• Energy Research

Abstract Measurements of the exchange of ammonia between the atmosphere and moorland vegetation using micrometeorological methods at a site in southern Scotland are reported. The median concentration of continuous measurements over seven months of the log-normally distributed ammonia data at the site is 0.45 μg NH3 m-3 with a geometric standard deviation of 3.4. The measurements made using a continuous wet annular denuder sampling system with a separate denuder at three heights above the surface provided satisfactory fluxes by the aerodynamic flux-gradient method for over 70% of the time between January and August 1995. The site which consists of unimproved moorland vegetation represented an efficient sink for ammonia during the winter months with deposition velocities (Vd) in the range 15 to 30 mm s-1 and canopy resistances (Rc) close to zero. The monthly median Vd declined with time from 25 mm s-1 in February to 5 mm s-1 in August as the result of a steady increase of the canopy resistance in the dry, warmer, summer conditions to typically 100 s m-1 during the daytime. The canopy compensation point increased from zero during winter months to about 0.2 μg m-3 in August and short periods of NH3 emission were observed whenever ambient concentration fell below 0.2 μg m-3 during the summer. The annual input of gaseous NH3 to this moorland surface is approximately 2 kg N ha-1, and is similar to the input of NH+4-N in wet deposition.

Existing descriptions of bi-directional ammonia (NH 3 ) land–atmosphere exchange incorporate temperature and moisture controls, and are beginning to be used in regional chemical transport models. However, such models have typically applied simpler emission factors to upscale the main NH 3 emission terms. While this approach has successfully simulated the main spatial patterns on local to global scales, it fails to address the environment- and climate-dependence of emissions. To handle these issues, we outline the basis for a new modelling paradigm where both NH 3 emissions and deposition are calculated online according to diurnal, seasonal and spatial differences in meteorology. We show how measurements reveal a strong, but complex pattern of climatic dependence, which is increasingly being characterized using ground-based NH 3 monitoring and satellite observations, while advances in process-based modelling are illustrated for agricultural and natural sources, including a global application for seabird colonies. A future architecture for NH 3 emission–deposition modelling is proposed that integrates the spatio-temporal interactions, and provides the necessary foundation to assess the consequences of climate change. Based on available measurements, a first empirical estimate suggests that 5°C warming would increase emissions by 42 per cent (28–67%). Together with increased anthropogenic activity, global NH 3 emissions may increase from 65 (45–85) Tg N in 2008 to reach 132 (89–179) Tg by 2100.

Under the United Nations Framework Convention on Climate Change (UNFCCC), industrialized countries and countries with economies in transition (so called Annex 1 countries) are encouraged to move towards more sophisticated approaches for national greenhouse gas reporting. To develop a model-based approach for estimating nitrous oxide (N2O) emissions from agricultural soils, model calibration is one of the first important steps. Extensive multisite field observations are necessary for this purpose, as agricultural management in Western Europe is complex (e.g., diverse crop rotations, different types of fertilizer and soil tillage). In the present study, we used ca. 24,000 daily N2O flux observations from six cropland sites, two in France and four in Switzerland, to conduct an automatic data-driven calibration of the biogeochemical model DayCent. This model is planned to be used for greenhouse gas reporting in the entire European Union as well as in Switzerland. After a site-specific calibration, a leave-one-out (LOO) cross-evaluation was conducted to assess the model’s ability to predict N2O emissions for sites it was not calibrated for. Mean observed N2O fluxes for 54 interactions of crop cycles, field studies and treatments were used to evaluate the model. The LOO cross-evaluation resulted in a R2 of 0.63 for the prediction of mean N2O fluxes per crop cycle, compared to an R2 of 0.51 obtained with default parameterization. Our results showed that the improvement in N2O predictions was associated with the adjustment of only seven parameters controlling the N cycle in soil (e.g., the maximum daily nitrification amount and the inflection point for the effect of water-filled pore space on denitrification) out of several hundred parameters. These parameters showed a wide range of values between sites, revealing an important challenge for calibration-based improvement of N2O simulations. Despite the remaining uncertainty, our model-based estimates of N2O emission per crop cycle (2.64 kg N ha-1) were clearly closer to measurements (2.67 kg N ha-1) than commonly used emission factor approaches (1.60–1.71 kg N ha-1). Based on extensive field observations, our results suggest that, after data-driven calibration of only few N cycle parameters, DayCent simulations are useful for reporting N2O emissions of complex cropland management. These model based-estimates were more accurate, because they consider key drivers that are disregarded by simpler approaches. Moving towards more complex methods of N2O reporting, is therefore expected to improve the accuracy and additionally allows to assess mitigation options. European Journal of Agronomy, 141 ISSN:1161-0301 ISSN:1873-7331

