Plastic litter in River Sabaki and Tana riverbanks

Rivers act as conduits for plastic litter from land-based sources to the Ocean. However, only 2% of plastic litter finds its way to the ocean; the rest remains in terrestrial environments. This hints at plastic litter being held in riverbanks, estuaries, river beds, and upstream infrastructure. This motivates the need to monitor these river sections to understand the dynamics of plastic litter retention. The objective of this study was therefore to monitor riverbanks in the rivers Sabaki and Tana to understand plastic litter distribution in these river systems. Monitoring of the selected river bank types in the respective rivers was assessed over one year, from October/November 2021 to January 2023, to capture seasonal variation. The selected riverbank types were sampled in two replicates to assess their capacity to retain plastic litter. For source identification, factor and cluster analysis statistical tools were applied, complemented with local and expert knowledge. 8,793 plastic litter items, weighing 65.38 kg, and 8,429 plastic litter items, weighing 85.08 kg, were documented in Rivers Sabaki and Tana, respectively. On plastic litter densities, 0.06 to 2.17 items m-2, with a mass range of 0.40 to 25.96 g m-2, were recorded in River Sabaki, and 0.12 to 0.70 items m-2, with a mass range of 1.40 to 8.96 g m-2 in River Tana. Seasonal variation was observed with high peak of plastic litter accumulation for River Sabaki recorded in December 2021, and River Tana in January 2022. Sources of plastic litter in the River Sabaki were associated with upstream sources, tourism, recreational activities, agricultural activities, and informal settlements. River Tana sources were: Fishing activities, illegal dumpsites, local sources, littering, navigation activities, and upstream sources. The information derived from this research could benefit policymakers and other stakeholders in developing strategies to combat riverine plastic litter in River Sabaki and Tana.