A Methodological Framework for Defining Beach Litter Footprints: Application in the Iberian Peninsula, Macaronesia, and the Balearic Islands

The definition of assessment methods for determining the good environmental status of beaches with respect to marine litter is an essential requirement for the implementation of the European Marine Strategy Framework Directive. Government monitoring programmes, citizen-science initiatives, and the scientific community are generating large amounts of data on marine-litter abundance, particularly on macrolitter and especially on beaches. Interestingly, these litter counts are reported in a specific and detailed manner by item categories, enabling the exploration of potential pollution sources. However, most existing assessments rely on the total count of litter categories, without considering their heterogeneity or origin. This approach limits the development of effective, source-focused management strategies.

The present study introduces an assessment based on a set of seven indicators related to marine-litter sources, accounting for both the potential origins and size classes of different litter categories. We refer to this integrated approach as the Beach Litter Footprint. This multidimensional analysis leads a more comprehensive assessment, as it allows impacts to be weighted according to the typology and origin of the litter found at each location.
The applicability of the Beach Litter Footprint was examined through a large-scale analysis along the coastline of the Iberian Peninsula and its surrounding environment, namely the North African continent, the Azores, Madeira, and the Canary Islands in the Atlantic Ocean, and the Balearic Islands in the Mediterranean Sea. The choice of this region of interest (ROI) for the proof of concept was based on two factors. First, the availability of data in this area, especially from citizen-science activities; and second, the wide environmental diversity of the region, comprising two distinct water masses (the Atlantic Ocean and the Mediterranean Sea), two continents with relevant socioeconomic differences, abundant archipelagos, and major coastal cities and rivers.

The Beach Litter Footprint clearly identified contamination hotspots and well-preserved areas, revealing previously unreported patterns regarding the origin and distribution of litter at both local and regional scales. Our analysis also highlighted the remarkable value of citizen science for this type of assessment. The Beach Litter Footprint provides a comprehensive and easily replicable diagnostic tool based on routine beach-litter monitoring data. Unlike other indicators, it provides a detailed view of both the mass and the origin of beach-litter pollution, helping decision-makers to design source-targeted mitigation strategies.