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。     

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.     

南京市不同功能区城市林业土壤有机碳含量与分布

为了解城市化过程中人为活动对城市林业土壤性质及土壤碳库的影响,以南京市土壤为对象,测定了7类功能区城市林业土壤0～30 cm土层的总有机碳(SOC)、溶解有机碳(DOC)、微生物量碳(MBC)、易氧化态碳(ROC)和轻组有机碳(LFOC)的含量,分析了城市林业土壤有机碳的分布规律及其相互关系。结果表明:城市林业土壤表层(0～10 cm)活性有机碳富集特征明显,土壤活性有机碳含量随着土层加深而减小,人为干扰对土壤有机碳含量影响较大; 城郊天然林土壤积累了较高含量的ROC和MBC,道路绿化带土壤由于交通源有机物质的输入,SOC、DOC、LFOC含量较高。人类活动频繁的居民区、公园和校园的土壤活性有机碳各组分含量多处于较低水平。研究表明,土壤总有机碳与各活性有机碳之间有显著相关关系。     

干旱影响森林土壤有机碳周转及积累的研究进展

随着全球气候变暖趋势加剧,伴之而来的干旱问题成为全球关注的热点。干旱对森林生态系统碳积累和周转可能产生显著影响,其主要过程包括植被地上部分和地下部分凋落物对土壤有机碳的输入、凋落物的分解及土壤有机碳的矿化等。笔者综合分析了近年来国内外相关研究成果,对干旱影响森林土壤有机碳的主要过程与机制进行了归纳和总结,结果表明:①干旱通过促进叶片提前脱落,短期增加森林凋落物量,长期干旱则影响森林植物生长,降低森林初级生产力从而降低植物地上凋落物量。轻度和中度干旱下植物为补偿水分缺失增加细根生物量维持植物生命力,重度干旱下植物丧失自我修复能力导致细根生物量降低,干旱也会造成细根死亡率增加。平均而言,全球范围内干旱会造成森林凋落物量降低(1.9%)和细根生物量降低(8.7%),最终减少植物有机碳向土壤的输入量。②干旱可通过改变凋落物化学性质,对分解者——土壤动物、微生物产生胁迫,从而引起凋落物分解速率下降(10%~70%)。干旱使凋落物碳氮含量变化,造成凋落物次生代谢物,如纤维素、木质素、单宁等积累,改变根系分泌物化学组分,从而影响凋落物分解。干旱导致真菌生物量和分解者等土壤动物丰度降低,增加分解者捕食压力,使相关微生物和酶活性下降,造成凋落物分解速率下降。③干旱驱动微生物群落组成变化(真菌细菌比、革兰阳阴细菌比增加),造成微生物生物量下降,活性减弱,此外还会降低腐食动物的摄食活性、酶活性,最终导致土壤有机碳矿化速率下降(10%~50%)。④干旱对土壤有机碳不同组分影响不同,干旱会减小土壤微生物生物量碳(MBC)库(2%~30%),造成表层土壤溶解性有机碳(DOC)积累(30%~60%)。而在全球范围内的不同区域,干旱对土壤有机碳积累的影响也不同,亚热带森林中干旱对土壤有机碳积累的影响多是负面的,热带森林中则相反。总体而言,干旱对森林土壤有机碳库储量影响可能不大,但降低了土壤碳周转效率。而森林土壤有机碳周转过程不仅受干旱这一单一因素影响,温度、物种等因素会共同作用于土壤有机碳的周转与积累,且单因子的简单叠加模拟可能与现实环境中多因子综合对土壤碳通量的影响有一定差别。未来需要通过长期观测、延长控制实验时间、模拟原生环境条件等,开展多因素综合实验,加强干旱对土壤动物和微生物影响的研究,以深入了解干旱对森林土壤有机碳影响的生物学与生态学的过程与机制。     

