首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献，搜索用时 109 毫秒
1.
How dissolved organic matter (DOM) undergoes chemical changes during its transit from river to ocean remains a challenge due to its complex structure. In this study, DOM along a river transect from black waters to marine waters is characterized using an offline combination of reversed-phase high performance liquid chromatography (RP-HPLC) coupled to electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS), as well as tandem ESI-FTICR-MS. In addition, a water extract from degraded wood that mainly consists of lignins is used for comparison to the DOM from this transect. The HPLC chromatograms of all DOM samples and the wood extract show two major well-separated components; one is hydrophilic and the other is hydrophobic, based on their elution order from the C18 column. From the FTICR-MS analysis of the HPLC fractions, the hydrophilic components mainly contain low molecular weight compounds (less than 400 Da), while the hydrophobic fractions contain the vast majority of compounds of the bulk C18 extracted DOM. The wood extract and the DOM samples from the transect of black waters to coastal marine waters show strikingly similar HPLC chromatograms, and the FTICR-MS analysis further indicates that a large fraction of molecular formulas from these samples are the same, existing as lignin-like compounds. Tandem mass spectrometry experiments show that several representative molecules from the lignin-like compounds have similar functional group losses and fragmentation patterns, consistent with modified lignin structural entities in the wood extract and these DOM samples. Taken together, these data suggest that lignin-derived compounds may survive the transit from the river to the coastal ocean and can accumulate there because of their refractory nature.  相似文献   

2.
Reversed-phase liquid chromatography/mass spectrometry (LC/MS) is introduced as a new molecular fingerprinting technique for tracing terrigenous dissolved organic matter (DOM) and its photochemical decay in the ocean. DOM along a transect from the mangrove-fringed coast in Northern Brazil to the shelf edge was compared with mangrove-derived porewater DOM exposed to natural sunlight for 2–10 days in a photodegradation experiment. DOM was isolated from all samples via solid-phase extraction (C18) for LC/MS analysis. DOM in the estuary and ocean showed a bimodal mass distribution with two distinct maxima in the lower m/z range from 400 to 1000 Da (intensity-weighted average of 895 Da). Terrigenous porewater DOM from the mangroves was characterized by a broad molecular mass distribution over the detected range from 150 to 2000 Da (intensity-weighted average of 1130 Da). Polar compounds, i.e., those that eluted early in the reversed-phase chromatography, absorbed more UV light and had on average smaller molecular masses than the more apolar compounds.  相似文献   

3.
Dissolved organic matter (DOM) and dissolved copper-organic complexes were isolated from the estuarine waters of Narragansett Bay, RI, using reverse-phase liquid chromatography (RPLC). Different types of reverse-phase BOND ELUT columns (Analytichem International), including C2, C18 and phenyl-bonded phases, were studied to determine their adsorption efficiency for extracting DOM. Extraction efficiencies followed the order phenyl > C18 > C2, and phenyl − C18 > C2 for DOM and organic copper, respectively. However, comparisons of BOND ELUT and C18 SEP-PAK (Waters Associates) columns indicated that SEP-PAK columns were the most efficient when both DOM and organic copper were considered. Chromatographic profiles of the isolated DOM obtained using high-performance liquid chromatography were similar in elution characteristics and resembled chromatograms typical of fulvic acid. The UV-absorption characteristics of the DOM showed small differences and suggested that the different reverse-phase columns isolated material that was qualitatively similar.Copper-organic complexes isolated using C18 RPLC were studied to examine the dissociation of organically bound copper in seawater as the pH is lowered. Only a small amount of the complexed copper was displaced by the H+ with about 40% of the copper remaining bound at pH 3. However, the chromatographic elution behavior of the DOM and organic copper was significantly altered under acidic conditions as a result of protonation of acidic functional sites on the organic matter.  相似文献   

4.
Dissolved organic matter (DOM) was investigated along a gradient across the Subtropical Convergence (STC) off the South Island, New Zealand. Ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), excitation emission matrix fluorescence (EEM) spectroscopy, and molecular lignin analysis techniques were used to study this DOM. The analysis revealed a group of compounds found only in the coastal DOM samples, which were also characterized by an elevated terrestrial DOM fluorescence pattern and elevated lignin content if compared to the offshore samples. This group exhibited a high degree of carbon unsaturation, as evident from high double bond equivalence minus oxygen values (DBE-O > 9) and maximum fluorescence intensity. Sulfur-containing molecular formulae for summer DOM samples were much more abundant across the entire transect of the STC compared to winter and exhibited distinctly different hydrogen:carbon and oxygen:carbon elemental ratios, suggesting a possible correlation between biological activity and sulfur compounds. The molecular formulae common to all STC samples were compared with those calculated for DOM extracted from freshwater collected from a stream discharging into Doubtful Sound (West Coast, New Zealand). ESI-FT-ICR-MS measurements undertaken in negative electrospray ionization (ESI?) mode indicated that 30% of the molecular formulae were present in both types of DOM, while in positive ESI mode (ESI+) over 90% of the formulae were present in all samples. Hence, a significant portion of the molecular formulae assigned to the solid-phase extractable DOM pool (SPE-DOM) appear to be identical in oceanic and freshwater samples.  相似文献   

