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1.
The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS 15N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by 15N NMR. Liquid state 15N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (1H–15N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.  相似文献   

2.
The role of organic matter (OM) concentration, structure and composition and how these relate to mineral protection is important for the understanding of long term soil OM dynamics. Various OM–clay complexes were constructed by sequential sorption of lignin and dodecanoic acid to montmorillonite. Humic acid–montmorillonite complexes were prepared at pH 4 and 7 to vary OM conformation prior to sorption. Results obtained with constructed OM–clay complexes were tested with isolated mineral fractions from two soils. Oxidation with an acidic NaClO2 solution was used to chemically oxidize lignin in the OM–clay complexes, sand-, silt- and clay-size soil fractions to test whether or not it can be protected from chemical attack. Gas chromatography–mass spectrometry was used to analyze lignin-derived phenols, cutin OH–acid (after CuO oxidation), fatty acid and n-alkanol concentrations and composition. We found that carbon content was not solely responsible for lignin stability against chemical oxidation. Lignin was protected from chemical oxidation through coating with dodecanoic acid and sorption of humic acid to clay minerals in a stretched conformation at pH 7. Therefore, interactions between OM constituents as well as OM conformation are important factors that protect lignin from chemical oxidation. Lignin-derived phenol dimers in the Grassland-Forest Transition soil fractions were protected from chemical oxidation to a greater extent compared to those in Grassland soil fractions. Therefore, although lignin was protected from degradation through mineral association, the extent of this protection was also related to OM content and the specific stability of lignin components.  相似文献   

3.
The molecular structural features of humic acid (HA) fractions isolated from recent sediments from the estuaries and continental platform along the Huelva littoral (SW Iberian Peninsula, Spain) were studied using complementary analytical tools. The approach included elemental analysis, solid state, 13C cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (13C CP-MAS NMR), pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) and stable C and N isotopic composition (δ13C, δ15N). The results point to the presence of vascular plant matter contributing to all the HAs, even those far from the coastal area. A contribution of lignocellulose material was detected from 13C NMR signals at 152 ppm (O-aryl C), 55 ppm (methoxyl C) and 33 ppm (alkyl chain) and confirmed by the presence of lignin derived structures (methoxy phenols) in the pyrolysis chromatograms. Nevertheless, the HAs from the westernmost part of the continental platform had the lowest aromatic and the highest C-alkyl abundance (13C NMR spectroscopy). These data, combined with low C/N and high H/C values, a relative enrichment in δ13C and the presence in the pyrolysates of conspicuous n-alkyl nitrile and amide series, together with n-alkane/ene homologues, pointed towards a relevant marine (autochthonous) contribution to this sedimentary organic matter (OM). In contrast, HAs from sediments collected from the Tinto-Odiel River mouth and Guadiana Estuary areas revealed a major input of terrestrial OM. In general, the data support the idea that the HAs still contain valuable information about the signature of aliphatic and aromatic biomacromolecules contributing to the deposited OM.  相似文献   

4.
The acid-base properties of 14 standard and reference materials from the International Humic Substances Society (IHSS) were investigated by potentiometric titration. Titrations were conducted in 0.1 M NaCl under a nitrogen atmosphere, averaging 30 min from start to finish. Concentrations of carboxyl groups and phenolic groups were estimated directly from titration curves. Titration data were also fit to a modified Henderson-Hasselbalch model for two classes of proton-binding sites to obtain “best fit” parameters that describe proton-binding curves for the samples. The model was chosen for its simplicity, its ease of implementation in computer spreadsheets, and its excellent ability to describe the shapes of the titration curves. The carboxyl contents of the IHSS samples are in the general order: terrestrial fulvic acids > aquatic fulvic acids > Suwannee River natural organic matter (NOM) > aquatic humic acids > terrestrial humic acids. Overall, fulvic acids and humic acids have similar phenolic contents; however, all of the aquatically derived samples have higher phenolic contents than the terrestrially derived samples. The acid-base properties of reference Suwannee River NOM are surprisingly similar to those of standard Suwannee River humic acid. Results from titrations in this study were compared with other published results from both direct and indirect titrations. Typically, carboxyl contents for the IHSS samples were in agreement with the results from both methods of titration. Phenolic contents for the IHSS samples were comparable to those determined by direct titrations, but were significantly less than estimates of phenolic content that were based on indirect titrations with Ba(OH)2 and Ca(OAc)2. The average phenolic-to-carboxylic ratio of the IHSS samples is approximately 1:4. Models that assume a 1:2 ratio of phenolic-to-carboxylic groups may overestimate the relative contribution of phenolic groups to the acid-base chemistry of humic substances.  相似文献   

