Concentration Depth Profiles of Microplastic Particles in River Flow and Implications for Surface Sampling.

Area of Science:

• Environmental Science
• Hydrology
• Oceanography

Background:

• Rivers are key pathways for microplastic pollution transfer from land to oceans.
• Current microplastic monitoring in rivers often uses surface sampling, leading to potential inaccuracies in estimating overall concentrations.

Purpose of the Study:

• To adapt the Rouse profile for microplastic transport, including low-density particles.
• To assess the uncertainty and bias associated with surface sampling for microplastic estimation.
• To propose improved methods for microplastic monitoring in rivers.

Main Methods:

• Adapted the Rouse profile to incorporate microplastic transport domains: bed load, settling suspended load, wash load, rising suspended load, and surface load.
• Applied the modified Rouse profile to model positively buoyant particle concentration depth profiles.
• Compared model predictions with field observations.
• Developed a procedure to quantify uncertainty and bias from surface sampling estimations.

Main Results:

• Microplastic transport in rivers encompasses more domains than previously considered, especially for low-density particles.
• Surface sampling can introduce significant uncertainty and bias in estimating depth-averaged microplastic concentrations.
• The modified Rouse profile effectively describes particle concentration depth profiles.

Conclusions:

• Rethinking microplastic transport models beyond traditional methods is crucial for accurate riverine pollution assessment.
• Depth-integrated sampling and characterizing concentration profiles are recommended for reliable microplastic monitoring.
• Quantifying sampling uncertainties is essential for robust environmental monitoring data.