Chamber measurement methods and aeration effect on greenhouse gas fluxes during composting

초록

Composting has the potential to mitigate methane (CH<inf>4</inf>) and nitrous oxide (N<inf>2</inf>O) emissions from manure. The heterogeneous nature of emitting surfaces makes it difficult to quantify these emissions. CH<inf>4</inf> and N<inf>2</inf>O fluxes measured using eight small chambers (0.72 m2) and a mega chamber (90 m2) were compared, and the effect of aeration on the fluxes during composting was studied. Two batches of compost were placed in three channels and 2-3 small flux chambers were deployed on each channel. The channels were enclosed by a building serving as a mega chamber. Chamber location significantly affected gas fluxes, pointing to strong spatial heterogeneity. Mean CH4 fluxes from the small chambers were similar or 1.4 times higher compared to the mega chamber. Mean N<inf>2</inf>O fluxes from the small chambers were 50%-55% lower compared to the mega chamber. Channel edges, not captured by the small chambers, were potentially significant 'hot spots' for N<inf>2</inf>O production. When only small chambers are used for flux measurements, a large number should be strategically positioned to cover different areas of the emitting surface so as to capture a representative flux. On the other hand, if a few small chambers are used, they should be moved frequently to different locations on the emitting surface. Temporal variations in CH<inf>4</inf> and N<inf>2</inf>O fluxes were similar for all the chambers, including periods with active aeration. Correlation of total aeration time with CH<inf>4</inf> fluxes was insignificant (r = -0.097), but was positive with N<inf>2</inf>O (r = 0.556). The flushing of stored CH4 at the onset of aeration, likely promoted fluxes, as opposed to the expected flux decrease with higher aeration time. The purging of stored N<inf>2</inf>O enhanced the expected stimulation of N<inf>2</inf>O production at high aeration times, resulting in the positive trend observed for N<inf>2</inf>O fluxes. Our results suggest that a mega chamber that covers a larger emitting surface area can avoid biases in flux estimates due to spatial variability of the source.

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