Long-term high-frequency isotope-specific monitoring of H2O, CO2, CH4 and N2O exchange between atmosphere and ecosystems

The central goal of this project is to establish long-term isotope-specific monitoring of H₂O, CO₂, CH₄ and N₂O exchange between terrestrial ecosystems and the atmosphere with high temporal resolution at grassland, arable land and forest sites. The exchange of H₂O and CO₂ between ecosystem and atmosphere will be determined online with rapid (10 Hz) isotope-specific laser analyzers using the eddy covariance (EC) method. The objective of this measurement is to determine the isotopologue fluxes of the respective gases and the source/sink partitioning, i.e., evaporation and transpiration in the case of water vapor or photosynthetic uptake and ecosystem respiration in the case of CO₂. Measurements will be conducted using fully automated measurement systems for a minimum of two years. In addition, a mobile automated sampling system will be developed for isotope-specific recording of CH₄ and N₂O ecosystem exchange using the profile method with off-line isotope analysis by isotope ratio mass spectrometry to ensure the highest possible precision of isotope measurements. The aim of the isotope-specific flux measurements is to partition the CH₄ flux into CH₄ production (methanogenesis, if relevant) and CH₄ uptake (methane oxidation), and the N₂O flux into nitrification and denitrification as sources and N₂O reduction as an N₂O sink. Furthermore, the measurements will permit the determination of the isotopic composition across seasons and during peak emission periods, such as fertilization or freeze-thaw events. All approaches will be evaluated for their relevance in identifying greenhouse gas source/sink processes and their potential for long-term deployment. This presentation will introduce the measurement concepts and present first results.