Efficient export of carbon to the deep ocean through dissolved organic matter

Oceanic dissolved organic carbon (DOC) constitutes one of the largest pools of reduced carbon in the biosphere. Estimated DOC export from the surface ocean represents 20% of total organic carbon flux to the deep ocean, which constitutes a primary control on atmospheric carbon dioxide levels. DOC is the carbon component of dissolved organic matter (DOM) and an accurate quantification of DOM pools, fluxes and their controls is therefore critical to understanding oceanic carbon cycling. DOC export is directly coupled with dissolved organic nitrogen and phosphorus export. However, the C:N:P stoichiometry (by atoms) of DOM dynamics is poorly understood. Here we study the stoichiometry of the DOM pool and of DOM decomposition in continental shelf, continental slope and central ocean gyre environments. We find that DOM is remineralized and produced with a C:N:P stoichiometry of 199:20:1 that is substantially lower than for bulk pools (typically >775:54:1), but greater than for particulate organic matter (106:16:1--the Redfield ratio). Thus for a given mass of new N and P introduced into surface water, more DOC can be exported than would occur at the Redfield ratio. This may contribute to the excess respiration estimated to occur in the interior ocean. Our results place an explicit constraint on global carbon export and elemental balance via advective pathways.     

南黄海及长江口邻近海域夏季溶解有机碳的分布特征及其影响因素

【目的】海水中溶解有机碳(DOC)的研究对于碳的生物地球化学循环具有重要意义。通过对南黄海及长江口邻近海域夏季溶解有机碳的分布特征及其影响因素的研究,为进一步丰富我国陆架边缘海碳循环的研究提供数据支持和参考依据。【方法】利用高温燃烧氧化法对2013年夏季南黄海及长江口邻近海域水体中的DOC进行测定,初步分析夏季南黄海DOC的分布特征,并结合水文、化学、生物同步观测参数,探讨影响DOC分布的主要因素。【结果】2013年夏季南黄海及长江口邻近海域DOC的含量为0.24~2.37mg/L,平均值为(1.34±0.42)mg/L。整体而言,调查海区平面分布呈现北部浓度高,向南部逐渐降低,近岸浓度高远岸浓度低的分布趋势。DOC的垂直分布呈现表层高,逐渐向底层减小,在底层又有所增加的趋势。【结论】研究海区DOC的分布受水团物理混合控制作用十分明显,近岸DOC高值区的分布主要受鲁北沿岸流和陆源输入影响,南部的低值区主要受黑潮表层水及台湾暖流的稀释作用影响,而生物作用对DOC的分布影响较弱。     

The contribution of species richness and composition to bacterial services

Bacterial communities provide important services. They break down pollutants, municipal waste and ingested food, and they are the primary means by which organic matter is recycled to plants and other autotrophs. However, the processes that determine the rate at which these services are supplied are only starting to be identified. Biodiversity influences the way in which ecosystems function, but the form of the relationship between bacterial biodiversity and functioning remains poorly understood. Here we describe a manipulative experiment that measured how biodiversity affects the functioning of communities containing up to 72 bacterial species constructed from a collection of naturally occurring culturable bacteria. The experimental design allowed us to manipulate large numbers of bacterial species selected at random from those that were culturable. We demonstrate that there is a decelerating relationship between community respiration and increasing bacterial diversity. We also show that both synergistic interactions among bacterial species and the composition of the bacterial community are important in determining the level of ecosystem functioning.     

滨海滩涂不同土地利用类型土壤活性有机碳含量与垂直分布

近年来,滨海滩涂已成为人类围垦开发的主要区域。围垦,一方面改变了土壤基本的理化性质,另一方面也加速了土壤有机碳库的变化,特别是对围垦活动比较敏感的活性有机碳,因此研究围垦区不同土地利用类型下土壤有机碳及其活性组分的含量与差异,能够为合理开发利用滨海湿地,了解围垦区的土壤碳循环特征提供参考。     

Rapid worldwide depletion of predatory fish communities

Serious concerns have been raised about the ecological effects of industrialized fishing, spurring a United Nations resolution on restoring fisheries and marine ecosystems to healthy levels. However, a prerequisite for restoration is a general understanding of the composition and abundance of unexploited fish communities, relative to contemporary ones. We constructed trajectories of community biomass and composition of large predatory fishes in four continental shelf and nine oceanic systems, using all available data from the beginning of exploitation. Industrialized fisheries typically reduced community biomass by 80% within 15 years of exploitation. Compensatory increases in fast-growing species were observed, but often reversed within a decade. Using a meta-analytic approach, we estimate that large predatory fish biomass today is only about 10% of pre-industrial levels. We conclude that declines of large predators in coastal regions have extended throughout the global ocean, with potentially serious consequences for ecosystems. Our analysis suggests that management based on recent data alone may be misleading, and provides minimum estimates for unexploited communities, which could serve as the 'missing baseline' needed for future restoration efforts.     

