Modeling of nitric oxide emissions from temperate agricultural ecosystems.

48 p.Arable soils are a significant source of nitric oxide (NO), most of which is derived from nitrogen fertilizers. Precise estimates of NO emissions from these soils are thus essential to devise strategies to mitigate the impact of agriculture on tropospheric ozone regulation. This paper presents the implementation of a soil NO emissions submodel within the environmentally-orientated soil crop model, CERES-EGC. The submodel simulates the NO production via nitrification pathway, as modulated by soil environmental drivers. The resulting model was tested with data from 4 field experiments on wheat- and maize-cropped soils representative of two agricultural regions of France, and for three years encompassing various climatic conditions. Overall, the model gave correct predictions of NO emissions, but shortcomings arose from an inadequate vertical distribution of fertilizer N in the soil surface. Inclusion of a 2-cm thick topsoil layer in an 'micro-layer' version of CERES-EGC gave more realistic simulations of NO emissions and of the under-lying microbiological process. From a statistical point, both versions of the model achieved a similar fit to the experimental data, with respectively a MD and a RMSE ranging from 1.8 to 6.2 g N-NO ha−1 d−1, and from 22.8 to 25.2 g N-NO ha−1 d −1 across the 4 experiments. The cumulative NO losses represented 1 to 2% of NH+4 fertilizer applied for the maize crops, and about 1% for the wheat crops. The 'micro-layer' version may be used for spatialized inventories of biogenic NO emissions to point mitigation strategies and to improve air quality prediction in chemistry transport models

Variability of methane fluxes over high latitude permafrost wetlands

Atmospheric methane plays an important role in the global climate system. Due to significant amounts of organic material stored in the upper layers of high latitude permafrost wetlands and a strong Arctic warming trend, there is concern about potentially large methane emissions from Arctic and sub-Arctic areas. The quantification of methane fluxes and their variability from these regions therefore plays an important role in understanding the Arctic carbon cycle and changes in atmospheric methane concentrations. However, direct measurements of methane fluxes in permafrost regions are sparse, very localized, inhomogeneously distributed in space, and thus difficult to use for accurate model representation of regional to global methane contributions from the Arctic. We aim to contribute to reducing uncertainty and improve spatial coverage and spatial representativeness of flux estimates by using airborne eddy covariance measurements across large areas. The research aircraft POLAR 5 was equipped with a turbulence nose boom and a fast response methane analyzer and served as the platform for measurements of methane emissions. The measuring campaign was carried out from 28 June to 10 July 2012 across the entire North Slope of Alaska and the Mackenzie Delta in Canada. The supplemented simulations from the Weather Research and Forecasting (WRF) model exploring the dynamics of the atmospheric boundary layer were used to analyze high methane concentrations occasionally observed within the boundary layer with a distinct drop to background level above. Strong regional differences were detected over both investigated areas showing the non-uniform distribution of methane sources. In order to cover the whole turbulent spectrum and at the same time to resolve methane fluxes on a regional scale, different integration paths were analyzed and validated through spectral analysis. Methane emissions measured over the Mackenzie Delta were higher and generally more variable in space, especially in the outer Delta with known geogenic methane seepage. On the North Slope, methane fluxes were larger in the western part than in the central and eastern parts. The obtained results are essential for the advanced, scale dependent quantification of methane emissions. Our contribution will present an overview of the experiment as well as preliminary results from more than 52 flight hours over high latitude permafrost wetlands

Continuous measurements of O3 fluxes by covariance over forest and arable cropland in France

