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Controls of carbon exchange in a boreal minerogenic mire

Nilsson, Mats; Sagerfors, Jörgen; Buffam, Ishi; Eriksson, Tobias; Grelle, Achim; Laudon, Hjalmar; Klemedtsson, Leif; Weslien, Per; Lindroth, Anders


Based on theories on both mire development and their response to environmental change, the current role of mires as a net carbon sink has been questioned. A rigorous evaluation of the contemporary net C-exchange in mires requires direct measurements of all relevant fluxes. We use data on carbon exchange from a boreal minerogenic oligotrophic mire (Degerö Stormyr, 64°11’ N, 19°33E) to derive a contemporary carbon budget and to analyze the main controls on the C exchange. Data on the following fluxes were collected: land-atmosphere CO2 (continuous Eddy Covariance measurements, 7 years) and CH4 (static chambers during the snow free period, 4 years) exchange; DOC in precipitation; loss of TOC, CO2 and CH4 through water runoff, 4 years (continuous discharge measurement and regular C-content measurements). The annual NEE was fairly constant between years and varied between -48 – -61 gCm-2yr-1 during six out of the seven years, despite a large variation in weather combinations, the average being -53±5 gCm-2yr-1. During a year with exceptional dry late summer the NEE droped to -17 gCm-2yr-1. During this period the water table level was approximately 15 cm below the long-term lowest level. Data indicate that most of the reduction in NEE comes from decreased GPP while the ecosystem respiration was relatively stable between years. Including all component fluxes the mire still is a sink of atmospheric C during average weather conditions. During the years 2004 and 2005 the Net Ecosystem Balance (NECB) was -20±3.3 gCm-2yr-1. Both emission of methane and runoff export of carbon contributed significantly to the loss of carbon. During the dry year with a NEE of -17 gCm-2yr-1 the methane emission and runoff C export resulted in a NECB not different from 0. In addition to climatic conditions also atmospheric deposition of nitrogen is postulated to importantly affect the mire carbon balance. Based on a 12 year old field addition experiment data indicate significantly increased C accumulation. Even if the initial rate of CO2-production from the peat litter seems to be slightly increased from increased nitrogen input the increased input of peat litter resulted in an increased net accumulation of organic material

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Greenhouse gases and aerosols: Interactions between northern ecosystems and climate A conference given by the NECC and BACCI Nordic Centres of Excellence