Spatial and temporal variations of microplastic concentrations in Portland's freshwater ecosystems

Area of Science:

• Environmental Science
• Ecotoxicology
• Urban Hydrology

Background:

• Microplastics are a growing environmental concern, yet their sources and transport in urban rivers remain understudied.
• Understanding microplastic pathways is crucial for effective pollution management in aquatic ecosystems.

Purpose of the Study:

• To investigate the relationship between microplastic concentrations and spatiotemporal factors in urban rivers.
• To identify key drivers influencing microplastic pollution in two watersheds along an urban-rural gradient in Portland.

Main Methods:

• Collected microplastic samples in August, September, and February across two watersheds.
• Analyzed microplastic count, type, and size distribution.
• Utilized nonparametric statistics to correlate microplastic levels with land use, road length, water velocity, and precipitation.

Main Results:

• Microplastic concentrations were significantly higher in August than February, correlating negatively with flow rate.
• Smaller microplastic particles (<100 μm) were more prevalent in August, while larger particles dominated in February.
• Near-stream variables, such as agricultural land use during the wet season, showed stronger correlations with microplastic concentrations than subwatershed-scale factors.

Conclusions:

• Lower flow rates facilitate microplastic accumulation in urban rivers.
• Near-stream environmental characteristics play a more significant role in microplastic pollution than broader watershed attributes.
• Findings can inform targeted management strategies and identify pollution hotspots for remediation.