Plastic floating debris along a summer-winter estuarine environmental gradient in a coastal lagoon: how does plastic debris arrive in a conservation unit?

Improper management of plastic waste is an important contributor to the pollution in water bodies. However, how floating plastic debris is transported to coastal lagoons and marine conservation units is still poorly understood. This work determined the level of contamination due to floating plastic debris in Acaraí Lagoon by establishing density distribution patterns along the lagoon ecocline in the winter and summer. Four areas were chosen that followed the estuarine gradient of the lagoon (external, lower, middle, and upper), and in each area, three samples of were collected by trawling with a plankton net. The plastic debris was classified into paint fragments, hard solids, plastic filaments, and soft plastics, and the plastic debris density and surface area were determined in each sampling area. The concentrations of the plastics in the downstream and upstream areas resulted from the high density of debris that occurred during the winter due to the absence of rain and the entry of coastal waters into the lagoon. The reduced abundance and surface area of the plastics in the summer were related to the substantial output of water from the interior of the lagoon to the mouth of the lagoon due to high rainfall during this season. The absence of plastic waste management actions and developed areas at the mouth of the lagoon that were associated with the spatial and temporal fluctuations in the environmental variables favored the occurrence and high abundance of plastic debris in the water column, contaminating the entire system of Acaraí State Park.