PhD Thesis, 2010 - University College Cork

ABSTRACT
Nitrous oxide (N 2 O) is a powerful greenhouse gas with global warming potential
298 times that of carbon dioxide in the 100-year horizon. It also a highly-reactive gas
that has a damaging influence on the ozone layer. These properties of the nitrous oxide
require attention to the influence of the anthropogenic activities on the production and
emission into the atmosphere. In Ireland one the major sources of the nitrous oxide
emission is the agricultural activity. Since the intensive use of grassland pastures
requires nitrogen fertiliser application, the ecosystems exist in almost permanent state
of nitrogen abundance. Such conditions make them prone to nitrous oxide production
and emissions. The temporal patterns and variations of the N 2 O flux were the primary
interest of this research. We analysed intra-annual dependency of the instantaneous
flux on management and environmental conditions, inter-annual changes in the
grassland undergoing afforestation; and approaches to gap-filling of the time series for
the purpose of calculating the annual sums. As a result of these sub-projects a method
was developed to separate peak from background emissions, it was used to analyse
events preceding the peaks and this information was in turn used for fine-tuning of a
gap-filling approach. The quantitative separation showed that the peak flux, while is a
dominant component of the annual emission, depends in part on environmental
conditions that are hard to manage or predict. The long-term observations of the nitrous
oxide emission from the grassland undergoing afforestation showed that while
significant decrease in emissions over the years was not entirely surprising forestestablishment
works might lead to major emission bursts. The explored gap-filling
techniques introduced the simple estimates and laid the foundation for more elaborated
approaches.
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