Modeling Seasonal to Annual Carbon Balance of Mer Bleue Bog, Ontario, Canada

University of New Hampshire University of New Hampshire Scholars' Repository Earth Sciences Scholarship Earth Sciences 9-2002 Modeling seasonal to annual carbon balance of Mer Bleue Bog, Ontario, Canada Steve Frolking University of New Hampshire - Main Campus, [email protected] Nigel T. Roulet McGill University Tim R. Moore McGill University P M. Lafleur Trent University Jill L. Bubier Mount Holyoke College See next page for additional authors Follow this and additional works at: https://scholars.unh.edu/earthsci_facpub Recommended Citation Frolking, S., N. T. Roulet, T. R. Moore, P. M. Lafleur, J. L. Bubier, and P. M. Crill, Modeling seasonal to annual carbon balance of Mer Bleue Bog, Ontario, Canada, Global Biogeochem. Cycles, 16(3), doi:10.1029/ 2001GB001457, 2002. This Article is brought to you for free and open access by the Earth Sciences at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Earth Sciences Scholarship by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. Authors Steve Frolking, Nigel T. Roulet, Tim R. Moore, P M. Lafleur, Jill L. Bubier, and P Crill This article is available at University of New Hampshire Scholars' Repository: https://scholars.unh.edu/ earthsci_facpub/329 GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 16, NO. 3, 1030, 10.1029/2001GB001457, 2002 Modeling seasonal to annual carbon balance of Mer Bleue Bog, Ontario, Canada Steve Frolking,1 Nigel T. Roulet,2 Tim R. Moore,2 Peter M. Lafleur,3 Jill L. Bubier,4 and Patrick M. Crill1 Received 9 July 2001; revised 10 February 2002; accepted 18 February 2002; published 4 July 2002. [1] Northern peatlands contain enormous quantities of organic carbon within a few meters of the atmosphere and play a significant role in the planetary carbon balance. We have developed a new, process-oriented model of the contemporary carbon balance of northern peatlands, the Peatland Carbon Simulator (PCARS). Components of PCARS are (1) vascular and nonvascular plant photosynthesis and respiration, net aboveground and belowground production, and litterfall; (2) aerobic and anaerobic decomposition of peat; (3) production, oxidation, and emission of methane; and (4) dissolved organic carbon loss with drainage water. PCARS has an hourly time step and requires air and soil temperatures, incoming radiation, water table depth, and horizontal drainage as drivers. Simulations predict a complete peatland C balance for one season to several years. A 3-year simulation was conducted for Mer Bleue Bog, near Ottawa, Ontario, and results were compared with multiyear eddy covariance tower CO2 flux and ancillary measurements from the site. Seasonal patterns and the general magnitude of net ecosystem exchange of CO2 were similar for PCARS and the tower data, though PCARS was generally biased toward net ecosystem respiration (i.e., carbon loss). Gross photosynthesis rates (calculated directly in PCARS, empirically inferred from tower data) were in good accord, so the discrepancy between model and measurement was likely related to autotrophic and/or heterotrophic respiration. Modeled and measured methane emission rates were quite low. PCARS has been designed to link with the Canadian Land Surface Scheme (CLASS) land surface model and a global climate model (GCM) to examine climate-peatland carbon feedbacks at regional scales in future analyses. INDEX TERMS: 1615 Global Change: Biogeochemical processes (4805); 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 1890 Hydrology: Wetlands; 9350 Information Related to Geographic Region: North America; KEYWORDS: peatland, decomposition, NPP, NEE, carbon accumulation, model 1. Introduction carbon) being sequestered in a total peatland area of 3.5 million km2 [Gorham, 1991; Turunen et al., 2002], 10% of [2] Relative to other ecosystems, northern peatlands have the total non-ice-covered land area north of 45°N. In many low rates of annual net primary productivity (NPP) [Thor- regions of Canada, Finland, and western Siberia, peatlands mann and Bayley, 1997], decomposition [e.g., Bartsch and can occupy >50% of the landscape. Despite the large Moore, 1985; Johnson and Damman, 1993; Belyea, 1996], quantity of carbon that peatlands contain, they generally and net CO exchange [Frolking et al., 1998], but over 2 have been ignored in global biogeochemistry and ecosys- millennia, NPP has been greater than decomposition. Hence tem modeling efforts. This is largely due to the difficulty of northern peatlands have been a persistent sink for CO , 2 modeling peatland hydrology. In previous work we have averaging 20–30 g CO -C mÀ2 yrÀ1 over the past 5000– 2 described how we have parameterized [Letts et al., 2000] 10,000 years [Gorham, 1995; Tolonen