Abstract
Fe-rich mobile colloids play vital yet poorly understood roles in the biogeochemical cycling of Fe in groundwater by influencing organic matter (OM) preservation and fluxes of Fe, OM, and other essential (micro-)nutrients. Yet, few studies have provided molecular detail on the structures and compositions of Fe-rich mobile colloids and factors controlling their persistence in natural groundwater. Here, we provide comprehensive new information on the sizes, molecular structures, and compositions of Fe-rich mobile colloids that accounted for up to 72% of aqueous Fe in anoxic groundwater from a redox-active floodplain. The mobile colloids are multi-phase assemblages consisting of Si-coated ferrihydrite nanoparticles and Fe(II)-OM complexes. Ferrihydrite nanoparticles persisted under both oxic and anoxic conditions, which we attribute to passivation by Si and OM. These findings suggest that mobile Fe-rich colloids generated in floodplains can persist during transport through redox-variable soils and could be discharged to surface waters. These results shed new light on their potential to transport Fe, OM, and nutrients across terrestrial-aquatic interfaces.
| Original language | English |
|---|---|
| Article number | 119990 |
| Journal | Water Research |
| Volume | 238 |
| DOIs | |
| State | Published - Jun 30 2023 |
| Externally published | Yes |
Funding
Funding was provided by the U.S. Department of Energy (DOE) office of Biological and Environmental Research (BER), Environmental System Sciences Division, through its support of the SLAC Floodplain Hydro-Biogeochemistry Science Focus Area (SFA) under Contract No. DE-AC02–76SF00515. SSRL and SLAC are supported by the U.S. Department of Energy , Office of Science, Office of Basic Energy Sciences. The technical staff at SSRL are gratefully acknowledged for their support of the X-ray absorption measurements. We further acknowledge the use and support of the Stanford-SLAC Cryo-EM Facilities, which is supported by the National Institutes of Health Common Fund Transformative High-Resolution Cryo-Electron Microscopy program (U24 GM129541). W.Z is funded by the Stanford Interdisciplinary Graduate Fellowship program. A portion of this research was performed on a project award (10.46936/lser.proj.2021.51929/60000375) from the Environmental Molecular Sciences Laboratory, a DOE Office of Science User Facility sponsored by the Biological and Environmental Research program under Contract No. DE-AC05–76RL01830.
Keywords
- EXAFS
- Electron microscopy
- Fe mineral
- Mössbauer spectroscopy
- Oxidation–reduction