Unravelling spatio-temporal patterns of suspended microplastic concentration in the Natura 2000 Guadalquivir estuary (SW Spain): Observations and model simulations.

Abstract Microplastics (MPs) patterns in a weakly-stratified estuary were investigated using a combined approach of observations and modeling. The study was conducted in the Guadalquivir River Estuary, which is of high environmental value, yet significantly altered by human activities. The study aims to contribute to understanding and quantifying the land-ocean transport of MPs. Mean concentrations of MPs in the estuary were 0.041 items m−3, with maximum values up to 0.20 items m−3, in agreement with the range reported in other estuaries. Polyethylene floating MPs were predominant. Relationships between increases in MP concentration and local rainfall events were identified in the middle estuary when there were no significant discharges from the head dam. Modeling results mimicked observations and revealed the effects of tidal straining, density-driven, and river flow-induced circulation on the net transport. Convergence of transports favors the MPs trapping in the vicinity of Donana National Park, overlapping the location of the Estuarine Turbidity Maximum.