A parameterization of respiration in frozen soils based on substrate availability
Respiration in frozen soils is limited to thawed substrate within the thin water films surrounding soil particles. As temperatures decrease and the films become thinner, the available substrate also decreases, with respiration effectively ceasing at −8 °C. Traditional exponential scaling factors to...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-04-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/1991/2016/bg-13-1991-2016.pdf |
| Summary: | Respiration in frozen soils is limited to thawed substrate within
the thin water films surrounding soil particles. As temperatures decrease and
the films become thinner, the available substrate also decreases, with
respiration effectively ceasing at −8 °C. Traditional exponential
scaling factors to model this effect do not account for substrate
availability and do not work at the century to millennial timescales
required to model the fate of the nearly 1100 Gt of carbon in permafrost
regions. The exponential scaling factor produces a false, continuous loss of
simulated permafrost carbon in the 20th century and biases in estimates of
potential emissions as permafrost thaws in the future. Here we describe a new
frozen biogeochemistry parameterization that separates the simulated carbon
into frozen and thawed pools to represent the effects of substrate
availability. We parameterized the liquid water fraction as a function of
temperature based on observations and use this to transfer carbon between
frozen pools and thawed carbon in the thin water films. The simulated
volumetric water content (VWC) as a function of temperature is consistent
with observed values and the simulated respiration fluxes as a function of
temperature are consistent with results from incubation experiments. The
amount of organic matter was the single largest influence on simulated VWC
and respiration fluxes. Future versions of the parameterization should
account for additional, non-linear effects of substrate diffusion in thin
water films on simulated respiration. Controlling respiration in frozen soils
based on substrate availability allows us to maintain a realistic permafrost
carbon pool by eliminating the continuous loss caused by the original
exponential scaling factors. The frozen biogeochemistry parameterization is a
useful way to represent the effects of substrate availability on soil
respiration in model applications that focus on century to millennial timescales in permafrost regions. |
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| ISSN: | 1726-4170 1726-4189 |