Particulate organic carbon (POC) is an important component of carbon cycling in bays, and its source and transport processes have significant impacts on the evolution of depositional environments and the stability of bay systems. This study focuses on Shidao Bay, located on the eastern Shandong Peninsula. In September 2024, hydrological parameters, surface sediments, and surface and bottom suspended particulate matter samples were collected from 43 stations in this area. By comprehensively analyzing sediment grain size characteristics, organic carbon and nitrogen contents, and stable carbon isotope (δ¹³C) compositions, the source characteristics, spatial distribution, and transport mechanisms of POC in Shidao Bay were systematically investigated.
The results show that the water body inside Shidao Bay is relatively warm and low-salinity, while the water body outside the bay is colder and higher in salinity. Stratification of water temperature and salinity is more pronounced during the flood tide stage than during the ebb tide stage. The mean grain size of surface sediments ranges from 6.0 to 57.0 μm. Inside the bay, sediment grain size shows large variation with moderate sorting, whereas outside the bay, stronger hydrodynamic conditions result in smaller variations in sediment grain size. The δ¹³C values of surface sediments range from -23.0‰ to -15.1‰, and C/N ratios range from 8.5 to 16.1. In the inner bay area, POC is predominantly derived from marine planktonic inputs, with minor mixing of terrestrial plant debris. In the outer bay area, the influence of terrestrial rock weathering and plant debris inputs is enhanced. Nearshore surface and bottom suspended particulate matter POC concentrations can reach 1.5 mg/L and 2.5 mg/L, respectively, showing distinct characteristics of anthropogenic input. The transport of POC is primarily controlled by tidal dynamics: during flood tide, marine-derived POC enters the bay with water masses and deposits; during ebb tide, a portion of POC diffuses outward from the bay. Meanwhile, the southeast-facing open topography of Shidao Bay, differences in substrate types, and human activities collectively regulate the spatial distribution and enrichment characteristics of POC.
Keywords: particulate organic carbon; stable carbon isotope; sediment dynamics; bay carbon cycling; Shidao Bay