Effect of the rural-urban binary structure on the spatial distribution and sources of heavy metals in the sediments of a typical mountainous river

The spatial distribution of heavy metals in the sediments of mountainous rivers is significantly influenced by population density and industrial structure. In December 2019, sediment samples were collected from the Taohuaxi River–a typical mountainous river spanning both urban and rural areas in Changshou District, Chongqing–to investigate heavy metal contamination. The concentrations of eight heavy metals were measured, revealing that their average contents in the urban section were higher than those in the rural section, with cadmium (Cd) and copper (Cu) showing significant differences. Population density was found to be a key factor shaping the spatial distribution of heavy metals in river sediments. According to the improved geoaccumulation index (I_m), 20.59% of the monitored sites exhibited near moderate or moderate pollution, indicating localized enrichment of heavy metals along the river. Based on the potential ecological risk index (RI), 67.65% of sites presented medium or high potential ecological risks. The sediment quality guidelines (SQGs) assessment further indicated that heavy metals posed a moderate toxicological risk to aquatic organisms. Overall, the ecological risk of heavy metals in the sediments of the Taohuaxi River should not be overlooked. Positive matrix factorization (PMF) model analysis identified five major sources of heavy metals, with contributions in the order of aquaculture sources (38.79%) > natural sources (20.40%) > mixed anthropogenic sources (20.35%) > industrial sources type Ⅱ (16.69%) > industrial sources type Ⅰ (3.78%).