Detection and attribution of an anomaly in terrestrial photosynthesis in Europe during the COVID-19 lockdown

Carbon dioxide (CO2) uptake by plant photosynthesis, referred to as gross primary production (GPP) at the ecosystem level, is sensitive to environmental factors, including pollutant exposure, pollutant uptake, and changes in the scattering of solar shortwave irradiance (SWin) - the energy source for photosynthesis. The 2020 spring lockdown due to COVID-19 resulted in improved air quality and atmospheric transparency, providing a unique opportunity to assess the impact of air pollutants on terrestrial ecosystem functioning. However, detecting these effects can be challenging as GPP is influenced by other meteorological drivers and management practices. Based on data collected from 44 European ecosystem-scale CO2 flux monitoring stations, we observed significant changes in spring GPP at 34 sites during 2020 compared to 2015-2019. Among these, 14 sites showed an increase in GPP associated with higher SWin, 10 sites had lower GPP linked to atmospheric and soil dryness, and seven sites were subjected to management practices. The remaining three sites exhibited varying dynamics, with one experiencing colder and rainier weather resulting in lower GPP, and two showing higher GPP associated with earlier spring melts. Analysis using the regional atmospheric chemical transport model (LOTOS-EUROS) indicated that the ozone (O-3) concentration remained relatively unchanged at the research sites, making it unlikely that O-3 exposure was the dominant factor driving the primary production anomaly. In contrast, SWin increased by 9.4 % at 36 sites, suggesting enhanced GPP possibly due to reduced aerosol optical depth and cloudiness. Our findings indicate that air pollution and cloudiness may weaken the terrestrial carbon sink by up to 16 %. Accurate and continuous ground-based observations are crucial for detecting and attributing subtle changes in terrestrial ecosystem functioning in response to environmental and anthropogenic drivers

High-resolution laser system for the S3-Low Energy Branch

In this paper we present the first high-resolution laser spectroscopy results obtained at the GISELE laser laboratory of the GANIL-SPIRAL2 facility, in preparation for the first experiments with the S$^3$-Low Energy Branch. Studies of neutron-deficient radioactive isotopes of erbium and tin represent the first physics cases to be studied at S$^3$. The measured isotope-shift and hyperfine structure data are presented for stable isotopes of these elements. The erbium isotopes were studied using the $4f^{12}6s^2$ $^3H_6 \rightarrow 4f^{12}(^3 H)6s6p$ $J = 5$ atomic transition (415 nm) and the tin isotopes were studied by the $5s^25p^2 (^3P_0) \rightarrow 5s^25p6s (^3P_1)$ atomic transition (286.4 nm), and are used as a benchmark of the laser setup. Additionally, the tin isotopes were studied by the $5s^25p6s (^3P_1) \rightarrow 5s^25p6p (^3P_2)$ atomic transition (811.6 nm), for which new isotope-shift data was obtained and the corresponding field-shift $F_{812}$ and mass-shift $M_{812}$ factors are presented

4D-Var inversion of European NH3 emissions Using CrIS NH3 measurements and GEOS-Chem adjoint with bi-directional and uni-directional flux schemes

We conduct the first 4D-Var inversion of NH3 accounting for NH3 bi-directional flux, using CrIS satellite NH3 observations over Europe in 2016. We find posterior NH3 emissions peak more in springtime than prior emissions at continental to national scales, and annually they are generally smaller than the prior emissions over central Europe, but larger over most of the rest of Europe. Annual posterior anthropogenic NH3 emissions for 25 European Union members (EU25) are 25% higher than the prior emissions and very close (<2% difference) to other inventories. Our posterior annual anthropogenic emissions for EU25, the UK, the Netherlands, and Switzerland are generally 10%–20% smaller than when treating NH3 fluxes as uni-directional emissions, while the monthly regional difference can be up to 34% (Switzerland in July). Compared to monthly mean in-situ observations, our posterior NH3 emissions from both schemes generally improve the magnitude and seasonality of simulated surface NH3 and bulk NHx wet deposition throughout most of Europe, whereas evaluation against hourly measurements at a background site shows the bi-directional scheme better captures observed diurnal variability of surface NH3. This contrast highlights the need for accurately simulating diurnal variability of NH3 in assimilation of sun-synchronous observations and also the potential value of future geostationary satellite observations. Overall, our top-down ammonia emissions can help to examine the effectiveness of air pollution control policies to facilitate future air pollution management, as well as helping us understand the uncertainty in top-down NH3 emissions estimates associated with treatment of NH3 surface exchange

