Heavy metals in the continuous river−estuary−sea system of the Yellow River Delta, China: Spatial patterns, potential sources, and influencing factors

Present study investigated heavy metal pollution in the continuous upper river−estuary−sea systems of the Yellow River Delta (YRD). Significant seasonal differences (p < 0.05) for the heavy metal overall profile were observed, although there were no significant spatial variations among the different water bodies. Positive matrix factorization indicated that heavy metals primarily originated from anthropogenic activities (e.g., oil field development, mining, and agricultural activities). Chemical oxygen demand, water temperature, electrical conductivity, dissolved oxygen, pH, and salinity influenced the distribution of heavy metals in water. The NO₃⁻ and total phosphorus concentrations were the main influencing factors in sediment, with both showing positive correlations with all heavy metals. Furthermore, low ecological risks were observed for sediment based on the values of the ecological risk and potential ecological risk indexes in the YRD. This study will assist with the effective control and management of heavy metal pollution in a continuous river−estuary−sea system.