Can continental bogs with stand the pressure due to climate change?

Not all peatlands are alike. Theoretical and process based models suggest that ombrogenic, oligotrophic peatlands can withstand the pressures due to climate change because of the feedbacks among ecosystem production, decomposition and water storage. Although there have been many inductive explanations inferring from paleo-records, there is a lack of deductive empirical tests of the models predictions of these systems’ stability and there are few records of the changes in the net ecosystem carbon balance (NECB) of peatlands that are long enough to examine the dynamics of the NECB in relation to climate variability. Continuous measurements of all the components of the NECB and the associated general climatic and environmental conditions have been made at the Mer Bleue (MB) peatland, a large, 28 km2, 5 m deep, raised ombro-oligotrophic, shrub and Sphagnum covered bog, near Ottawa, Canada from May 1, 1998 until the present. The sixteen-year daily CO2, CH4, and DOC flux and NECB covers a wide range of variability in peatland water storage from very dry to very wet growing seasons. We used the MB data to test the extent of MB peatland’s stability and the strength of the underlying key feedback between the NECB and changes in water storage projected by the models. In 2007 we published a six-year (1999-2004) net ecosystem carbon balance (NECB) for MB of ∼22 ± 40 g C m-2 yr-1, but we have since recalculated the 1998-2004 NECB to be 32 ± 40 g C m-2 yr-1 based on a reanalyzed average NEP of 51 ± 41 g C m-2 yr-1. Over the same period the net loss of C via the CH4 and DOC fluxes were -4 ± 1 and -15 ± 3 g C m-2 yr-1. The 1998-2004 six-year MB average NECB is similar to the long-term C accumulation rate, estimated from MB peat cores, for the last 3,000 years. The post 2004 MB NEP has increased to an average of ∼96 ± 32 g C m-2 yr-1 largely to there being generally wetter growing seasons. The losses of C via DOC (18 ± 1 g C m-2 yr-1) and CH4 (7 ± 4 g C m-2 yr-1) while showing considerable year-to-year variability are not significantly different post 2004. Hence, the proportional loss of C as DOC and CH4 in the MB NECB is slightly less post-2004 than it was before 2004 though the cumulative errors preclude statistically differences. As a result the MB NECB has increased to 79 ± 29 g C m-2 yr-1 post 2004 yielding a 14 year contemporary NECB of 56 ± 36 g C m-2 yr-1, which is double the long-term accumulation rate of C. The variability in the annual NECB and growing season mean NEP for the MB bog can be explained (r2 = 0.35, p \u3c 0.01) by the variability in growing season water table depth. These results suggest the carbon balance – water table feedback is sufficient enough to create stability in continental bogs so they will withstand a considerable amount of climate change

Measurement and modeling of the sources and sinks of greenhouse gases from northern wetlands

Northern wetlands contain ≈30% of the world’s terrestrial carbon store, resulting from the incomplete decomposition of plant material inhibited because oxygen diffusion is limited by water saturation of the soil. While this behaviour results in a sink for CO2, anaerobic pathways of decomposition result in wetlands being a large, but variable, source of CH4. Northern wetlands tend to be nitrogen-impoverished, therefore they are not an important source of N2O. However, nitrogen deposition, peat extraction, and other land-use changes have the potential to alter their greenhouse gas (GHG) sink/source function. Until recently, most of the studies on the atmosphere-biosphere exchange of greenhouse gases from northern wetlands were short-term and seasonal. In 1998 the Peatland Carbon Study began continuous measurements of the carbon dynamics of a northern peatland and developed several ecosystem models to be used in simulations of the response of peatlands to climate variability and change. The continuous measurements have established the dominant role of climate variability in determining the magnitude and sign of the fluxes of GHGs. The Peatland Carbon Simulator (PCARS) was developed to use either direct measurements or modeled climate from a land surface process model such as the Canadian Land Surface Scheme (CLASS) which has been modi- fied to incorporate the physical attributes of wetlands as inputs. PCARS illustrates the relative importance of various components of the ecosystem in determining the interannual variability in GHG exchange. Evaluation of PCARS has helped identify significant gaps in our knowledge of peatland systems. A second, more phenomenological model, the Peat Accumulation Model (PAM), demonstrates the overall importance of precipitation in controlling decadal to millennial scale variations in sink/source strength of CO2. The Canadian Global Coupled Climate Carbon Model (CGC3M) Network is attempting to parameterize wetland processes for the inclusion in a global terrestrial ecosystem model for climate simulations, but it is a significant challenge to develop an efficient, yet realistic, wetland simulator for global scale modelling

Burn severity influences postfire CO2 exchange in Arctic tundra

Author Posting. © Ecological Society of America, 2011. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 21 (2011): 477–489, doi:10.1890/10-0255.1.Burned landscapes present several challenges to quantifying landscape carbon balance. Fire scars are composed of a mosaic of patches that differ in burn severity, which may influence postfire carbon budgets through damage to vegetation and carbon stocks. We deployed three eddy covariance towers along a burn severity gradient (i.e., severely burned, moderately burned, and unburned tundra) to monitor postfire net ecosystem exchange of CO2 (NEE) within the large 2007 Anaktuvuk River fire scar in Alaska, USA, during the summer of 2008. Remote sensing data from the MODerate resolution Imaging Spectroradiometer (MODIS) was used to assess the spatial representativeness of the tower sites and parameterize a NEE model that was used to scale tower measurements to the landscape. The tower sites had similar vegetation and reflectance properties prior to the Anaktuvuk River fire and represented the range of surface conditions observed within the fire scar during the 2008 summer. Burn severity influenced a variety of surface properties, including residual organic matter, plant mortality, and vegetation recovery, which in turn determined postfire NEE. Carbon sequestration decreased with increased burn severity and was largely controlled by decreases in canopy photosynthesis. The MODIS two-band enhanced vegetation index (EVI2) monitored the seasonal course of surface greenness and explained 86% of the variability in NEE across the burn severity gradient. We demonstrate that understanding the relationship between burn severity, surface reflectance, and NEE is critical for estimating the overall postfire carbon balance of the Anaktuvuk River fire scar.This work was supported by NSF grants #0632139 (OPP-AON), #0808789 (OPP-ARCSS SGER), #0829285 (DEB-NEON SGER), and #0423385 (DEBLTER) to the Marine Biological Laboratory