Riverine export of aged terrestrial organic matter to the North Atlantic Ocean

Global riverine discharge of organic matter represents a substantial source of terrestrial dissolved and particulate organic carbon to the oceans. This input from rivers is, by itself, more than large enough to account for the apparent steady-state replacement times of 4,00-6,000 yr for oceanic dissolved organic carbon. But paradoxically, terrestrial organic matter, derived from land plants, is not detected in seawater and sediments in quantities that correspond to its inputs. Here we present natural 14C and 13C data from four rivers that discharge to the western North Atlantic Ocean and find that these rivers are sources of old (14C-depleted) and young (14C-enriched) terrestrial dissolved organic carbon, and of predominantly old terrestrial particulate organic carbon. These findings contrast with limited earlier data that suggested terrestrial organic matter transported by rivers might be generally enriched in 14C from nuclear testing, and hence newly produced. We also find that much of the young dissolved organic carbon can be selectively degraded over the residence times of river and coastal waters, leaving an even older and more refractory component for oceanic export. Thus, pre-ageing and degradation may alter significantly the structure, distributions and quantities of terrestrial organic matter before its delivery to the oceans.     

Self-organization of dissolved organic matter to micelle-like microparticles in river water

In aquatic systems, the concept of the 'microbial loop' is invoked to describe the conversion of dissolved organic matter to particulate organic matter by bacteria. This process mediates the transfer of energy and matter from dissolved organic matter to higher trophic levels, and therefore controls (together with primary production) the productivity of aquatic systems. Here we report experiments on laboratory incubations of sterile filtered river water in which we find that up to 25% of the dissolved organic carbon (DOC) aggregates abiotically to particles of diameter 0.4-0.8 micrometres, at rates similar to bacterial growth. Diffusion drives aggregation of low- to high-molecular-mass DOC and further to larger micelle-like microparticles. The chemical composition of these microparticles suggests their potential use as food by planktonic bacterivores. This pathway is apparent from differences in the stable carbon isotope compositions of picoplankton and the microparticles. A large fraction of dissolved organic matter might therefore be channelled through microparticles directly to higher trophic levels--bypassing the microbial loop--suggesting that current concepts of carbon conversion in aquatic systems require revision.     

Variable ageing and storage of dissolved organic components in the open ocean

Seawater dissolved organic matter (DOM) is the largest reservoir of exchangeable organic carbon in the ocean, comparable in quantity to atmospheric carbon dioxide. The composition, turnover times and fate of all but a few planktonic constituents of this material are, however, largely unknown. Models of ocean carbon cycling are thus limited by the need for information on temporal scales of carbon storage in DOM subcomponents, produced via the 'biological pump', relative to their recycling by bacteria. Here we show that carbohydrate- and protein-like substances in the open Atlantic and Pacific oceans, though often significantly aged, comprise younger fractions of the DOM, whereas dissolved lipophilic material exhibits up to approximately 90 per cent fossil character. In contrast to the millennial mean ages of DOM observed throughout the water column, weighted mean turnover times of DOM in the surface ocean are only decadal in magnitude. An observed size-age continuum further demonstrates that small dissolved molecules are the most highly aged forms of organic matter, cycling much more slowly than larger, younger dissolved and particulate precursors, and directly links oceanic organic matter age and size with reactivity.     

Fate of secondary effluent dissolved organic matter during soil-aquifer treatment

