Stable Isotope Feasibility Study for Testing the Role of Algal Carbon in a Tropical Floodplain

奥里诺科河流域是少数几个大型 未受管制的河流毗邻变化极小的洪泛区。 的 因此，奥里诺科河为研究 自然洪泛区现象。 过去对质量通量的研究沿着 奥里诺科河的主要河流和物理，化学， 小部分洪泛平原上的生物事件 产生了几条证据，表明一个意外的 藻类有机物（浮游植物， 在维持奥里诺科河的水生食物网方面 洪泛区生态系统 其他重要的有机物质来源 包括来自上游的颗粒材料 陆地环境、河岸凋落物和水生环境 维管植物 然而，目前的证据表明， 来自这些来源的大部分生物质通过微生物降解 而不会有效地进入消费者的食物链。 稳定 同位素似乎提供了最好的前景的直接测试， 这个假设。 然而，稳定同位素的用途是 在某种程度上，由于同位素的变化， 签名和车厢的数量，必须 通过使用这些签名来解决。 基于这个理由， 目前的建议概述了一项测试可行性的计划 使用稳定同位素来解决 关于奥里诺科河漫滩的藻类碳 手段和 将为C的稳定同位素特征建立方差， N和S在主要有机物隔室中的代表性 在奥里诺科河漫滩的网站，和物理方法， 分离功能不同的隔室，例如 并会测试碎石及悬浮藻类。 这些信息 将用于量化稳定的分辨率 奥里诺科河漫滩的同位素

The Orinoco basin is one of the few locations where a large unregulated river adjoins a minimally-altered floodplain. The Orinoco therefore presents special opportunities for the study of natural floodplain phenomena. Past studies of mass flux along the Orinoco main stream and of the phasing in physical, chemical, and biological events on small segments of floodplain have produced several lines of evidence that indicate an unexpectedly high importance of algal organic matter (phytoplankton, periphyton) in sustaining the aquatic food webs of the Orinoco floodplain ecosystem. Other prominent sources of organic matter for the system include particulate material from upstream terrestrial environments, riparian litterfall, and aquatic vascular plants. However, current evidence indicates that the majority of biomass from these sources is degraded microbially without passing efficiently into consumer food chains. Stable isotopes appear to offer the best prospect for a direct test of this hypothesis. However, the usefulness of stable isotopes is to some degree site-specific because of variations in isotope signatures and in the number of compartments that must be resolved through the use of these signatures. For this reason, the present proposal outlines a plan for testing the feasibility of using stable isotopes in resolving the broad hypothesis concerning algal carbon in the Orinoco floodplain. Means and variances will be established for stable isotope signatures of C, N, and S in major organic-matter compartments at a representative site on the Orinoco floodplain, and methods for physical separation of functionally different compartments such as detritus and suspended algae will be tested. This information will be used in quantifying the resolving power of stable isotopes in the Orinoco floodplain.