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@PHDTHESIS{Waldschlger:808605,
author = {Waldschläger, Kryss Lisanne},
othercontributors = {Schüttrumpf, Holger and Hollert, Henner},
title = {{T}ransport processes of microplastic particles in the
fluvial environment : erosion, transport and deposition},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2020-12172},
pages = {1 Online-Ressource (XVI, 174 Seiten) : Illustrationen,
Diagramme},
year = {2020},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2021; Dissertation, Rheinisch-Westfälische
Technische Hochschule Aachen, 2020},
abstract = {Microplastic enters the environment in different ways and
accumulates there due to the persistence of the material.
For a long time, microplastic was exclusively considered and
studied in the marine environment: From the first
environmental studies, to ecotoxicological studies with
marine organisms, to hydro-numeric models that were intended
to describe the distribution of microplastic in the seas and
oceans. However, studies have gradually concluded that most
of the microplastic is discharged into the oceans by land
and therefore by rivers, and the focus has widened to
include the fluvial environment. Initially, rivers were
considered to be only transport pathways for microplastic
from the land-based sources to the open sea. However, it
soon became clear that microplastic can also be retained and
deposited in rivers and that the concentrations in the
fluvial environment are as high asin some hot spots in the
marine environment. Due to the limited knowledge about the
transport behavior of microplastic in the aquatic
environment, the basics of classical sediment transport were
simply adapted to the properties of microplastic. However,
whether this transfer is appropriate was not examined. The
differences between microplastic and classic sediment are
undeniable: While sediment has an average density of 2.65
kg/cm³, microplastic can be both lighter and heavier than
water, but it is always significantly lighter than natural
sediment. Moreover, microplastic has very variable shapes,
so it can appear either as pellets or microbeads, but also
as fragments, fibers or films. Sediment, on the other hand,
consists mainly of granular grains. Finally, the different
trends of mean grain diameters along the course of the river
are also to be mentioned. While classical sediment is ground
smaller and smaller along the course of the river,
microplastic is introduced via numerous sources along the
course, so that no trend in grain sizes can be formed. Based
on these fundamentals, a transferability of the theoretical
principles from sediment transport must therefore at least
be questioned. Thus, in this thesis the behavior of
microplastic is compared with the theoretical calculations
from classical sediment transport by using physical model
experiments. The transport process is herein divided up into
erosion, sedimentation and rise as well as infiltration into
the river bed. A special focus was layed on the effects of
particle properties such as density, diameter and shape of
the microplastic on the transport mechanisms. The
sedimentation and rise behavior was examined by experiments
in a sedimentation column and thus the terminal settling and
rise velocities of different microplastic particles were
determined. These velocities could not be represented
sufficiently by the typical formulas from sediment transport
(e.g. Stokes settling formula), so that new theoretical
approaches based on the physical model experiments were
determined. The erosion behavior was investigated in the
annular flume of the IWW by applying single microplastic
particles to different sediment beds and then slowly
increasing the shear stress on the bottom of the channel
until the particle started to move. Based on these
experiments, the critical shear stresses of the different
microplastic particles were determined as a function of
their particle properties and the sediment bed and compared
with the calculation methods from classical sediment
transport, namely Shields diagram and hiding-exposure
effect. In the comparison it became clear that microplastic
moves earlier than determined by the theoretical approaches
so that a greater mobility of the microplastic than
previously thought is to be expected. Finally, new
approaches were developed todescribe the erosion behavior of
microplastic more accurately. For investigating the
infiltration behavior of microplastic into the river bed, an
infiltration column with glass spheres of different
diameters (1.5 - 11 mm) was used, on which water was evenly
sprinkled from above. Different microplastic particles were
applied to the surface of the glass spheres and then their
infiltration depth was determined as a function of their
shape, density, and size and the grain size of the glass
spheres. The subsequent comparison with the basic principles
of fine sediment infiltration showed that these could be
transferred so that on this basis the ideal sampling depth
of fluvial sediment could be determined. This work therefore
offers a first investigation of the transport mechanisms of
microplastic in the fluvial environment. When examinating
the transferability of theoretical principles from classical
sediment transport to microplastic transport, it became
clear that the application of these principles produces only
insufficient results. Therefore, new approaches were
developed, which can be used in the future for the
simulation of the transport behavior of microplastic.},
cin = {314410},
ddc = {624},
cid = {$I:(DE-82)314410_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2020-12172},
url = {https://publications.rwth-aachen.de/record/808605},
}
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