5.
Results are presented from an investigation of the relationship between molecular mass distribution and optical properties for colored dissolved organic matter (CDOM); a complex assembly of organic macromolecules of marine and freshwater origin found throughout the surface ocean. Unique data are derived from the application of a new technique, a combination of a hydrophilic–lipophilic copolymer-based solid phase extraction (SPE) with electrospray ionization (ESI) continuous flowing ion trap mass spectrometry (cf-MS), for the direct determination of CDOM mass distribution. An evaluation of this copolymer-based extraction technique for the analysis of Suwannee River Natural Organic Matter (SRNOM) reference material revealed that the current method compares favorably with C18 modified silica or XAD resin-based extraction methods reported in the literature when considering extraction efficiency or low extraction bias for CDOM. The mass distribution of CDOM in several freshwater to marine transition zones along coastal southwestern Florida has been determined with this technique. All rivers in the study region had a bimodal distribution of masses. A case study of the Caloosahatchee River outflow CDOM mass distribution data are presented as an example of the modification in mass distributions. The lower mass mode of the bimodal distribution was observed to have a relatively stable mean throughout the study region at 406±9 Da, while decreasing in concentration in a non-conservative manner with salinity. In contrast, the upper mass mode of the bimodal distribution was observed to have a variable mean, reaching 1408 Da in the least saline waters and decreasing by 174 Da through the transect toward higher salinity coastal waters. Coinciding with this reduction in mean mass for the upper distribution is a non-conservative reduction in concentration when compared with salinity. We define apparent organic carbon (AOC) as a function of the cf-MS determined total integrated area and use this value to determine concentration of the total extracted CDOM. Unique correlations between the CDOM fluorescence (350-nm excitation/450-nm emission) and the AOC for these coastal samples have been observed for each of three rivers in the study region. The steepest slope and highest correlation between optical and mass spectral properties are observed in rivers with strongly absorbing waters originating in the Florida Everglades and lowest in rivers draining clearer waters from widely variable and anthropogenic influenced regions. The trends in molecular mass distribution and corresponding optical properties support the theory that CDOM in coastal zones is environmentally processed material from terrestrial sources. Probable cause of the reduction in mean mass and suggestions for further investigation of sources and transformations of CDOM are discussed.  相似文献   

6.
北极孔斯峡湾表层沉积物中溶解有机质的来源与转化历史   总被引：7，自引：0，他引：7  
在北极地区孔斯峡湾采集28个表层沉积物样品,测定了其中水溶性有机质(也称溶解有机质,DOM)的分子量分布、紫外/可见吸收光谱和三维荧光光谱特征,并利用平行因子分析(PARAFAC)模型对DOM的荧光组分和来源进行了解析。结果表明:孔斯峡湾表层沉积物中有色溶解有机质(CDOM)及其中的荧光溶解有机质(FDOM)含量均从内湾向外湾方向呈逐渐累积的趋势,但CDOM中的FDOM所占比例逐渐减小,与DOM趋于老龄化密切相关。沉积作用减弱以及长期的光化学降解和微生物降解作用对此起主要贡献,并导致腐殖质和小分子组分在沉积物DOM中所占的比例呈逐渐递增的趋势。沉积物DOM包含陆源类腐殖质、自生源类腐殖质和类蛋白等三个荧光组分,但是其组成比例空间差异很大。吸收光谱斜率比(SR)随自生源所占百分比增加而减小,随DOM腐殖质组分中陆源与自生源的比值增加而增加;腐殖化指数(HIX)随类腐殖质与类蛋白质比值和水深的增加而增加,生物源指数(BIX)随自生源比例增加而增加。峡湾沉积物DOM的组成和来源存在着高度的空间差异,在冰川湾区由水体颗粒有机质(POM)的近期转化和迁移而来,而在峡湾中央及口门附近以较老的腐殖质为优势,主要源于水体DOM长期迁移和转化。研究表明,FDOM/CDOM,SR,HIX和BIX等构成的CDOM光谱指纹信息可以作为揭露沉积物溶解有机质来源及迁移转化历史的工具,对探索海洋与冰川相互作用影响下的峡湾环境演变有着重要意义。  相似文献   

