Lead sources in seagrass sediments deciphered by isotopic signatures: Implications for organic matter-regulated...

Understanding the sources and accumulation of lead (Pb) in seagrass sediments remains a challenge, despite widespread observations of Pb enrichment in these carbon-rich ecosystems. This study addresses this knowledge gap by combining Pb isotopic fingerprinting with chemical extraction techniques to investigate Pb contamination in a rapidly developing coastal region of Hainan Island, China. While Pb concentrations were relatively low, Bayesian isotope mixing models reveal that natural lithogenic sources dominate the sedimentary Pb inventory (59.4 ± 18.4%). Among anthropogenic inputs, agricultural activities emerged as the primary contributor (23.2 ± 11.5%), exceeding the combined impact of coal combustion and traffic emissions. These results underscore agricultural runoff as a critical, yet frequently overlooked, terrestrial pathway for Pb in coastal environments. Furthermore, we found that anthropogenic Pb accumulation is strongly coupled with sedimentary organic matter content. This suggests that the degradation of seagrass meadows may not only diminish their capacity as carbon sinks but also risk remobilizing legacy Pb into the water column. Our work provides novel isotopic constraints and advances the mechanistic understanding of Pb biogeochemistry in seagrass ecosystems.