Growing season CHsub4/sub and Nsub2/subO fluxes from a subarctic landscape in northern Finland; from chamber to landscape scale

摘要

Subarctic and boreal emissions of CHsub4/sub are important contributors to the atmospheric greenhouse gas (GHG) balance and subsequently the global radiative forcing. Whilst Nsub2/subO emissions may be lower, the much greater radiative forcing they produce justifies their inclusion in GHG studies. In addition to the quantification of flux magnitude, it is essential that we understand the drivers of emissions to be able to accurately predict climate-driven changes and potential feedback mechanisms. Hence this study aims to increase our understanding of what drives fluxes of CHsub4/sub and Nsub2/subO in a subarctic forest/wetland landscape during peak summer conditions and into the shoulder season, exploring both spatial and temporal variability, and uses satellite-derived spectral data to extrapolate from chamber-scale fluxes to a 2?km??×??2?km landscape area.brbrFrom static chamber measurements made during summer and autumn campaigns in 2012 in the Sodankyl? region of northern Finland, we concluded that wetlands represent a significant source of CHsub4/sub (3.35?±?0.44?mg?C?msup?2/sup?hsup?1/sup during the summer campaign and 0.62?±?0.09?mg?C?msup?2/sup?hsup?1/sup during the autumn campaign), whilst the surrounding forests represent a small sink (?0.06?±?&?0.01?mg?C?msup?2/sup?hsup?1/sup during the summer campaign and ?0.03?±?&?0.01?mg?C?msup?2/sup?hsup?1/sup during the autumn campaign). Nsub2/subO fluxes were near-zero across both ecosystems.brbrWe found a weak negative relationship between CHsub4/sub emissions and water table depth in the wetland, with emissions decreasing as the water table approached and flooded the soil surface and a positive relationship between CHsub4/sub emissions and the presence of iSphagnum/i mosses. Temperature was also an important driver of CHsub4/sub with emissions increasing to a peak at approximately 12?°C. Little could be determined about the drivers of Nsub2/subO emissions given the small magnitude of the fluxes.brbrA multiple regression modelling approach was used to describe CHsub4/sub emissions based on spectral data from PLEIADES PA1 satellite imagery across a 2?km??×??2?km landscape. When applied across the whole image domain we calculated a CHsub4/sub source of 2.05?±?0.61?mg?C?msup?2/sup?hsup?1/sup. This was significantly higher than landscape estimates based on either a simple mean or weighted by forest/wetland proportion (0.99?±?0.16, 0.93?±?0.12?mg?C?msup?2/sup?hsup?1/sup, respectively). Hence we conclude that ignoring the detailed spatial variability in CHsub4/sub emissions within a landscape leads to a potentially significant underestimation of landscape-scale fluxes. Given the small magnitude of measured Nsub2/subO fluxes a similar level of detailed upscaling was not needed; we conclude that Nsub2/subO fluxes do not currently comprise an important component of the landscape-scale GHG budget at this site.