5.
Carbohydrates are major organic components of dung and are likely to contribute substantially to increased carbon stocks in manured soils. To investigate this hypothesis, a field-scale experiment was conducted on a temperate grassland site in Devon, UK. C4 dung (bulk δ13C value ?12.6‰) was applied to a temperate grassland C3 soil (bulk δ13C value ?30.3‰) in April and the surface soil beneath cow pats sampled at seven dates over a year. Total carbohydrates were extracted as their monosaccharide components and analysed as the alditol acetates using gas chromatography. The δ13C values of the major monosaccharides glucose (?11.5 ±0.6‰), xylose (?10.4 ±0.4‰), arabinose (?10.4 ±0.5‰) and galactose (?8.3 ±1.6‰) extracted from the C4 dung via acid hydrolysis were indicative of their source. Their weighted mean δ13C value was ?10.8‰, 1.8‰ more 13C-enriched than the bulk dung value. The δ13C values of individual monosaccharides recovered by acid hydrolysis in the 0–1 cm and 1–5 cm soil horizons beneath C4 cow pats, compared with control soils determined over 372 days, allowed assessment of the extent of incorporation and fluxes of dung-derived monosaccharides. A maximum of 60% of the dung C in soil was derived from carbohydrates after 56 days, declining to around 20% after 372 days. Incorporation dynamics varied between monosaccharide species. Glucose, xylose and arabinose behaved in a similar manner because of their predominantly plant cell wall derived provenance in the dung, whilst dung-derived galactose and mannose appeared to have a microbial source in the soil. The dynamics of total dung-derived monosaccharides in the top 5 cm was comparable to incorporation and flux of bulk dung C, previously estimated using bulk δ13C values. The movement of dung-derived carbohydrates into the soil was inequivalent between the 0–1 cm and 1–5 cm horizons. The lack of a significant difference in concentration, but the evidence for the persistence of dung-derived monosaccharides in soil based on δ13C values, indicated replacement of existing pools in the soil, suggesting that the ability of this particular soil to sequester further C derived from carbohydrates was limited.  相似文献   

6.
《Applied Geochemistry》2006,21(7):1226-1239
Natural organic matter (NOM) from the Han River, Korea was fractionated into humic and non-humic fractions by absorbing onto XAD-7HP, and these fractions were analyzed using UV-absorption, and for dissolved organic C (DOC). The humic fraction (i.e. humic substances; HS) was extracted and its characteristics were compared to commercial humic materials using various spectroscopic methods such as Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H-NMR) and fluorescence spectroscopy. The humic fraction as organic C was 47.0% on the average, however, a rainfall event brought a higher humic fraction into Han River water. The molar ratios of H/C and O/C in the HS from Han River water (HRHS) were 1.40 and 0.76, respectively, and the ratio of aliphatic to aromatic protons in the HS (PAl/PAr ratio) was 5.8. Aromaticity and humification degree (i.e., degree of condensation) of HRHS were relatively lower than those from other humic materials, while the portion of oxygenated functional groups was relatively higher. FT-IR, 1H-NMR and fluorescence spectroscopy showed distinct differences between HRHS and the commercial humic materials. Commercial humic materials are not representative of HS extracted from Han River water. The fluorescence spectra, relatively simple measurements, were found to be most useful as fingerprints for humic materials from particular sources.  相似文献   

