Destination of floating plastic debris released from ten major rivers around the Korean Peninsula

Using a Lagrangian particle tracking model the coastal accumulation of debris from 10 major Chinese and Korean rivers discharging to the seas around the Korean Peninsula is investigated. The amount of debris from each river is proportional to the population over the catchment area of the river and the mismanaged plastic waste (MPW) ratio of the country the river belongs to. The debris generally washes up on the coast near the originating river mouth. When only the debris originating from the rivers on the Korean Peninsula is considered the model results are consistent with the observations for the Korean coast reported in previous studies in that the amount of microplastic and macroplastic are greater near the Han and Nakdong Rivers. The amount of debris from Chinese rivers calculated based on the MPW ratios is 75 times greater than that from the rivers on the Korean Peninsula and if the Chinese rivers are added the model the results differ from the observed patterns. Macroplastic distribution also exhibits a similar discrepancy between the model and observation results if debris from the Chinses Rivers are taken into account. Observed data from Korea's Marine Litter Information System show that the accumulation of foreign-originating macroplastic most of which is Chinese is highest around the southwestern corner of the Korean Peninsula. Debris from the Chinese Yangtze and Yellow Rivers reproduces this observed distribution. Based on the observational data more debris originates from Korea than from foreign sources but Chinese-originating debris is dominant in the model. There are two possibilities for this discrepancy. The first is the presence of sinking due to biofouling; if 50% of the plastic sinks every 20 days or so the model results become similar to the observations. The second is the large difference in the MPW ratios between China and Korea employed in the model. Reducing the Chinese MPW ratio to 25% or lower the model results more closely reflect the observations made along the Korean coast.