Nitrogen Isotopes in Palaeolimnology
Nitrogen Isotopes in Palaeolimnology
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DOI：
10.1007/0-306-47670-3_15
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发表时间：
2002
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影响因子：
--
通讯作者：
M. Talbot
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文献类型：
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作者：
M. Talbot
氮是所有生物体的一种小但必不可少的成分，因此可以被视为关键营养素。与磷和硅一起，它通常被视为最终限制有机生产力的营养素之一。事实上，在许多湖泊中，N可能是限制性营养物。氮在有机生产中的基本作用意味着氮源或循环的变化通常对湖泊沉积有机质（OM）的生产，组成和积累产生深远的影响。因此，过去的变化在这些和其他方面的N循环的知识可能提供独特的古湖沼学信息，可以与区域或全球环境变化。施莱辛格（1997）全面概述了氮对所有有机生命的核心重要性，以及氮的地球化学循环。湖泊沉积物中的氮传统上被表征为总氮（TN）的重量百分比或碳：氮比（C/N）。后者通常也被认为是确定OM来源的一种手段（例如，Meyers & Ishiwatari，1993; Tyson，1995; Meyers & Lallier-Vergès，1999）。在古湖沼学中，尽管必要的分析技术和同位素分馏效应已经被人们所知超过40年，但氮同位素分析作为表征沉积氮的方法的使用却少得多（Hoering，1955; Létolle，1980; Owens，1987）。这有两个主要原因，一个是实际的，另一个是解释性的。直到最近，只有极少数实验室配备了进行氮同位素分析的设备，即使配备了设备，由于离线样品制备的费力，可进行的分析数量通常也有限。解释的问题有关的事实，测量的同位素值可能不一定有一个明确的解决方案，由于各种地球化学过程和N源，可以有助于生产沉积OM。在过去的十年中，由于分析技术的快速和改进，以及人们越来越认识到，即使是明显模糊的N同位素值，当与其他类型的地球化学数据相结合时，也可以解释，情况发生了根本性的变化。
Nitrogen is a small but essential constituent of all organisms and as such can be regarded as a key nutrient. Together with phosphorous and silicon, it is commonly viewed as one of the nutrients that ultimately limit organic productivity. Indeed, in many lakes, N is probably the limiting nutrient. The fundamental role of nitrogen in organic production means that changes in N sources or cycling commonly have far-reaching consequences for the production, composition and accumulation of sedimentary organic matter (OM) in lakes. Knowledge of past variations in these and other aspects of the N cycle may thus provide unique palaeolimnological information that can be related to regional or global environmental change. A comprehensive overview of the central importance of N to all organic life, and of the N biogeochemical cycle, is given in Schlesinger (1997). Nitrogen in lacustrine sediments has traditionally been characterised either as weight percent total nitrogen (TN) or by the carbon: nitrogen ratio (C/N). The latter is also commonly regarded as a means of identifying the source of the OM (eg, Meyers & Ishiwatari, 1993; Tyson, 1995; Meyers & Lallier-Vergès, 1999). In palaeolimnology considerably less use has been made of N-isotope analysis as a method of characterising sedimentary nitrogen, even though the necessary analytical techniques and isotope fractionation effects have been known for over 40 years (Hoering, 1955; Létolle, 1980; Owens, 1987). There are two principal reasons for this, one practical, the other interpretational. Until comparatively recently, very few laboratories were equipped to carry out nitrogen isotope analyses and in those that were, the number of analyses that could be performed was commonly limited, because of the laborious, offline sample preparation. Interpretational problems were related to the fact that measured isotopic values may not necessarily have an unambiguous solution, due to the variety of biogeochemical processes and N sources that can contribute to the production of sedimentary OM. The situation has changed radically over the last decade, thanks to faster and improved analytical techniques and the growing realisation that even apparently ambiguous N-isotopic values may be interpretable when combined with other sorts of geochemical data.