Interplay between flow and bioturbation enhances metal efflux from low-permeability sediments

Area of Science:

• Environmental Science
• Marine Biology
• Geochemistry

Background:

• Assessing contaminated sediments requires understanding the complex interactions between hydrodynamic forcing, sediment resuspension, and bioturbation.
• Bioturbation, the disturbance of sediments by living organisms, can significantly alter sediment properties and contaminant mobility.
• Copper (Cu) is a common contaminant in marine environments, and its release from sediments is a major environmental concern.

Purpose of the Study:

• To evaluate the independent and combined effects of hydrodynamic forcing, sediment resuspension, and bioturbation by Nereis virens on dissolved copper efflux.
• To investigate how bioturbation by Nereis virens alters sediment stability and susceptibility to resuspension under varying hydrodynamic conditions.
• To quantify the enhancement of copper release due to the interplay between fluid shear and bioturbation in low-permeability sediments.

Main Methods:

• A six-month flume experiment was conducted to simulate environmental conditions.
• Hydrodynamic forcing was applied at various shear stresses (0.11-0.58 Pa).
• The presence and absence of the marine polychaete Nereis virens were tested to assess bioturbation effects, alongside sediment resuspension dynamics.

Main Results:

• Hydrodynamic forcing alone slightly increased dissolved copper efflux.
• Sediment resuspension released considerable amounts of dissolved copper.
• Bioturbation by Nereis virens destabilized the sediment bed, leading to resuspension under all tested shear stresses.
• Interactions between hydrodynamics and worm burrowing significantly enhanced copper efflux, with Cu efflux being 360x and 15x greater at 0.47 Pa and 0.58 Pa, respectively, after worm introduction compared to no-worm conditions.
• Increases in fluid shear following bioturbation caused rapid releases of dissolved copper within hours.

Conclusions:

• Bioturbation by Nereis virens plays a critical role in enhancing the release of dissolved copper from contaminated sediments.
• The interaction between hydrodynamic forces and bioturbation dramatically increases contaminant efflux, particularly in low-permeability sediments.
• Understanding these combined processes is crucial for accurate risk assessment and management of contaminated marine sediments.