Dredging and dumping impact coastal fluxes of sediment and organic carbon

The disturbance and relocation of coastal sediments by human activities constitutes a potentially large disruption to natural sediment and organic carbon fluxes, but large-scale estimates of these impacts are lacking. Here, we estimate the amounts of sediment and organic carbon disturbed and relocated in the North Sea resulting from (1) dredging in the form of mineral aggregate extraction and (2) material dumping during waterway maintenance. We show that despite disturbing less sediment than aggregate extraction, dumping causes greater carbon disturbance. We estimate carbon disturbance by both activities to be higher than by marine construction, but lower than by bottom-contacting fisheries. Simulations indicate that most dumped material re-deposits near the coast. Globally, dumping of organic carbon is estimated to 0.09-0.46 GtC yr^-1, and disturbance by material extraction to 0.04-0.08 GtC yr^-1. Comparison to natural processes suggests that these activities should be considered in regional to global sediment and carbon budgets.