DIACODE
Status of diatom barcode databases for improved assessments in DNA metabarcoding for WFD phytobenthos reporting in Luxembourg
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Diatom DNA barcoding: setting the baseline for implementing metabarcoding in Luxembourg in the context of the EU Water Framework Directive
Aquatic ecosystems are essential to biodiversity, ecosystem functioning, and human well-being. Ensuring their good ecological status is a central objective of the EU Water Framework Directive (WFD), which relies on biological indicators such as diatoms to assess water quality. Through indices like the IPS (Indice de Polluosensibilité Spécifique), diatoms provide a sensitive measure of environmental conditions and anthropogenic pressures.
However, current monitoring approaches are based exclusively on microscopy, which is time-consuming, requires high taxonomic expertise, and limits reproducibility and scalability. At the same time, DNA metabarcoding offers new opportunities for faster, standardised, and high-throughput assessments.
Despite its potential, the application of metabarcoding to diatom monitoring is constrained by incomplete barcode reference libraries, limiting accurate species identification. This creates a critical need to strengthen these resources and prepare for the future integration of DNA-based methods into WFD reporting.
The DiaBase4WFD project addresses a key bottleneck in diatom metabarcoding by developing a comprehensive and targeted DNA barcode reference library for Luxembourg’s freshwater ecosystems. The project focuses on cultivating and sequencing the 100 most important diatom indicator species currently missing or underrepresented in genetic databases.
Beyond barcode library development, the project evaluates how improved taxonomic coverage influences ecological assessments. It will compare Ecological Status Classes derived from the IPS index using both microscopy and DNA metabarcoding.
DiaBase4WFD will also produce a best-practice guideline for implementing diatom DNA metabarcoding in Luxembourg’s WFD reporting. This guideline will be aligned with European standards developed by the European Committee for Standardization (CEN), ensuring compatibility with emerging EU methodologies.
DiaBase4WFD will deliver key scientific and operational outputs to support water quality assessment and environmental management in Luxembourg. The project directly contributes to the missions of the Administration de la gestion de l’eau (AGE), strengthening preparedness for the future adoption of DNA-based methods in WFD reporting.
Its main outputs include a significantly expanded barcode reference library, improved accuracy in ecological status classification, and a quantitative assessment of how library completeness influences IPS scores. In addition, a proof of concept will explore how pollution affects benthic diatom communities as detected through eDNA metabarcoding.
At a broader scale, the project contributes to international efforts to complete diatom reference databases and harmonise DNA-based monitoring. By advancing reliable, standardised, and scalable assessment tools, DiaBase4WFD supports the transition towards next-generation biodiversity monitoring and a more integrated water management.