Terrestrial ecosystems are significant sources of atmospheric gases such as reactive nitrogen (NH3, NO and N2O). Conversely, they can be a sink for NH3, NOx, and O3, which can lead to several adverse effects (acidification and eutrophication, direct effects). But deposition also contributes to decreasing their lifetime in the atmosphere, and is therefore an efficient “depollution process”. In this context, continuous measurements of O3 fluxes as well as other compounds have been set up at two sites in France. The fluxes of O3, CO2/H2O are measured continuously with the eddy covariance method over the “LeBray” pine forest near Bordeaux since 2003, and over a cropland field near Paris since mid-2004. The Bray forest site is 35 year old plantation of maritime pine (Pinus pinaster Ait.) with an understorey of graminae. It is currently a CarboEurope site and has been part of the Euroflux network since 1996. The trees are distributed in parallel rows along the NE-SW axis. The inter row distance is 4m and the stand density is about 500 trees ha-1. The mean tree height is 20 m and the LAI around 2.6. The site is flat and the fetch is over 600 m in the prevailing wind direction. The climate is oceanic with 900 mm of rainfall per year. Instruments are installed at 43 m. The cropland site is a CarboEurope site, with a rotation of mustard, maize, wheat and barley, with a nitrogen supply of 120 kg ha-1 y-1, as mineral fertiliser, and an additional 100 kg ha-1 every three years as cattle slurry. The climate is continental-oceanic, with 600 mm of rainfall per year, the soil is a luvisol with 60% of silt, and 30% of clay. Instruments are installed at 2.5 to 4.5 m. At both sites, the eddy-covariance equipment set includes a Gill RGA3-50 or a Gill R2 sonic anemometer, a H20 and CO2 Licor 7500 analyser, and a fast O3 chemiluminescent based close-path sensor (ATDD V2.0) with solid-plates “targets” coated with Coumarin. Additional absolute measurements are performed at both sites. Automatic chambers measuring N2O and NO emission will be installed in 2005 in Grignon, as well as NH3 gradient measurements. Initial results from these two sites will be presented

High net CO2 and CH4 release at a eutrophic shallow lake on a formerly drained fen

Drained peatlands often act as carbon dioxide (CO2) hotspots. Raising the groundwater table is expected to reduce their CO2 contribution to the atmosphere and revitalise their function as carbon (C) sink in the long term. Without strict water management rewetting often results in partial flooding and the formation of spatially heterogeneous, nutrient-rich shallow lakes. Uncertainties remain as to when the intended effect of rewetting is achieved, as this specific ecosystem type has hardly been investigated in terms of greenhouse gas (GHG) exchange. In most cases of rewetting, methane (CH4) emissions increase under anoxic conditions due to a higher water table and in terms of global warming potential (GWP) outperform the shift towards CO2 uptake, at least in the short term. - Based on eddy covariance measurements we studied the ecosystem–atmosphere exchange of CH4 and CO2 at a shallow lake situated on a former fen grassland in northeastern Germany. The lake evolved shortly after flooding, 9 years previous to our investigation period. The ecosystem consists of two main surface types: open water (inhabited by submerged and floating vegetation) and emergent vegetation (particularly including the eulittoral zone of the lake, dominated by Typha latifolia). To determine the individual contribution of the two main surface types to the net CO2 and CH4 exchange of the whole lake ecosystem, we combined footprint analysis with CH4 modelling and net ecosystem exchange partitioning. - The CH4 and CO2 dynamics were strikingly different between open water and emergent vegetation. Net CH4 emissions from the open water area were around 4-fold higher than from emergent vegetation stands, accounting for 53 and 13 g CH4 m−2 a−1 respectively. In addition, both surface types were net CO2 sources with 158 and 750 g CO2 m−2 a−1 respectively. Unusual meteorological conditions in terms of a warm and dry summer and a mild winter might have facilitated high respiration rates. In sum, even after 9 years of rewetting the lake ecosystem exhibited a considerable C loss and global warming impact, the latter mainly driven by high CH4 emissions. We assume the eutrophic conditions in combination with permanent high inundation as major reasons for the unfavourable GHG balance

Comparison of O3 fluxes measured with the eddy covariance and the gradient methods above a maize field

