Anthropogenic influences on the sources and distribution of organic carbon, black carbon, and heavy metals in Daya Bay's surface sediments

The total organic carbon (TOC), total nitrogen (TN), black carbon (BC), delta 13CTOC, delta 15N, delta 13CBC, grain size, and heavy metals of surface sediments collected from Daya Bay were determined to investigate the spatial distributions of these parameters and to evaluate the influences of human activities. Marine organic matter was found to constitute approximately 84.41 +/- 7.70 % of these sediments on average. The western and northern regions of Daya Bay exhibited relatively fine grain sizes, weak hydrodynamic conditions, and high sedimentation rates, which favored the burial and preservation of organic matter. The high concentration of organic matter could be attributed to the influence of petroleum and aquaculture industries. Fossil fuels were the main source of BC. The enrichment factor (EF) and geo-accumulation index (Igeo) were used to evaluate the sources and pollution levels of heavy metals. The results revealed that the source and distribution of heavy metals were strongly influenced by human activities, resulting in moderate pollution levels across most regions of Daya Bay. A strong correlation was observed between the Igeo values of heavy metals and BC, TOC, TN, and mean particle grain size (Mz). This suggests that the ability of sediments in Daya Bay to enrich and adsorb heavy metals depends on the sediment grain size, the content and type of organic matter. Importantly, sediments in the inner bay of Daya Bay exhibited a greater capacity to impede the migration of heavy metals compared to those in the outer bay.