Stage-dependent enhancement of sedimentary organic carbon burial driven by mussel raft farming on Gouqi Island

Intensive bivalve raft farming profoundly influences coastal carbon cycling through enhanced biodeposition, yet long-term dynamics of sedimentary organic carbon (OC) burial under multi-decadal mariculture remain poorly constrained. Here, we reconstructed a 65-year history of mussel farming in Gouqi Island, China, the largest Mytilus coruscus farming region, by integrating 210 Pb radioisotope dating with biogenic silica (BSi) density profiles in sediment cores. This framework allowed quantification of total organic carbon (TOC) burial, accumulation, and particulate OC lateral transport across four farming stages: non-farming, early farming, farming development, and large-scale farming. BSi served as a robust geochronological proxy, with three major transitional layers corresponding to historical milestones (1960, 1976, and 2000). Since the onset of mariculture, sedimentation rates in the farming area reached 1.33 cm yr −1 . Large-scale farming substantially increased TOC burial, with a mean flux of 91.2 ± 1.22 g C m −2 yr −1 , a 23.6% rise relative to early farming, comparable to global blue carbon ecosystems. The concurrent declines in TOC and BSi during early farming development suggest a potential short-term ecological threshold, possibly associated with high-density filtration, reduced light availability, grazing pressure, and phytoplankton community shifts. After age correction, the positive TOC/BF–sand relationships weakened or disappeared, indicating that the observed relationships arise from shared temporal trends rather than a direct effect of grain size. Overall, TOC burial was jointly regulated by farming intensity, primary productivity, and depositional environment.