Oyster culture and hydrological characteristics regulate the distribution and accumulation of sedimentary organic matter in two subtropical mariculture areas

Abstract

Coastal oyster culture significantly regulates the content and composition of sedimentary organic matter (SOM), but its specific mechanism remains unclear. In this study, the dynamics and influencing factors of SOM in two subtropical oyster farming bays of Dapeng Cove (DPC, strong hydrodynamic force) and Zhanjiang Bay (ZJB, week hydrodynamic force), northern South China Sea, were compared and analyzed. Results showed comparable organic carbon (OC) levels between DPC (0.81 ± 0.48 %) and ZJB (0.81 ± 0.29 %) in sediments, while the content of total nitrogen (TN) in the DPC (0.073 ± 0.049 %) was notably lower than that in the ZJB (0.102 ± 0.050 %), reflecting regional variations in SOM composition. Source analysis revealed that marine primary production dominated SOM (64.50 ± 12.17 %) in the DPC, followed by oyster biodeposition (20.05 ± 6.99 %) and terrestrial input (15.45 ± 12.97 %). In contrast, the SOM in the ZJB mainly originated from terrestrial input (43.42 ± 16.20 %) and marine primary production (40.96 ± 6.94 %), with minimal oyster contribution (15.62 ± 10.39 %). Spatially, the SOM in the DPC and ZJB showed significant heterogeneity across horizontal/vertical gradients, driven by integrated physical-biogeochemical interactions. The SOM dynamics in the DPC were mainly governed by bottom-water oxygen, sediment grain-size composition and tidal action, while it in the ZJB was driven by terrestrial input, marine primary production and sediment grain-size composition. Oyster farming also enhanced SOM accumulation through biodeposition and hydrodynamic attenuation, particularly in mariculture areas of the ZJB due to low-energy environment.