Soils and sediments of coastal ecology: A global carbon sink

Abstract The global extent of coasts is huge and it has a massive impact on the planetary C balance. Coasts are again very heterogeneous with their soils and sediments possessing varying C storing capacity. In this review, we tried to capture such capacity of soils and sediments of coastal natural ecologies (like estuary, mangrove, mudflat, tidal marsh, seagrass, lagoon, continental shelf etc.) and croplands collectively in a mechanistic way. A detail discussion highlights very high C accrual in coastal soils and sediments due to terrigenous C deposition, tidal sedimentation and presence of fine clay particles. Very high biomass of coastal mangrove, tidal marsh and seagrass beds also results huge C burial in soils and sediments (blue C). Further, salinity and waterlogging induced low microbial activities, high soil aggregation and occlusion of C within aggregates impart prolonged residence time to C in coastal soils. All these confirm coastal ecology as a global C hotspot. However, climate change associated events like sea-level rise, ocean temperature increase, ocean acidification as well as human interferences have already affected the coasts and projected trend indicates severe possible damage of the coastal blue C in near future. Holistic sustainable measures will be required from different ends like government, local as well as international organizations to protect and restore the coastal C sink.