Experimental studies on the effects of exopolymers on the settling dynamics and interactions between solid particles in density-stratified aquatic systems

The project addresses the problem of particle settling in a column of saltwater with vertical variation of density and rheological properties. Such conditions may occur in stratified seas during algal blooms. Algae and cyanobacteria secrete extracellular polymeric substances (EPSs), also known as exopolymers, which locally change the rheological properties of seawater turning it into non-Newtonian liquid. Biologically-modified rheology of seawater affects settling dynamics of marine particles such as minerals, marine snow, faecal pellets and microplastics.

The aim of the project is to assess how EPSs modify rheological properties of saltwater and how the content of EPSs and salinity affect the settling dynamics of individual particles and interactions between particles in a density-stratified aquatic environment.
The aim of this project is achieved by laboratory research – settling experiments and rheology analyses. Rheological measurements show that model polymers induce shear-thinning and viscoelastic properties of seawater. A series of small-scale settling experiments is conducted in homogeneous saltwater with EPS and in a two-layered configuration to address settling through a pycnocline. Settling of model particles is examined by visualisation and image analysis methods and the results are analysed along with the rheological data.

The results of the project will advance our understanding of fundamental settling processes significant to the development of research on small-scale physics of the ocean and sedimentation in a macroscale.

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