Achieving harmonized and integrated long-term environmental observation of essential ecosystem variables - eLTER's Framework of Standard Observations

The development of harmonized, standardized, and integrated environmental observation systems is a key challenge in Earth system science and essential for advancing interdisciplinary research to support global sustainability. The Integrated European Long-Term Ecosystem, Critical Zone and Socio-ecological Research Infrastructure (eLTER RI) is a recently developed pan-European network of in-situ research sites that facilitates long-term, comprehensive observation, analysis, and modeling of environmental and ecosystem change. The eLTER RI is guided by the ”Whole System Approach for in-situ research on Life Supporting Systems in the Anthropocene” (WAILS). This initiative focuses on Europe’s primary ecosystems, encompassing the atmosphere, geosphere, hydrosphere, biosphere, and their socio-ecological interactions with the anthroposphere. A fundamental prerequisite for effective environmental monitoring is a standardized and harmonized design that facilitates consistent and comparable environmental data across diverse spatial and temporal scales. The present study proposes the eLTER Framework of Standard Observations (eLTER SOs), which delineates essential ecosystem variables, their measurement methods, and protocols. These SOs constitute the conceptual foundation of eLTER RI. The eLTER SOs provide a basis for overcoming existing disciplinary barriers to the international harmonization of environmental research and a foundation for cross-sphere observation concepts. The eLTER SO combines both, the scientific-academic perspective, as known from ”classical” Essential Variable concepts, with the operational perspective required for the establishment and long-term operation of in-situ observatories. This framework provides a robust basis for international harmonization of environmental research and fosters stronger global collaboration in addressing environmental challenges.