Simulating net ecosystem exchange under seasonal snow cover at an Arctic tundra site

Estimates of winter (snow-covered non-growing season) CO 2 fluxes across the Arctic region vary by a factor of 3.5, with considerable variation between measured and simulated fluxes. Measurements of snow properties, soil temperatures, and net ecosystem exchange (NEE) at Trail Valley Creek, NWT, Cana...

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Bibliographic Details
Published in:Biogeosciences
Main Authors: Dutch, Victoria R., Rutter, Nick, Wake, Leanne, Sonnentag, Oliver, Hould Gosselin, Gabriel, Sandells, Melody, Derksen, Chris, Walker, Branden, Meyer, Gesa, Essery, Richard, Kelly, Richard, Marsh, Phillip, Boike, Julia, Detto, Matteo
Format: Text
Language:English
Published: 2024
Subjects:
Tundra
Online Access:https://doi.org/10.5194/bg-21-825-2024
https://bg.copernicus.org/articles/21/825/2024/
Description
Summary:Estimates of winter (snow-covered non-growing season) CO 2 fluxes across the Arctic region vary by a factor of 3.5, with considerable variation between measured and simulated fluxes. Measurements of snow properties, soil temperatures, and net ecosystem exchange (NEE) at Trail Valley Creek, NWT, Canada, allowed for the evaluation of simulated winter NEE in a tundra environment with the Community Land Model (CLM5.0). Default CLM5.0 parameterisations did not adequately simulate winter NEE in this tundra environment, with near-zero NEE ( &lt; 0.01 g C m - 2 d - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="56pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="78072cfdbc7010cdeed814ceb747a7c2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-825-2024-ie00001.svg" width="56pt" height="15pt" src="bg-21-825-2024-ie00001.png"/> </svg:svg> ) simulated between November and mid-May. In contrast, measured NEE was broadly positive (indicating net CO 2 release) from snow-cover onset until late April. Changes to the parameterisation of snow thermal conductivity, required to correct for a cold soil temperature bias, reduced the duration for which no NEE was simulated. Parameter sensitivity analysis revealed the critical role of the minimum soil moisture threshold of decomposition ( Ψ min ) in regulating winter soil respiration. The default value of this parameter ( Ψ min ) was too high, preventing simulation of soil respiration for the vast majority of the snow-covered season. In addition, the default rate of change of soil respiration with temperature (Q10) was too low, further contributing to poor model performance during winter. As Ψ min and Q10 had opposing effects on the magnitude of simulated winter soil respiration, larger negative values of Ψ min and larger positive values of Q10 are required to simulate wintertime NEE more adequately.

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