧原子以多种配位形式和铀形成配位键。此结果验证了前人的一些结论,并直观地展现了有机质的主要官能团与铀离子在溶液中的一些迁移形式。模拟实验结果也显示了烃类在水热条件下对铀成矿的还原作用,它能将六价铀还原成四价铀而沉淀下来。     

Research on the carbon isotopic composition of organic matter from Lake Chenghai and Caohai Lake sediments

The carbon isotopic composition of organic matter from lake sediments has been extensively used to infer variations in productivity. In this paper, based on the study of the contents and δ13C values of organic matter in different types of lakes, it has been found that δ13C values of organic matter have different responses to lake productivity in different lakes. As to the lakes dominated by aqutic macrophytes such as Lake Caohai, organic matter becomes enriched in 13C with increasing productivity. As to the lakes dominated by aquatic algae such as Lake Chenghai, δ13C values of organic matter decrease with increasing productivity, and the degradation of aquatic algae is the main factor leading to the decrease of δ13C values of organic matter with increasing productivity. Therefore, we should be cautious to use the carbon isotopic composition of organic matter to deduce lake productivity.     

Variability of tetraether lipids in Yellow River-dominated continental margin during the past eight decades: Implications for organic matter sources and river channel shifts

Glycerol dialkyl glycerol tetraethers (GDGTs) and bulk organic geochemical parameters were examined for a short core from the Bohai Sea, a Yellow River-dominated continental margin. A three end member mixing model using branched/isoprenoid tetraethers (BIT) index, δ¹³C and C/N shows that the average fractions of soil, marine and plant organic matter (OM) during the period of 1933–2011 are 67.7% (38–92%), 26.1% (0–58%) and 6.2% (0–23%), respectively. Abrupt changes of sedimentary OM compositions around 1953, 1976 and 1996 are synchronous with the Yellow River mouth relocations. The BIT index values (0.33–0.80) present a stronger correlation with crenarchaeol abundance (R² = 0.88) than branched GDGTs abundance (R² = 0.27), suggesting that variations of marine Thaumarchaeota abundance rather than soil OM inputs is the first order factor controlling the BIT index values, although this proxy has been widely used for soil OM. The comparison between the BIT index, nutrient status and historical Yellow River sediment load indicates that the high sensitivity of the BIT index to the Yellow River channel shifts cannot be explained by a nutrient stimulation mechanism, but instead is likely caused by the restriction of Thaumarchaeota growth in highly turbid water due to the enormous sediment inputs from Yellow River. Our study demonstrates that local conditions should be considered when applying the BIT index as an environmental proxy.     

HT-IRMS测定有机物氧同位素过程的影响因素及方法改进

高温裂解元素分析仪与气体同位素质谱仪联用系统（HT-IRMS）是测定有机物氧同位素的重要方法,优化HT-IRMS的参数、提高其可靠性和稳定性一直是各实验室努力的方向。本研究基于国际标准物质IAEA-601和IAEA-C3的多次测量,对HT-IRMS测定结果的稳定性进行了检验。结果显示,手动进样模式下,测定值比较稳定（标准偏差分别为0.16‰和0.25‰）,而自动进样模式的测定结果波动变化显著且呈现偏负漂移趋势,IAEA-601和IAEA-C3最大波动程度分别达到3.00‰和4.26‰。通过对比分析测定结果,本文推断自动进样模式下氧同位素的漂移可能源于空气中的水汽的污染。通过在自动进样盘位置加装隔离罩装置,将自动进样盘与实验室空气进行隔离之后,自动进样模式下再次重复测定结果较为稳定（标准偏差分别为0.35‰和0.25‰）,有机物氧同位素负漂移趋势基本消除,表明使用隔离罩装置可以有效减少实验室空气中水汽对样品的干扰,降低实验室环境参数变化对同位素测定结果的影响,提高HT-IRMS系统测定有机物氧同位素的稳定性。

     

Heavy metals in sediments of a large, turbid tropical lake affected by anthropogenic discharges

 Bottom-water data and trace metal concentration of Cu, Cr, Ni, Pb, Co, Zn, and organic matter in surficial sediment samples from 13 sampling stations of Lake Chapala in Mexico were studied. The lake is turbid with a great amount of flocculated sediments as a result of wind mixing, sediment re-suspension, and Lerma River discharges. Al distribution pattern in sediments was used as an indicator of the Lerma River discharges into Lake Chapala. The highest values of Cu (33.27 ppm), Cr (81.94 ppm), Pb (99.8 ppm), and Zn (149.7 ppm) were detected in sediments near the lake outlet. The bioavailable metal fraction is low for all metals except Pb, which shows 65–93% of the total metal concentration in bioavailable form. The minimum energy zone in the lake was related to organic matter concentration and was located in the SE part of the lake. An analysis of the studied parameters shows two zones: eastern zone (fluvio-deltaic) and central-western zone (lacustrine). Received: 9 September 1998 · Accepted: 16 November 1998     

