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A comparison of methane flux in a boreal landscape between a dry and a wet year
Author(s) -
Bubier Jill,
Moore Tim,
Savage Kathleen,
Crill Patrick
Publication year - 2005
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2004gb002351
Subject(s) - environmental science , permafrost , flux (metallurgy) , wetland , boreal , soil water , taiga , atmospheric sciences , atmosphere (unit) , spatial variability , land cover , precipitation , hydrology (agriculture) , physical geography , geology , soil science , oceanography , geography , ecology , land use , forestry , chemistry , meteorology , paleontology , statistics , mathematics , geotechnical engineering , biology , organic chemistry
We used field measurements of methane (CH 4 ) flux from upland and wetland soils in the Northern Study Area (NSA) of BOREAS (BOReal Ecosystem‐Atmosphere Study), near Thompson, Manitoba, during the summers of 1994 and 1996 to estimate the overall CH 4 emission from a 1350 km 2 landscape. June–September 1994 and 1996 were both drier and warmer than normal, but summer 1996 received 68 mm more precipitation than 1994, a 40% increase, and had a mean daily air temperature 0.6°C warmer than 1994. Upland soils consumed CH 4 at rates from 0 to 1.0 mg m −2 d −1 , with small spatial and temporal variations between years, and a weak dependence on soil temperature. In contrast, wetlands emitted CH 4 at seasonal average rates ranging from 10 to 350 mg CH 4 m −2 d −1 , with high spatial and temporal variability, and increased an average of 60% during the wetter and warmer 1996. We used Landsat imagery, supervised classification, and ground truthing to scale point CH 4 fluxes (<1 m 2 ) to the landscape (>1000 km 2 ). We performed a sensitivity analysis for error terms in both areal coverage and CH 4 flux, showing that the small areas of high CH 4 emission (e.g., small ponds, graminoid fens, and permafrost collapse margins) contribute the largest uncertainty in both flux measurements and mapping. Although wetlands cover less than 30% of the landscape, areally extrapolated CH 4 flux for the NSA increased by 61% from 10 to16 mg CH 4 m −2 d −1 between years, entirely attributed to the increase in wetland CH 4 emission. We conclude that CH 4 fluxes will tend to be underestimated in areas where much of the landscape is covered by wetlands. This is due to the large spatial and temporal variability encountered in chamber‐based measurements of wetland CH 4 fluxes, strong sensitivity of wetland CH 4 emission to small changes in climate, and because most remote sensing images do not adequately identify small areas of high CH 4 flux.