Coupled organic carbon and iron biogeochemical cycling in polar soils and wetlands under a future warming climate
Massive amounts of organic carbon (OC) in stored in soils and wetlands found in the polar regions. The cold, oxygen-limited and (seasonally) waterlogged conditions in these environments allow the accumulation of OC in soils. With the advent of continuously warming climate conditions, however, these current carbon sink can potentially be a carbon source and release CO2 and CH4. These gases can further exacerbate the warming climate as they are very potent greenhouse gases.
Fieldwork campaign in Oct. 2022 to collect soils, particulates and water samples from the wetland
I am currently investigating how polar soils will respond to a future warming climate by studying waterlogged sub-Arctic wetlands as a natural analogue of thawing permafrost environments. Specifically, I look at the role of iron minerals in the release (or sequestration) of carbon in these wetlands. I also complement these field-based investigations with laboratory analogues by incubating these soils in controlled laboratory settings. By combining mineralogical, organic (geo)chemistry and microbial ecology approaches, I aim to provide a more detailed molecular information on the coupling of iron and carbon biogeochemical cycling in polar soils in today’s climate, as well as in projected climatic conditions.
Green rust formation, transformation and reactivity with nutrient and contaminants
Green rust (GR) is a highly reactive, Fe(II)-Fe(III) layered hydroxide mineral that forms in oxygen-limited, Fe2+-rich subsurface environments (e.g., soils, aquifers). GR minerals can effectively sequester toxic elements such as arsenic (As).
Green rust (GR) is a mixed valence layered iron hydroxide [1,2] that forms in Fe2+-rich oxygen-limited environments (i.e., non-sulfidic), influencing nutrient availability and contaminant mobility in soils and aquatic ecosystems. It often forms through the transformation of metastable Fe(III) phases like ferrihydrite or schwertmannite [2]. Although its solid phase stability in the environment is enhanced by sorbed nutrients or contaminants, it eventually transforms to other crystalline Fe(II)-bearing phases like magnetite in oxygen-poor settings. Since they have high sorption affinity, it is therefore important to understand how form or transform in nature, and follow the uptake and potential release of these nutrients and contaminants [3,4].
A brief summary of this research project is explained in the invited talk I gave at for the European Synchrotron Radiation Facility (ESRF). Here, I also demonstrate how I use extremely brilliant X-rays to help me understand molecular-level reactions of contaminants on Fe mineral surfaces.
Recent publication:
Perez et al. (2025). Coexisting phosphate controls arsenate speciation and partitioning during Fe(II)-catalyzed ferrihydrite transformation. ACS Earth Space Chem., 9(6), 1642–1653.
Perez et al. (2024). Synergistic inhibition of green rust crystallization by co-existing arsenic and silica. Environ. Sci. Processes Impacts, 26, 632–643.
Perez et al. (2021). Arsenic removal from natural groundwater using ‘green rust’: Solid phase stability and contaminant fate. J. Haz. Mat., 401, 123327.
Perez et al. (2021). Arsenic species delay structural ordering during green rust sulfate crystallization from ferrihydrite. Environ. Sci. Nano, 8, 2950–2963.
Development of nanomaterials for contaminant remediation
Top: The reactivity of core-shell iron nanoparticles with chlorinated contaminants decreases as it ‘ages’ in groundwater due to corrosion. Bottom left: Mercury (Hg2+) was sequestered at the thiol (-SH) functional groups in the metal organic framework (UiO-66-SH2). Bottom right: Magnetic iron oxide nanoparticles supported on a covalent triazine framework (CTF-1) is an effective sorbent material for the removal of As and Hg species from water.
In addition to (synthetic) minerals, I am also interested in the development and synthesis of nanomaterials for treating heavy metals and chlorinated solvents in water. I have worked on nanoporous materials (MOFs and COFs) for the removal of mercury (Hg2+) species during my MSc research. Through the introduction of functional groups or incorporation of iron nanoparticles, I was able to improve the Hg sorption capacities of the nanoporous materials I have synthesized. I am currently working together with research collaborators to prepare novel functionalized nanoporous materials for metal sequestration/recovery.
I have also been closely involved in the development of sulfidated nanoscale zero-valent iron nanoparticles (S-nZVI) through the Metal-Aid ITN. The S-nZVI material exhibits high reactivity over extended periods in groundwater because the iron sulfide shell protects it against aqueous corrosion. By modifying its shell properties, it was possible to fine tune its selectivity and reactivity for various chlorinated compounds, even in complex contaminant mixtures in natural groundwater.
Jeffrey Paulo H. Perez 