Untersuchungen zu anthropogenen Einflüssen auf die fluviale Morphodynamik und die Verteilung erhöhter Spurenelementgehalte in kleinen Flusseinzugsgebieten: das Beispiel der Wurm, Flussgebietseinheit Maas

This thesis broaches the issue of the anthropogenic impact on fluvial morphodynamics and the distribution of elevated trace element contents in floodplain sediments of a low-order stream by the example of the Wurm River. The investigation period is 1810 to 2012, covering the early industrial to post-industrial eras. The Wurm River is a left tributary of the Rur River within the River Basin District Meuse. The catchment size covers an area of approximately 350 km²; stream length is approximately 57 km. The headwater is encompassed by the city of Aachen, an old industrial and heavily urbanized region, bearing a variety of sources for potentially toxic trace elements (PTE) that have emitted pollutants since the Middle Ages. By means of different case studies along the river, with a focus on the upper river course between the cities of Aachen and Herzogenrath, the elevated PTE contents in the floodplain sediments and along the river are utilized to reconstruct the pollution history. In combination with the investigation of the floodplain architecture, an assessment of the geomorphological and geochemical impact caused by human activities is achieved. In contrast to the straightened middle and lower river course, the upper reaches are in a near-natural state. Here, the impact on fluvial morphodynamics of the abandonment of historic water mills is evaluated by the example of the Adamsmühle near the city of Würselen. The pollution by elevated contents of Cu, Pb, and Zn, that are indicative for industrial processes and urban areas, is investigated on the basis of different bank profiles and core drillings, which were sampled for grain size and elemental analyses. Inflexion points in the vertical distribution of the pollution-sensitive PTEs and 137Cs are used to differentiate between pre-industrial, industrial and post-industrial periods. Planform changes of the river, changes of the channel geometry, the development of terraces and the effects of the former coal mining industry are examined on the basis of the recent digital elevation model, historical maps and documents, and also interviews with contemporary witnesses. The results show that the anthropogenic impact within the last 200 years expresses by a wide range of effects. Besides direct interventions like channel relocation and straightening, the indirect influences alter the longitudinal profile and channel geometry, cause terrace development and meander cut-offs and triggers channel incision and lateral erosion of the river banks. The inventory of PTEs is heterogenous along the river and in the floodplain, both on a vertical and horizontal level. The distribution of PTEs highly varies depending on the accretion processes, resulting in different pollution patterns in the upper and lower soil that reflect gradients from geogenic background contents to significantly polluted sediments