Variations in net ecosystem exchange of carbon dioxide in a boreal mire: Modeling mechanisms linked to water table position

Abstract

[1] In mires, which occupy large areas of the boreal region, net ecosystem CO 2 exchange (NEE) rates vary significantly over various timescales. In order to examine the effect of one of the most influencing variables, the water table depth, on NEE the general ecosystem model GUESS-ROMUL was modified to predict mire daily CO 2 exchange rates. A simulation was conducted for a lawn, the most common microtopographical feature of boreal oligotrophic minerotrophic mires. The results were validated against eddy covariance CO 2 flux measurements from Degerö Stormyr, northern Sweden, obtained during the period [2001][2002][2003]. Both measurements and model simulations revealed that CO 2 uptake was clearly controlled by interactions between water table depth and temperature. Maximum uptake occurred when the water table level was between 10 and 20 cm and the air temperature was above 15°C. When the water table was higher, the CO 2 uptake rate was lower, owing to reduced rates of photosynthetic carbon fixation. When the water table was lower, NEE decreased owing to the increased rate of decomposition of organic matter. When the water table level was between 10 and 20 cm, the NEE was quite stable and relatively insensitive to both changes within this range and any air temperature changes above +15°C. The optimal water table level range for NEE corresponds to that characteristic of mire lawn plant communities, indicating that the annual NEE will not change dramatically if climatic conditions remain within the optimal range for the current plant community.

ORCHIDEE-PEAT (revision 4596), a model for northern peatland CO<sub>2</sub>, water, and energy fluxes on daily to annual scales

“…The permanently saturated deep catotelm carbon pool receives a prescribed fraction of the acrotelm carbon, and is decomposed only anaerobically at a very slow rate. While the acrotelm depth is fixed to 30 cm in some peat decomposition models (Yurova et al, 2007;Wania et al, 2009a;Spahni et al, 2013), we used the average of simulated minimum summer water table position (WT min ) over the observational period to demarcate the boundary between the acrotelm and the catotelm at each site to take into account local site conditions. We conducted a "preparation run (S0)", in which the model was run at each site using the same protocol (Sect.…”

Integrating peatlands into the coupled Canadian Land Surface Scheme (CLASS) v3.6 and the Canadian Terrestrial Ecosystem Model (CTEM) v2.0

“…The boundary is usually estimated to be 30 cm below the soil surface in wetlands (Canada Committee on Ecological (Biophysical) Land Classification: National Wetland Working Group, 1997), and has been widely used as the bottom of the first soil layer in two-layer soil decomposition models (e.g. Granberg et al, 1999;Yurova et al, 2007;Spahni et al, 2013). To capture the effect of the fluctuating water table on the transfer of water and energy within the soil, we used a multi-layer configuration rather than the standard three-layer configuration of the soil layers in CLASS.…”

“…On the other hand, several peatland models have been developed and evaluated for individual sites. For example, the McGill Wetland Model (MWM) simulates the C exchange in Degerö Stormyr and the Mer Bleue bog (St-Hilaire et al, 2010); the peatland version of the General Ecosystem Simulator -Model of Raw Humus, Moder and Mull (GUESS-ROMUL) simulates the variation of net ecosystem production (NEP) with water table position in a fen (Yurova et al, 2007); and the PEATBOG model simulates C and N cycles in peatlands, specifically the Mer Bleue bog ). These models have been shown to reproduce well the processes occurring in the peatlands that they were designed for.…”

Modelling CH<sub>4</sub> emissions from arctic wetlands: effects of hydrological parameterization

“…Two runs were performed with two different water table files. The first was the measured water table and the second was simulated using equations based on the Mixed Mire Water and Heat Model (MMWH) of Granberg et al (1999) as modified by Yurova et al (2007). The hydrology of the model is represented by a simple bucket approach describing the change in water content of a unit area (Granberg et al, 1999).…”

“…Changes in both substrate availability and oxidation state during the growing season affect the population dynamics of methanogenic and methanotrophic bacteria (Svensson and Rosswall, 1984;Whiting and Chanton, 1993) and are reflected in the net CH 4 flux (Kettunen et al, 1999).…”