Christian Stolz

Budgeting soil erosion from floodplain sediments of the central Rhenish Slate Mountains (Westerwald), Germany

The distribution, thickness and composition of the floodplain sediments in the valleys of the Gelbach (Lower Westerwald) and Große Nister (Upper Westerwald) depend on the occurrence of loessic periglacial cover beds in their catchments as well as on historical land use. The budget of floodplain sedimentation was derived from a study of the floodloams underlying the monastery garden of Marienstatt, a village in the Große Nister valley. From the study of two occupation levels, pottery shards and radiocarbon dating, 55% of the floodloam can be attributed to the Modern period (younger than c. AD 1450). From the radiocarbon age of a charcoal fragment extracted from the base of the floodloam at another site in the Nister valley, it can be concluded that the floodloams were almost exclusively deposited by human impact since the time of High Medieval expansion of settlement into the Uplands. The fine-grained loamy sediments blanket a rather irregular floodplain of channels and gravel bars. Similar results as to the age of the floodplain sediments were obtained from radiocarbon datings obtained for the Gelbach valley. Floodloam sediment budgets of the rivers and their tributaries have been calculated for the Große Nister and the Gelbach valleys of the Westerwald and, for including a catchment of higher sedimentation, the Aar River of the Taunus Mountains, followed by a comparative analysis of the results in relation to potential erosion areas in the catchment. The amount of areal soil erosion in upland areas in historical times has been found to be considerably higher than generally assumed. Average amounts of anthropogenic soil erosion could thus be calculated from the floodloam deposition: 1677.4 t/ha for the Aar catchment, 1084.5 t/ha for the Gelbach catchment, and 841.8 t/ha for that of the Nister. The calculated total amount of soil erosion is then subdivided by periods.

The formation of alluvial fans and young floodplain deposits in the Lieser catchment, Eifel Mountains, western German Uplands: A study of soil erosion budgeting

This study deals with the exploration and spatiotemporal quantification of the young Holocene, nearly skeleton-free floodplain sediments of the Lieser River, a tributary of the Mosel River in the Eifel Mts. The deposits are primarily a consequence of anthropogenic-triggered soil erosion in the catchment. To observe the phenomenon of corresponding soil erosion on multiple levels two small alluvial fans of tributary catchments were investigated. For comparison, one location in the neighboring Salm valley was described. The results were compared with those of other streams. With extensive fieldwork more than 100 drillings and pits were made at 12 locations. For dating the sediments OSL dating, 14C dating of organic contents and archaeological artifacts were used. In the floodplains of the Lieser and its tributaries, 35.1 × 106 t of overbank fines are stored. To achieve this, an average soil erosion of 61.4 mm in the whole catchment would have been necessary. About 28% of young floodplain sediments in upper and lower course were deposited before ad 1000. However, prehistoric deposits could not be positively proven. Only 18% of floodplain sediments were deposited between ad 1000 and 1320 (early and high Middle Ages) and 54% during late Middle Ages and early Modern Time (ad 1320–1850), respectively. The thickness of floodplain sediments is mostly independent of the valley gradient. The largest sediment thickness (> 5 m) was found by drilling in the upper reaches. However, a part of this could be dated to the early Holocene. In the narrow middle reaches, the maximum thickness of the skeleton-free deposits was only 1.2–2 m. The average thickness of the floodplain sediments rose again in the depression of Wittlich up to 2.4 m. The formation of the investigated small fans was quite different. Sedimentation occurred within limited periods as a result of single events.

Reconstructing fluvial, lacustrine and aeolian process dynamics in Western Mongolia

At the eastern rim of the Mongol Els, the largest dune field of Mongolia, the rivers Shurgyn Gol and Zavkhan Gol converge and form a flood plain at the dune front. Interfingering fluvio-lacustrine and aeolian sediments are found in different spatial contexts in the area. By investigating the chronostratigraphy of these sediments, valuable information can be derived for the reconstruction of geomorphological processes and forcing-response relations in the past. The flood plain is locally covered by lacustrine sediments representing an Early to Mid-Holocene lake only a few meters deep. This can be deduced from several 14C and OSL dates and tachymetric measurements, and is in accordance with high stands of other lakes in Western Mongolia. Relics of a lake sediment on top of an old dune 17 m above the floodplain have been OSL-dated to 114 10, 119 10, and 127 10 ka, indicative of an Eemian age. At that time a large and deep lake must have covered the plain. There is evidence of two causes of lake formation: increased discharge of the rivers due to increased precipitation in the mountainous catchment areas and, at the same time, ponding of the rivers by strong dune advance due to persistingly arid conditions in the foreland. The transition phase to more humid con ditions, together with a relatively high humidity gradient, appears to have been morphodynamically very efficient. No evidence could be found of the assumed modern climate change. Recent reduction of the sparse grass cover of the region reflects overgrazing, and the reduction of river discharge is due to water-consuming irrigation.