Hydrodynamic forcing and sand permeability influence the distribution of anthropogenic microparticles in beach sediment

The distribution of anthropogenic microparticles (Mps), such as plastic and natural fibres used in textiles, in beach sediments was studied in a human-influenced pocket beach in Liguria (NW Mediterranean Sea). Information on environmental parameters such as rainfall, hydrodynamic characteristics and sediment texture was collected at the same time as the sediment samples. The Mps (416 +- 202 Mps kg-1 on average) were mainly fibres (57–100%), while fragments and spheres showed irregular abundances linked to the draining action of waves on the beach. Uni- and multivariate statistical analyses highlighted that the different spatial and seasonal distribution of fibres primarily depended on the action of the waves that force seawater into the sand, rather than on sedimentation following depositional processes. Wave height and direction had a role in fibre distribution in the sand, as well as sediment permeability and sorting. The occurrence of short-term and spatially-localised hydrodynamic events such as rip currents were observed to influence the abundance of fibres, overlapping the seasonal sequences of beach accretion and erosion that is typical of the area and increasing fibre abundance by transporting those accumulated in the sediments of the submerged beach during winter.