人工素材漂着ごみによる海浜汚染とそれを測る適切な単位

Abstract

Serious pollution of the beach environment by plastic marine debris (litter) has been reported around the world. However, these reports are recorded in two types of measurement units: /m and /m2. Therefore, we investigated which measurement is the more appropriate unit to measure beach debris. Our analysis is based on our 146 surveys of anthropogenic debris larger than or almost equal to plastic resin pellets from November 2004 to November 2009 at five relatively deserted beaches in Tottori, Japan. A total of 173, 981 fragments and items with a total weight of 433kg were collected. Surprisingly, about ten percent were thermal-fused plastic lumps, presumably due to incomplete burning. The floating marine debris washed up on the beaches normally forms a wrack belt, and the debris in the belt is over half of the total number and weight of the debris from shoreline to upper wrack limit. Since the wrack belts are narrow, the depth of sandy beaches affects neither the wash-up of floating debris nor the formation of debris belts. In fact, the correlation coefficients between the depth of beach and the number and weight of debris are very low (rn=0.20 and rw=0.19). The quantity of beach debris is significantly correlated with the length of the beach line because the wrack belt is usually parallel to the shoreline. Since the floating debris is ideally washed up on a one-dimensional intersection between beach and water surfaces,the unit of measure to quantify beach debris ought to be defined by the length of the beach line.