Observation of Floating Inorganic Macro-debris in The Downstream Citarum River using Manual Counting

Inorganic Macro-debris (IMD) such as plastics can negatively affect aquatic life and human wellbeing. Information about IMD transport in river systems is required to optimize prevention, mitigation, and reduction strategies. However, this data is currently lacking. Manual counting technique can be used to quantify and characterize macro-debris contamination and its transport in rivers. We demonstrate how this method can provide a rapid and cost-effective tool for characterization and quantification of floating macro-debris. This study aims to quantify the abundance of IMD, explore the spatio-temporal trends, and identify the composition of floating IMD in the downstream section of the Citarum River, West Java, Indonesia. Data collection was carried out in March and May 2021. Observations were performed between 8 AM and 5 PM across the whole river width across several days. Results showed that IMD transport varies between days, ranging from 60 to 350 pieces in March and 40 to 4700 IMD pieces per day in May. The magnitude of macro-debris is correlated with precipitation (r = 0.793 and 0.622 for March and May, respectively). Spatially, concentration of macro-debris fluxes was observed close to river shores across the channel widths. The most frequent IMD category observed in March and May 2021 was Polystyrene (60% to 70%).