Variation in human activities has greatly impacted the processes and intensities of erosion, sediment transport and storage throughout the Late Holocene, and many lowland rivers around the world have responded to these variations. Although this long-term process–response relationship has been established before, the effects of short-term (c.200-year) changes in human impact on lowland rivers are less well studied. Here, we followed an integrated approach whereby observations of floodplain changes are evaluated against detailed data on human impact for three lowland rivers in the Belgian loess belt: Dijle, Mombeek and Gete rivers. Pollen data were used to reconstruct changes in local and regional vegetation and to calculate human impact scores. Corings along transects and a database of c.160 radiocarbon ages were used to reconstruct geomorphic changes in the river valleys. Our results show a decrease in human impact between 200 and 800 AD, which can be related to the decreased population density in Europe during the first millennium AD. During this period, forests in the studied catchments regenerated, soil erosion decreased, hillslope–floodplain connectivity decreased due to the regeneration of valley-side vegetation barriers, and sediment input in the floodplain decreased. A reaction to this decreased human impact can be observed in the river valleys during the first millennium AD, with a regrowth of the alder carr forest and an increase in the organic matter content of the alluvial deposits with a local reactivation of peat growth. The observed trajectories of Belgian river valleys during the first millennium AD provide more insight into the sensitivity of these river valleys to short-term variations in human impact. These results can in turn be used to better estimate the effects of future changes in the catchments on the fluvial system.

中文翻译：

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公元一千年比利时黄土带洪泛区地质生态变化

人类活动的变化极大地影响了整个晚全新世的侵蚀、沉积物运输和储存的过程和强度，世界各地的许多低地河流都对这些变化做出了反应。虽然这种长期的过程-反应关系以前已经建立，但短期（C。200 年）人类对低地河流影响的变化研究较少。在这里，我们采用了一种综合方法，根据比利时黄土带三条低地河流的人类影响详细数据评估洪泛区变化的观察结果：Dijle、Mombeek 和 Gete 河流。花粉数据用于重建当地和区域植被的变化并计算人类影响分数。沿样带取芯和数据库C。160 个放射性碳年龄被用来重建河谷的地貌变化。我们的研究结果显示，公元 200 年至 800 年间人类影响减少，这可能与公元第一个千年期间欧洲人口密度下降有关。在此期间，研究流域内的森林再生，水土流失减少，由于河谷侧植被屏障的更新，山坡与洪泛区的连通性降低，洪泛区的泥沙输入减少。在公元第一个千年期间，在河谷中可以观察到对这种人类影响减少的反应，桤木森林的再生和冲积沉积物中有机物含量的增加，以及当地泥炭生长的重新激活。在公元第一个千年期间观察到的比利时河谷轨迹提供了更多关于这些河谷对人类影响的短期变化的敏感性的见解。这些结果又可以用来更好地估计流域未来变化对河流系统的影响。