Modelling LAI at a regional scale with ISBA-A-gs: comparison with satellite-derived LAI over southwestern France

International audienceA CO2-responsive land surface model (the ISBAA- gs model of M´et´eo-France) is used to simulate photosynthesis and Leaf Area Index (LAI) in southwestern France for a 3-year period (2001–2003). A domain of about 170 000 km2 is covered at a spatial resolution of 8 km. The capability of ISBA-A-gs to reproduce the seasonal and the interannual variability of LAI at a regional scale, is assessed with satellite-derived LAI products. One originates from the CYCLOPES programme using SPOT/VEGETATION data, and two products are based on MODIS data. The comparison reveals discrepancies between the satellite LAI estimates and between satellite and simulated LAI values, both in their intensity and in the timing of the leaf onset. The model simulates higher LAI values for the C3 crops than the satellite observations, which may be due to a saturation effect within the satellite signal or to uncertainties in model parameters. The simulated leaf onset presents a significant delay for C3 crops and mountainous grasslands. In-situ observations at a mid-altitude grassland site show that the generic temperature response of photosynthesis used in the model is not appropriate for plants adapted to the cold climatic conditions of the mountainous areas. This study demonstrates the potential of LAI remote sensing products for identifying and locating models' shortcomings at a regional scale

Nitrous oxide emissions from European agriculture - An analysis of variability and drivers of emissions from field experiments

Nitrous oxide emissions from a network of agricultural experiments in Europe were used to explore the relative importance of site and management controls of emissions. At each site, a selection of management interventions were compared within replicated experimental designs in plot-based experiments. Arable experiments were conducted at Beano in Italy, El Encin in Spain, Foulum in Denmark, Logården in Sweden, Maulde in Belgium, Paulinenaue in Germany, and Tulloch in the UK. Grassland experiments were conducted at Crichton, Nafferton and Peaknaze in the UK, Gödöllö in Hungary, Rzecin in Poland, Zarnekow in Germany and Theix in France. Nitrous oxide emissions were measured at each site over a period of at least two years using static chambers. Emissions varied widely between sites and as a result of manipulation treatments. Average site emissions (throughout the study period) varied between 0.04 and 21.21 kg N₂O-N ha⁻¹ yr⁻¹, with the largest fluxes and variability associated with the grassland sites. Total nitrogen addition was found to be the single most important determinant of emissions, accounting for 15% of the variance (using linear regression) in the data from the arable sites (<i>p</i> < 0.0001), and 77% in the grassland sites. The annual emissions from arable sites were significantly greater than those that would be predicted by IPCC default emission factors. Variability of N₂O emissions within sites that occurred as a result of manipulation treatments was greater than that resulting from site-to-site and year-to-year variation, highlighting the importance of management interventions in contributing to greenhouse gas mitigation

Quality Control of CarboEurope Flux Data - Part I: Coupling Footprint Analyses with Flux Data Quality Assessment to Evaluate Sites in Forest Ecosystems

We applied a site evaluation approach combining Lagrangian Stochastic footprint modelling with a quality assessment approach for eddy-covariance data to 25 forested sites of the CarboEurope-IP network. The analysis addresses the spatial representativeness 5 of the flux measurements, instrumental effects on data quality, spatial patterns in the data quality, and the performance of the coordinate rotation method. Our findings demonstrate that application of a footprint filter could strengthen the CarboEurope-IP flux database, since only one third of the sites is situated in truly homogeneous terrain. Almost half of the sites experience a significant reduction in eddy-covariance data 10 quality under certain conditions, though these effects are mostly constricted to a small portion of the dataset. Reductions in data quality of the sensible heat flux are mostly induced by characteristics of the surrounding terrain, while the latent heat flux is subject to instrumentation-related problems. The Planar-Fit coordinate rotation proved to be a reliable tool for the majority of the sites using only a single set of rotation angles. 15 Overall, we found a high average data quality for the CarboEurope-IP network, with good representativeness of the measurement data for the specified target land cover types.JRC.H.2-Air and Climat

Long-term impacts of season of grazing on soil carbon sequestration and selected soil properties in the arid Eastern Cape, South Africa

