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Abstract
Abstract. The northern terrestrial net ecosystem carbon balance (NECB) is contingent on inputs from vegetation gross primary productivity (GPP) to offset the ecosystem respiration (Reco) of carbon dioxide (CO2) and methane (CH4) emissions, but an effective framework to monitor the regional Arctic NECB is lacking. We modified a terrestrial carbon flux (TCF) model developed for satellite remote sensing applications to evaluate wetland CO2 and CH4 fluxes over pan-Arctic eddy covariance (EC) flux tower sites. The TCF model estimates GPP, CO2 and CH4 emissions using in situ or remote sensing and reanalysis-based climate data as inputs. The TCF model simulations using in situ data explained > 70% of the r2 variability in the 8 day cumulative EC measured fluxes. Model simulations using coarser satellite (MODIS) and reanalysis (MERRA) records accounted for approximately 69% and 75% of the respective r2 variability in the tower CO2 and CH4 records, with corresponding RMSE uncertainties of &amp;leq; 1.3 g C m−2 d−1 (CO2) and 18.2 mg C m−2 d−1 (CH4). Although the estimated annual CH4 emissions were small (< 18 g C m−2 yr−1) relative to Reco (> 180 g C m−2 yr−1), they reduced the across-site NECB by 23% and contributed to a global warming potential of approximately 165 ± 128 g CO2eq m−2 yr−1 when considered over a 100 year time span. This model evaluation indicates a strong potential for using the TCF model approach to document landscape-scale variability in CO2 and CH4 fluxes, and to estimate the NECB for northern peatland and tundra ecosystems.
Highlights
Northern peatland and tundra ecosystems are important components of the terrestrial carbon cycle and store over half of the global soil organic carbon reservoir in seasonally frozen and permafrost soils (Hugelius et al, 2013)
Over 95 % of the resulting total carbon pool was allocated to Crec by the terrestrial carbon flux (TCF) model, with 2–3 % stored as consisting of metabolic (Cmet) and the remainder partitioned to Cstr
The TCF model simulated carbon stock for Lena River was less than a 2.9 kg C m−2 average determined from in situ (≤ 10 cm depth) measurements of nearby river terrace soils (Zubrzycki et al, 2013), but this could have resulted from site spatial heterogeneity and the use of recent climate records in the model spin-up that may not reflect past conditions
Summary
Northern peatland and tundra ecosystems are important components of the terrestrial carbon cycle and store over half of the global soil organic carbon reservoir in seasonally frozen and permafrost soils (Hugelius et al, 2013). These systems are becoming increasingly vulnerable to carbon losses as CO2 and CH4 emissions, resulting from climate warming and changes in the terrestrial water balance (Kane et al, 2012; Kim et al, 2012) that can increase soil carbon decomposition. Northern peatland and tundra (≥ 50◦ N) reportedly contribute between 8 and 79 Tg C in CH4 emissions each year, but these fluxes have been difficult to constrain due to uncertainty in the parameterization of biogeochemical models, the regional characterization of wetland extent and water table depth, and a scarcity of ecosystem-scale CH4 emission observations (Petrescu et al, 2010; Riley et al, 2011; Spahni et al, 2011; McGuire et al, 2012; Meng et al, 2012)
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