Coupled eco-hydrology and biogeochemistry algorithms enable the simulation of water table depth effects on boreal peatland net CO<sub>2</sub> exchange

Abstract

Abstract. Water table depth (WTD) effects on net ecosystem CO 2 exchange of boreal peatlands are largely mediated by hydrological effects on peat biogeochemistry and the ecophysiology of peatland vegetation. The lack of representation of these effects in carbon models currently limits our predictive capacity for changes in boreal peatland carbon deposits under potential future drier and warmer climates. We examined whether a process-level coupling of a prognostic WTD with (1) oxygen transport, which controls energy yields from microbial and root oxidation-reduction reactions, and (2) vascular and nonvascular plant water relations could explain mechanisms that control variations in net CO 2 exchange of a boreal fen under contrasting WTD conditions, i.e., shallow vs. deep WTD. Such coupling of eco-hydrology and biogeochemistry algorithms in a process-based ecosystem model, ecosys, was tested against net ecosystem CO 2 exchange measurements in a western Canadian boreal fen peatland over a period of drier-weather-driven gradual WTD drawdown. A May-October WTD drawdown of ∼ 0.25 m from 2004 to 2009 hastened oxygen transport to microbial and root surfaces, enabling greater microbial and root energy yields and peat and litter decomposition, which raised modeled ecosystem respiration (R e ) by 0.26 µmol CO 2 m −2 s −1 per 0.1 m of WTD drawdown. It also augmented nutrient mineralization, and hence root nutrient availability and uptake, which resulted in improved leaf nutrient (nitrogen) status that facilitated carboxylation and raised modeled vascular gross primary productivity (GPP) and plant growth. The increase in modeled vascular GPP exceeded declines in modeled nonvascular (moss) GPP due to greater shading from increased vascular plant growth and moss drying from near-surface peat desiccation, thereby causing a net increase in modeled growing season GPP by 0.39 µmol CO 2 m −2 s −1 per 0.1 m of WTD drawdown. Similar increases in GPP and R e caused no significant WTD effects on modeled seasonal and interannual variations in net ecosystem productivity (NEP). These modeled trends were corroborated well by eddy covariance measured hourly net CO 2 fluxes (modeled vs. measured: R 2 ∼ 0.8, slopes ∼ 1 ± 0.1, intercepts ∼ 0.05 µmol m −2 s −1 ), hourly measured automated chamber net CO 2 fluxes (modeled vs. measured: R 2 ∼ 0.7, slopes ∼ 1 ± 0.1, intercepts ∼ 0.4 µmol m −2 s −1 ), and other biometric and laboratory measurements. Modeled drainage as an analog for WTD drawdown induced by climate-changedriven drying showed that this boreal peatland would switch from a large carbon sink (NEP ∼ 160 g C m −2 yr −1 ) to carbon neutrality (NEP ∼ 10 g C m −2 yr −1 ) should the water table deepen by a further ∼ 0.5 m. This decline in projected NEP indicated that a further WTD drawdown at this fen would eventually lead to a decline in GPP due to water limitation. Therefore, representing the effects of interactions among hydrology, biogeochemistry and plant physiological ecology on ecosystem carbon, water, and nutrient cycling in global ca...

Use of Surface Motion Characteristics Determined by InSAR to Assess Peatland Condition

“…The interpretation presented carries important implications: Surface motion attributed to changes in water budget, water table depth, and energy balance are also linked to carbon balance and net ecosystem exchange (Laine et al, ; Mezbahuddin et al, ; Moore et al, ). Hence, if the InSAR time series capture meaningful characteristics of the surface motion, this will open up a new view of peatland dynamics on an unprecedented scale that could not be practically achieved using standard field‐based techniques.…”

Quantifying carbon budget, crop yields and their responses to environmental variability using the ecosys model for U.S. Midwestern agroecosystems

“…In addition, ecosys outputs profiles and fluxes of many easily measurable chemicals, including different phase existences of CO2, CH4, N2O, NH3, NO3, HPO4 (2-) , etc. Finally, ecosys resolves many common agricultural practices, such as mixed cropping, depth dependent irrigation and tillage (Grant, 1997), banded vs broadcast fertilization (Grant et al, 2001b), soil liming, manure application (Grant et al, 2001c), denitrification inhibitor (Grant et al, 2020), and tile-drainage system (Mezbahuddin et al, 2017) etc. Finally, ecosys generally requires no calibration for the soil and hydrological processes due to its complete mechanistics thus provides scalability to regional scale applications (Grant et al, 2012).…”

Peat Carbon Vulnerability to Projected Climate Warming in the Hudson Bay Lowlands, Canada: A Decision Support Tool for Land Use Planning in Peatland Dominated Landscapes

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