International audienceBetween June and September 2002, the fluxes of carbon dioxide (CO2) and ozone (O3), and nitrogen oxides (NO and NO2) were measured above a growing maize crop, together with the components of the energy balance - sensible (H) , ground (G) and latent heat fluxes (H), net radiation (Rn) – , the meteorology, and the canopy structure. All the fluxes, except the NOx, were measured simultaneously with the gradient and the covariance technique. The gradient mast consisted in 9 levels extending from 0.3 to 10 m above ground, where CO2 and H2O was measured with a Licor Li6262, and O3 and NOx was measured with two separate analysers (2 Environnement SA 41M for O3 and 2 ThermoEnvironnement 42C for NOx), each screening the 5 uppermost and the 5 lowermost levels, with a common level allowing for cross calibration. Wind speed and temperature was also measured, and the fluxes were determined using 3 to 4 levels above the canopy. The covariance mast consisted in a Gill R3-50, a Licor Li7500 and a fast O3 chemiluminescent based close-path sensor from ATDD V2.0 with solid-plates “targets” coated with Coumarin. Two identical covariance masts were compared during 15 days, to determine the lifetime of a “target”. In this study, the momentum, energy, CO2, and O3 fluxes estimated with the gradient method and the two eddy-covariance masts are compared, with a special focus on O3

Lidar sur drone pour évaluer la biodiversité des ripisylves

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Predicting the global warming potential of agro-ecosystems

International audienceNitrous oxide, carbon dioxide and methane are the main biogenic greenhouse gases (GHG) contributing to the global warming potential (GWP) of agro-ecosystems. Evaluating the impact of agriculture on climate thus requires a capacity to predict the net exchanges of these gases in an integrated manner, as related to environmental conditions and crop management. Here, we used two year-round data sets from two intensively-monitored cropping systems in northern France to test the ability of the biophysical crop model CERES-EGC to simulate GHG exchanges at the plot-scale. The experiments involved maize and rapeseed crops on a loam and rendzina soils, respectively. The model was subsequently extrapolated to predict CO2 and N2O fluxes over an entire crop rotation. Indirect emissions (IE) arising from the production of agricultural inputs and from cropping operations were also added to the final GWP. One experimental site (involving a wheat-maize-barley rotation on a loamy soil) was a net source of GHG with a GWP of 350 kg CO2‑C eq ha‑1 yr‑1, of which 75% were due to IE and 25% to direct N2O emissions. The other site (involving an oilseed rape-wheat-barley rotation on a rendzina) was a net sink of GHG for ‑250 kg CO2‑C eq ha‑1 yr‑1, mainly due to a higher predicted C sequestration potential and C return from crops. Such modelling approach makes it possible to test various agronomic management scenarios, in order to design productive agro-ecosystems with low global warming impact

Modeling of nitric oxide emissions from temperate agricultural soils

Arable soils are a significant source of nitric oxide (NO), most of which is derived from nitrogen fertilizers. Accurate estimates of NO emissions from these soils are essential to devise strategies to mitigate the impact of agriculture on tropospheric ozone production and destruction. This paper presents the implementation of a soil NO emissions submodel within the environmentally-orientated soil-crop model, CERES-EGC. The submodel simulates NO production via the nitrification pathway, as modulated by soil environmental drivers. The resulting model was tested with data from 4 field experiments on wheat- and maize-cropped soils representative of two agricultural regions of France, over three years, and encompassing various climatic conditions. Overall, the model provided accurate predictions of NO emissions, but shortcomings arose from an inadequate vertical distribution of N fertilizer in the soil surface. Inclusion of a 2-cm thick topsoil layer in a ‘micro-layer’ version of CERES-EGC gave more realistic simulations of NO emissions and under-lying microbiological process. From a statistical point of view, both versions of the model achieved a similar fit to the experimental data, with respectively a MD and a RMSE ranging from 1.8 to 6.2 g N–NO ha-1d-1, and from 22.8 to 25.2 g N–NO ha-1d-1 across the 4 experiments. The cumulative NO losses represented 1–2% of NH4+ fertilizer applied in the case of maize crops, and about 1% in the case of wheat crops. The ‘micro-layer’ version may be used for spatialized inventories of NO emissions to improve air quality prediction