Fine-scale phylogenetic architecture of a complex bacterial community

Although molecular data have revealed the vast scope of microbial diversity, two fundamental questions remain unanswered even for well-defined natural microbial communities: how many bacterial types co-exist, and are such types naturally organized into phylogenetically discrete units of potential ecological significance? It has been argued that without such information, the environmental function, population biology and biogeography of microorganisms cannot be rigorously explored. Here we address these questions by comprehensive sampling of two large 16S ribosomal RNA clone libraries from a coastal bacterioplankton community. We show that compensation for artefacts generated by common library construction techniques reveals fine-scale patterns of community composition. At least 516 ribotypes (unique rRNA sequences) were detected in the sample and, by statistical extrapolation, at least 1,633 co-existing ribotypes in the sampled population. More than 50% of the ribotypes fall into discrete clusters containing less than 1% sequence divergence. This pattern cannot be accounted for by interoperon variation, indicating a large predominance of closely related taxa in this community. We propose that such microdiverse clusters arise by selective sweeps and persist because competitive mechanisms are too weak to purge diversity from within them.     

不同蓝莓品种根际phoD基因相关土壤解磷细菌群落结构分析

【目的】研究不同品种兔眼蓝莓(Vaccinium ashei Reade,简称RB)对phoD(碱性磷酸酶基因)相关土壤解磷细菌群落组成的影响,阐明解磷细菌对土壤磷素的转化以及植物生长的意义。【方法】通过对12个兔眼蓝莓品种根际土壤中phoD进行高通量测序,分析phoD基因相关土壤解磷细菌群落的多样性及组成,解析根际解磷细菌与蓝莓品种以及土壤理化性质之间的相互作用关系。【结果】在12个兔眼蓝莓品种中,蓝莓‘森土里昂’(‘Centurion’, RB4)品种具有最高的群落多样性;蓝莓根际phoD基因相关土壤解磷细菌群落核心细菌群由α-变形菌纲根瘤菌目、红螺菌目、β-变形菌纲伯克氏菌目、γ-变形菌纲黄单胞菌目、海洋螺菌目、假单胞菌目和放线菌门链霉菌目组成;蓝莓根际phoD基因相关土壤解磷细菌群落可以分为RBⅠ、RBⅡ两组,其中RBⅠ组的α-变形菌纲细菌相对丰度显著高于RBⅡ组;土壤总磷(TP)和phoD基因相关土壤解磷细菌群落组成是速效磷(AP)的主要影响因素。【结论】蓝莓不同品种和土壤性质对根际phoD基因相关解磷细菌群落丰度有显著影响,而群落多样性则与对照无显著差异,这可为进一步阐明酸性土壤条件下植物和根际解磷细菌之间的共生关系提供有效的数据支持。     

互花米草入侵对黄河口盐沼湿地土壤溶解性有机碳空间分布的影响

互花米草是我国滨海盐沼湿地中广泛分布的入侵植物,可对盐沼土壤的元素循环产生深远影响. 本研究以黄河三角洲典型互花米草分布区为研究对象,沿垂直于潮沟方向选择连续带状互花米草区(CR)、斑块状互花米草区(P)、斑块间裸滩(BL)以及互花米草与盐地碱蓬交错区(MZ)样地,分别分层采集土壤剖面样品,探讨互花米草入侵对土壤溶解性有机碳(DOC)质量分数 w 的空间分布特征的影响. 研究结果表明:研究区表层(0~20cm)及深层(>20~100cm) 土壤 w(DOC)的变化范围分别为5.68~112.17与4.27~94.28mg·kg-1;互花米草入侵显著增加了表层土壤w(DOC) (P<0.05),土壤 w(DOC)沿互花米草扩散方向逐渐降低. 除斑块状互花米草区外,土壤 w(DOC)随着土壤深度增加逐渐降低.Spearman相关性分 析 结 果 表 明, 表 层 土 壤 w(DOC) 与 土 壤 有 机 碳 即 w(SOC) (P<0.05) 以 及 w(黏 粒) (P<0.01)呈显著正相关关系,而与pH 呈负相关关系(P<0.01). 多元分析表明表层土壤与深层土壤的 DOC与土壤理化因子之间呈现不同的作用关系,说明互花米草入侵改变了滨海盐沼土壤 DOC的空间分布特征,本文研究结果为深入开展滨海盐沼湿地碳循环研究提供基础      

