Northern peatlands contain up to 25% of the world’s soil carbon (C) and have an estimated annual exchange of CO2-C with the atmosphere of 0.1–0.5 Pg yr � 1 and of CH4-C of 10–25 Tg yr � 1 . Despite this overall importance to the global C cycle, there have been few, if any, complete multiyear annual C balances for these ecosystems. We report a 6-year balance computed from continuous net ecosystem CO2 exchange (NEE), regular instantaneous measurements of methane (CH4) emissions, and export of dissolved organic C (DOC) from a northern ombrotrophic bog. From these observations, we have constructed complete seasonal and annual C balances, examined their seasonal and interannual variability, and compared the mean 6-year contemporary C exchange with the apparent C accumulation for the last 3000 years obtained from C density and agedepth profiles from two peat cores. The 6-year mean NEE-C and CH4-C exchange, and net DOC loss are � 40.2 � 40.5 (� 1 SD), 3.7 � 0.5, and 14.9 � 3.1 g m � 2 yr � 1 , giving a 6-year mean balance of � 21.5 � 39.0 g m � 2 yr � 1 (where positive exchange is a loss of C from the ecosystem). NEE had the largest magnitude and variability of the components of the C balance, but DOC and CH4 had similar proportional variabilities and their inclusion is essential to resolve the C balance. There are large interseasonal and interannual ranges to the exchanges due to variations in climatic conditions. We estimate from the largest and smallest seasonal exchanges, quasi-maximum limits of the annual C balance between 50 and � 105 g m � 2 yr � 1 . The net C accumulation rate obtained from the two peatland cores for the interval 400–3000 BP (samples from the anoxic layer only) were 21.9 � 2.8 and 14.0 � 37.6 g m � 2 yr � 1 , which are not significantly different from the 6-year mean con

http://home.mtholyoke.edu/courses/jbubier/pdf/RouletetalGCB2007.pdf

Contemporary carbon balance and late Holocene carbon accumulation in a northern peatland

Drained organic soils are a significant source of greenhouse gas (GHG) emissions to the atmosphere. Rewetting these soils may reduce GHG emissions and could also create suitable conditions for return of the carbon (C) sink function characteristic of undrained organic soils. In this article we expand on the work relating to rewetted organic soils that was carried out for the 2014 Intergovernmental Panel on Climate Change (IPCC) Wetlands Supplement. We describe the methods and scientific approach used to derive the Tier 1 emission factors (the rate of emission per unit of activity) for the full suite of GHG and waterborne C fluxes associated with rewetting of organic soils. We recorded a total of 352 GHG and waterborne annual flux data points from an extensive literature search and these were disaggregated by flux type (i.e. CO2, CH4, N2O and DOC), climate zone and nutrient status. Our results showed fundamental differences between the GHG dynamics of drained and rewetted organic soils and, based on the 100 year global warming potential of each gas, indicated that rewetting of drained organic soils leads to: net annual removals of CO2 in the majority of organic soil classes; an increase in annual CH4 emissions; a decrease in N2O and DOC losses; and a lowering of net GHG emissions. Data published since the Wetlands Supplement (n = 58) generally support our derivations. Significant data gaps exist, particularly with regard to tropical organic soils, DOC and N2O. We propose that the uncertainty associated with our derivations could be significantly reduced by the development of country specific emission factors that could in turn be disaggregated by factors such as vegetation composition, water table level, time since rewetting and previous land use history.

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Greenhouse gas emission factors associated with rewetting of organic soils

[1] Mires are key landscape elements at high latitudes and have certainly accumulated carbon during the Holocene, but their current carbon balance at the present time is very unclear. The major carbon flux is the land-atmosphere CO2 exchange and full-year data are still limited. Here we present data from 3 a (2001-2003) of continuous Eddy Covariance measurements at Degero Stormyr (64 degrees 11'N, 19 degrees 33'E) an oligotrophic, minerotrophic mire in Sweden. The climate at the site is defined as cold temperate humid, with 30-a annual precipitation and temperature means of 523 mm and +1.2 degrees C, respectively, while the mean temperatures in July and January are +14.7 degrees C and -12.4 degrees C, respectively. The length of the vegetation period was 153 +/- 15 d during the measured years. The minerotrophic mire represented a net sink for the vertical exchange of atmospheric CO2-C during the 3 a, with an average net uptake of 55 +/- 7 g ( mean +/- SD) CO2-C m(-2) a(-1). The growing season average uptake was 92 +/- 10 g CO2-C m(-2), of which approximately 40% ( 37 +/- 5 g CO2-C m(-2)) was lost during the nongrowing season. The daily average uptake over the growing season was 0.65 +/- 0.57, 0.73 +/- 0.61, and 0.68 +/- 0.62 g CO2-C m(-2) d(-1) in 2001, 2002, and 2003, respectively. The daily average net uptake for the month with highest uptake was 1.10 +/- 0.33, 1.11 +/- 0.63, and 1.22 +/- 0.55 g CO2-C m(-2) d(-1) in July 2001, July 2002, and June 2003, respectively. The daily average efflux during the nongrowing season was 0.14 +/- 0.28, 0.15 +/- 0.20, and 0.20 +/- 0.19 g CO2-C m(-2) d(-1) in the years 2001, 2002, and 2003, respectively. (Less)

