Coupled effects of land-use patterns and hydrological regimes on fecal indicator bacteria in a coastal watershed

Monitoring and assessing fecal indicator bacteria (FIB) can inform aquatic ecosystem health and management. However, knowledge of the patterns of fecal coliforms and the underlying mechanisms in rivers is still limited. In this study, we aimed to investigate the coupled effects of land-use patterns and hydrological regimes on FIB patterns in a subtropical coastal watershed, the Jiulong River Watershed (JRW). Water samples were collected quarterly for nutrient and FIB measurements across the watershed, from October 2020 to July 2021. The results indicate that Escherichia coli and Fecal E. coli concentrations peaked in summer and autumn, with significantly higher concentrations observed in urban watersheds than in natural watersheds. Redundancy analysis further revealed that of the four sampling seasons, the relative contribution of land use to FIB characteristics in the JRW was the highest in autumn, whereas that of water quality was the highest in the other three seasons. Water flow showed the lowest relative contribution in all the seasons and a positive correlation between high nutrient concentrations and E. coli counts exhibited. This study enhances our understanding on the coupled effects of seasonal hydrological regimes and land-use patterns on FIB characteristics, which might provide implications for mitigating the risk of E. coli contamination in similar human-impacted watersheds.