et al., 1992]. This and evaluated [Comer et al., 2000] the Canadian Land has resulted in 200–450 Pg C (15–30% of total world soil Surface Scheme (CLASS) [Verseghy, 2000] for peatland ecosystems. The second step in the assessment of 1 Institute for the Study of Earth, Oceans, and Space, University of New response of the carbon stored in peatlands to climate Hampshire, Durham, New Hampshire, USA. 2Department of Geography and Centre for Climate and Global Change change has been to develop a process-based ecosystem Research, McGill University, Montreal, Quebec, Canada. model that could be coupled to CLASS and used in 3Department of Geography, Trent University, Peterborough, Ontario, climate simulation studies. In this paper we discuss the Canada. 4 development, evaluation, and sensitivity of this model, the Department of Earth and Environment, Mount Holyoke College, South Peatland Carbon Simulator (PCARS). PCARS links Hadley, Massachusetts, USA. directly to the recently developed Peatland Decomposition Copyright 2002 by the American Geophysical Union. Model, which simulates long-term peat accumulation 0886-6236/02/2001GB001457 [Frolking et al., 2001]. 4 - 1 4 - 2 FROLKING ET AL.: MODELING PEATLAND CARBON BALANCE [3] Slow decomposition rates in northern peatlands result productivity (NEP) based on measured aboveground net from the combined effects of limited oxygen diffusion into primary productivity and total soil respiration. Potter et al. saturated peat leading to anoxic conditions for a large [2001] applied a process-based ecosystem model, NASA- portion of the peat profile [Clymo, 1992], the generally CASA, to the same Canadian peatland site. The NASA- cool temperatures of peat due to the large heat capacity of CASA model can function across a range of ecosystem wet peat and the low thermal conductivity of moss [Roulet types; for the wetland simulations, it was modified to include et al., 1997], and the inherent resistance to decomposition of run-on from the surrounding uplands and a moss ground- some peatland vegetation tissues, particularly Sphagna cover, simulating both CO2 and CH4 exchange. Rivers et al. [e.g., Johnson and Damman, 1993; Hogg, 1993]. Since soil [1998] developed an empirically based stochastic model to moisture and temperature partially control the slow decom- estimate the net carbon balance and its uncertainty for the position, C sequestration rates in peatlands are susceptible Rapid River Watershed in Minnesota, U.S.A. Using a Monte to change with a changing climate [Gorham, 1995]. Climate Carlo technique to randomly sample from distributions of change is expected to be greatest at high latitudes, where input parameters (e.g., dissolved carbon concentration in most peatlands are located [Kattenberg et al., 1996]. These precipitation), drivers (e.g., annual precipitation), and pro- latitudes also contain discontinuous permafrost, and climate cesses (NEE), Rivers et al. [1998] derived a distribution of change induced permafrost degradation [Anisimov et al., estimates of the net carbon balance of the large peatland 1997] could result in shifts in peatland hydrology, which is complex. Their study is the only one to include inputs and the dominant control of peatland maintenance. Thus there is outputs of dissolved organic carbon (DOC) and dissolved a need to understand and be able to predict the carbon inorganic carbon (DIC) in the peatland carbon budget. balance of northern peatlands under current and projected [6] In this paper we present a new peatland ecosystem conditions. In the first year-round eddy covariance carbon model, PCARS (Peatland Carbon Simulator), developed in balance study on a northern peatland in North America, conjunction with ongoing field studies at Mer Bleue Bog near Lafleur et al. [2001] found net annual sequestration rates of Ottawa, Canada [Lafleur et al., 2001]. Like the NASA-CASA 60 g C mÀ2 yrÀ1, higher than would be expected based on model, PCARS is process based; PCARS has been designed long-term accumulation of 25 g C mÀ2 yrÀ1. They cannot in a generalized form that should be suitable for all northern yet conclude if this was due to favorable weather conditions peatlands. PCARS parameterization included one set of in the measurement year or represents a real shift in peatland parameters typical of northern bogs (e.g., decomposition net ecosystem exchange of CO2 (NEE) toward higher and photosynthesis functions) and a second set representing sequestration, perhaps due to ongoing nitrogen deposition, the Mer Bleue site (e.g., vegetation type and biomass). Model CO2 fertilization, and/or some other factor. output was compared with measurements of CO2 exchange [4] In addition to their role as a carbon reservoir,

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