Relationships between marine litter and type of coastal area, in Northeast Atlantic sandy beaches

Marine litter represents a threat to the marine environment, being estimated that around eight million items are discarded daily in the ocean. Monitoring marine debris became a relevant topic of research as marine litter is one of the descriptors of the Marine Strategy Framework Directive, for European Union's member states. Nevertheless, the patterns and processes governing the disposal of waste in coastal areas are still not clear. Our study relates characteristics of eleven coastal areas in Portugal (urbanization, slope, distance to an estuary, length, and type of substrate) to the type and abundance of marine litter found. A total of 7743 items were identified, with the main types of litter found being plastic (71.2%), paper (16.3%), and sanitary waste (9.1%). A clear spatial distribution pattern was observed, with more litter items recorded in the zone corresponding to the high tide line (2.3 items m^-2). It was also verified that both beaches and seasons influenced the amount of litter found. Plastic, the dominant marine litter group, was abundant on the vast majority of beaches. It was possible to identify litter with land and sea origins. The litter with land origin came mainly from sanitary and sewage-related waste while the litter with marine origin came mainly from fisheries, including aquaculture.