Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Department of Geography and Geosciences, GeoZentrum Nordbayern, Schlossgarten 5, 91054, Erlangen, Germany.
Institute of Science and Technology. Avenida Três de Março, São Paulo State University (UNESP), 511. Alto da Boa Vista, Sorocaba, São Paulo, 18087-180, Brazil.
Sci Rep. 2020 Aug 6;10(1):13187. doi: 10.1038/s41598-020-69912-0.
Sources of particulate organic carbon (POC) play important roles in aqueous carbon cycling because internal production can provide labile material that can easily be turned into CO. On the other hand, more recalcitrant external POC inputs can cause increased loads to sedimentary organic matter that may ultimately cause CH release. In order to differentiate sources, stable isotopes offer a useful tool. We present a study on the Itupararanga Reservoir (Brazil) where origins of POC were explored by comparing its isotope ratios (δC) to those of dissolved inorganic carbon (δC). The δC averaged around - 25.1‰ in near-surface waters, which indicates higher primary production inferred from a fractionation model that takes into account carbon transfer with a combined evaluation of δC δC and aqueous CO. However, δC values for water depths from 3 to 15 m decreased to - 35.6‰ and indicated different carbon sources. Accordingly, the δC values of the reservoir averaged around + 0.6‰ in the top 3 m of the water column. This indicates CO degassing and photosynthesis. Below this depth, DIC isotope values of as low as - 10.1‰ showed stronger influences of respiration. A fractionation model with both isotope parameters revealed that 24% of the POC in the reservoir originated from detritus outside the reservoir and 76% of it was produced internally by aqueous CO fixation.
颗粒有机碳 (POC) 的来源在水碳循环中起着重要作用，因为内部产生的 POC 可以提供易转化为 CO 的不稳定物质。另一方面，更多的外部难降解 POC 输入会导致沉积物中有机物质的负荷增加，最终可能导致 CH 释放。为了区分来源，稳定同位素提供了一个有用的工具。我们对伊图帕朗加水库（巴西）进行了一项研究，通过将其同位素比值（δC）与溶解无机碳（δC）的同位素比值进行比较，来探索 POC 的来源。近地表水的 δC 平均值约为 -25.1‰，这表明从考虑到与水合 CO 结合的碳转移的分馏模型推断出较高的初级生产。然而，水深为 3 至 15 m 的 δC 值降低到 -35.6‰，表明有不同的碳源。因此，水库的 δC 值在水柱的顶部 3 m 左右平均为+0.6‰，这表明 CO 脱气和光合作用。在这个深度以下，DIC 同位素值低至 -10.1‰，表明呼吸作用的影响更强。具有两个同位素参数的分馏模型表明，水库中 24%的 POC 来自水库外部的碎屑，76%的 POC 是通过水合 CO 固定在内部产生的。
