Bridging sanitary surveys and microbial evidence: Advancing recreational water risk assessment through community-based microbial source-tracking

• MetaMST attributed enterococci to multiple faecal sources in mixed catchments. • MetaMST revealed dynamic links between enterococci levels and antecedent rainfall. • Sanitary surveys missed spatial and temporal trends without metaMST pairing. • MetaMST enabled a more specific understanding of faecal contamination hazard. To evaluate the suitability of water environments for water-based recreation, water quality guidelines rely on a risk framework based on the quantification of faecal indicator bacteria (FIB), and sanitary surveys. The purpose of sanitary surveys is to identify the sources of faecal pollution and their likelihood to contaminate the water environment. In general, FIBs such as enterococci are assumed to be primarily human-derived; an assumption that can lead to a disconnect between measured FIB levels and the broader site context, particularly in environments with multiple faecal sources. As a result, the framework often struggles to accurately link microbial contamination to specific sources and risks. This study investigates the application of community-based microbial source tracking (MST) with adjustment of FIB concentrations, via metaMST, to generate source-specific FIB profiles for eight Australian beaches. Results demonstrated that metaMST source proportioning could attribute enterococci levels across multiple faecal sources, better reflecting the reality of mixed catchments inputs. MetaMST analysis also revealed dynamic relationships between enterococci and antecedent rainfall, varying by source and site. However, sanitary surveys, when not conducted concurrently with metaMST sampling, often failed to capture site-specific spatial and temporal variability. In combination it was demonstrated that through integration of metaMST, hazard identification becomes more precise, enabling better-informed risk assessments and mitigation strategies that can better inform long-term management of risks to recreational water quality, in addition to reduced public health alerts associated with faecal contamination in recreational waters.