Carbon and nitrogen stable isotope analysis and source identification of organic matter in sediments of Sanggou Bay

Abstract:

In this study, the following spatial and temporal distribution characteristics of surface sediments in Sanggou Bay were analyzed: grain size, total organic carbon (TOC), total nitrogen (TN), and carbon-nitrogen stable isotopes (δ13C and δ15N). Additionally, the contribution of shellfish-seaweed biodeposition to the organic matter in coastal sediments was estimated. The results showed that the sediment composition of Sanggou Bay is primarily silt, and that particle size distribution is closely related to mariculture and hydrodynamic conditions. The seasonal variation and horizontal distribution of TOC and TN showed similar patterns: highest in spring and lowest in autumn, with little seasonal difference, and higher values in shellfish seaweed, fish shellfish, and shellfish culture areas. However, there were larger differences in the seasonal variation and horizontal distribution of δ13C and δ15N. According to the correlation analysis, there was a significant positive correlation between TOC and TN (r=0.955, P<0.001), indicating that TOC and TN in the surface sediments of Sanggou Bay were homologous. In addition, according to the comprehensive analysis of δ13C and C/N, the main sources of sedimentary organic matter are shellfish biodeposition, kelp, and soil organic matter. Using a three-end-member mixed model, it is estimated that the contribution rates of shellfish biodeposition, soil organic matter, and kelp are 67.52%, 26.47%, and 5.97%, respectively. Therefore, marine shellfish-seaweed biodeposition has a significant impact on coastal carbon burial.