Iron Isotope Fractionation During Weathering: Insights from the Gleysols Profiles in Mun River Basin, Northeast Thailand

Iron Isotope Fractionation During Weathering: Insights from the Gleysols Profiles in Mun River Basin, Northeast Thailand

Leaching

Weathering

Process control

Rivers

Groundwater

Biogeochemistry

Organic compounds

Isotopes

Watersheds

Iron (Fe) isotope is an effective tool for tracing Fe transformation, migration, and biogeochemical cycling in the Earth's surface system. In this study, the Fe content and stable isotope composition (56Fe/54Fe) in two Gleysol profiles (M1 and M2) were investigated to distinguish the potential mechanisms and processes of controlling the Fe isotope fractionation during weathering in the Mun River Basin (MRB), Northeast Thailand. The 56Fe composition (relative to the IRMM-014 standard) of soils ranged from 0.18 to +0.54 in the M1 profile and from +0.04 to +0.27 in the M2 profile, and the Fe isotope composition was extremely light in the Fe nodule-containing zone. The lowest 56Fe value was measured in the Fe nodule-containing zone likely resulted from the formation of iron (hydr)oxides in Fe-rich groundwater with a light Fe isotope composition. The positive correlation between 56Fe and chemical index of alteration (CIA) values suggests that strong weathering of sandstone induces Fe mobility and isotope fractionation in soils without oxide nodules. However, the Fe content and 56Fe composition of the Fe nodule-containing zone are mainly controlled by redox processes. Leaching is likely an important factor leading to a decrease in Fe content and the enrichment of heavy Fe isotopes in the topsoil of the M1 profile. However, in addition to the leaching process, organic matter plays a crucial role in Fe isotope fractionation, resulting in the enrichment of light Fe in the organic matter-rich topsoil of the M2 profile. Our findings provide new insight into the Fe isotope compositions of Gleysols and elucidate the controlling factors and procedures related to Fe isotope fractionation, which will aid in the understanding of Fe cycling during weathering in the MRB. 2022, The Authors. All rights reserved.

2022

Zhang, Qian

Han, Guilin

Zeng, Jie

Wang, Lingqing

Zhu, Guangyou

Liu, Man

Liang, Bin

Qu, Rui

Li, Xiaoqiang

journalArticle

15565068