A FIELD SURVEY ON CHARACTERISTICS OF DRIFTING AND DRIFTED LITTER IN THE YAMATO RIVER

Abstract

 The increase in marine debris is concerned to have an irreversible negative impact on ecosystems. Riverine litter, a major source of marine debris, is causing damage to the landscape and adverse effects on the ecosystem of rivers themselves. This study con-ducted field surveys to materials and quantity of dumped and drifted litter on riverbanks and litter by a screen in an upstream channel in the Yamato River. From the field survey in the riverbank of the Yamato River, the correlation coefficient between the weight of litter and coverage is 0.82. The litter weight per 1 % coverage ratio was estimated to be 26.8 g/m2. The weight of litter can be estimated using the coverage ratio, but the value is affected by types of litter and is more overestimated when the sampled litter contains more plastic and paper wastes. The analysis of drifting litter trapped by a silt screen deployed in the channel in the Saho river, the upstream of the Yamato River, during dredging maintenance clarified that about 43.1 % of the litter was PET bottles on weight basis, and it was estimated that about 112 kg of litter would have passed through the river during a period of 54 days. The best-by date of plastic bottles and cans and the estimated date of manufacture by subtracting the best before period shows that about 91.2% of the plastic bottles and cans have been manufactured within one year before the screening.