Nitrous oxide release from agricultural riparian ecosystems

Machefert, Séverine (2005). Nitrous oxide release from agricultural riparian ecosystems. PhD thesis The Open University.



The closed chamber technique and acetylene inhibition method were applied to the investigation of the environmental factors controlling nitrous oxide (N2O) emissions in the field and denitrification, both in situ and in the laboratory, from agricultural riparian ecosystems. N2O emissions were measured along with environmental factors weekly to fortnightly over a whole year and were found to be mainly controlled by water-filled pore space (WFPS) and soil temperature with a threshold response at 35% WFPS and 8°C, below which N2O emissions were very low. Nitrate (NO3) was not a limiting factor at either of the two experimental sites. There was also a ‘threshold’ effect of rainfall, in which major rainfall events (> 10mm) triggered a pulse of high N2O emission if none of the other environmental factors were limiting. The best model for denitrification in riparian ecosystems included water-filled pore space as the main explanatory variable and soil nitrate. Denitrification rates were measured in an intact riparian site and were exponentially correlated to the water-filled pore space of the soil. A threshold response at 60-80% WFPS was also found. The absolute denitrification rate was also related to the soil NO3 concentration. Annual denitrification fluxes were determined on different levels of the riparian zone and were 5.0 and 4.8 kg N ha-1 at the intermediate and upper levels respectively, farthest from the stream surface where the moisture status of the soil was not significantly different and 71.7 kg N ha-1 at the near-stream site where the soil moisture was higher. These results were used to calibrate the INCA model and run an advance version of the model, INCA-N Riparian in order to predict denitrification rates in riparian ecosystems. Annual denitrification rates were well simulated in response to moisture changes.

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