Advancing benthic diatom-based freshwater health assessment in China: from an index application to an integrated assessment framework

Benthic diatoms are widely used as bioindicators in freshwater assessment, and diatom-based biomonitoring tools have been applied in China for several decades. However, existing knowledge in China remains fragmented across Chinese and English literature, geographical regions, ecosystem types, and methodological traditions. Here, we conducted a review of 62 studies that used benthic diatoms for freshwater bioassessment in China and summarized their geographical distribution, ecosystem coverage, publication trends, and bioassessment methods, and identified the future research needs in diatom monitoring. The review shows that selected studies are unevenly distributed across provinces and are dominated by riverine systems. Traditional, mainly European morphology-based indices remain central also in China, but localized and fine-tuned multimetric indices, molecular diatom indices, and environmental DNA-based approaches indicate a shift toward regional calibration and methodological integration while also highlighting the use of many fit-for-purpose approaches (e.g., diatom teratological forms). We argue that the key challenge is no longer whether diatoms can indicate freshwater conditions in China, but how diatom-based assessment tools can be standardized, calibrated, and scalable across diverse freshwater ecosystems and biogeographical regions. Future progress requires development of standardized protocols and fit-for-purpose approaches, national taxonomic and molecular reference databases, long-term monitoring, and integration of emerging technologies.