A multidriver assessment of beach litter accumulation rates

Anthropogenic marine litter poses ecological and economic risks to coastal environments, and its accumulation dynamics remain poorly understood at precise spatial and temporal scales. Most studies lack high-frequency data and rarely consider variations between beach use zones. Therefore, we investigate how social and environmental factors influence the daily accumulation rates of anthropogenic marine debris in different use zones of a tourist beach in Jericoacoara National Park, a conservation unit in Brazil's northeast. Sampling was conducted for one full week each month, from July 2022 to June 2023, across three distinct user zones. Two hierarchical generalized additive models (HGAMs) were applied to test the influence of monthly rainfall and number of monthly tourists on zonal daily litter accumulation rates. A total of 22,375 litter items were recovered, with average daily accumulation rates (1.77 items.m^-1.day^-1) peaking during the tourist season. The accumulation varied notably between zones, with the most impacted site reaching nearly triple the rates of the other sites. Cigarette butts emerged as the most abundant item (average = 0.95 items.m^-1.day^-1), followed by metals (0.24 items.m^-1.day^-1), paper (0.20 items.m^-1.day^-1), hard plastics (0.16 items.m^-1.day^-1) and flexible plastics (0.13 items.m^-1.day^-1). Modeling revealed that litter accumulation patterns were significantly shaped by temporal dynamics, followed by zonation, the number of visitors, and rainfall regimes. These findings highlight the interplay between human activity and environmental factors in driving litter accumulation on urban beaches, offering key insights for targeted coastal management strategies.