Tracing anthropogenic contamination in a riverine source-reservoir continuum: Insights from molecular markers.

Anthropogenic contamination poses a growing threat to water quality, yet most studies focus on discrete river segments rather than entire hydrological continuums where contaminant transformation occurs. This study explored this gap by investigating the spatial distribution, sources, and transport pathways of organic pollutants across a complete hydrological continuum, using the Xinfengjiang Reservoir Basin as a case study. Sampling sites were classified into three hydrological units: riverine sources, watercourses and reservoir. Anthropogenic molecular markers were systematically applied to elucidate spatial contamination patterns, apportion pollutant sources, and identify key driving factors. Key findings revealed distinct spatial trends: concentrations of sewage and petroleum contamination markers peaked in watercourses but remained low in both riverine sources and the reservoir, suggesting anthropogenic contamination was primarily localized to the watercourses. Land-use patterns emerged as key drivers of anthropogenic contamination distribution. Notably, the reservoir exhibited a strong self-purification capacity, maintaining relatively low contamination levels despite substantial upstream inputs. The dam modulated the fate of pollutants, promoting accumulation of particulate pollutants while facilitating the attenuation of readily degradable organic contaminants. This study highlights the effectiveness of molecular markers in tracing contamination dynamics across river-reservoir systems, providing essential insights for water quality management and strategies to mitigate anthropogenic impacts in reservoir ecosystems.