7.
Humic substances were isolated from ocean, estuarine water and fresh water using a two column array of XAD-8 and XAD-4 resins in series. The extracted fulvic acids and XAD-4 fraction from different origins were characterized using UV–vis., molecular fluorescence, Fourier transform infrared (FTIR) spectroscopy and cross polarization magic angle spinning (CPMAS)-13C nuclear magnetic resonance (NMR) spectroscopy. The isolation procedure allowed us to obtain the necessary amount of sample for characterization, even in the case of open ocean water, which has a very low amount of dissolved organic carbon (DOC). Humic substances from the open ocean showed the lowest chromophore and fluorophore contents and showed relatively greater fluorescence at lower wavelengths than those from fresh water. FTIR and 13C NMR spectra highlighted the idea that humic substances from a marine environment have a more branched aliphatic structure and less aromatic structure than those highly influenced by terrestrial sources. The spectra also suggest that the open ocean humic substances have a higher content of olefinic carbons than aromatic- or alkyl-substituted carbons.  相似文献   

8.
Inherent chemical recalcitrance and association of organic matter (OM) with minerals are mechanisms responsible for the long term preservation of OM in soils. The structural characteristics of OM are also believed to control specific interactions between OM and soil minerals. However, the extent of the relationship between recalcitrance and mineral protection and the specificity of these chemically driven interactions are not clearly understood at the molecular level. To measure chemical patterns of OM sequestration in sand-, silt-, clay-size and light fractions, we analyzed three soils, which mainly differed in carbon content and overlying vegetation, but have similar clay mineralogy, using biomarker analysis and nuclear magnetic resonance (NMR). Despite differences in environmental controls, long chain aliphatic compounds generally accumulated in the fine fractions of all soils. This accumulation is likely due to the strong interaction between recalcitrant forms of OM and soil minerals. For example, polymethylene and >C20 organic acids accumulated in fine fractions, while lignin-derived phenols were protected from oxidation in silt-size fractions. Diffusion edited solution state 1H NMR suggested that contributions from microbial-derived OM was greater in finer fractions, which is likely due to the accumulation of microbial-derived compounds or higher microbial activity in clay micro-sites. Our data suggest that, for these Prairie soils, the specific structure of OM and not environmental factors is responsible for long term preservation of OM in mineral fractions. Further research is necessary to understand the interplay between these preservation mechanisms such that the long term fate of OM can be further elucidated.  相似文献   

9.
A number of rivers have been found to transport highly aged organic matter [OM]; however, the sources of this aged material remain a matter of debate. One potential source may be erosion and weathering of headwater lithologies rich in ancient sedimentary OM. In this study, waters, suspended particulates, streambed sediments, rocks and soils from fourteen small headwater watersheds of a mid-size, temperate, passive margin river were sampled and characterized by Δ14C, δ13C, and POC/TPN ratios to identify sources of particulate and dissolved OM delivered to the river mainstem. These headwater sites encompass a range in lithology (OM-rich shales, OM-lean carbonate/mudstone facies, and OM-free crystalline rocks) and land use types (forested and agricultural), and allow investigation of the influence of agriculture and bedrock types on stream OM characteristics. Streams draining large areas of both agricultural land use and OM-rich lithology contain particulate OM [POM] that is more 14C-depleted than streams draining forested, shale-free watersheds. However, this is not sufficient to account for the significantly lower Δ14C-POC measured in the river mainstem. Dissolved OM [DOM] Δ14C are in all cases enriched compared to POM from the same stream, but are otherwise highly variable and unrelated to either land use or lithology. POC/TPN ratios were likewise highly variable. POC and DOC δ13C signatures were similar across all watersheds. Based on isotope mass balance, 14C-free fossil OM sources contribute 0-12% of total stream POM. Although these results do not unequivocally separate the influences of land use and lithology, watershed coverage by shale and agriculture are both important controls on stream Δ14C-POC. Thus export of aged, particle-associated OM may be a feature of river systems along both passive and active continental margins.  相似文献   

