稳定同位素技术在水域生态系统研究中的应用

Applications of stable isotope techniques in aquatic ecological studies

稳定同位素作为一种天然的示踪物,应用十分广泛,其在水域生态学中的应用也日益受到重视。生物同位素组成总是与其食物同位素组成相一致,能随食物的改变而相应地发生改变,是生物生存状况的理想指示物,为水域生态系统食物网结构与功能、物质流与能量流的研究提供了有力的技术支撑。在综评稳定同位素技术原理与方法的基础上,较为详细地对其应用于水域生态研究的理论基础与进展进行了总结。该方法的应用以水域中生产者同位素组成差异为前提,主要涉及确定食物来源、食物的贡献比例、营养级的确定、食物网结构的构建及鱼类等水生生物的洄游及迁移路线等方面,这些研究对了解生态系统的动态变化与外界环境对其影响具有重要意义。并对我国此类研究的前景和存在问题进行了探讨。

Stable isotopes have been used in many research areas as natural labels and are becoming an important tool in aquatic ecological research. The theoretical basis and application of stable isotope analysis in aquatic ecology as well as its principle and method are reviewed in this paper. An organism＇s stable isotope ratios （δ^15N and δ^13C etc. ） are an integration of the isotopic signatures of prey items that have been assimilated through time, the organism will come into isotopic equilibrium with its diet with the time to equilibrium depending on growth and tissue turnover rates. Stable nitrogen isotope ratios increase with trophic level by approximately 3‰ to 4‰; this provides a powerful analytical tool to quantify relative trophic position. In contrast, stable carbon isotope ratio changes very little with trophic level （0 to 1‰ enrichment per trophic level）. Instead, stable carbon isotope values of organisms reflect the average δ^13C of their diets. When an organism moves to a different habitat, its stable isotope ratios will change. From the stable ratios of the different habitats and the organism, we can judge the migration routine of the organism. Stable isotopes are often used to quantify the contributions of multiple sources to an organism. In general, the proportional contributions of n＋ 1 different sources can be uniquely determined by the use of n isotope groups with linear mixing models based on mass balance equations. When there are n isotope groups and 〉 n ＋ 1 sources, all possible combinations of each sources contribution can be obtained by a computer program （IsoSource）, but the proportional contributions aren＇t unique. The above two cases presume that the proportional contribution of a source to an organism is the same for all isotope elements, while not all cases are so. An isotope element concentration-weighted linear mixing model was developed, whose quantified results are more reasonable, but only determined the proportional contributions of n＋1 sources with n isotope groups. Prey sources, trophic level and prey proportional contributions etc. are basic information needed to construct aquatic ecosystem food web patterns and functions and material and energy flows, which are fundamental to understand the dynamic of ecosystems and effects of environment to the ecosystems. The prospect of such studies in China and some existing problems are also discussed.