Temporal dynamics of pathogen removal and faecal source tracking in a Norwegian nature-based solution/system treating urban waters

Nature-based solutions (NBS) have been broadly adopted to strengthen water and wastewater sanitation by effectively removing microbial pollutants and limiting significant health risks to aquatic environments and humans. However, temporal variations of pathogen removal efficiencies in NBS and the specific link with faecal pollutants remain understudied. In this study, a Norwegian urban NBS operating as a nature-based treatment system (NBTS) for water purification was monitored on pathogen removal capacities and faecal source tracking through a 1-year study. Applying coupled molecular analyses, i.e., pathogen molecular detection and genetic microbial source tracking, enabled the systemic assessment of this NBTS's remediation performance while unveiling the intrinsic link between pathogen prevalence and the faecal pollution sources. Notably, the system exhibited stronger pathogen attenuation activity on Enterococcus faecalis, Salmonella enterica serovar Typhimurium, Clostridium perfringens, and Legionella pneumophila (linked closely to human origin in the studied NBTS) than Shigella species and Giardia lamblia sourced mainly from animals. Moreover, the studied system displayed temporal dynamics of its functioning. As such, more fluctuations often occurred in cold months than in the warm period and under varying impacts of measured environmental conditions (i.e., water temperature, pH, electrical conductivity, dissolved oxygen, total dissolved solids, salinity, and oxidation reduction potential). Collectively, the findings of this study consolidate the functional potential of NBS in combating the microbial pollution that results specifically from waterborne enteric pathogens in a tight link with faecal contamination. The disclosed performance seasonality also calls for extra consideration for better-informed system management and remediation enhancement. Last but not least, the holistic study outcomes underscored the explicit value of applying complementary molecular approaches to achieve deeper insights into the functional status of a target NBS over time.