The annual ammonia budget of fertilised cut grassland - Part 1: Micrometeorological flux measurements and emissions after slurry application

Two commercial ammonia (NH(3)) analysers were customised to allow continuous measurements of vertical concentration gradients. The gradients were used to derive ammonia exchange fluxes above a managed grassland site at Oensingen (Switzerland) by application of the aerodynamic gradient method. The measurements from July 2006 to October 2007 covered five complete growth-cut cycles and included six applications of liquid cattle slurry. The average accuracy of the flux measurements during unstable and near-neutral conditions was 20% and the detection limit was 10 ng NH(3) m(-2) s(-1). Hence the flux measurements are considered sufficiently accurate for studying typical NH(3) deposition rates over growing vegetation. Quantifying the overall emissions after slurry applications required the application of elaborate interpolations because of difficulties capturing the initial emissions during broadspreading of liquid manure. The emissions were also calculated with a mass balance method yielding similar fluxes. NH(3) losses after slurry application expressed as percentage of emitted nitrogen versus applied total ammoniacal nitrogen (TAN) varied between 4 and 19%, which is roughly a factor of three lower than the values for broadspreading of liquid manure in emission inventories. The comparatively low emission factors appear to be a consequence of the low dry matter content of the applied slurry and soil properties favouring ammonium adsorption

Enhanced terrestrial photosynthesis in Europe during the COVID-19 lockdown.

International audienc

Accounting for Field-Scale Dry Deposition in Backward Lagrangian Stochastic Dispersion Modelling of NH3 Emissions

A controlled ammonia (NH3) release experiment was performed at a grassland site. The aim was to quantify the effect of dry deposition between the source and the receptors (NH3 measurement locations) on emission rate estimates by means of inverse dispersion modelling. NH3 was released for three hours at a constant rate of Q = 6.29 mg s(-1) from a grid of 36 orifices spread over an area of 250 m(2). The increase in line-integrated NH3 concentration was measured with open-path optical miniDOAS devices at different locations downwind of the artificial source. Using a backward Lagrangian stochastic (bLS) dispersion model (bLSmodelR), the fraction of the modelled release rate to the emitted NH3 (Q(bLS)/Q) was calculated from the measurements of the individual instruments. Q(bLS)/Q was found to be systematically lower than 1, on average between 0.69 and 0.91, depending on the location of the receptor. We hypothesized that NH3 dry deposition to grass and soil surfaces was the main factor responsible for the observed depletion of NH3 between source and receptor. A dry deposition algorithm based on a deposition velocity approach was included in the bLS modelling. Model deposition velocities were evaluated from a 'big-leaf' canopy resistance analogy. Canopy resistances (generally termed R-c) that provided Q(bLS)/Q = 1 ranged from 75 to 290 s m(-1), showing that surface removal of NH3 by dry deposition can plausibly explain the original underestimation of Q(bLS)/Q. The inclusion of a dry deposition process in dispersion modelling is crucial for emission estimates, which are based on concentration measurements of depositing tracers downwind of homogeneous area sources or heterogeneously-distributed hot spots, such as, e.g., urine patches on pastures in the case of NH3

Boucler les grands cycles, Biologie des sols et matière organique, GES

SPEPôle ECOLDUR14 slidesColloque international Agroécologie et RechercheLe 17 octobre 2013 l'Inra a organisé à Paris, sous le haut patronage du Ministre en charge de l’Agriculture, en partenariat avec Agreenium et l’alliance de recherche AllEnvi, un colloque "Agroécologie et Recherche". Cet événement a constitué un point d’étape important dans la réflexion nationale sur ces questions.L’agro-écologie a pour projet de concevoir une agriculture qui réponde à nos besoins futurs, guidée par les outils de l’écologie et des sciences sociales pour en améliorer les performances environnementales et économiques.Boucler les grands cycles, Biologie des sols et matière organique, GES. Colloque Agroécologie et Recherche INR