A taxa-area relationship for bacteria

A positive power-law relationship between the number of species in an area and the size of that area has been observed repeatedly in plant and animal communities. This species-area relationship, thought to be one of the few laws in ecology, is fundamental to our understanding of the distribution of global biodiversity. However, such a relationship has not been reported for bacteria, and little is known regarding the spatial distribution of bacteria, relative to what is known of plants and animals. Here we describe a taxa-area relationship for bacteria over a scale of centimetres to hundreds of metres in salt marsh sediments. We found that bacterial communities located close together were more similar in composition than communities located farther apart, and we used the decay of community similarity with distance to show that bacteria can exhibit a taxa-area relationship. This relationship was driven primarily by environmental heterogeneity rather than geographic distance or plant composition.     

高效反硝化菌强化固相碳源生物脱氮特性研究

以聚丁二酸丁二醇酯(PBS)作为固相可生物降解模式碳源的生物填充床,针对分离获得的高效反硝化菌开展强化生物脱氮的特性研究,并利用荧光定量PCR解析反应器的微生物群落结构。结果表明,投加反硝化菌(W14)可以明显地提高反硝化脱氮效率,当水力停留时间(HRT)为0.5 h时,反硝化菌强化脱氮生物反应器的脱氮效率达到90%以上,且能有效地降低出水残余的DOC浓度。荧光定量PCR结果表明,高效反硝化菌投加强化能够增加nir S基因丰度和比例,较好地解释了不同接种生物反应器的脱氮效果差异,即反硝化菌的强化作用能有效增加反硝化菌数量并强化脱氮效果。     

带状采伐对毛竹林土壤细菌群落结构及多样性的影响

【目的】研究带状采伐后毛竹(Phyllostachys edulis)林土壤细菌群落结构及多样性的变化,认识带状采伐对毛竹林土壤生态系统的影响,为利用带状采伐实现毛竹林规模化经营提供指导。【方法】对毛竹林进行不同宽度(3、9、15 m)的带状采伐,25 d后采集样地内土壤样品,采用Illumina MiSeq 高通量测序技术分析土壤细菌特定基因片段V3-V4区域,鉴定菌种类群,预测细菌功能,并结合7种土壤养分指标(有机质、全氮、全磷、全钾、碱解氮、有效磷、速效钾)的测定结果,探讨带状采伐对毛竹林地土壤细菌群落及土壤养分的影响。【结果】随着采伐宽度的增加,土壤有效磷、全钾、速效钾含量降低,土壤有机质、全氮、碱解氮含量先增后降。适当采伐可以提高土壤肥力,但采伐宽度超过一定限度后,土壤肥力降低,速效养分含量减少。不同带状采伐对毛竹林土壤中细菌类群的丰度、多样性、均匀度的影响各不相同;3 m采伐宽度的毛竹林地内土壤细菌群落丰富度最高,且物种分布最均匀,随着采伐宽度的增大,其毛竹林地内的细菌群落丰富度和物种均匀度均降低,当采伐宽度超过9 m时,群落间的物种组成变化差异减小。带状采伐后变形菌门(Proteobacteria)相对丰度增多,酸杆菌门(Acidobacteria)、绿湾菌门(Chloroflexi)相对丰度减少,这3种菌门同放线菌门(Actinobacteria)一起占据着毛竹林带状采伐土壤细菌群落种的主要地位,对土壤中碳(C)、氮(N)元素固定及其他养分的转化分解发挥着重要的作用。带状采伐后土壤细菌群落代谢通路中最重要的是碳水化合物代谢和氨基酸代谢,说明带状采伐后土壤细菌的优势功能主要集中在C、N两种元素的固定和转化。【结论】毛竹林带状采伐对土壤细菌群落结构及多样性产生显著影响,3 m宽度的带状采伐能够增加细菌类群的丰度、多样性、均匀度以及土壤养分含量,当采伐宽度增大,上述各项指标降低;综合分析表明带状采伐后土壤微生物类群主要参与C、N元素的固定和转化的相关功能通路。     

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.     

