Macroplastic Transport and Deposition in the Environs of Pulauan River, Dapitan City, Philippines

Plastic pollution is an emerging threat in the riverine ecosystem that affects the marine ecosystem. The Philippines, being an archipelago, is heavily dependent on its marine ecosystem. It is also considered the largest emitter of plastic via rivers. Despite this, limited field studies have been conducted to validate this finding, which is mainly based on numerical models. In this study, we determined the prevalence of macroplastics in Pulauan River, Dapitan City by observing the plastic flux and further comparing the morning and afternoon flux. Macroplastic collection was also performed to compare the plastic densities of three stream areas: upstream, midstream, and downstream. Results show that macroplastic flux in the morning (304 items/h) was significantly higher than in the afternoon (91 items/h). The correlation of macroplastic flux and flow velocity was determined to be positive – suggesting that as macroplastic flow velocity increases, plastic flux tends to increase. Macroplastic collection results showed that upstream density (0.074 items/m2) is significantly lower than midstream (0.559 items/m2) and downstream (0.473 items/m2) densities. This shows that the nearer the area is to the river mouth, the more susceptible it is to plastic litter deposition. The composition of the macroplastic litters observed and collected was attributed to the influences of human activities (aquaculture, fishing, and residential) – where food packaging, plastic bags, and plastic fragments are the top three most abundant. Due to the limitations of this study, there is a need to investigate further the different factors on the transportation and deposition of macroplastic litters in Pulauan River that can help to avoid threats in the aquaculture sector, for which the river is known.