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006JG000306

Annual CO2 exchange between a nutrient-poor, minerotrophic, boreal mire and the atmosphere

Peatland ecosystems have been consistent carbon (C) sinks for millennia, but it has been predicted that exposure to warmer temperatures and drier conditions associated with climate change will shift the balance between ecosystem photosynthesis and respiration providing a positive feedback to atmospheric CO 2 concentration. Our main objective was to determine the sensitivity of ecosystem photosynthesis, respiration and net ecosystem production (NEP) measured by eddy covariance, to variation in temperature and water table depth associated with interannual shifts in weather during 2004-2009. Our study was conducted in a moderately rich treed fen, the most abundant peatland type in western Canada, in a region (northern Alberta) where peatland ecosystems are a significant landscape component. During the study, the average growing season (May-October) water depth declined approximately 38 cm, and temperature [expressed as cumulative growing degree days (GDD, March-October)] varied approximately 370 GDD. Contrary to previous predictions, both ecosystem photosynthesis and respiration showed similar increases in response to warmer and drier conditions. The ecosystem remained a strong net sink for CO 2 with an average NEP ( ± SD) of 189 ± 47 g C m ―2 yr ―1 . The current net CO 2 uptake rates were much higher than C accumulation in peat determined from analyses of the relationship between peat age and cumulative C stock. The balance between C addition to, and total loss from, the top 0-30 cm depth (peat age range 0-70 years) of shallow peat cores averaged 43 ± 12 g C m ―2 yr ―1 . The apparent long-term average rate of net C accumulation in basal peat samples was 19-24 g C m ―2 yr ―1 . The difference between current rates of net C uptake and historical rates of peat accumulation is likely a result of vegetation succession and recent increases in tree establishment and productivity.

Stimulation of both photosynthesis and respiration in response to warmer and drier conditions in a boreal peatland ecosystem

Dating recent peat deposits (i.e., past } 300 yrs of peat accumulation) has emerged as an important yet challenging task for estimating rates of organic matter accumulation and atmospheric pollutant deposition in peatlands. Due to their ombrotrophic nature and the tendency for Sphagnum-derived peat to have high cation exchange capacity, peatlands are ideal archives of atmospheric pollution. However, efforts to establish depth-age relationships in peats are complicated by the difficulty of dating deposits reliably. Assumptions underlying the techniques available for dating peat deposits often are poorly understood and generally untested. We outline the approaches used to establish depth-age relationships in peat chronologies, including brief descriptions of the theory, assumptions, methodology, and logistics of each technique. We include both continuous dating methods (i.e., methods based on 14C, 210Pb, constant bulk density, acidinsoluble ash, moss increment, pollen density) and chrono-stratigraphic markers (i.e., fallout isotopes from the Chernobyl accident and nuclear weapons testing, pollen stratigraphies, isothermal remanence magnetism, charcoal particles, spherical carbonaceous particles, PAHs, PCBs, DDT, toxaphene) that can be measured in peat and correlated temporally with known historical events. We also describe the relatively new radiocarbon application of wiggle matching and use hypothetical data to highlight the potential of this developing technique for dating recent peat. Until the uncertainty associated with each of these dating approaches is clarified, we recommend employing multiple techniques to allow for corroboration between different methods.

Dating recent peat deposits

Net ecosystem productivity (NEP) was studied in a bog located in the middle taiga of Siberia using two approaches, the accumulation of peat above the hypocotyl of pine trees, and the eddy covariance flux methodology. NEP was 0.84 tC ha −1 yr −1 using the peat accumulation method; it was 0.43–0.62 tC ha −1 yr −1 using eddy covariance over three growing seasons. These data were compared with NEP of the surrounding forest, which was 0.6 tC±1.1 ha −1 yr −1 . The trees growing on the bog reached a total height of about 3 m and an age of 80–120 yr when peat accumulation reached 0.5–0.6 m. At that stage the growth rate of the oldest trees declined. This indicates that there is a maximum age that can be reached by trees growing on hummocks (<150 yr), depending on conditions. The data show that the determination of NEP in bogs by using the peat accumulation above the hypocotyl is a useful method which can be applied on a wide range of bog types, but it may systematically overestimate NEP. The total sink capacity for carbon assimilation of bogs is comparable to that of forest, although methane emissions and losses of dissolved organic carbon must be taken into account when assessing the regional carbon cycle. DOI: 10.1034/j.1600-0889.2002.01386.x

A. Prokuschkin

Papers

Net ecosystem productivity and peat accumulation in a Siberian Aapa mire