Lakes and reservoirs are a significant source of atmospheric methane (CH4), with emissions comparable to the largest global CH4 emitters. Understanding the processes leading to such significant emissions from aquatic systems is therefore of primary importance for producing more accurate projections of emissions in a changing climate. In this work, we present the first deployment of a novel membrane inlet laser spectrometer (MILS) for fast simultaneous detection of dissolved CH4, C2H6 and d13CH4. During a 1-day field campaign, we performed 2D mapping of surface water of Lake Aiguebelette (France). In the littoral (pelagic) area, average dissolved CH4 concentrations and d13CH4 were 391.9 ± 156.3 (169.8 ± 26.6) nmol L-1 and -67.3 ± 3.4 (-61.5 ± 3.6) ‰, respectively. The dissolved CH4 concentration in the pelagic zone was fifty times larger than the concentration expected at equilibrium with the atmosphere, confirming an oversaturation of dissolved CH4 in surface waters over shallow and deep areas. The results suggest the presence of CH4 sources less enriched in 13C in the littoral zone (presumably the littoral sediments). The CH4 pool became more enriched in 13C with distance from shore, suggesting that oxidation prevailed over epilimnetic CH4 production, that was further confirmed by an isotopic mass balance technique with the high-resolution transect data. This new in situ fast response sensor allows to obtain unique high-resolution and high-spatial coverage datasets within a limited amount of survey time. This tool will be useful in the future for studying processes governing CH4 dynamics in aquatic systems.

We present EuropeAgriDB v1.0, a dataset of crop production and nitrogen (N) flows in European cropland 1961–2019. The dataset covers 26 present-day countries, detailing the cropland N harvests in 17 crop categories as well as cropland N inputs in synthetic fertilizers, manure, symbiotic fixation, and atmospheric deposition. The study builds on established methods but goes beyond previous research by combining data from FAOSTAT, Eurostat, and a range of national data sources. A key contribution is the comprehensive and detailed coverage of crop production, in particular fodder crops such as temporary grassland, green maize, and forage legumes. For these crops, we have combined the Eurostat crop production statistics database with a range of national databases, statistical yearbooks, and other sources. For other arable and permanent crops, we use the FAOSTAT database which apart from fodder crops offers the longest and most complete time series of crop production. Our crop production dataset, divided into 17 crop categories, provides a solid basis for understanding how crop mix and productivity have varied over time. A second key contribution is the detailed estimation of synthetic N fertilizer application to cropland and permanent grassland. We have assembled a comprehensive dataset based on a wide range of data sources and devised a rigorous method to process it. The result, we believe, is to date the most comprehensive and consistent estimate of the allocation of synthetic N fertilizer between cropland and permanent grassland in Europe. In summary, EuropeAgriDB v1.0 is a detailed, complete, and consistent dataset which will be useful both to understand Europe’s recent agricultural history and to make informed decisions about its future. This is particularly relevant in the current context of the EU Farm to Fork strategy, which requires major reduction in N inputs and surpluses and therefore the best possible quantification.