Key drivers of heavy metal bioavailability in river sediments and microbial community responses under long-term high-concentration pollution.

Given the urgent need for effective environmental management of metal-polluted ecosystems, understanding the drivers of heavy metal bioavailability and microbial adaptation is crucial. The Dongdagou River, a major pollution source to the upper Yellow River, presents significant risks to regional water quality and biodiversity. This study investigates heavy metal bioavailability and its drivers, alongside microbial community responses, in 39 surface sediment samples from the river. The results revealed severe contamination, particularly with cadmium (Cd). Statistical analysis revealed that effective sulfur (ES) plays a crucial role in driving bioavailability. High-throughput sequencing indicated that bacterial communities were primarily dominated by Proteobacteria, with increased microbial diversity observed downstream. Functional predictions highlighted the prevalence of chemoheterotrophy and nitrogen cycling processes, alongside a significant presence of metal-resistance genes and enzymes, such as Cu-Zn superoxide dismutase and metal-efflux transporters. These adaptations imply that microbial communities are developing mechanisms of resilience in response to prolonged heavy metal exposure. These findings offer valuable insights for formulating targeted remediation strategies in environments affected by heavy metal pollution.