Nitrous oxide flux to the atmosphere from the littoral zone of a boreal lake

Abstract

[1] The surface‐atmospheric exchange of nitrous oxide (N₂O) was investigated in the vegetated littoral zone of a eutrophied midboreal lake (Lake Kevätön, Finland) with a static chamber technique. During a dry summer (three to six samplings per site), the meadow site and two marsh sites in the temporarily flooded eulittoral zone and the Phragmites australis‐dominated site in the continuously flooded infralittoral zone had mean daytime N₂O‐N emissions from 11 ± 7 to 22 ± 7 μg m⁻² h⁻¹, whereas the Nuphar lutea‐dominated site in the infralittoral zone had a mean N₂O flux close to zero. During a wet summer (13–14 samplings per site), the mean daytime N₂O‐N fluxes ranged from 4 ± 1 to 15 ± 5 μg m⁻² h⁻¹ at the three eulittoral sites and were negligible at the two infralittoral sites. The littoral zone occupied 26% of the lake area but was estimated to account for most of the N₂O emissions from the lake. The studied eulittoral zone, which did not have adjacent nitrogen fertilization, exhibited higher N₂O emissions during the summer than seen in northern natural ecosystems in general, including peatlands, forests, and the pelagic regions of lakes. Thus in lake‐rich landscapes the littoral zone and other lake‐associated wetlands must be considered as potential sources of atmospheric N₂O. An assessment of their atmospheric importance requires further data on the N₂O fluxes and their regulation in different littoral areas and on the total littoral coverage, neither of which is yet available.