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Redox oscillations destabilize and mobilize colloidal soil organic carbon
Mohammad Zafar Afsar1, Jing Yan1, Bruce Vasilas1
1Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, United States.
The Science of the Total Environment
|December 26, 2022
Summary
Soil redox conditions significantly impact organic carbon (OC) release. Anoxic conditions released the most OC, while redox oscillations altered its composition and size fractions, affecting soil carbon cycling.
Area of Science:
- Soil Science
- Biogeochemistry
- Environmental Science
Background:
- Soil organic carbon (OC) fate and transport are influenced by redox-driven biogeochemical processes.
- Oxic-anoxic events in soil can significantly alter the release of OC.
Purpose of the Study:
- To investigate the influence of static oxic (SO), static anoxic (SA), and redox oscillation (RO) events on OC release from soil.
- To characterize the size fractions and molecular composition of released OC under different redox conditions.
Main Methods:
- A 18-week laboratory soil column study.
- Incubation of soil columns under static oxic, static anoxic, or redox oscillation conditions.
- Collection and spectrofluorometric analysis of size-fractionated leachate (dissolved, nanoparticle, fine colloid, particulate OC).
Main Results:
- OC release followed the order: SA > RO > SO.
- After 9 weeks, SA columns showed a 54-fold increase in OC release compared to controls.
- After 18 weeks, SO OC release doubled, while SA OC release decreased by 50%; RO showed intermediate release and varied OC composition.
- RO events promoted the formation of larger OC fractions (>100 nm).
Conclusions:
- Redox conditions profoundly affect soil OC release and transformation.
- Redox oscillations create distinct dynamics in OC release and composition compared to static conditions.
- Alternating redox processes regulate OC cycling and organo-mineral associations, influencing the size continuum of soil OC.
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