In this study, we compared measured and simulated Net Ecosystem Exchange (NEE) values from three wide spread ecosystems in the southeast of Ireland (forest, arable and grassland), and investigated the suitability of the DNDC (the DeNitrification–DeComposition) model to estimate present and future NEE. Although, the field-DNDC version overestimated NEE at temperatures >5°C, forest-DNDC under-estimated NEE at temperatures >5°C. The results suggest that the field/forest DNDC models can successfully estimate changes in seasonal and annual NEE from these ecosystems. Differences in NEE were found to be primarily land cover specific. The annual NEE was similar for the grassland and arable sites, but due to the contribution of exported carbon, the soil carbon increased at the grassland site and decreased at the arable site. The NEE of the forest site was an order of magnitude larger than that of the grassland or arable ecosystems, with large amounts of carbon stored in woody biomass and the soil. The average annual NEE, GPP and Reco values over the measurement period were −904, 2379 and 1475gCm−2 (forest plantations), −189, 906 and 715gCm−2 (arable systems) and −212, 1653 and 1444gCm−2 (grasslands), respectively. The average RMSE values were 3.8gCm−2 (forest plantations), 0.12gCm−2 (arable systems) and 0.21gCm−2 (grasslands). When these models were run with climate change scenarios to 2060, predictions show that all three ecosystems will continue to operate as carbon sinks. Further, climate change may decrease the carbon sink strength in the forest plantations by up to 50%. This study supports the use of the DNDC model as a valid tool to predict the consequences of climate change on NEE from different ecosystems.

Emissions of nitrous oxide (N2O) from an Irish arable soil were simulated using the DeNitrification–DeComposition (DNDC) model. The soil chosen was a free-draining sandy loam typical of the majority of cereal growing land in Ireland, and one that has been previously used to test and validate DNDC-model. DeNitrification–DeComposition model was considered suitable to estimate N2O fluxes from Irish arable soils however, underestimated the flux by 24%. The objectives of this study were to estimate future N2O fluxes from a spring barley field under conventional (moulboard plowing) and reduced (chisel plowing) tillage and different N-fertilzer application rates. Three climate scenarios, a baseline of measured climatic data from the weather station at Kilkenny and a high- and low-temperature-sensitive scenarios predicted by the Hadley Global Climate Model (HadCM4) based on the AB1 emission scenario of the Intergovernment Panel on Climate Change (IPCC) were investigated. For conventional tillage under all scenarios, three peaks of N2O emissions were predicted; an early spring peak coinciding mostly with soil plowing, a mid/late spring peak coinciding with fertilizer application and an early autumn peak coinciding with residue incorporation and onset of autumn rainfall. Under reduced tillage, due to the less amount of soil disturbance, the early spring peak was not predicted. In all cases, the total amount of N2O emitted in the late spring peak due to fertilizer application was less than the sum of the other peaks. Under climate change, using the high-temperature-increase scenario, DNDC predicted an increase in N2O emissions from both conventional and reduced tillage, ranging from 58% to 88% depending upon N application rate. In contrast, annual fluxes of N2O either decreased or increased slightly in the low temperature increase scenario relative to N application (−26 to +16%). Outputs from the model indicate that elevated temperature and precipitation increase N mineralization and total denitrification leading to greater fluxes of N2O. Annual uncertainties due to the use of two different future climate scenarios were significantly high, ranging from 74% to 95% and from 71% to 90% for the conventional and reduced tillage.

Soil/atmosphere exchange fluxes of nitrous oxide were monitored for a 3-year period at 10 grassland sites in eight European countries (Denmark, France, Hungary, Ireland, Italy, The Netherlands, Switzerland and United Kingdom), spanning a wide range of climatic, environmental and soil conditions. Most study sites investigated the influence of one or several management practices on N2O exchange, such as nitrogen fertilization and grazing intensity. Fluxes were measured using non-steady state chambers at most sites, and alternative measurement techniques such as eddy covariance and fast-box using tunable diode laser spectroscopy were implemented at some sites. The overall uncertainty in annual flux estimates derived from chamber measurements may be as high as 50% due to the temporal and spatial variability in fluxes, which warrants the future use of continuous measurements, if possible at the field scale. Annual emission rates were higher from intensive than from extensive grasslands, by a factor 4 if grazed (1.77 versus 0.48 kg N2O-N ha−1 year−1) and by a factor 3 if ungrazed (0.95 versus 0.32 kg N2O-N ha−1 year−1). Annual emission factors for fertilized systems were highly variable, ranging from 0.01% to 3.56%, but the mean emission factor across all sites (0.75%) was substantially lower than the IPCC default value of 1.25%. Emission factors for individual fertilization events increased with soil temperature and were generally higher for water-filled pore space values in the range 60–90%, though precipitation onto dry soils was also shown to lead to high losses of N2O-N from applied fertilizer. An empirical, multiple regression model to predict N2O emission factors on the basis of soil temperature, moisture and rainfall is developed, explaining half of the variability in observed emission factors.

The overall aim of the project is to produce inventories and projections of UK greenhouse gas emissions by sources and removals by sinks due to Land Use, Land USe Change and Forestry (LULUCF). The project report contains the methods and numbers for these inventories and progress reports on the science undertaken to support and develop the inventory.

BOOK Risø National Laboratory Roskilde Denmark April 2005 Author: Anette Werner, Lise Lotte Sørensen Title: ACCENT-BIAFLUX Workshop 2005, Trace gas and aerosol flux measurement and techniques Department: Wind Energy Department Risø-R-1508(EN)