10.
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11.
Mineral-organic associations act as mediators of litter-derived N flow to the mineral soil, but the time scales and pathways involved are not well known. To close that gap, we took advantage of decade old 15N litter labeling experiments conducted in two European forests. We fractionated surface soils by density with limited disaggregating treatment and investigated organic matter (OM) characteristics using δ13C, δ15N and the C/N ratio. Mineral properties were studied by X-ray diffraction and selective dissolution of pedogenic oxides.Three types of associations were isolated: plant debris with few trapped minerals (<1.65 g/cm3), aggregates dominated by phyllosilicates (1.65-2.4 g/cm3), and single mineral grains and pedogenic oxides with little OM (>2.4 g/cm3). A small proportion of 15N tracer was rapidly attached to single mineral grains, while most of it moved from plant debris to aggregates of low density and progressively to aggregates of higher density that contain a more microbially processed OM. After a decade, 60% of the 15N tracer found in the investigated horizon was retained in aggregates, while plant debris still contained 40% of the tracer.We present a conceptual model of OM and N flow through soil mineral-organic associations, which accounts for changes in density, dynamics and chemistry of the isolated structures. It suggests that microbial reworking of OM entrapped within aggregates (1.65-2.4 g/cm3) causes the gradient of aggregate packing and, further on, controls the flow of litter-derived N through aggregates. For associations with denser material (>2.4 g/cm3), mineralogy determines the density of the association, the type of patchy OM attached to mineral surfaces and controls the extent of litter-derived N incorporation.  相似文献   

12.
Soil interstitial waters in the Green Lakes Valley, Front Range, Colorado were studied to evaluate the capacity of the soil system to buffer acid deposition. In order to determine the contribution of humic substances to the buffering capacity of a given soil, dissolved organic carbon (DOC) and pH of the soil solutions were measured. The concentration of the organic anion, Ai−, derived from DOC at sample pH and the concentration of organic anion, Ax− at the equivalence point were calculated using car☐yl contents from isolated and purified humic material from soil solutions. Subtracting Ax− from Ai− yields the contribution of humic substances to the buffering capacity (Aequiv.−). Using this method, one can evaluate the relative contribution of inorganic and organic constituents to the acid neutralizing capacity (ANC) of the soil solutions. The relative contribution of organic acids to the overall ANC was found to be extremely important in the alpine wetland (52%) and the forest-tundra ecotone (40%), and somewhat less important in the alpine tundra sites (20%). A failure to recognize the importance of organic acids in soil solutions to the ANC will result in erroneous estimates of the buffering capacity in the alpine environment of the Front Range, Colorado.  相似文献   

13.
Large shifts in the isotopic compositions of organic matter (OM) in lake sediments, over the last few hundred years, are commonly interpreted as representing changes in photosynthetic productivity corresponding to eutrophication or in the input of terrestrial OM due to human disturbances. Based on multiple-proxy data (C:N ratio, δ13C and δ15N of OM, δ13C of calcite, lithology and fossil pollen) from a 700-year sediment core at White Lake, New Jersey (USA), we propose a new explanation that relates these large shifts in OM δ13C and δ15N to human-induced changes in aquatic OM producers. Combined records of geochronology, fossil pollen and lithology from White Lake reveal that the upland forest was cleared by European settlers for farmland beginning around 1745 A.D. and has gradually reforested since 1930 after the abandonment of the farmlands. For the pre-agricultural period, OM had relatively constant but extremely low δ13CVPDB (−35.8 to −34.5‰) and δ15NAir (−3.5 to −2.5‰) and high atomic C:N ratios (13.7 to 16.7), indicating a stable anoxic lake environment with prominent microbial producers. Following the human disturbance (since 1745), high OM mass accumulation rates and abundances of the green alga Pediastrum indicate an increase in aquatic photosynthetic productivity due to enhanced nutrient input from disturbed uplands. However, carbonate δ13C remains constant or even decreases during this period, implying that increasing productivity did not elevate the δ13C of dissolved inorganic carbon and thus cannot explain the observed large increase in OM δ13C (7.4‰) and δ15N (5.8‰) over this period. Instead, δ13C, δ15N and C:N ratios of OM and differences in δ13C between calcite and OM suggest that the large increase in OM δ13C and δ15N can be attributed to a human-induced ecological shift in the predominant organic source from anaerobic bacteria to autotrophic phytoplankton. During the post-agricultural period, mass accumulation rates of OM, carbonate and silicate, and the δ13C of OM and calcite all decreased significantly, corresponding to stabilization of the uplands. However, over the last 70 years, an intensifying aquatic stress from the deposition of 15N-enriched industrial pollutants has resulted in a steady increase of 1.9‰ in δ15N. Proxy records for lake (δ13C and δ15N of OM) and upland conditions (pollen and silicates) at White Lake show complex trajectories of the aquatic and terrestrial ecosystems in response to past human disturbances.  相似文献   

