PhD Thesis, 2010 - University College Cork

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General discussion methods of gap-filling on a two-year data set. Generally, the annual emissions calculated by different approaches were similar. However, in the presence of the very long gaps, the performance of most of the techniques studied is likely to be unsatisfactory. The look-up table technique produced satisfactory results and was based on the environmental parameters (soil temperature, rainfall, fertiliser application), whose influence was quantified in the first sub-project. It was, however, necessary to use a two-year data set to build the table due to the existence of a long gap in one of the years. In this research we focused on the analysis of the eddy-covariance time series of nitrous oxide flux from intensive grassland and young forestry. It was established that the most important conditions affecting the flux at the site were: • preceding rainfall (between 12 and 40 hours prior to a given averaging period); • recent fertilisers application (between 2 and 4 days); • mechanical disturbances of the soil; • grazing. Our work on gap-filling of nitrous oxide time series proposed an easy-toimplement technique, and presented the evaluation of already known methods. We hope that the contribution made towards the improved understanding of the nature of nitrous oxide emission from the agricultural ecosystems, and tools developed will enable further research and better accounting of flux of this significant greenhouse gas. 61
Recommendations for further research 8. RECOMMENDATIONS FOR FURTHER RESEARCH The result of the present work identifies additional questions that could be recommended for further investigation. • Method used for distinguishing peak and background flux need to be tested under various conditions and different ecosystems. The analysis carried out on the basis of the peak-background flux separation might indicate different criteria affecting the burst emission or time lags characteristic for these triggers. • The long-term study is necessary to be continued as some research indicates an increase of the N 2 O emissions as the forest matures. Such scenario seems particularly likely due to the presence of alder which was reported to produce high emission in the mature forests. Essential part of such studies needs to be continuous monitoring of the amounts of soil nitrogen and environmental conditions in the afforested area. • Our work on the subject of gap-filling was only a beginning of the methodological research in this area. A more extensive study examining varied approaches under different environmental conditions and scales is needed. While it might be unrealistic to try to gap-fill the instantaneous flux time series, gap-filling of the daily and monthly time series should be very valuable for understanding the short-term and management driven patterns of emission. • When focusing on the nitrogen cycle of the wet grassland, it is also important to analyse nitrate leaching and ammonia volatilisation as possible exit routes of the labile nitrogen. Observation of the water regime at the site suggest that 62
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National University of Ireland, Cor
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4.5. Discussion 26 4.5.1. Peak trig
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DECLARATION I declare that this the
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ABSTRACT Nitrous oxide (N 2 O) is a
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Introduction little information exi
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Literature review 2. LITERATURE REV
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Literature review NH 3 → NH 2 OH
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Literature review 2.2. Managed gras
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Page 71 and 72: References REFERENCES Ball, B. C.,
Page 73 and 74: References Flechard, C. R., P. Ambu
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Page 77 and 78: References Müller, C., R. J. Steve
Page 79: References Yashiro, Y., W. R. Kadir
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PhD Thesis, 2010 - University College Cork

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