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Incorporating concentration-dependent sediment microbial activity into methylmercury production kinetics modeling
Grace E Schwartz1, Katherine A Muller2, Saubhagya S Rathore1
1Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA. brookssc@ornl.gov.
Environmental Science. Processes & Impacts
|November 2, 2021
Summary
Researchers modeled mercury methylation in sediments using the transient availability model (TAM). Modifying the TAM with concentration-dependent microbial activity improved accuracy, showing its applicability for understanding mercury cycling in sediments.
Area of Science:
- Environmental Science
- Microbiology
- Geochemistry
Background:
- Anaerobic microorganisms with the hgcAB gene cluster transform inorganic mercury (Hg(II)) to methylmercury (MMHg).
- The transient availability model (TAM) previously modeled Hg(II) methylation kinetics in periphyton, incorporating sorption and redox reactions.
- Understanding Hg(II) methylation in sediments is crucial for mercury biogeochemical cycling.
Purpose of the Study:
- To apply and evaluate the transient availability model (TAM) for describing methylmercury (MMHg) production in sediments.
- To investigate the influence of sediment type and microbial activity on Hg(II) methylation kinetics.
- To refine the TAM by incorporating concentration-dependent microbial activity for improved modeling accuracy.
Main Methods:
- Incubation of two distinct East Fork Poplar Creek (EFPC) sediment types (anoxic/carbon-rich vs. oxic/carbon-poor) in microcosms.
- Measurement of MMHg production and ancillary data (e.g., CO2 production) to assess microbial activity.
- Application and modification of the TAM, including the integration of Monod-type kinetics for microbial activity.
- 16S rRNA sequencing to characterize microbial community structure and dynamics.
Main Results:
- The general TAM paradigm effectively described MMHg production in both sediment types.
- Distinct patterns of MMHg production were observed, correlated with sediment characteristics and microbial community differences (specifically Euryarchaeota).
- Modification of the TAM with Monod-type kinetics significantly improved model fit for the carbon-rich, microbially active sediment.
Conclusions:
- The transient availability model (TAM) is applicable for describing Hg(II) methylation in sediments.
- Incorporating concentration-dependent microbial activity into the TAM enhances its accuracy in modeling mercury methylation.
- This study provides insights into mercury biogeochemical cycling in sediment environments and the role of microbial kinetics.
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