Greenhouse gas emissions from the grassy outdoor run of organic broilers

International audienceNitrous oxide (N2O), methane (CH4) and carbondioxide (CO2) fluxes over the grassy outdoor run of organ-ically grown broilers were monitored using static chambersover two production batches in contrasted seasons. MeasuredN2O and CH4fluxes were extremely variable in time andspace for both batches, with fluxes ranging from a small up-take by soil to large emissions peaks, the latter of which al-ways occurred in the chambers located closest to the broilerhouse. In general, fluxes decreased with increasing distanceto the broiler house, demonstrating that the foraging of broil-ers and the amount of excreted nutrients (carbon, nitrogen)largely control the spatial variability of emissions. Spatial in-tegration by kriging methods was carried out to provide rep-resentative fluxes on the outdoor run for each measurementday. Mechanistic relationships between plot-scale estimatesand environmental conditions (soil temperature and watercontent) were calibrated in order to fill gaps between mea-surement days. Flux integration over the year 2010 showedthat around 3±1 kg N2O-N ha−1were emitted on the out-door run, equivalent to 0.9 % of outdoor N excretion andsubstantially lower than the IPCC default emission factor of2 %. By contrast, the outdoor run was found to be a net CH4sink of about−0.56 kg CH4-C ha−1, though this sink com-pensated less than 1.5 % (in CO2equivalents) of N2O emis-sions. The net greenhouse gas (GHG) budget of the outdoorrun is explored, based on measured GHG fluxes and short-term (1.5 yr) variations in soil organic carbon

Modeling Carbon and Water Fluxes of Managed Grasslands: Comparing Flux Variability and Net Carbon Budgets between Grazed and Mowed Systems

The CenW ecosystem model simulates carbon, water, and nitrogen cycles following ecophysiological processes and management practices on a daily basis. We tested and evaluated the model using five years eddy covariance measurements from two adjacent but differently managed grasslands in France. The data were used to independently parameterize CenW for the two grassland sites. Very good agreements, i.e., high model efficiencies and correlations, between observed and modeled fluxes were achieved. We showed that the CenW model captured day-to-day, seasonal, and interannual variability observed in measured CO2 and water fluxes. We also showed that following typical management practices (i.e., mowing and grazing), carbon gain was severely curtailed through a sharp and severe reduction in photosynthesizing biomass. We also identified large model/data discrepancies for carbon fluxes during grazing events caused by the noncapture by the eddy covariance system of large respiratory losses of C from dairy cows when they were present in the paddocks. The missing component of grazing animal respiration in the net carbon budget of the grazed grassland can be quantitatively important and can turn sites from being C sinks to being neutral or C sources. It means that extra care is needed in the processing of eddy covariance data from grazed pastures to correctly calculate their annual CO2 balances and carbon budgets

Impact of water-table dynamics on the destabilization of soil organic matter in a temperate agricultural catchment

International audienceSoil organic matter (SOM) destabilization produces gaseous and dissolved species and plays a key-role toward environmental and climatic issues. This process can be viewed as a combination of abiotic (solubilization) and biotic (biodegradation) processes. Both of them are controlled by the water occurring in soils since this molecule is at the same time the solvent and the living media. The soil water content has been shown to control the emission of soil carbon dioxide and the water-table dynamic to control the temporal variations of dissolved organic carbon in soil solutions. The aim of this study is to explore how the fluctuations of water-table levels can impact the gaseous and dissolved components of SOM destabilization. This was performed on the Kervidy-Naizin catchment (AgrHys critical zone observatory) localized in Brittany and that is part of the OZCAR Research Infrastructure. Measurments of CO 2 fluxes and soil solution species (dissolved organic and inorganic carbon DOC/DIC and ferrous cation FeII as a) sampled in the macroporosity were performed fortnightly during the hydrologic year 2014-2015 from October to May at two sampling sites. They were chosen along a topographic transect equipped to monitor water-table levels with one downslope (Down) and one midslope (Mid). The difference in water-table fluctuations were measured by the mean residence time and mean return time. Down the residence and return times were 47 and 4 days, respectively, while Mid they were 2 and 12 days, respectively. Along the sampling period, the flux of CO 2 was higher at Mid (1.5 ± 0.5 µmol m-2 s-1 ; mean ± standard deviation) than at Down (1.0 ± 1.0 µmol m-2 s-1). At both sites CO 2 decreased from October to February and then increased up to May, however the kinetics were different. DIC and DOC were differently correlated in the two sites. At Mid, they were inversely correlated, with a steady DOC decrease from 14 to 8 mg/l from October to March and a steady DIC increase from 9 mg/l to 30 mg/l. At Down two periods were defined by the occurrence of FeII that is a marker of reducing conditions. Before the reducing period DIC and CO 2 were inversely correlated, while during reducing conditions DIC, DOC and CO 2 were positively correlated and increased by 4, 3 and 8 respectively, highlighting reducing period as a hot moments for soil organic matter biodegradation in lowland wetlands. The results of this study, together with literature survey, are used to propose a conceptual model of SOM destabilization