14.
《Chemical Geology》2006,225(1-2):77-90
Using density-gradient centrifugation, within-sample heterogeneity in C/N, δ13C, and δ15N was determined for a sample of the Blue Gem coal bed (Middle Pennsylvanian, Duckmantian (Westphalian B), Breathitt Formation) and related to maceral (petrographically identifiable organic component) composition. Relatively pure macerals were separated by density, with purities up to 99% in the case of vitrinite in fractions around 1.3 g/mL. Lower density fractions (∼ 1.2 g/mL) contain predominantly liptinite (∼ 75%) but also significant amounts of vitrinite (∼ 20%). Denser fractions contain increasing amounts of inertinite, with several fractions between 1.37 and 1.44 g/mL containing > 98% total inertinite. Within these denser fractions, semifusinite concentrated at lower densities than did fusinite. The separation of macerals by density allowed a more detailed evaluation of the isotopic composition of relatively pure macerals within a single coal. δ13C becomes increasingly heavy across the density gradient, with δ13C values being lightest in the liptinites, followed by vitrinite, and then semifusinite and fusinite; by contrast, δ15N becomes lighter across the same density range. C/H increases with density, reflecting a general decrease in aliphatic components and increase in aromatic components. C/N follows a similar pattern, ranging from < 40 to over 100, increasing significantly at densities > 1.32, the point at which inertinite macerals begin to predominate over vitrinite.The isotopic composition of macerals reflects chemical composition, which in turn reflects: 1) the original composition of plant tissues from which the macerals originated; 2) early diagenetic changes; and 3) changes during coalification. Macerals derived from lipid-rich precursor materials (liptinites) have more depleted δ13C values (∼ 2‰) relative to those derived from woody tissues (vitrinite). Fusinized material, derived from fossil charcoal, has δ13C values enriched by ∼ 0.5‰ compared with the vitrinite, consistent with the results from combustion experiments using modern plant tissues. Vitrinite fractions have enriched δ15N values relative to inertinite fractions, which may reflect early diagenetic changes in woody tissues involving preferential loss of 14N, possibly due to bacterial activity during the peat-forming stage. Due to the within-sample variability in carbon isotopic composition reported here, it is suggested that chemostratigraphic studies based on Type III kerogen (including both dispersed organic matter and coals) carefully consider the associated effects of variability in maceral composition.  相似文献   

