PhD Thesis, 2010 - University College Cork

Distinguishing peaks from background emission of nitrous oxide
irregular events: intensive rainfall, fertilizers’ applications, etc. In the background
portion of the time series, no such phenomenon was observed, which confirms that
background flux notion as a permanent low-intensity flux. Many peak periods (about
42%) occur surrounded by non-peak periods, be it background periods or gaps,
suggesting possible limitations on the variables influencing N 2 O production.
4.5. Discussion
4.5.1. Peak triggers
When peak occurrences are analysed with respect to preceding meteorological and
management events, it is notable that certain conditions caused significant changes in
the frequency of peak occurrence (Figure 4.3). Compared to the average “peak rate” of
5.3%, the peak occurrence increases more than twice that value within 22 hours of an
occurrence of intense (>3 mm / 30 min) rainfall. Across all rain intensities it is notable
that the maximum peak rate values occur between 12 and 40 hours after the rain event,
but stay elevated for as long as 4 days after the event.
Interestingly, periods immediately following rainfall were characterised by
significantly diminished (as low as zero) peak rates, and the duration of these periods
was up to 3.5 hours. In our opinion, it might be explained by saturation of the soil
pores in the surface layer, preventing any intensive gaseous exchange with the
atmosphere. Within two hours after heavy rains (> 3.2 mm/30 min) no reliable flux
values were observed, producing gaps in the flux time series. This was likely due to
wetting of the surface of the transducers of the 3D sonic anemometer resulting in its
temporary failure as indicated by CSAT diagnostic value.
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