Preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis
Preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis
复制标题
DOI：
10.1016/s0016-7037(02)00968-7
复制
发表时间：
2002-10-01
影响因子：
5
通讯作者：
McKenzie, JA
中科院分区：
文献类型：
--
作者：
Lehmann, MF;Bernasconi, SM;McKenzie, JA
有机质的碳、氮同位素组成已被广泛用于示踪海洋和湖泊环境中的生物地球化学过程。为了从沉积有机质重建过去的环境变化，关键是要考虑水柱中细菌降解和沉积物早期成岩过程中初级同位素信号的潜在变化。在一系列的缺氧和缺氧培养实验中，我们研究了有机质在微生物降解过程中的去向及其碳、氮同位素组成的变化。用双指数衰减模型测定的分解速率表明，在缺氧和缺氧条件下，有机质的活性部分以相似的速率降解。但在好氧条件下，有机质耐降解的比例远低于缺氧条件下，在培养3个月内，整体有机物的~(13)C比初始值下降了1.6个千分之1.6。这种耗竭可以归因于选择性地保存C-13耗尽的有机化合物。在缺氧衰变过程中，δ(15)N值持续下降到低于初始值的千分之三左右。减少的原因可能是细菌生长将N-15耗尽的生物量添加到残留物中。在氧化实验中，增量(15)N值增加了千分之三以上，然后下降到与初始同位素组成难以区分的值。缺氧和缺氧条件的不同可能归因于类型的不同。微生物活动和优先降解的时间和程度。与缺氧培养实验一致的是，富营养化的卢加诺湖沉积物。平均来说。在一项长期的沉积物捕集研究中收集的沉降性颗粒有机物中，碳13(-1.5ppm)和N-15(-1.2ppm)被耗尽。版权所有(C)2002爱思唯尔科学有限公司。
The carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments. In order to reconstruct past environmental changes from sedimentary organic matter, it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments.In a series of oxic and anoxic incubation experiments, we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation. The decomposition rates determined with a double-exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions. However, under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions, Within three months of incubation the delta(13)C of bulk organic matter decreased by 1.6parts per thousand with respect to the initial value. The depletion can be attributed to the selective preservation of C-13-depleted organic compounds. During anoxic decay, the delta(15)N values continuously decreased to about 3parts per thousand below the initial value. The decrease probably results from bacterial growth adding N-15-depleted biomass to the residual material. In the oxic experiment, delta(15)N values increased by more then 3parts per thousand, before decreasing to a value indistinguishable from the initial isotopic composition. The dissimilarity between oxic and anoxic conditions may be attributed to differences in the type. timing and degree of microbial activity and preferential degradation. In agreement with the anoxic incubation experiments, sediments from eutrophic Lake Lugano are. on average. depleted in C-13 (- 1.5parts per thousand) and N-15 (-1.2parts per thousand) with respect to sinking particulate organic matter collected during a long-term sediment trap study. Copyright (C) 2002 Elsevier Science Ltd.