ANALYSIS OF LONG-TERM DYNAMICS OF THE MASS-SIZE STRUCTURE OF PLASTIC LITTER ON THE CURONIAN SPIT BEACH (BALTIC SEA) AND ITS RELATIONSHIP WITH THE WIND-WAVE REGIME

Abstract

Sandy beaches, traditionally viewed as passive accumulation zones with low abrasive capacity, are in fact active and efficient physico-ecological systems. The results of a seven-year monitoring programme (July 2019 – October 2025) on the Curonian Spit, together with the revealed correlations, suggest that wave energy may contribute to the mechanical fragmentation of plastic; however, direct post-storm observations are required to confirm this. Over the observation period, a steady decline in the total amount of plastic litter by approximately an order of magnitude was recorded, from >500 items to 50–70 items per 100-m stretch, and litter density differed significantly between seasons (lower in winter than in summer and autumn). A sharp asymmetry between abundance and mass was identified: large fragments (>10 cm) accounted for only 29 % of all items but accumulated 78.6 % of the total mass, whereas small particles (<2.5 cm) contributed 35 % of the item count but only 3 % of the mass. The polymer composition revealed the dominance of PE and PP in the large fragments and an increasing share of PS and PET in the fine fraction, indicating the active fragmentation of brittle plastics on the beach. It was statistically confirmed that an increase in the mean significant wave height correlates with a decrease in the median size of plastic litter (r = –0.43, p = 0.03), while the predominance of westerly and northwesterly winds and waves correlates with an increase in both the amount and mass of litter on the beach (r = 0.4, p = 0.05). The Clean Coast Index (CCI) classified the beach as “very clean” to “clean”, showing a seasonal sensitivity to recreational pressure.