Universität zu Köln

Werner, Jennifer (2021). Retention Effects of Biofilms in the River Rhine. PhD thesis, Universität zu Köln.

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Abstract

The River Rhine is one of the most important navigation routes in Europe and has been affected by changes of the riverbed, in the form of canalization and straightening in the past. These changes have reduced and changed habitats for the river's flora and fauna, including the surfaces on which biofilms grow. Biofilms are found in all aquatic ecosystems and populate the contact layer between water and various substrates. These can be inorganic or organic substrates and are first colonized by bacteria, which initiate the formation of biofilms. The bacteria's excretion of extracellular polymeric substances (EPS) allows other organisms to attach to biofilms; in rivers, these are algae, flagellates, ciliates and various other organisms, which then feed on the biofilm and its inhabitants but also on the organisms and particles of the surrounding water. Biofilms as a habitat thus form a link between pelagic and benthic systems and therefore play an essential role in rivers. In a model study over a period of one year, the effect of biofilms and their organisms on the abundances of various pelagic organisms was investigated using the River Rhine at Cologne as an example for a large European river in the potamal region. The design of the experimental setup eliminated the influence of macrofauna, which was previously thought to have the most significant impact on the reduction of planktonic organisms in rivers. The biofilms reduced the bacterial abundance in the water flowing through by 22 - 63 % (47 % on average) and thus cleaned an average of 10.9 * 103 liters of water per square meter of biofilm per day of bacteria. In addition, the retention of phytoplankton was 30 % and of planktonic heterotrophic flagellates 26 % on an annual average, resulting in an elimination rate of 6.7 * 103 L m-2 d-1 for phytoplankton and 5.8 * 103 L m-2 d-1 for planktonic heterotrophic flagellates, respectively. Examinations of the biofilms revealed that especially peritrich and heterotrich ciliates were most likely responsible for reducing bacteria from the pelagic. Centric and pennate diatoms represented another significant component of the biofilm biovolume attaching to the biofilm from the pelagic of the River Rhine and promoting the complex three-dimensional structure of the biofilms. In a different part of the study, it was investigated whether the three-dimensional structure and the organisms of the biofilms can affect the retention or accumulation of microplastic particles and whether a transfer of microplastic particles via the food web to higher trophic levels is possible. The results of the experiments showd that biofilms had a significantly higher abundance of microplastic particles incorporated than other tested substrates, and up to 10,000 particles per square centimeter of biofilm could be embedded. Among the different size classes of microplastic particles tested (1 µm, 6 µm and 10 µm), the abundance in biofilms increased with the size of microplastic particles. Feeding experiments with the model ciliate Stentor coeruleus dominating in the River Rhine showed high rates of uptake for larger particles. Further, it was shown that ciliates containing microplastic particles were ingested by gammarids and fish larvae resulting in the transfer of microplastic particles up the food chain. The findings of the study highlight the role of biofilms in the river ecosystem. They serve as important sinks for bacteria (including pathogens). Further, they underline the necessity to preserve and enlarge surfaces for biofilm growth in river systems. On the other hand, microplastic particles can accumulate in biofilms, the consequences of this process still needs further investigations.

Item Type:	Thesis (PhD thesis)
Translated title:	Title Language Retentionseffekte von Biofilmen im Rhein German
Creators:	Creators Email ORCID ORCID Put Code Werner, Jennifer jennifer-werner@gmx.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-711365
Date:	2021
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Zoologisches Institut
Subjects:	Natural sciences and mathematics Life sciences
Uncontrolled Keywords:	Keywords Language Biofilms English Retention English River Rhine English
Date of oral exam:	28 January 2022
Referee:	Name Academic Title Arndt, Hartmut Prof. Dr. Borcherding, Jost Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/71136