BACKGROUND AND AIMS : The karoo biomes of South Africa are major feed resources, yet soil nutrient depletion and degradation is a major problem. The objective of this study was to assess impacts of long-term (>75 years) grazing during spring (SPG), summer (SUG), winter (WG) and exclosure (non-grazed control) treatments on soil nutrients, penetration resistance and infiltration tests. METHODS : A soil sampling campaign was carried out to collect soil to a depth of 60 cm to analyse bulk density, soil physical and chemical parameters as well as soil compaction and infiltration. RESULTS : Generally, grazing treatments reduced soil organic C (SOC) stocks and C:N ratios, and modified soil properties. There was higher SOC stock (0.128 Mg ha-1 yr-1) in the exclosure than in the SPG (0.096 Mg ha-1 yr- 1), SUG (0.099 Mg ha-1 yr-1) and WG (0.105 Mg ha-1 yr-1). The C:N ratios exhibited similar pattern to that of C. From the grazing treatments, the WG demonstrated 7 to 10% additional SOC stock over the SPG and SUG, respectively. CONCLUSIONS : Short period animal exclusion could be an option to be considered to improve plant nutrients in sandy soils of South Africa. However, this may require a policy environment which supports stock exclusion from such areas vulnerable to land degradation, nutrient and C losses by grazing-induced vegetation and landscape changes.Department of Science and Technology University of Pretoria) and the European Communities, 7th framework program under the grant agreement No. 266018, ANIMALCHANGE project.http://link.springer.com/journal/111042016-12-31hb201

Challenges in quantifying biosphere???atmosphere exchange of nitrogen species

El art??culo aborda las complejidades y dificultades que se enfrentan al intentar medir y comprender el intercambio de especies de nitr??geno entre la biosfera y la atm??sfera. Este intercambio es crucial para el ciclo del nitr??geno, que tiene implicaciones significativas para los ecosistemas, la calidad del aire y el cambio clim??tico. Uno de los principales desaf??os mencionados en el art??culo es la variabilidad espacial y temporal de las emisiones de nitr??geno. Las fuentes de nitr??geno, como la agricultura, la industria y los procesos naturales, pueden variar considerablemente en diferentes regiones y momentos del a??o. Esto hace que sea complicado establecer mediciones precisas y representativas del intercambio de nitr??geno. Adem??s, el art??culo destaca la falta de m??todos estandarizados para medir las diferentes especies de nitr??geno, como el ??xido nitroso (N2O), el amon??aco (NH3) y el ??xido n??trico (NO). Cada uno de estos compuestos tiene diferentes propiedades qu??micas y biol??gicas, lo que requiere enfoques espec??ficos para su cuantificaci??n. La diversidad de t??cnicas y equipos utilizados en diferentes estudios tambi??n contribuye a la inconsistencia de los datos. Otro aspecto importante que se menciona es la interacci??n entre los procesos biogeoqu??micos que afectan el ciclo del nitr??geno. Por ejemplo, la nitrificaci??n y la desnitrificaci??n son procesos clave que influyen en las emisiones de nitr??geno, pero su din??mica puede verse afectada por factores como la temperatura, la humedad y la disponibilidad de nutrientes. Esto a??ade una capa adicional de complejidad al intentar modelar y predecir el intercambio de nitr??geno. El art??culo tambi??n discute la importancia de integrar datos de diferentes escalas, desde estudios locales hasta modelos globales. La falta de datos a gran escala puede limitar nuestra comprensi??n de c??mo las emisiones de nitr??geno afectan el clima y la calidad del aire a nivel global. Por lo tanto, se enfatiza la necesidad de una colaboraci??n m??s estrecha entre cient??ficos de diferentes disciplinas y regiones para abordar estos desaf??os. Finalmente, el art??culo concluye con una llamada a la acci??n para mejorar las metodolog??as de medici??n y modelado del intercambio de nitr??geno. Se sugiere que el desarrollo de tecnolog??as m??s avanzadas y la estandarizaci??n de los m??todos de medici??n podr??an ayudar a superar algunas de las barreras actuales. Adem??s, se destaca la importancia de la educaci??n y formaci??n en este campo para asegurar que los futuros investigadores est??n equipados con las herramientas necesarias para abordar estos desaf??os. En resumen, el art??culo subraya que, aunque hay muchos obst??culos en la cuantificaci??n del intercambio de especies de nitr??geno entre la biosfera y la atm??sfera, hay oportunidades para mejorar nuestra comprensi??n y gesti??n de este ciclo vital. La colaboraci??n interdisciplinaria y el avance tecnol??gico son clave para avanzar en este campo de estudio