The reduction of mass and trihalomethane formation potential (THMFP) of dissolved organic matter (DOM) and its fractions from secondary effluent during laboratory-scale soil-aquifer treatment (SAT) soil columns were studied. Reduction in dissolved organic carbon (DOC), absorbance of ultraviolet light at 254 nm (UV-254), biodegradable dissolved organic carbon (BDOC) and nonbiodegradable dis- solved organic carbon (NBDOC) for the bulk DOM averaged 72.35%, 53.98%, 97.49% and 35.33% across the soil columns, respectively. Using XAD-8 and XAD-4 resins, DOM was fractionated into 3 fractions: hydrophobic acid (HPO-A), transphilic acid (TPI-A) and hydrophilic fraction (HPI). HPO-A was removed by 61.06%, TPI-A by 54.86% and HPI by 74.95% as DOC as a consequence of the laboratory-scale SAT, respectively. The reduction of THMFP from HPO-A, TPI-A and HPI was 27.24%, 26.24% and 36.08%, respectively. Proton nuclear magnetic resonance (1H-NMR) spectra revealed that the HPO-A isolated from the secondary effluent contained more aromatic functional groups than the corresponding TPI-A. Fourier-transform infrared (FT-IR) spectrum analysis illustrated that TPI-A had decreased hydrocarbon and increased aromatics content in the SAT columns. Specific ultraviolet light absorbance (SUVA) and specific THMFP for each DOM fraction increased across the soil columns and HPI exhibited greater increase in both than HPO-A and TPI-A. The most problematic THM precursor was found to be HPO-A with its high quantity present in recharged water and high chlorine reactivity.     

Snowball Earth prevention by dissolved organic carbon remineralization

The 'snowball Earth' hypothesis posits the occurrence of a sequence of glaciations in the Earth's history sufficiently deep that photosynthetic activity was essentially arrested. Because the time interval during which these events are believed to have occurred immediately preceded the Cambrian explosion of life, the issue as to whether such snowball states actually developed has important implications for our understanding of evolutionary biology. Here we couple an explicit model of the Neoproterozoic carbon cycle to a model of the physical climate system. We show that the drawdown of atmospheric oxygen into the ocean, as surface temperatures decline, operates so as to increase the rate of remineralization of a massive pool of dissolved organic carbon. This leads directly to an increase of atmospheric carbon dioxide, enhanced greenhouse warming of the surface of the Earth, and the prevention of a snowball state.     

Export of dissolved organic carbon from peatlands under elevated carbon dioxide levels

Peatlands represent a vast store of global carbon. Observations of rapidly rising dissolved organic carbon concentrations in rivers draining peatlands have created concerns that those stores are beginning to destabilize. Three main factors have been put forward as potential causal mechanisms, but it appears that two alternatives--warming and increased river discharge--cannot offer satisfactory explanations. Here we show that the third proposed mechanism, namely shifting trends in the proportion of annual rainfall arriving in summer, is similarly unable to account for the trend. Instead we infer that a previously unrecognized mechanism--carbon dioxide mediated stimulation of primary productivity--is responsible. Under elevated carbon dioxide levels, the proportion of dissolved organic carbon derived from recently assimilated carbon dioxide was ten times higher than that of the control cases. Concentrations of dissolved organic carbon appear far more sensitive to environmental drivers that affect net primary productivity than those affecting decomposition alone.     

添加有机肥对滨海盐渍土壤溶解性有机碳特征的影响

【目的】研究添加有机肥对滨海盐渍土壤溶解性有机碳(DOC)的影响,探究土壤DOC的组分来源以及滨海盐渍土壤碳库的稳定性,为改良滨海盐渍土并发挥其碳汇效应提供依据。【方法】以江苏大丰滨海两种不同盐分的盐渍土壤为研究对象,利用紫外-可见光谱和三维荧光光谱结合平行因子分析法,分析添加牛粪有机肥后两种盐渍土壤中DOC含量及紫外-可见光谱、三维荧光光谱特征的动态变化。【结果】添加有机肥的土壤DOC含量显著增加,且有机肥的添加提高了土壤DOC的腐殖化程度,试验第15天和第60天时高盐土壤DOC的腐殖化程度更高,土壤中DOC主要来源于添加的有机肥。三维荧光光谱特征显示,添加有机肥后土壤DOC中类富里酸峰较为明显。平行因子分析法将土壤DOC分为4个荧光组分:C1为外源类短波类腐殖质组分(紫外光区为类富里酸、海洋类富里酸),C2为外源类腐殖质组分(紫外光区、可见光区均为类富里酸),C3为内源类蛋白质组分(类络氨酸、类色氨酸),C4为内源类蛋白质组分(类络氨酸),随时间的变化各组分的占比也表现出不同的情况。【结论】滨海两种盐渍土壤添加牛粪有机肥后,土壤中DOC的含量、类腐殖质组分占比及腐质化程度均显著提高,类络氨酸组分的占比显著降低(P<0.05)。添加有机肥有利于盐渍土壤中活性碳库的稳定,但由于影响DOC的因素众多,不同的盐渍土壤表现情况各异。     