7.
Particulate matter from the atmosphere over the Atlantic Ocean along the South American and African Continents has been analyzed for organic tracers from natural and biomass burning emissions. The major biomarker compounds characterized are natural products from continental vegetation consisting primarily of epicuticular wax components. For example, n-alkanes ranged from C25 to C35, with an odd carbon number predominance and carbon maxima (Cmax) at 29 or 31. Concentrations of n-alkanes varied from 0.3 to 680 ng/m3. Nevertheless, n-alkanols are the dominant terrestrial tracers in almost all samples (concentrations from 0.1 to 780 ng/m3) and ranged from C22 to C34 with an even carbon number predominance. Despite the major presence of the natural tracers, organic components from biomass burning emissions are also present in the particulate matter. The major tracers from this source are thermal degradation products from the biopolymer cellulose, namely the dianhydromonosaccharide derivatives levoglucosan, galactosan, and mannosan. In general, the concentrations of levoglucosan, the major derivative from this source in all samples, varied from 0.0008 to 0.15 ng/m3 in atmospheric samples collected over the ocean and from 0.04 to 4860 ng/m3 in terrestrial particulate matter, used as reference in this study. Dehydroabietic acid, another marker compound emitted from burning of Gymnosperm fuel, is also detectable in most oceanic samples at concentrations ranging from 0.0001 to 0.4 ng/m3, whereas in terrestrial aerosol particulate matter, this component is present at much higher concentrations (0.23–440 ng/m3). The presence of these tracers in atmospheric particulate matter over the ocean confirms the long-range transport of smoke from biomass burning off the continents.  相似文献   

8.
Concurrent distributions of dissolved and suspended particulate organic carbon (DOC and POCsusp), nitrogen (DON and PONsusp) and phosphorus (DOP and POPsusp), and of suspended particulate inorganic phosphorus (PIPsusp), are presented for the open ocean water column. Samples were collected along a three-station transect from the upper continental slope to the abyssal plain in the eastern North Pacific and from a single station in the Southern Ocean. The elemental composition of surface sedimentary organic matter (SOM) was also measured at each location, and sinking particulate organic matter (POMsink) was measured with moored sediment traps over a 110-d period at the abyssal site in the eastern North Pacific only. In addition to elemental compositions, C : N, C : P and N : P ratios were also calculated. Surface and deep ocean concentrations of dissolved organic matter (DOM) and inorganic nutrients between the two sites displayed distinct differences, although suspended POM (POMsusp) concentrations were similar. Concentrations of DOM and POMsusp displayed unique C, N and P distributions, with POMsusp concentrations generally about 1–2 orders of magnitude less than the corresponding DOM concentrations. These differences were likely influenced by different biogeochemical factors: whereas the dissolved constituents may have been influenced more by the physical regime of the study site, suspended particulate matter may have been controlled to a greater extent by biological and chemical alteration. Up to 80% of total particulate P in POMsusp, POMsink and SOM consisted of PIP. For all organic matter pools measured, elemental ratios reveal that organic P is preferentially remineralized over organic C and organic N at both sites. Increases in C : P and N : P ratios with depth were also observed for DOM at both sites, suggesting that DOP is also preferentially degraded over C and N as a function of depth. A simple one-dimensional vertical eddy diffusion model was applied to estimate the contributions of dissolved and suspended particulate organic C, N and P fluxes from the upper mixed layer into the permanent thermocline. Estimated vertical DOM fluxes were 28–63% of the total organic matter fluxes; POMsusp and POMsink fluxes were 8–20 and 28–52% of the total.  相似文献   

9.
Temporal and spatial variations in the composition of particulate organic matter (POM) from Florida Bay, USA were examined. The predominance of short-chain homologues for n-alkanes, n-alcohols and n-fatty acids as well as relatively high abundance of C27 and C28 sterols suggested that an autochthonous/marine source of OM was dominant bay-wide. Several biomarker proxies such as Paq [(C23 + C25)/(C23 + C25 + C29 + C31) n-alkanes], short/long chain n-alkanes, (C29 + C31) n-alkanes and taraxerol indicated a spatial shift in OM sources, where terrestrial OM rapidly decreased while seagrass and microbial OM markedly increased along a northeastern to southwestern transect. Regarding seasonal variations, POM collected during the dry season was enriched in terrestrial constituents relative to the wet season, likely as a result of reduced primary productivity of planktonic species and seagrasses during the dry season. Principal component analysis (PCA) classified the sample set into sub-groups based on PC1 which seemed to be spatially controlled by OM origin (terrestrial-mangrove vs. marine-planktonic/seagrass). The PC2 seemed to be more seasonally controlled suggesting that hydrological fluctuations and seasonal primary productivity are the drivers controlling the POM composition in Florida Bay.  相似文献   

10.
Carbon overconsumption, i.e. the consumption of inorganic carbon relative to inorganic nitrogen in excess of the Redfield ratio at the sea surface, was examined in relation to the dynamics of dissolved organic carbon and nitrogen (DOC and DON) in the northeast Atlantic. We observed the presence of N-poor dissolved organic matter (DOM) in surface water during summer, requiring the consumption of inorganic carbon and nitrogen in a ratio exceeding the Redfield ratio. The C : N ratio of bulk DOM is not only different from the Redfield ratio but also variable, i.e. no fixed conversion factor of C and N exists where DOM is important in C and N transformations. The existence of N-poor DOM is recognized as a feature typical of oligotrophic systems. At the same time, the C : N ratios of particles conform to Redfield stoichiometry as does deep-ocean chemistry. The implications of this finding are discussed, the conclusion being that, while DOM buildup contributes to CO2 drawdown seasonally, its impact on long-term carbon and nitrogen balance of the ocean is small.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号