Abstract
Colloids exist widely in rivers which can act as contaminants or carries
of contaminants. Hyporheic exchange drives colloids to transport into
the hyporheic zone. However, the variation of the particle size of
colloids has seldom been considered in previous transport theories of
colloids. This study aims to investigate the variation of the particle
size of colloids and functions for different sized particles via
laboratory experiments and simulations. The results show that the
settlement and convection-diffusion of colloids play a dominant role in
the exchange of colloidal particles between the stream and the
streambed. Large particles can settle into the streambed more rapidly as
settlement domains the process, which however can hardly be detected in
the overlying water during the later period of the experiment; the
exchange process of small-sized particles is affected more by convection
and diffusion, and a retarded trace release can be monitored from the
streambed to the stream; while for middle-sized particles, mass transfer
coefficient and settling velocity affect exchange process together.
Because the variation of particle size (affecting specific surface area,
surface electrochemical characteristics) can have a substantial effect
on the contaminants carriers (colloids) in the hyporheic zone, the
knowledge of it should be taken into account in future studies.