沣河洪水过程溶解有机物的荧光特征及来源分析研究

利用三维荧光光谱技术对陕西西安境内的沣河秦渡镇水文站和高桥水文站的暴雨期间洪水过程的溶解有机物进行研究,讨论了荧光溶解有机物的来源、组成、分子结构等特征.结果表明强降水带来了更多荧光溶解有机物,表现为冲刷效应,洪水过程河流溶解有机物的荧光峰主要以代表陆源有机物的类富里酸荧光为主,类蛋白荧光较弱或没有检测出,表明人为污染影响较小.结构特征为腐化程度高、芳香性大,以大分子的有机物为主.春季首次强降水冲刷的有机物结构成分较为复杂,点源污染稀释作用和水库泄洪作用对洪水过程有机物的浓度、组成、结构等变化特征也有很大影响.     

Polysaccharide aggregation as a potential sink of marine dissolved organic carbon

The formation and sinking of biogenic particles mediate vertical mass fluxes and drive elemental cycling in the ocean. Whereas marine sciences have focused primarily on particle production by phytoplankton growth, particle formation by the assembly of organic macromolecules has almost been neglected. Here we show, by means of a combined experimental and modelling study, that the formation of polysaccharide particles is an important pathway to convert dissolved into particulate organic carbon during phytoplankton blooms, and can be described in terms of aggregation kinetics. Our findings suggest that aggregation processes in the ocean cascade from the molecular scale up to the size of fast-settling particles, and give new insights into the cycling and export of biogeochemical key elements such as carbon, iron and thorium.     

Uptake of dissolved organic carbon and trace elements by zebra mussels

Zebra mussels (Dreissena polymorpha) are widespread and abundant in major freshwater ecosystems in North America, even though the phytoplankton food resources in some of these systems seem to be too low to sustain them. Because phytoplankton biomass is greatly depleted in ecosystems with large D. polymorpha populations and bacteria do not seem to be an important food source for this species, exploitation of alternative carbon sources may explain the unexpected success of D. polymorpha in such environments. Here we examine the possibility that absorption of dissolved organic carbon (DOC) from water could provide a nutritional supplement to zebra mussels. We find that mussels absorb 14C-labelled DOC produced by cultured diatoms with an efficiency of 0.23%; this indicates that DOC in natural waters could contribute up to 50% of the carbon demand of zebra mussels. We also find that zebra mussels absorb some dissolved metals that have been complexed by the DOM; although absorption of dissolved selenium was unaffected by DOC, absorption of dissolved cadmium, silver and mercury by the mussels increased 32-, 8.7- and 3.6-fold, respectively, in the presence of high-molecular-weight DOC.     

冻融条件下溶解性有机物在冰-水-沉积物体系中的迁移

通过设置室内控制实验,测定冻融过程中冰水两相的三维荧光光谱（EEMs）、SUVA254、TN、TP、DOC,并对三维荧光特征指数、SUVA254、TN、TP、DOC进行相关性分析。结果表明,冻结过程中水相的三维荧光光谱中类色氨酸峰A、类酪氨酸峰B、类腐殖酸峰C的荧光强度增强,TN、TP质量浓度增加至原水样的1.47、1.13倍。说明在冻结过程中由于冷冻浓缩效应,类色氨酸、类酪氨酸、类腐殖酸三类溶解性有机物、TN、TP由冰相向水相迁移。随着冰相体积的增加,三类溶解性有机物、TN、TP向沉积物迁移,并在溶解过程中,由沉积物向水体释放。通过测定冻融条件下冰水两相中BPA、E2、EE2的质量浓度发现,在冻结过程中BPA、E2、EE2向水相中迁移,结合相关性分析结果说明芳香族物质更易向水相中迁移。     

