Vol. 144, No. 1 · Research article Quantification and dating of floodplain sedimentation in a DIE ERDE Journal of the medium-sized catchment of the Geographical Society of Berlin German uplands: a case study from the Aar Valley in the southern Rhenish Massif, Germany Christian Stolz1, Jörg Grunert2, Alexander Fülling3 1 Interdisziplinäres Institut für Umwelt-, Sozial- und Humanwissenschaften, Abteilung Geographie, Universität Flensburg, Auf dem Campus 1, 24943 Flensburg, Germany, [email protected] 2 Geographisches Institut, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany, [email protected] 3 Geographisches Institut, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany, alexander. [email protected] Manuscript submitted: 23 May 2011 / Accepted for publication: 12 April 2012 / Published online: 2 September 2013 Abstract The distribution, thickness and composition of the floodplain sediments in the valleys of the Aar and its tributaries (Taunus Mountains) were investigated by way of extensive fieldwork at 25 locations. In the entire catchment area, 48.8 million tons of loamy floodplain fines could be assessed. Most of these were deposited since late medieval times due to extensive historical land use and forest clearing, especially in the mining region along the middle course of the Aar. In its lower course, the enhanced sedimentation of loamy floodplain sediments started during the Bronze Age. Zusammenfassung Die Verteilung, Mächtigkeit und Zusammensetzung der Auelehme in den Tälern der Aar und ihrer Neben- flüsse wurden im Rahmen ausgedehnter Geländearbeiten an 25 Standorten untersucht. Im gesamten Ein- zugsgebiet der Aar konnten insgesamt 48,8 Mill. t Auelehm erfasst werden. Der Großteil davon wurde seit dem Spätmittelalter als Folge der historischen Landnutzung und Entwaldung, insbesondere im Berg- baugebiet am Mittellauf der Aar, sedimentiert. Im Unterlauf der Aar begann die verstärkte Sedimentation von Auelehm bereits in der Bronzezeit. Keywords Alluvial sediments; dating and budgeting; Taunus Mountains; Aar River; mining region Stolz, Christian, Jörg Grunert and Alexander Fülling of the German uplands: a case study from the Aar Valley in the southern Rhenish Massif, Germany – DIE ERDE 144 (1): 30-50 : Quantification and dating of floodplain sedimentation in a medium-sized catchment DOI: 10.12854/erde-144-3 30 DIE ERDE · Vol. 144 · 1/2013 a case study from the Aar Valley in the southern Rhenish Massif, Germany Quantification and dating of floodplain sedimentation in a medium-sized catchment of the German uplands: 1. Introduction (Oberpfalz, eastern Bavaria), Raab et al. (2010) de- - 1.1 The formation and characteristics of floodplain mer mining, deforestation and iron smelting when sediments theytected found historical respective overbank contamination fines as the resultwith ofheavy for metals. The situation in the Vils area is similar to that in the Aar catchment. Furthermore, recent stud- ies and reviews in various Central European regions The deposition of loamy overbank fines results from have rendered similar results (Stolz et al. 2012, Stolz aphases catchment with (cf.accelerated Hoffmann fluvial et al. activity,2010). Along in reaction larger 2011a, Stolz 2011b, Stolz and Grunert 2010, Hoffmann to either climatic or land-use related influences to et al. 2010, 2008, 2007, De Moor and Verstraeten 2008, Houben et al. 2006, Klimek et al. 2006, Coulthard et al. clearlyrivers, evidencedclimatically (Schirmer caused etEarly al. 2005). and Mid-HoloceneRepeated dis- 2002, Heusch et al. 1996, Pörtge and Molde 1989). As placementfloodplain ofdeposition river branches and erosionwith lateral phases deposition could beof not every single event which triggered soil erosion coarse levee sediments and the horizontal deposition colluvia deposits on the slopes may be used instead (cf.can Borkbe evidenced and Kranz by 2008).floodplain Niller profiles, (2001) in evidenced many cases in of silty overbank fines caused the formation of several the Kleine Laber catchment (eastern Bavaria) that the Holocene river terraces which can be identifiedMäckel in1969, the - middlefield as Lahnsmall River).steps. However,Within smaller these maycatchments be covered the horizontaland leveled sedimentationby younger overbank predominates, fines ( but sand- comparedHolocene colluvium the sequence could of beseveral much serially older than connected the al sedimentluvial deposits stores within with a the system same of fluvial cascades. catchment. He as well. In many catchments, 2-3 superimposed gen- and gravel-filled palaeochannels can be evidencedBrosche 1984; Neumeister 1964). 