Constraining the Ediacaran oceanic dissolved organic carbon reservoir: Insights from carbon isotopic records from a drill core from South China

The evolution of the atmospheric oxygen content through Earth’s history is a key issue in paleoclimatic and paleoenvironmental research. There were at least two oxygenation events in the Precambrian that involved fundamental changes in both biotic innovation and the surface environment. However, a large dissolved organic carbon (DOC) pool maintained in deep oceans during the Neoproterozoic may have extended the time interval between the two oxygenation events. To test the DOC hypothesis, we conducted detailed micro-drilled analyses of carbonate carbon isotopes (δ13C_carb) of a long Ediacaran drill core (the Wangji drill core), for which whole-rock δ13C_carb and organic carbon isotope (δ13C_org) records were available. The micro-drilled δ13C_carb values obtained in this study are consistent with whole-rock δ13C_carb results, precluding the influence of severe authigenic carbonate incorporation. Importantly, the multiple negative δ13C_carb excursions in the Wangji drill core were likely linked with upwelling events, during which DOC was supplied to the surface water and oxidized. Using box models, we estimate that ~3.6 × 1019 mol and ~2.0 × 1019 mol DOC were converted to bicarbonate during two negative δ13C_carb excursions spanning millions of years. The estimations are approximately 1000 times the modern marine DOC reservoir. Our results support a relatively high oxidation capacity (elevated atmospheric pO₂ and/or oceanic [\begin{document}${\rm{SO}}_4^{2 - }$\end{document}]) of the Earth’s surface during the early Ediacaran Period.     

Biomineralization process occurring in iron mud of coastal seepage area of Zhoushan Island, Zhejiang province

The biomineralization process of iron oxidizing bacteria and its influence on accumulation of metals were investigated by modern biological observation techniques （i.e., SEM and TEM） and geochemical methods, in coastal area of Zhoushan Island, Zhejiang province where a thick ancient wood layers were buried, Results show that the iron mud samples mainly contain Leptothrix-like sheaths and Gallionella-like stalks, which are known as neutrophilic iron-oxidizing bacteria. These two bacteria are present as obviously different abundance in two sampling sites, which may be regulated by the geochemistry of seepage water. The biomineralization product of iron oxidizing bacteria is ferrihydrite, a poorly ordered iron oxide, and formation of amorphous mineral is affected by the factors of bacteria, minor Si and temperature preventing any further transformation into more crystalline phases. Organic functional groups, extracellular polymers and surface charges can provide favorable nucleation sites or template for formation of iron precipitates on the bacterial surface. The mineralization process of the iron oxidizing bacteria is divided into different stages, i.e., extracellular mineralization, intracellular mineralization and the whole cell mineralization. Furthermore, due to BIOS containing the bacterial organic matter, the accumulation capacity of metals specially Fe and Co is highly increased, suggesting that BIOS exert a degree of controlling in the cycling of metal elements in seepage area.     

滇池浮游植物群落结构的时空变化及与环境因子的关系

在滇池外海选取8个样点, 调查分析主要的环境因子和浮游植物群落的季节和年际变化, 并识别其相关关系。在滇池共检测出浮游植物6门49 属84种, 其中绿藻门的种类数最多, 占59.2%, 其次是蓝藻门, 占16.67%, 硅藻门占5.95%; 全年蓝藻门占优势, 春季隐球藻(Aphanocapsa sp.)占优势, 其他季节微囊藻(Microcystis sp.)占绝对优势。研究结果表明: 1) 藻密度和生物量的季节变化不一致, 与藻类组成的季节演替以及不同藻类的生物量大小存在较大差异有关; 2) Shannon-Wiener物种多样性指数(H)较小, 季节变化不显著; 3) 藻密度和生物量与TP正相关, 与 NO₃^-和N:P负相关; 而H与TP负相关, 与NO₃^-和N:P正相关; 4) 营养盐是影响浮游植物群落分布的关键因子, 滇池最重要的优势种微囊藻的密度和生物量与pH、NH₄⁺和TP浓度正相关, 与NO₃^-、N:P、TN、DOC和TOC的浓度负相关。推测除环境因子外, 绿藻、硅藻等优势度较小的藻类受其他生物因素的影响较大(如种间竞争和捕食等), 掩盖了环境因子对藻类的真实影响。     

Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry

Several hypotheses have been proposed to explain recent, widespread increases in concentrations of dissolved organic carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe. Some invoke anthropogenic forcing through mechanisms related to climate change, nitrogen deposition or changes in land use, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional carbon balances. The increase in DOC concentrations in these regions appears unrelated to other climatic factors.