Tidal intensity and suspended sediment concentration drive microplastic distribution in the Pearl River Estuary: Insights from remote sensing retrieval

This study investigated microplastic (MP) pollution in the Pearl River Estuary (PRE), focusing on the effects of tidal intensity and suspended sediment concentrations (SSC) on their distribution. Tidal intensity, a key hydrodynamic driver, influences MP transport by altering water flow and sediment resuspension in estuaries, shaping pollution patterns. Surface water samples were collected from 16 sites during spring and neap tides, revealing an average MP abundance of 10.48 ± 3.60 items/L during spring tides (average SSC: 20.00 ± 4.74 mg/L), significantly higher than 7.58 ± 3.78 items/L during neap tides (average SSC: 19.12 ± 3.90 mg/L, p = 0.005). Fibers were the dominant shape (54.2 %), while small MPs (<1 mm) accounted for 88.7 % of the total during spring tides and 91.2 % during neap tides, indicating extensive weathering and hydrodynamic sorting within the estuary. Stronger tidal forces during spring tides enhanced MP transport via sediment resuspension, while neap tides promoted localized accumulation. A significant positive Spearman correlation between SSC and MP abundance was observed during spring tides (R = 0.4525, p = 0.004), but not during neap tides. By integrating remote sensing-derived SSC data with field observations, this study demonstrates the potential for satellite-based monitoring of MP distribution in dynamic estuarine systems. These findings highlighted the critical role of tidal dynamics in MP distribution and emphasize the need for targeted pollution management, including reducing upstream plastic inputs, in estuarine systems. This study provides valuable insights into MP behavior under varying hydrodynamic conditions, offering an innovative foundation for improved monitoring and mitigation strategies in coastal environments.