## 1 Introduction  
Reservoirs are increasingly used for energy and drinking water production worldwide. Only in Germany, are there 371 \"larger\" dams (defined by either a height \(\geq\) 15 m or a reservoir storage volume \(\geq\) 3,000,000 m\({}^{3}\)), the majority of which were built between 1900 and 2000 [1]. These reservoirs are mainly used for energy production and drinking water supply, and they are operated by private companies or federal states [2, 3]. In addition, several reservoirs are used to regulate the water level of rivers and thus represent important instruments for the operation of federal waterways [4]. Dam rehabilitation, sediment dredging from the reservoir bottom, and other measures that serve to maintain their functionality are necessary works [5] that have to be increasingly carried out in recent years since most of the reservoirs in Germany are older than 80-100 years [2].  
European regulations consider sediments as waste when they are removed from a waterbody [6]. Thus, dredged reservoir sediments have to be recycled or deposited in landfills. Due to continuous sedimentation and the increasing ages of dams, the utilization and disposal of reservoir sediments is a task of increasing importance beyond Germany, and beyond Europe [7, 8, 9]. Reservoir sediments characteristically act as a sink for contaminants [10]. This phenomenon can be explained by the fact that fine-grained, organic-rich sediments are capable of binding large amounts of potential contaminantssuch as metal(loid)s and reservoirs are the preferred deposition areas of such fine sediments within running water systems [11; 12]. Due to the high enrichment potential of metal(loid)s, dredged material from reservoirs often exceeds legal limits that must be met for recycling or landfilling [13; 14]. In Germany, for example, this concerns the precautionary values of the Federal Soil Protection Ordinance, which regulate the application to arable land [15] (Table S1).  
The enrichment of elements in reservoir sediments is mostly attributed to (historical) anthropogenic emissions that may result, for example, from atmospheric deposition, geogenic enrichments, historical mining, sewage water inlets, or the influence of further local point sources [16; 17; 18; 19; 20]. The long-term and continuous release of elements from catchment soils and their subsequent deposition in impoundments is usually less frequently considered as a factor of element enrichment in reservoir sediments. However, the fact that elevated concentrations of trace elements can also occur in reservoirs where an affection by geogenic enrichments, anthropogenic point sources, or atmospheric depositions is supposed to be very low [e.g., drinking water reservoirs] leads to the assumption, that significant amounts of metal(loid)s may be continuously transferred from catchments into reservoirs. The properties of catchment soils are expected to become increasingly important as a determinant of reservoir sediment quality, particularly in regions of retrogressive anthropogenic metal(loid) emissions. In order to prevent future management problems of the dredged material, it is crucial to find the connections between catchment soils and reservoir sediment quality.  
In this study, the fate of metal(loid)s in forest dominated catchments of German low mountain ranges was investigated. The aims of the study were to describe (1) to which concentrations metal(loid)s are present in representative reservoirs of German low mountain regions, (2) which elements are preferentially enriched in reservoir sediments, and (3) which soil and sediment properties decisively influence the element transfer originating from catchment soils.