This paper presents the greenhouse gas (GHG) budget of an organic broiler production system in France, composed of a broiler house and an outdoor run. The study was conducted over 1 year on an experimental farm. In the broiler house, emissions of N2O and CH4 were measured using photo-acoustic infrared spectrometryand air flow rates were estimated using SF6 as tracer gas. On the outdoor run, N2O and CH4 fluxes were measured using static chambers. Spatial and temporal gap-filling methods were used to provide annual estimates of emissions. In the broiler house, CH4 and N2O annual emissions from manure represented about 49 and 71 g CO2-equivalents (CO2-eq.)/kg live weight (LW), while non-biotic CO2 emissions (heating) represented about 68 g CO2-eq./kg LW, suggesting that manure accounted for about 65% of total indoor CO2-eq. emissions. On the outdoor run, N2O emissions were estimated to 86 g CO2-eq./kg LW, while CH4 emissions were found negligible (-1 g CO2-eq./kg LW). However, long-term C sequestration on the outdoor run should be investigated since measured short-term variations in soil organic carbon suggested that the run could display a sink activity and thus compensate for a portion of GHG emissions.

This is the 2024-1 release of the ICOS final quality ecosystem data product that includes eddy covariance fluxes, meteorological observations, ancillary and biometric data and full metadata at 73 labelled ICOS stations in the ecosystem domain. The archives contain more detailed description of the different data files contained in the archives. Measurements have been collected using the following instructions: ICOS Ecosystem Instructions for Air Meteorological Measurements (TA, RH, PA, WS, WD), https://doi.org/10.18160/NHEG-4KWW ICOS Ecosystem Instructions for Turbulent Flux Measurements of CO2, Energy and Momentum, https://doi.org/10.18160/QWV4-639G

Abstract. The impact of atmospheric reactive nitrogen (Nr) deposition on carbon (C) sequestration in soils and biomass of unfertilized, natural, semi-natural and forest ecosystems has been much debated. Many previous results of this dC∕dN response were based on changes in carbon stocks from periodical soil and ecosystem inventories, associated with estimates of Nr deposition obtained from large-scale chemical transport models. This study and a companion paper (Flechard et al., 2020) strive to reduce uncertainties of N effects on C sequestration by linking multi-annual gross and net ecosystem productivity estimates from 40 eddy covariance flux towers across Europe to local measurement-based estimates of dry and wet Nr deposition from a dedicated collocated monitoring network. To identify possible ecological drivers and processes affecting the interplay between C and Nr inputs and losses, these data were also combined with in situ flux measurements of NO, N2O and CH4 fluxes; soil NO3- leaching sampling; and results of soil incubation experiments for N and greenhouse gas (GHG) emissions, as well as surveys of available data from online databases and from the literature, together with forest ecosystem (BASFOR) modelling. Multi-year averages of net ecosystem productivity (NEP) in forests ranged from −70 to 826 g C m−2 yr−1 at total wet + dry inorganic Nr deposition rates (Ndep) of 0.3 to 4.3 g N m−2 yr−1 and from −4 to 361 g C m−2 yr−1 at Ndep rates of 0.1 to 3.1 g N m−2 yr−1 in short semi-natural vegetation (moorlands, wetlands and unfertilized extensively managed grasslands). The GHG budgets of the forests were strongly dominated by CO2 exchange, while CH4 and N2O exchange comprised a larger proportion of the GHG balance in short semi-natural vegetation. Uncertainties in elemental budgets were much larger for nitrogen than carbon, especially at sites with elevated Ndep where Nr leaching losses were also very large, and compounded by the lack of reliable data on organic nitrogen and N2 losses by denitrification. Nitrogen losses in the form of NO, N2O and especially NO3- were on average 27 % (range 6 %–54 %) of Ndep at sites with Ndep < 1 g N m−2 yr−1 versus 65 % (range 35 %–85 %) for Ndep > 3 g N m−2 yr−1. Such large levels of Nr loss likely indicate that different stages of N saturation occurred at a number of sites. The joint analysis of the C and N budgets provided further hints that N saturation could be detected in altered patterns of forest growth. Net ecosystem productivity increased with Nr deposition up to 2–2.5 g N m−2 yr−1, with large scatter associated with a wide range in carbon sequestration efficiency (CSE, defined as the NEP ∕ GPP ratio). At elevated Ndep levels (> 2.5 g N m−2 yr−1), where inorganic Nr losses were also increasingly large, NEP levelled off and then decreased. The apparent increase in NEP at low to intermediate Ndep levels was partly the result of geographical cross-correlations between Ndep and climate, indicating that the actual mean dC∕dN response at individual sites was significantly lower than would be suggested by a simple, straightforward regression of NEP vs. Ndep.