Untersuchungen zur fluvialen Morphodynamik und zur rezenten Schadstoffausbreitung in Flusssystemen - Beispiele aus der Grenzregion Belgien, Niederlande und Deutschland
- Investigations on fluvial morphodynamics and recent pollutant dispersion in river systems - examples from the border region of Belgium, the Netherlands and Germany
Esser, Verena; Lehmkuhl, Frank (Thesis advisor); Schüttrumpf, Holger (Thesis advisor)
Aachen (2020, 2021)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020
The present thesis investigates the relationship between recent fluvial morphodynamics and pollutant dispersion in river systems. The subject is discussed based on the neighboring catchments of the rivers Geul, Wurm, and Inde. The catchments are located at the border triangle of Belgium, Netherlands and Germany, and have a similar size of approximately 325 km2 whilst the length of the rivers is about 55 km. This study area is representative of the transition zone between low mountain ranges and lowlands, and is amongst the oldest regions influenced by industry in Europe. Therefore, the existing pollution is not only originated from present-day sources, but also from the region’s past mining and other industries. The investigations are based on a comparison of the catchments by means of sediment analysis and the outcome of historical research, complemented by a comprehensive deep dive into the Inde catchment.The study region has a history of anthropogenic pollution of soil, water, and air. The Inde and Geul catchments were rich in ore which resulted in lead, zinc and iron mining, processing and subsequent slag dumping. The first evidence of mining dates back to the Pre-Roman age, whereas the zenith took place during the early industrial era and disappeared in the early 20th century. On the other hand, the Wurm catchment was rich in coal. Subsequent mining took place between the Early Middle Ages and the 20th century. The same applies to the Inde catchment between the 14th and 20th century. Mining activities led to the establishment of industry in the study area, especially related to iron, steel, and brass manufacturing. Other important industries were textile production as well as glass and needle factories. Until the late 18th century, the rivers were an important source of energy and therefore the location where these industrial activities took place. Moreover, rivers were used for the disposal of industrial and municipal wastewater as well as shaft water. Additional disposal occurred in the form of widespread dumps, which still partially exist nowadays. Another pollution source was air emissions from the industry, which had a considerable negative impact on the environment as in Stolberg and Eschweiler. All these factors led to an accumulation of various pollutants in the region which entered the fluvial systems, intensified by relocation processes. Since the 20th century, environmental regulations improved river management’s sustainability. However, a large number of past direct pollutant sources have been converted into diffuse secondary sources that still influence today's river systems. This is caused by the remobilization of contaminated floodplain or riverbed sediments. In addition, erosion of dump material, partially still active mine drainage, geogenic sources, and the current discharges by industries and settlements have an important impact. The sediment analysis is performed by measuring the pollutant elements which are characteristic of the study region. That is, chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), tin (Sn) and lead (Pb). Grain size, pH value, and color analysis are also used to complement the metrics. These markers are used to trace the transportation and spreading of pollutants, and correlate the results with the fluvial morphodynamics and historical developments. Multiple sampling campaigns were performed between 2016 and 2020. These included the collection of sediments out of floodplain, riverbed, and floodwater. Methods consisted of sediment extraction out of water and directly from the surface and deeper layers. The campaigns considered both flood events and dry weather seasons. The key findings of investigating pollutant dispersion caused by fluvial morphodynamics can be summarized as follows: Each river has its own geochemical “fingerprint”, which is characterized by different pollutant hotspots. Their comparison provides valuable information on pollutant sources and the geogenic background. While the Geul River shows particularly strong geochemical signals caused by Pb’s- and Zn’s- ore mining and smelting, the Inde catchment is characterized by strong contamination, which is in addition caused by sources from different industrial sectors. On the other hand, the impact of urban sources and various industrial sectors on the Wurm River is much more heterogeneous and less significant. The dispersion processes are controlled by secondary pollutant sources and flood events. Flood sediments differ in their levels of enrichment of trace elements. This is determined by spatial variations in the remobilization of sediments from the river sections with anthropogenically caused sources and from those that are geogenically influenced. River renaturation can influence the process in different ways. The activation of pollutant sources must be avoided. After 15 years, the new 12 km long river section of the Inde River shows detectable accumulations of various trace elements, which can be used as markers for the evaluation of natural morphodynamic processes and sediment connectivity. The secondary pollution sources, which are related to past mining and industrial areas, will continue affecting regions such as the study area, since a remediation of the affected fluvial systems is not realistic. Future changes in the frequency and amplitude of flood events, as a consequence of climate change, will lead to an increased mobilization of contaminated or non-contaminated sediment, depending on the catchment area.