Exportation of coseismic deposits in areas affected by the Wenchuan earthquake

Coseismic deposits are easily transported outside of valleys, thereby inflicting damage through debris flows or aggregating and elevating riverbeds in the fluvial network. The evolution of coseismic deposits is crucial for predicting the sediment transport capacity and export time for managing postseismic geohazards; however, this evolution remains unclear. In this study, the spatiotemporal evolution of coseismic deposits due to rainfall is quantified at the valley scale to further obtain the sediment transport capacity. The results show that the relative average thickness predominantly controls the evolution pattern of the coseismic deposits. The sediment transport capacity, which is primarily influenced by rainfall conditions and topography, can be drastically increased by dam breaching and channel narrowing. Moreover, the computed export time, which significantly varies with the spatiotemporal distribution of deposits and the local climate, ranges from 2 to 80 years in the areas affected by the Wenchuan earthquake. This study contributes to providing scientific guidelines for efficiently managing postseismic geohazards and planning for disaster mitigation.

     

Bacteriohopanepolyol biomarker composition of organic matter exported to the Arctic Ocean by seven of the major Arctic rivers

Bacteriohopanepolyols (BHPs) are a diverse group of membrane lipids produced by a wide variety of bacteria and can be used as molecular biomarkers for bacterial processes and populations in both modern and ancient environments. A group of BHPs, including adenosylhopane and structurally related compounds, have been identified as being specific to soils, enabling the transport of terrestrial organic matter (terrOM) to the marine realm to be monitored. Estuary surface sediment samples were obtained from the five Great Russian Arctic Rivers (GRARs; Ob, Yenisey, Lena, Indigirka and Kolyma) and river sediments were obtained from two North American Rivers (Yukon and Mackenzie). Analysis of the BHP signatures, using high performance liquid chromatography–tandem mass spectrometry (HPLC–MSⁿ), indicated the presence of 15 different BHPs originating from a variety of different bacteria, as well as a significant presence of terrestrially derived OM. Total BHP abundance and the contribution of the “soil-marker” BHPs to the total BHP pool increased eastwards among the GRAR sediments. This suggests increasing terrestrial OM or increased preservation of OM as a result of shorter periods of permafrost thawing. The North American rivers showed greatly differing BHP levels between the Yukon and Mackenzie rivers, with a greater BHP input and thus a relatively higher soil OM contribution from the Yukon. The Indigirka River basin in the eastern Siberian Arctic appeared to be the epicentre in the pan-Arctic BHP distribution trend, with the highest “soil-marker” BHPs but the lowest tetrafunctionalised BHPs. Aminobacteriohopanepentol, an indicator of aerobic methane oxidation, was observed in all the sediments, with the source being either the marine environment or methane producing terrestrial environments.     

Changes in the composition of organic matter from prodeltaic sediments after a large flood event (Po River, Italy)

The Po River (Italy) experienced a 100-year flood in October 2000. Surface sediments (0-1 cm) from cross-shelf transects were collected in the Po prodelta area (Adriatic Sea) in December 2000, in order to describe the distribution of organic matter (OM) along the main sediment dispersal system immediately after the flood event. Stations were subsequently reoccupied in October 2001 and April 2002. This sampling program provided a special opportunity to characterize the initial surficial flood deposit and the evolution of its associated OM over the course of 2 years. CuO oxidation, elemental, δ¹³C, Δ¹⁴C, and grain-size analyses were carried out to characterize the source, age, and spatial variability of sedimentary OM. Statistical analysis (PERMANOVA) was then applied to investigate temporal changes in different portions of the Po prodelta area. Isotopic and biomarker data suggest that the sedimentary OM in the flood deposit was initially dominated by aged (Δ¹⁴C_Dec-00 = −298.7 ± 56.3‰), lignin-poor OM (Λ_Dec-00 = 1.96 ± 0.33 mg/100 mg OC), adsorbed on the fine material (clay_Dec-00 = 72.1 ± 4.8%) delivered by the flood. In the 2 years following the flood, post-depositional processes significantly increased the content of lignin (Λ_Oct-01 = 2.19 ± 0.51 mg/100 mg OC; Λ_Apr-02 = 2.61 ± 0.63 mg/100 mg OC); and coarse material (silt and sand), while decreasing the contributions from aged OC (Δ¹⁴C_Oct-01 = −255.7 ± 32.8‰; Δ¹⁴C_Apr-02 = −213.2 ± 30.4‰) and fine fraction (clay_Oct-01 = 54.8 ± 9.5%; clay_Apr-02 = 44.6 ± 13.3%). The major changes were observed in the northern and central portions of the prodelta.     