1.3 Open questions and approaches erations of overbank fines were proven (e.g. 1.2 Triggering of soil erosion by deforestation and Aar and its tributaries in detail. The main focus is on iron industries theThis genesis study investigates and the age ofthe these loamy sediments overbank of fines potential of the- ly anthropogenic origin, which leads to the following In the catchment of the Aar River (Taunus Mountains) questions: When did the sedimentation start, and dur- excessive soil erosion as a result of various kinds of ing which periods was it most effective? What were the land use was a major problem of the past. This was main triggering factors, anthropogenic or natural, and predominantly caused by the strong deforestation how effective was the impact of the local iron industry? for iron smelting in the local ironworks of Michelbach sections, and how strong was the preceded soil erosion small, decentralised iron-smelting works which exist- How much sediment was accumulated in different river ed(since before. 1656 Particularly AD; Michelbacher on the Hütte)slopes andin the in numerouswide mid- plain sediments can be distinguished and, moreover, dle reaches of the Aar, gullies up to 10 m deep, young arein the they catchment? visible as lowFurthermore, terraces? which types of flood- alluvial fans and colluvial layers are widespread (Stolz 2008, Stolz and Grunert 2006). Regarding these facts, Reliable written sources about phases of sedimenta- the considerable thickness of up to 5.5 m of the loamy tion in the Aar area do not exist. Therefore, we used Auelehm primarily radiocarbon datings of plant residues em- isand not gravel-free surprising, overbank however, fines it is ( distinctly, flood above-av loam)- completed by Optically Stimulated Luminescence eragein the whenfloodplains compared of the with Aar otherRiver riverand its systems. tributaries The (OSL)bedded datings. in the Morefines. reliable Furthermore, datings these could results be obtained were in combination with historical reports such as the of the widespread loess-rich periglacial cover-beds in thelarge catchment amount of (cf. fines Semmel can be1968). explained by the erosion it was possible to involve pond sediments and histori- specific land use of an area at a given time. InStolz one caseand In eastern Belgium, the early modern iron industry Grunert describedcal slag deposits and discussed in the Aar regarding floodplain their (cf. formation iron slag (Gautier et al. 2009). In the Vils catchment and human 2008). impact. Typical Based profiles on this of the knowledge, floodplains it was are triggered the formation of overbank fines containing DIE ERDE · Vol. 144 · 1/2013 31 a case study from the Aar Valley in the southern Rhenish Massif, Germany Quantification and dating of floodplain sedimentation in a medium-sized catchment of the German uplands: Tab. 1: The beginning of anthropogenically affected floodplain deposition in various parts of Germany Catch- Earliest No. Region River Dating methods Authors ment deposition Basin of Leipzig Radiocarbon, 1 Weiße Elster Saale 3000 BC Tinnap et al. 2008 (Saxony) archeological Leine Hills Older 2 Leine Weser Pollen Pretsch 1994 (Lower Saxony) Subboreal Weser Hills Younger 3 Upper Weser Weser Pollen, radiocarbon Thomas 1993 (Lower Saxony) Subboreal Black Forest Mts. Dreisam, Basin Upper Mäckel and 4 1500 BC Radiocarbon (Baden-Württemberg) of Zarten Rhein Friedmann 1999 Palatinate Forest 5 Schwarzbach Saar 1300 BC Radiocarbon Stolz 2011b (Rhineland-Palatinate) Lower Bavaria 6 Vils Donau 1200 BC Radiocarbon Raab et al. 2005 (Bavaria) Lower Bavaria 7 Kleine Laaber Donau 500 BC Radiocarbon Niller 2001 (Bavaria) Wetterau Basin Lang and Nolte 8 Wetter Main 250 BC IRSL (Hesse) 1999 Franconian Switzerland 9 Aufsess Main 400 BC OSL Fuchs et al. 2010 (Bavaria) Marburg/Gießen area Younger Iron Radiocarbon, 10 Lahn Rhein Urz 2003 (Hesse) Age archaeological Alpine Foothills 11 Lech Donau 100-400 AD Archaeological Dietz 1968 (Bavaria) Lower Westerwald Mts. 12 Gelbach Lahn 400 AD Radiocarbon Stolz 2011a (Rhineland-Palatinate) Solling Mts. 700 AD (at 13 Ilme Weser Pollen, radiocarbon Rother 1989 (Lower Saxony) the latest) Volcanic Eifel Mts. 700 AD (at Radiocarbon, 14 Lieser Mosel Stolz et al. 2012 (Rhineland-Palatinate) the latest) archeological, OSL Wetterau Basin 15 Wetter Main 850 AD Radiocarbon Houben 2002 (Hesse) High Westerwald Mts. Radiocarbon, 16 Große Nister Sieg 900 AD Stolz 2011a (Rhineland-Palatinate) archeological possible to calculate the total amount of overbank with the knowledge about two streams in the Wester- wald Mountains and one in the Palatinate Forest. stated in tons and in cubic metres (see Sections 5 and 6).fines Moreover, stored inthe the results Aar catchment.from the Aar The will results be quan are- 2. State of research catchment, knowing that we cannot make any clear statementtified