Seasonal difference in marine litter along the coast of Dar es Salaam, Tanzania

Abstract

Marine litter accumulation poses a significant threat to marine ecosystems and biodiversity. Marine litter and the influence of river discharge on marine litter accumulation during wet and dry seasons along the coast of Dar es Salaam was investigated. Litter samples collected between 2019 and 2021 from transects on beaches and by nets spanned across two rivers were counted, dried and weighed, and litter counts and weight (kg) calculated by area (litter/m2) and volume (litter/m3). Over three years, a total of 127,658 marine litter items weighing 470 kg were sampled from beaches, and 1,365 items from rivers, in nine different litter categories. Most of the litter (70 %) was produced locally and the marine litter density decreased by 61 % over the three years of the study. Litter densities at beaches and rivers were significantly greater during the wet than the dry season, attributed to the transport of litter in rivers to the ocean, especially plastics, which had a higher density than other riverine litter. It is concluded that high local plastic pro- duction and poor waste disposal systems require an intervention, and that a policy to minimize and reduce marine litter should be developed and implemented.