Extensive processing of sediment pore water dissolved organic matter during anoxic incubation as observed by high-field mass spectrometry (FTICR-MS).
Extensive processing of sediment pore water dissolved organic matter during anoxic incubation as observed by high-field mass spectrometry (FTICR-MS).
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DOI：
10.1016/j.watres.2017.11.015
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发表时间：
2018-02
期刊：
影响因子：
12.8
通讯作者：
J. Valle;M. Gonsior;M. Harir;A. Enrich-Prast;P. Schmitt‐Kopplin;D. Bastviken;R. Conrad;N. Hertkorn-N.-He
中科院分区：
文献类型：
--
作者：
J. Valle;M. Gonsior;M. Harir;A. Enrich-Prast;P. Schmitt‐Kopplin;D. Bastviken;R. Conrad;N. Hertkorn-N.-He
湖泊沉积物中的溶解有机物(DOM)是许多微生物降解过程的碳源，包括好氧和厌氧矿化。在厌氧降解过程中，DOM被部分消耗并转化为新的分子，同时产生温室气体甲烷(CH4)和二氧化碳(CO2)。在这项研究中，我们使用超高分辨质谱仪跟踪从三个北方湖泊表层沉积物中分离出的固相可萃取(PPL树脂)孔隙水DOM(SPE-DOM)在缺氧培养40天前后的组成差异，并同时测定CH4和CO2的释放。气相色谱检测到的CH4和CO2产生量在不同重复之间差异很大，分别占CO2沉积有机碳的∼2-4×10-−4和CH4的∼0.8-2.4×10-−-5的一部分。与之相反，矿化过程中的分子系列相对比例、元素比例、平均质量和不饱和度等关键体积参数的相对变化规律地在百分比范围内(化合物减少1-3%，化合物增加4-10%)，即比单独成矿高几个数量级。对湖泊孔隙水DOM中CHO分子的平均碳氧化态的计算表明，在孵化过程中，有机质发生了相当非选择性的大规模转化，高度氧化和高度还原的CHO分子被耗尽，形成了相当不稳定的黄腐酸类分子。总体而言，CHO化合物的比例略有下降。在孵化过程中，接近饱和的CHO和CHO类脂物质减少：与特定的化合物相比，这些相当常见的分子不是湖泊沉积物变化的特异性指标，例如某些含氧芳烃和富含羧基的脂环酸(CRAM)在孵化后发现更丰富。在孵化过程中，所有湖泊中的许多CHNO化合物都有显著的普遍增加。湖泊间DOM转化的差异与湖泊大小和水体停留时间有关。在小湖Svarttjärn中，CRAM在孵化过程中增加，而在大湖Bisen中，木质素和单宁类化合物丰富，这表明这些相当不稳定的芳香化合物被选择性地保存下来，而不是最近的合成。孵化后的SPE-DOM可能代表新合成的化合物、主要由本质上难降解的分子和/或在我们的实验中没有消耗的微生物代谢物组成的剩余的散装DOM。尽管DOM在总DOM中被矿化成CO2和CH4的比例很低，但在孵化过程中分子DOM成分发生了更显著的变化，表明与完全矿化相比，有机质的成岩作用可能是实质性的。
Dissolved organic matter (DOM) contained in lake sediments is a carbon source for many microbial degradation processes, including aerobic and anaerobic mineralization. During anaerobic degradation, DOM is partially consumed and transformed into new molecules while the greenhouse gases methane (CH4) and carbon dioxide (CO2) are produced. In this study, we used ultrahigh resolution mass spectrometry to trace differences in the composition of solid-phase extractable (PPL resin) pore water DOM (SPE-DOM) isolated from surface sediments of three boreal lakes before and after 40 days of anoxic incubation, with concomitant determination of CH4and CO2evolution. CH4and CO2production detected by gas chromatography varied considerably among replicates and accounted for fractions of ∼2–4 × 10−4of sedimentary organic carbon for CO2and ∼0.8–2.4 × 10−5for CH4. In contrast, the relative changes of key bulk parameters during incubation, such as relative proportions of molecular series, elemental ratios, average mass and unsaturation, were regularly in the percent range (1–3% for compounds decreasing and 4–10% for compounds increasing), i.e. several orders of magnitude higher than mineralization alone. Computation of the average carbon oxidation state in CHO molecules of lake pore water DOM revealed rather non-selective large scale transformations of organic matter during incubation, with depletion of highly oxidized and highly reduced CHO molecules, and formation of rather non-labile fulvic acid type molecules. In general, proportions of CHO compounds slightly decreased. Nearly saturated CHO and CHOS lipid-like substances declined during incubation: these rather commonplace molecules were less specific indicators of lake sediment alteration than the particular compounds, such as certain oxygenated aromatics and carboxyl-rich alicyclic acids (CRAM) found more abundant after incubation. There was a remarkable general increase in many CHNO compounds during incubation across all lakes. Differences in DOM transformation between lakes corresponded with lake size and water residence time. While in the small lake Svarttjärn, CRAM increased during incubation, lignin-and tannin-like compounds were enriched in the large lake Bisen, suggesting selective preservation of these rather non-labile aromatic compounds rather than recent synthesis. SPE-DOM after incubation may represent freshly synthesized compounds, leftover bulk DOM which is primarily composed of intrinsically refractory molecules and/or microbial metabolites which were not consumed in our experiments. In spite of a low fraction of the total DOM being mineralized to CO2and CH4, the more pronounced change in molecular DOM composition during the incubation indicates that diagenetic modification of organic matter can be substantial compared to complete mineralization.