Nitrification and denitrification in the Community Land Model compared with observations at Hubbard Brook Forest
Cynthia Nevison1, Christine Goodale2, Peter Hess3
1Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA.
Summary
Simulating nitrogen (N) cycles in land models is challenging. This study found that the Community Land Model 5.0 (CLM5.0) needs adjustments to better match observed soil N fluxes at Hubbard Brook Forest, improving N cycle modeling.
Area of Science:
- Ecology
- Biogeochemistry
- Computational modeling
Background:
- Terrestrial ecosystem models often incorporate nitrogen (N) cycles to understand N limitations on carbon (C) uptake.
- Accurate simulation of soil N dynamics, including microbial immobilization, plant uptake, nitrification, and denitrification, is crucial but challenging.
Purpose of the Study:
- To compare key soil N fluxes and flux ratios simulated by the Community Land Model version 5.0 (CLM5.0) with observational data from the Hubbard Brook Forest.
- To identify necessary model modifications to improve the representation of N cycling processes in CLM5.0.
Main Methods:
- Utilized observational data from the Hubbard Brook Forest Long-Term Ecological Research site.
- Compared simulated soil N fluxes (microbial immobilization, plant uptake, nitrification, denitrification) from CLM5.0 with site observations.
- Evaluated model performance and proposed modifications to microbial competition for soil ammonium (NH4+) and nitrate (NO3-).
Main Results:
- CLM5.0 default configuration overemphasized ammonium (NH4+) in plant uptake and immobilization, and simulated a 1:1 nitrification:denitrification ratio.
- Hubbard Brook observations indicated a greater role for nitrate (NO3-) in plant uptake and a nitrification rate potentially ten times higher than denitrification.
- Adjustments increasing nitrifier competitiveness for NH4+ and decreasing denitrifier competitiveness for NO3- improved model-observation agreement.
Conclusions:
- Modifications to CLM5.0's representation of microbial competition for N forms are necessary to accurately simulate soil N flux ratios.
- Improved N cycle modeling enhances confidence in simulating N limitation on C uptake, though C fluxes show less sensitivity to these N-focused adjustments.
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