聚硅酸铁对溶解性有机物与浊度的去除

采用透射电镜法及光子相关光谱法对自制的氧化性聚硅酸铁(PSF)与聚合硫酸铁(PFS)进行微观表征,同时以254 nm的吸光度A(UV_(254))溶解性有机碳质量浓度c(DOC)、色度及比紫外吸光值A(SUV_(254))作为溶解性有机物(DOM)的检测指标,对PSF降低以上各指标与浊度去除效果及相关性进行研究.结果表明:PSF由很短的链节样物种及枝状结构组成,形态尺寸及分维数较大,并且较稳定;PSF具有良好的混凝效果,对浊度及色度的去除率超过95%,对A(UV_(254)),A(SUV_(254)),c(DOE)的去除率分别达到85%,80%,60%;用于评价PSF去除DOM性能的各指标间及其与余浊之间均具有良好的相关性.     

Characterization of dissolved organic matter in a dynamic membrane bioreactor for wastewater treatment

This paper systematically examined the characteristics of dissolved organic matter(DOM) in a dynamic membrane bioreactor(DMBR) for municipal wastewater with a laboratory-scale continuous-flow device.Experimental results showed that the system performed excellent pollutants’ removal efficiencies.The increase of trans-membrane pressure(TMP) for the dynamic membrane(DM) could be divided into three stages,i.e.,zero increase stage,slow increase stage and abrupt rise stage.The maximal fouling rate of the DM reached to 4.34 kPa/h in abrupt rise stage.It was observed that the polysaccharides(PS) concentration of DOM samples gradually increased from the anaerobic zone to the aerobic zone in sequence,but the proteins(PN) concentration performed an opposite trend.The DM could retain a small part of the large molecular substances(>10 kDa) in the aerobic zone.Two particular fluorescence peaks appeared in the anaerobic zone and in the anoxic zone were also found in the effluent,which illustrated the dynamic cake layer closed to the stainless steel mesh might induce an anaerobic/anoxic micro environment.Based on the three-dimensional excitation-emission matrix(EEM) fluorescence spectroscopy analysis,aromatic proteins,aromatic proteinlike substance,fulvic acid-like substances and soluble microbial by-product-like materials could be biodegraded effectively in the DMBR,and the DM could partly remove the humic acid-like substances and soluble microbial by-product-like materials.     

溶解性有机质-四环素-Zn共存体系中土壤对四环素和Zn的吸附作用

以畜禽粪便中的典型组分——溶解性有机质、四环素和锌作为研究对象,以东北典型黑土为供试土壤,采用批次实验法,研究了溶解性有机质、四环素和锌三元混合体系中土壤对四环素和锌的吸附作用。结果表明,土壤对四环素的吸附符合Freundlich吸附模型,土壤对Zn的吸附既符合Langmuir吸附模型,也符合Freundlich吸附模型;四环素和锌之间存在着相互促进吸附的作用;溶解性有机质抑制了四环素在土壤上的吸附,促进了Zn在土壤上的吸附;在溶解性有机质-四环素-Zn混合体系中,四环素和溶解性有机质共存促进了Zn的吸附;而对于四环素的吸附,溶解性有机质和Zn的共存可以表现为促进作用,也可以表现为抑制作用,二者的相对浓度是决定其作用的关键因素。     

生化-物化法处理渗滤液溶解性有机物光谱特征

为了研究垃圾渗滤液中溶解性有机物(DOM)在生化-物化组合工艺处理过程中的降解特性,采用XAD-8和XAD-4树脂将DOM分成五种组分,并结合紫外和荧光光谱对DOM及其组分降解变化进行探讨.研究表明,组合工艺能有效降低渗滤液中DOM,溶解性有机碳(DOC)去除率达99.64％,其各组分去除率在99.48％～99.73％...     