15.
《Organic Geochemistry》2011,42(12):1489-1501
Mineral–organic associations act as mediators of litter-derived N flow to the mineral soil, but the time scales and pathways involved are not well known. To close that gap, we took advantage of decade old 15N litter labeling experiments conducted in two European forests. We fractionated surface soils by density with limited disaggregating treatment and investigated organic matter (OM) characteristics using δ13C, δ15N and the C/N ratio. Mineral properties were studied by X-ray diffraction and selective dissolution of pedogenic oxides.Three types of associations were isolated: plant debris with few trapped minerals (<1.65 g/cm3), aggregates dominated by phyllosilicates (1.65–2.4 g/cm3), and single mineral grains and pedogenic oxides with little OM (>2.4 g/cm3). A small proportion of 15N tracer was rapidly attached to single mineral grains, while most of it moved from plant debris to aggregates of low density and progressively to aggregates of higher density that contain a more microbially processed OM. After a decade, 60% of the 15N tracer found in the investigated horizon was retained in aggregates, while plant debris still contained 40% of the tracer.We present a conceptual model of OM and N flow through soil mineral–organic associations, which accounts for changes in density, dynamics and chemistry of the isolated structures. It suggests that microbial reworking of OM entrapped within aggregates (1.65–2.4 g/cm3) causes the gradient of aggregate packing and, further on, controls the flow of litter-derived N through aggregates. For associations with denser material (>2.4 g/cm3), mineralogy determines the density of the association, the type of patchy OM attached to mineral surfaces and controls the extent of litter-derived N incorporation.  相似文献   

16.
土壤腐殖质提取和分组综述   总被引：4，自引：0，他引：4  
土壤腐殖质的定量提取、分离与纯化是深入研究土壤腐殖质的重要前提。本文详细综述了国内外腐殖质提取和分组的实验手段和研究进展;以国际腐殖质协会提供的标准方法为参考,对比论述了提取剂种类,提取次数、提取剂用量等的选择;对比讨论了两种主要的土壤腐殖质的分组方法。超滤分离和体积排阻色谱是腐殖质物理化学表征研究中的两种新兴技术,笔者认为组合使用两种实验手段对土壤腐殖质进行细致的分离与分组研究有助于深化理解土壤腐殖质的化学性质和分子结构。  相似文献   

17.
In 65 samples, we got values (unusually replicable and consistent for this type of work) of concentration, 14C/13C (AMS) age, and δ13C for: peat, dissolved organic carbon (DOC), peat fractions, and dissolved CO2 and CH4 at 50-cm intervals down to 700 cm in Ellergower Moss, a rainwater-dependent raised (domed) bog in southwest Scotland. (1) We attribute the consistency of the results to Ellergower Moss being unusually homogeneous, with unusually low hydraulic conductivity, and containing only a few gas spaces; and to the sampling methods including 18-month equilibration of in situ samplers. (2) The dissolved gas concentration depth profiles are convex and very similar to each other, though CO2 is 5-10 times more concentrated than CH4, while the profile of DOC is concave. (3) The age profile of peat is near linearly proportional to depth; that for DOC is about 500-1000 yr younger than the peat at the same depth; the dissolved gases are 500-4300 years younger than the peat. The age of the operational peat fractions humic acid and humin is similar to that of whole peat. (4) The δ13C profile for deep peat is almost constant; δ13C-CO2 is more enriched than the peat (δ13C-CO2 35‰ more); δ13C-CH4 is the same amount more depleted. Nearer the surface both dissolved gases become steadily more depleted, δ13C is about 20‰ less at the surface. (5) A simulation shows that mass flow can account for the concentration and age profiles of DOC, but for the gases diffusion and an additional source near the surface are needed as well, and diffusion accounts for over 99% of the dissolved gas movements. (6) The same processes must operate in other peatlands but the results for Ellergower should not be extrapolated uncritically to them.  相似文献   

18.
We present an organic geochemical study of surface sediments of Lake Sarbsko, a shallow coastal lake on the middle Polish Baltic coast. The aim was to provide evidence concerning the origin of the organic matter (OM) and its compositional diversity in surface deposits of this very productive, highly dynamic water body. The content and composition of the OM in the bottom sediments were investigated at 11 sampling stations throughout the lake basin. OM sources were assigned on the basis of bulk indicators [total organic carbon (TOC), total nitrogen (TN), δ13CTOC and δ15N and extractable OM yield], biomarker composition of extractable OM and compound-specific C isotope signatures. The source characterization of autochthonous compounds was verified via phytoplankton analysis. The distribution of gaseous hydrocarbons in the sediments, as well as temporal changes in lake water pH, the concentration of DIC (dissolved inorganic carbon) and δ13CDIC were used to trace OM decomposition.The sedimentary OM is composed mainly of well preserved phytoplankton compounds and shows minor spatial variability in composition. However, the presence of CH4 and CO2 in the bottom deposits provides evidence for microbial degradation of sedimentary OM. The transformation of organic compounds in surface, bottom and pore waters via oxidative processes influences carbonate equilibrium in the lake and seasonally favours precipitation or dissolution of CaCO3.The data enhance our understanding of the relationships between the composition of sedimentary OM and environmental conditions within coastal ecosystems and shed light on the reliability of OM proxies for environmental reconstruction of coastal lakes.  相似文献   

