Nonuniform organic carbon stock loss in soils across disturbed blue carbon ecosystems

Conserving blue carbon ecosystems (BCEs) has gained international attention in climate change mitigation, reflected in United Nations policies and voluntary carbon-offset projects. These efforts assume significant and uniform losses of soil organic carbon (Corg) throughout the top meter following disturbances, yet this assumption lacks robust empirical support. Here, we synthesized 239 paired observations of intact and disturbed BCEs globally. Soil Corg stock losses in the top meters vary widely: from -68.4% (agricultural conversion, ±13.4%, 95% confidence interval) to +0.8% (harvesting, ±46.2%) in mangroves, -25.9% (climate/hydrological change, ± 30.7%) to +48.6% (grazing, ±78.7%) in saltmarshes, and -34.2% (vegetation cover damage, ±22.4%) to -27.4% (dredging, ±33.6%) in seagrasses. Extensive disturbances deplete Corg down to 50-200 cm, while limited disturbances impact only the top 10-30 cm or resulted in negligible losses. This refinement contributes to improved global inventories of greenhouse gas emissions from BCEs, supporting abatement policy settings for nationally determined contributions commitments.