Impact of storms and proximity to entry points on marine litter and wrack accumulation along Mediterranean beaches:...

Beach litter can affect public health and economic activities worldwide forcing local authorities to expensive beach cleaning. Understanding the key mechanisms affecting the accumulation of this waste on beaches, such as sea state and proximity to entry points, is critical to plan effective management strategies. In this one-year study, we estimated the impact of storm events and waterways runoff on litter abundance and local economy using as a model a managed, peri-urban beach facing a north-western sector of the Mediterranean Sea. We also investigated the relationship between litter composition/density and beach proximity to major/closest harbors/rivers at regional scale by combining our data with those on litter density available in literature. Autumn/winter storms caused larger litter depositions than spring/summer ones in the peri-urban beach. No preferential accumulation occurred near to waterway mouths. Litter mainly consisted of plastic, and its composition in terms of micro-categories varied over seasons. In total, 367,070 items were deposited along 4.7 km of beach over one year, and the cost for the removal of this waste amounted to approximately 27,600 euros per km/year. At regional scale, beach litter density was positively correlated to the proximity of major harbors while its composition was related to the proximity to both major harbors and rivers. Results indicate that autumn/winter storms are important drivers of marine litter deposition. They also suggest that beaches in front of the convergence zone of littoral currents and close to major harbors can be particularly subjected to this kind of pollutant. To increase their effectiveness, litter mitigation/cleaning activities should be planned based on predictions of major storm events and performed at spatial scales encompassing at least coastal regional sectors.