Eocene global warming events driven by ventilation of oceanic dissolved organic carbon

'Hyperthermals' are intervals of rapid, pronounced global warming known from six episodes within the Palaeocene and Eocene epochs (～65-34 million years (Myr) ago). The most extreme hyperthermal was the ～170 thousand year (kyr) interval of 5-7 °C global warming during the Palaeocene-Eocene Thermal Maximum (PETM, 56?Myr ago). The PETM is widely attributed to massive release of greenhouse gases from buried sedimentary carbon reservoirs, and other, comparatively modest, hyperthermals have also been linked to the release of sedimentary carbon. Here we show, using new 2.4-Myr-long Eocene deep ocean records, that the comparatively modest hyperthermals are much more numerous than previously documented, paced by the eccentricity of Earth's orbit and have shorter durations (～40?kyr) and more rapid recovery phases than the PETM. These findings point to the operation of fundamentally different forcing and feedback mechanisms than for the PETM, involving redistribution of carbon among Earth's readily exchangeable surface reservoirs rather than carbon exhumation from, and subsequent burial back into, the sedimentary reservoir. Specifically, we interpret our records to indicate repeated, large-scale releases of dissolved organic carbon (at least 1,600 gigatonnes) from the ocean by ventilation (strengthened oxidation) of the ocean interior. The rapid recovery of the carbon cycle following each Eocene hyperthermal strongly suggests that carbon was re-sequestered by the ocean, rather than the much slower process of silicate rock weathering proposed for the PETM. Our findings suggest that these pronounced climate warming events were driven not by repeated releases of carbon from buried sedimentary sources, but, rather, by patterns of surficial carbon redistribution familiar from younger intervals of Earth history.     

Stability of organic carbon in deep soil layers controlled by fresh carbon supply

The world's soils store more carbon than is present in biomass and in the atmosphere. Little is known, however, about the factors controlling the stability of soil organic carbon stocks and the response of the soil carbon pool to climate change remains uncertain. We investigated the stability of carbon in deep soil layers in one soil profile by combining physical and chemical characterization of organic carbon, soil incubations and radiocarbon dating. Here we show that the supply of fresh plant-derived carbon to the subsoil (0.6-0.8 m depth) stimulated the microbial mineralization of 2,567 +/- 226-year-old carbon. Our results support the previously suggested idea that in the absence of fresh organic carbon, an essential source of energy for soil microbes, the stability of organic carbon in deep soil layers is maintained. We propose that a lack of supply of fresh carbon may prevent the decomposition of the organic carbon pool in deep soil layers in response to future changes in temperature. Any change in land use and agricultural practice that increases the distribution of fresh carbon along the soil profile could however stimulate the loss of ancient buried carbon.     

Effects of dissolved organic matter on the growth and pigments synthesis of Spirulina platensis (Arthrospira)

Excessive accumulation of dissolved organic matter (DOM) in the culture ponds of Spirulina platensis is usually considered to be one of the potential factors affecting the production of S. platensis, however, we are not quite aware of effects of DOM on the growth and pigments synthesis of S. platensis. In the present study, S. platensis was grown in batch or semi?continuous cultures using the filtrate in the culture ponds that had not been renewed for years. It was found that disssolved organic carbon up to 60 mg/L did not bring about an inhibitory effect on the growth of S. platensis, but increased the contents of chlorophyll a and phycocyanin instead. However, further accumulation of dissolved organic matter could decrease the content of chlorophyll a.     

基于Matlab的溶解有机物的三维荧光矩阵构建

三维荧光光谱(EEM)结合平行因子分析(PARAFAC)能够根据水体中有机物的荧光性质对荧光组分特征、种类进行区分。大量原始数据以及常规的手工处理方式直接影响着该方法的广泛应用。提出了一种基于Matlab软件的三维荧光光谱数据快速转化为荧光矩阵的思路与方法。该方法根据不同研究者测定参数的不同,结合不同校正方法,可快速地将大量样品的三维荧光数据整合为三维荧光矩阵,通过具体数据验证荧光矩阵形成进行平行因子分析。该方法能够实现整个过程操作简单,人工干预少,可达到快速、批量完成三维荧光光谱数据处理的目的。