The legacy of historic damming in Central European floodplains

在德国的一阶到三阶河流中，年龄未知的历史性水坝是一个普遍的特征。有人提出，由于森林砍伐和农业用地的使用，加速斜坡侵蚀是一些中欧洪泛平原恶化的原因，然而，这一过程只能解释向这些河流输送沉积物的原因。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，我们将确定人类对河谷底筑坝对河流景观的第一次影响的开始和程度，并研究其管理意义。泥沙淤积平原的广泛淤积是由大坝引起的流态变化引起的，从而导致河道由多线形向曲流渐变。这些洪泛平原的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，因为根据整个欧盟的水框架指令，这些水坝将被拆除。潜在地，这可能会导致大规模和持续的沉积物脉冲，因为遗留沉积物和富含碳的湿地土壤通过增加的河岸侵蚀被重新动员。因此，对可能被重新动员的沉积物进行量化是一项重要的知识，可用于支持对将受水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.