Spatial Heterogeneity of Microplastic Contamination in a Tropical Sandy Beach: Influence of Management Regimes and Recreational Use

Microplastic contamination is a growing environmental concern in coastal ecosystems, particularly on recreational beaches where human activities may influence plastic inputs. This study investigated microplastic abundance and particle characteristics across five recreational zones along Hatwanakorn Beach in the Gulf of Thailand, focusing on fine-scale variability within a spatially continuous beach system and across management regimes. Supratidal sediments were collected using a quadrat-based approach, and polymer types were identified using Fourier Transform Infrared spectroscopy (FTIR). Fibers were the predominant particle type, followed by fragments, and most particles were classified as large microplastics (1–5 mm). Significant spatial differences in abundance were observed among recreational zones (Kruskal–Wallis test, χ2 = 13.37, p = 0.0096). At the management regime scale, a negative binomial generalized linear model also indicated significant differences (χ2 = 30.58, p < 0.001), with higher abundance in the Hatwanakorn Forestry Research and Student Training Station (HWK Station) and Community regimes than in the National Park regime. These results indicate that microplastic distribution can be spatially heterogeneous even within a continuous recreational beach system, underscoring the importance of accounting for fine-scale spatial variability when assessing microplastic contamination in coastal environments.