19.
Ma  Bin  Liang  Xing  Liu  Shaohua  Jin  Menggui  Nimmo  John R.  Li  Jing 《Hydrogeology Journal》2017,25(3):675-688

Subsurface-water flow pathways in three different land-use areas (non-irrigated grassland, poplar forest, and irrigated arable land) in the central North China Plain were investigated using oxygen (18O) and hydrogen (2H) isotopes in samples of precipitation, soils, and groundwater. Soil water in the top 10 cm was significantly affected by both evaporation and infiltration. Water at 10–40 cm depth in the grassland and arable land, and 10–60 cm in poplar forest, showed a relatively short residence time, as a substantial proportion of antecedent soil water was mixed with a 92-mm storm infiltration event, whereas below those depths (down to 150 cm), depleted δ18O spikes suggested that some storm water bypassed the shallow soil layers. Significant differences, in soil-water content and δ18O values, within a small area, suggested that the proportion of immobile soil water and water flowing in subsurface pathways varies depending on local vegetation cover, soil characteristics and irrigation applications. Soil-water δ18O values revealed that preferential flow and diffuse flow coexist. Preferential flow was active within the root zone, independent of antecedent soil-water content, in both poplar forest and arable land, whereas diffuse flow was observed in grassland. The depleted δ18O spikes at 20–50 cm depth in the arable land suggested the infiltration of irrigation water during the dry season. Temporal isotopic variations in precipitation were subdued in the shallow groundwater, suggesting more complete mixing of different input waters in the unsaturated zone before reaching the shallow groundwater.

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20.
Vast amounts of knowledge about the proton- and metal-binding properties of dissolved organic matter (DOM) in natural waters have been obtained in studies on isolated humic and fulvic (hydrophobic) acids. Although macromolecular hydrophilic acids normally make up about one-third of DOM, their proton- and metal-binding properties are poorly known. Here, we investigated the acid-base and Cu-binding properties of the hydrophobic (fulvic) acid fraction and two hydrophilic fractions isolated from a soil solution. Proton titrations revealed a higher total charge for the hydrophilic acid fractions than for the hydrophobic acid fraction. The most hydrophilic fraction appeared to be dominated by weak acid sites, as evidenced by increased slope of the curve of surface charge versus pH at pH values above 6. The titration curves were poorly predicted by both Stockholm Humic Model (SHM) and NICA-Donnan model calculations using generic parameter values, but could be modelled accurately after optimisation of the proton-binding parameters (pH ? 9). Cu-binding isotherms for the three fractions were determined at pH values of 4, 6 and 9. With the optimised proton-binding parameters, the SHM model predictions for Cu binding improved, whereas the NICA-Donnan predictions deteriorated. After optimisation of Cu-binding parameters, both models described the experimental data satisfactorily. Iron(III) and aluminium competed strongly with Cu for binding sites at both pH 4 and pH 6. The SHM model predicted this competition reasonably well, but the NICA-Donnan model underestimated the effects significantly at pH 6. Overall, the Cu-binding behaviour of the two hydrophilic acid fractions was very similar to that of the hydrophobic acid fraction, despite the differences observed in proton-binding characteristics. These results show that for modelling purposes, it is essential to include the hydrophilic acid fraction in the pool of ‘active’ humic substances.  相似文献   

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