Heterogeneous organic matter from the surface horizon of a temperate zone marsh

Abundance, bulk chemical composition and sources of the organic matter in the surface horizon of the permanently water-covered part of an intermittently water-covered marsh were investigated. Lipids, insoluble non-hydrolysable macromolecular organic matter and black carbon fractions were isolated and examined via Rock-Eval pyrolysis, elemental analysis, Fourier transform infrared spectroscopy, isotopic (δ¹³C, δ¹⁵N) methods and high resolution transmission electron microscopy. Integration of bulk Rock-Eval data, elemental and isotopic composition, together with spectroscopic features, suggested immature Type III organic matter derived mainly from C₃ vascular plants. The distribution of n-alkanes from the non-aromatic lipid fraction exhibited the importance of emergent macrophytes and terrestrial plants, as well as a moderate input of submerged/floating macrophytes to the source biomass. Mathematical deconvolution of a Rock-Eval pyrogram revealed highly heterogeneous organic matter composed of a mixture of thermally labile biopolymers (36%) at various stages of decomposition, as well as humic substances and highly refractory organic matter (64%) in the whole sample. Markedly lower heterogeneity and aliphaticity, together with a higher proportion of humic substances and highly refractory organic matter (ca. 84%) were observed in the macromolecular fraction. An abundant contribution of black carbon to the macromolecular fraction was indicated by mathematical deconvolution of the Rock-Eval pyrogram and was clearly shown by the isolation of this fraction and chemical oxidation. The black carbon fraction appeared to account for ca. half of the macromolecular fraction, the carbon in these two fractions representing 30% and 14% of the initial carbon, respectively. The electron microscopy observations directly evidenced the presence of black carbon, which was comprised of both amorphous poorly organized particles and highly ordered onion-shaped particles.     

Kinetics of copper desorption from soils as affected by different organic ligands

Desorption of Cu and low molecular weight dissolved organics are the primary factors that impact fate and transport of Cu in soils. To improve predictions of the toxicity and threat from Cu contaminated soil, it is critical that time-dependent desorption behavior be understood. In this paper, the effect of organic ligands citrate, malate, and succinate on the kinetics of Cu desorption from contaminated soils varying widely in soil characteristics was investigated at 25° C and the soils used were referred to as clay, calcareous and sandy soils. The amount of Cu released by the used organic ligands varied greatly with physicochemical properties of the soils. The rate of Cu release by different extractants was in the order citric > malic > succinic, which was consistent with the stability constants of Cu complexes with these ligands. The modified Freundlich and the Elovich and Parabolic diffusion models were used to describe dsorption of Cu²⁺ from the three studied soils as affected by the organic ligands. All of the models fit the data well with correlation coefficients ranging from 0.83 to 1.00 (P < 0.01). Each Model has a set of assumptions for the different physical and chemical properties of the systems to which they are being applied. The uses of these equations yield different magnitudes for the calculated variable, but the relationships between the soil + organic ligands and their effect (i.e., increase or decrease) on these variables are the same. Such information is critical, since Cu is used in a variety of industrial and manufacturing processes and is one of the most common contaminants found at hazardous waste sites.     

Abandoned channel fill sequences in the tidal estuary of a small mountainous,dry‐summer river

This study proposes a modification of the current model for abandoned channel fill stratigraphy produced in unidirectional flow river reaches to incorporate seasonal tidal deposition. Evidence supporting this concept came from a study of two consecutive channel abandonment sequences in Ropers Slough of the lower Eel River Estuary in northern California. Aerial photographs showed that Ropers Slough was abandoned around 1943, reoccupied after the 1964 flood, and abandoned again in 1974 with fill continuing to the present. Planform geomorphic characteristics derived from these images were used in conjunction with sub‐centimetre resolution stratigraphic analyses to describe depositional processes and their resultant sedimentary deposits. Both abandonment sequences recorded quasi‐annual scale fluvial/tidal deposition couplets. In both cases, tidal deposits contained very little sand, were higher in organic and inorganic carbon content than the sandier, fluvially dominated deposits, and possessed millimetre‐scale horizontal laminations. The two abandonment fills differed significantly in terms of the temporal progression of channel narrowing and fluvial sediment deposition characteristics. Aerial photographic analysis showed that the first abandonment sequence led to a more rapid narrowing of Ropers Slough and produced deposits with a positive relationship between grain size/deposit thickness and discharge. The second abandonment resulted in a much slower narrowing of Ropers Slough and generally thinner fluvial deposits with no clear relationship between grain size/deposit thickness and discharge. The δ¹³C values and organic nitrogen to organic carbon ratios of deposits from the first phase overlapped with Eel River suspended sediment characteristics found for low flows (one to five times mean discharge), while those of the second phase were consistent with suspended sediment from higher flows (seven to ten times mean discharge). When considered together, the results indicate that the early fill sequence recorded a reach experiencing regular fluvial deposition through flow conditions during the wet season, while the latter fill sequence records a reach more disconnected from the main stem in terms of flow and sediment. The major factor affecting the difference in sedimentation between the two fill periods appears to have been the morphology of the upstream river bend in relation to the position of the bifurcation node. During the first fill period, the upstream entrance to Ropers Slough seems to have remained open, in part due to the placement of its entrance on the outside of the mainstem river bend, and despite stronger tidal effects caused by a larger tidal prism and closer proximity to the tidal inlet. By the second fill sequence, the upstream bend morphology had altered, placing the entrance to Ropers Slough on the inner bank of the mainstem bend, which resulted in more rapid plug bar formation. The role of tidal effects in the geomorphic trajectory of the two abandonment sequences is unclear, but appears to have been less important than local bifurcation geometry.