A literature overview of micrometeorological CH_4 and N_2O flux measurements in terrestrial ecosystems

摘要

The use of micrometeorological (MM) techniques for methane (CH_4) and nitrous oxide (N_2O) flux measurements in terrestrial ecosystems is increasing and a general outline which summarizes key results is needed. This work provides an overview of the current status of global flux measurements of CH_4 and N_2O by MM techniques in terrestrial ecosystems. Published studies were grouped into four main terrestrial land cover categories and the reported flux ranges, the consistency of different MM approaches over the same ecosystem types, the variability of the MM technique performances as regards the flux detection limit and environmental conditions, were analysed. Furthermore, the issue of the comparability between MM and soil chambers measurements was evaluated. The existing dataset, although temporally and spatially limited, shows that CH_4 and N_2O fluxes are extremely variable in both time and space with mean fluxes spanning within interquartile ranges of 1.33 ÷ 5.45, 11.02 ÷ 68.48, 5.38 ÷ 29.28, 13.87·10~3 ÷ 47.60·10~3 nmol CH_4 m~(-2) s~(-1) in forest, wetlands, croplands and artificial lands respectively, and of 0.09 ÷ 0.42, 0.24 ÷ 1.47, 9.13 ÷ 20.89 nmol N_2O m~(-2) s~(-1) in forest, croplands and artificial lands (no published works were found for wetlands). When environmental conditions were comparable, a general agreement of flux ranges was found within each ecosystem type, in particular when estimates were based on accurate footprint analysis. Exceptions were mainly related to site-specific aspects or to particular measurement periods. Not all the measurement set-ups were suitable for all ecosystems, environmental conditions, turbulence characteristics and flux intensity, however the latest technological improvements make the detection of fluxes feasible virtually in all ecosystems. MM studies of CH_4 and N_2O fluxes were unevenly distributed around the globe and, in particular, were lacking in sensitive areas like Africa, South America and Central Asia.