Toward “good” eutrophication data for marine policies and research: a multi-level quality control framework in EMODnet Chemistry

The increasing demand for reliable marine data to support environmental policies such as the Marine Strategy Framework Directive (MSFD) in Europe requires harmonized, high-quality datasets that are findable, accessible, interoperable, and reusable (FAIR). This paper presents a multi-level quality control (QC) protocol applied within the European Marine Observation and Data Network (EMODnet) Chemistry initiative, focused on eutrophication parameters (nutrients, chlorophyll, and oxygen) across European marine regions. The approach combines automated and expert-based validation and includes three consecutive QC steps performed by the data originators (Level 1 QC), the data centers (Level 2 QC), and the regional coordinators (Level 3 QC). Particular attention is also given to collecting and maintaining comprehensive metadata associated with the datasets, as well as methodological quality assurance (QA) information. The framework ensures transparent and consistent QC practices across different data providers, improving data comparability and usability. Additional procedures—including cross-parameter checks, derived variable analysis, and region-specific broad range comparisons—are implemented to detect outliers and enhance dataset reliability. The protocol supports the implementation of European marine policies by enabling coherent environmental assessments, and is adaptable to other variables such as ocean acidification and pollution. This work demonstrates the value of expert based, interoperable QC procedures to advance marine data quality and reusability.