The legacy of historic damming in Central European floodplains

历史悠久的大坝在德国的一至三级溪流中是一个普遍存在的特征，这些大坝的年代几乎不为人知。有人提出，由于砍伐森林和农业用地而加速的坡面侵蚀是一些中欧泛滥平原加剧的原因，但这一过程仅解释了泥沙向这些河流的输送。我们认为，谷底筑坝也是有效捕获这种增加的泥沙负荷的关键机制。在这项研究中，我们将确定人类由于谷底筑坝而对河流景观造成的第一次影响的开始和程度，并审查其管理含义。壤土泛滥平原的广泛淤积是由于大坝引起的流态变化而造成的，进而导致河道从多线程变为曲流型。这种洪泛平原壤土现在覆盖着古湿地土壤，这将形成一个有效的碳汇。这项研究的时机至关重要，因为根据欧盟各地的水框架指令，这些大坝将被拆除。潜在地，这可能会导致大量和持续的沉积物脉冲，因为遗留的沉积物和富含碳的湿地土壤通过增加的河岸侵蚀而被重新动员。因此，对可能被重新动员的沉积物进行量化是关键的知识，可用于支持将受到大坝拆除影响的河流的管理。

Historic dams of largely unknown age are a widespread feature within German 1st to 3rd order streams. It has been proposed that accelerated slope erosion due to deforestation and agricultural land use is the reason for the aggradation of some Central European floodplains, however this process only explains the delivery of sediment to these rivers. We propose that valley bottom damming was also a critical mechanism for the effective trapping of this increased sediment load. In this study we will determine the onset and magnitude of this first impact of humans on riverscapes as a result of valley bottom damming, and examine the management implications. The extensive sedimentation of loam floodplains was precipitated by dam induced changes to the flow regime, and in turn caused the channels to grade from multithread to meandering. This floodplain loam now blankets palaeo-wetland soils, which would have formed an efficient carbon sink. The timing of this study is paramount, given that these dams are due to be removed according to the Water Framework Directive throughout the EU. Potentially, this may lead to large and sustained sediment pulses as legacy sediments and carbon rich wetland soils are remobilised via increased bank erosion. The quantification of sediments that may potentially be remobilised is therefore critical knowledge that can be used to support the management of rivers that will be affected by dam-removal.