Do urban rivers in the amazon coast trap macroplastic?

Area of Science:

• Environmental Science
• Oceanography
• Ecology

Background:

• Amazon Rivers are significant pathways for macroplastic pollution entering marine ecosystems.
• Current macroplastic transport estimations often lack accuracy due to the omission of hydrodynamic factors and in-situ data.
• Urban rivers in the Amazon basin contribute substantially to oceanic plastic loads.

Purpose of the Study:

• To quantify floating macroplastics in the Acará and Guamá Rivers, Amazon urban rivers discharging into Guajará Bay.
• To provide the first annual transport estimate of macroplastics considering temporal scales and local hydrodynamics.
• To analyze the influence of river discharge and tidal stages on macroplastic distribution.

Main Methods:

• Conducted visual observations of floating macroplastics (>2.5 cm) across various river discharges and tidal stages.
• Measured current intensity and direction in the Acará, Guamá Rivers, and Guajará Bay.
• Quantified macroplastic abundance and calculated annual transport rates based on in-situ measurements.

Main Results:

• A total of 3481 floating macroplastics were quantified, with significant variations observed based on tidal cycles and seasonality.
• The urban estuarine system exhibited an import rate of 12 tons/year of macroplastics via the Guamá River.
• An export rate of 21.7 tons/year of macroplastics was recorded through Guajará Bay, influenced by local hydrodynamics.

Conclusions:

• Local hydrodynamics significantly impact macroplastic transport dynamics within the Amazon urban estuarine system.
• The study provides crucial in-situ data for more accurate macroplastic transport estimations in the Amazon basin.
• Understanding these dynamics is vital for developing effective strategies to mitigate plastic pollution in marine environments.