Radionuclides and heavy metals pose potential risks to marine ecosystems and human health. Daya Bay, the site of China’s first commercial nuclear power plant, has experienced significant anthropogenic impacts, yet the extent of radionuclide and heavy metal contamination remains unclear. Nineteen surface sediment samples were collected in January 2024 and analyzed for natural (²¹⁰Pb, ²²⁸Th, ²²⁶Ra, ²²⁸Ra, and ⁴⁰K) and anthropogenic (¹³⁷Cs) radionuclides, heavy metals (Cu, Pb, Zn, Cd, Cr, Mn, Hg, and As), grain size, and total organic carbon (TOC). The surface sediments of Daya Bay were predominantly fine-grained, with TOC levels ranging from 0.41% to 1.83%, influenced significantly by riverine input from the Dan’ao River. Natural radionuclides exhibited distinct spatial patterns: ²¹⁰Pb and ²²⁸Th activity levels were higher in fine-grained sediments, and correlated with TOC, indicating adsorption and sedimentation controls. In contrast, anthropogenic ¹³⁷Cs activity was low and showed no significant impact from the nuclear power plant. Notably, the absence in the samples of key anthropogenic radionuclides typically associated with nuclear power plant operations further confirmed the negligible impact of the power plant on local sediment contamination. The results indicated that the baseline levels of both natural and anthropogenic radionuclides and heavy metals were predominantly influenced by natural processes and local anthropogenic activities rather than the operation of the nuclear power plant. This study establishes critical baselines for radioactivity and heavy metals in Daya Bay, underscoring effective pollution control measures and the resilience of local ecosystems despite anthropogenic pressures.

Typhoons play a significant role in the marine sedimentary dynamic process and thus could significantly change the submarine geomorphology in their influence area. In this study, a high-resolution sub-bottom profiler and a side-scan sonar were used to detect the submarine geomorphology of the southeast coastal area of Nanri Island in the Taiwan Strait before and after Typhoon Soudelor—three times in 2015. The results show that the typhoon induced seaward movement of the sand dunes up to several tens of meters, resulting in significant changes in both the shape of the sand dunes and the scale of the exposed bedrocks. The typhoon also changed the submarine geomorphology, including the smoothing of anchor traces of fishing boats and the formation of relatively small sand dunes (groups). A comparison of the results of different surveys shows that the submarine geomorphology that was changed by Typhoon Soudelor could not recover within a short period of time. The wind field simulations of the typhoon process showed that the storm wave caused by the strong wind stress of the typhoon was a key dynamic factor for changing the submarine geomorphology.