Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550004, China.
Institute of Earth Sciences, China University of Geosciences (Beijing), Beijing 100083, China.
Sci Total Environ. 2023 Jun 20;878:162964. doi: 10.1016/j.scitotenv.2023.162964. Epub 2023 Mar 21.
Iron (Fe) isotope geochemistry in rivers is crucial for comprehending surficial weathering and geochemical cycle mechanisms. Lancang River is an important channel for material transport between the Tibet Plateau and the oceans of Southeast Asia. In this study, Fe contents and Fe isotope (δFe) compositions in the suspended particulate matter (SPM) are investigated to discuss the rock weathering processes in the Lancang River Basin. The δFe values of SPM range from 0.01 ‰ to 0.21 ‰, with an average of 0.12 ‰, close to the average δFe value of continental crust (0.07 ‰). The results indicate that the fractionation of Fe isotopes is limited caused of weathering process in the Lancang River Basin. Due to the interception of dense dams in the middle and lower reaches (1000-2000 m), the dissolved oxygen (DO) values of river water and the Fe contents of SPM remain at a relatively highest level, whereas the δFe values in SPM are more positive. The positive correlation between chemical index of alteration (CIA) values and the Fe contents suggest that Fe in the tributary SPM may represent the weathering degree of their source areas. The increase of DO in the mainstream water may promote the decomposition and dissolution of SPM, thus increasing the contents of Fe in the remaining SPM, and causing slight positive fractionation of Fe in SPM. This study presents a complete analysis of the Fe isotope's potential utility in identifying the source of SPM. In addition, the Fe isotope may represent some alterations encountered by SPM throughout the runoff process.
铁（Fe）同位素地球化学在河流中对于理解表层风化和地球化学循环机制至关重要。澜沧江是青藏高原与东南亚海洋之间物质输送的重要通道。本研究通过对悬浮颗粒物（SPM）中的 Fe 含量和 Fe 同位素（δFe）组成进行分析，探讨了澜沧江流域的岩石风化过程。SPM 的 δFe 值范围为 0.01‰至 0.21‰，平均值为 0.12‰，接近大陆地壳的平均 δFe 值（0.07‰）。结果表明，澜沧江流域风化作用过程中 Fe 同位素分馏有限。中下游（1000-2000m）密集大坝的拦截作用导致河水溶解氧（DO）值和 SPM 中的 Fe 含量仍保持在较高水平，而 SPM 中的 δFe 值更为正。SPM 的化学蚀变指数（CIA）值与 Fe 含量呈正相关，表明支流 SPM 中的 Fe 可能代表其源区的风化程度。主流水中 DO 的增加可能促进 SPM 的分解和溶解，从而增加剩余 SPM 中的 Fe 含量，并导致 SPM 中 Fe 的轻微正分馏。本研究全面分析了 Fe 同位素在识别 SPM 源方面的潜在应用。此外，Fe 同位素可能代表 SPM 在整个径流过程中遇到的某些蚀变作用。
