## 5 Conclusions  
The enrichments of As, Cd, Cr, Mn, Ni, Pb, V, and Zn confirm the sink function of reservoir sediments (RS) for potential contaminants. In addition, the comparison of RS, catchment soils (CS), and stream sediments (SS) indicates differences in the enrichment tendencies of individual metal(loid)s. Depending on a specific element, the enrichment can be influenced to varying degrees by grain sorting, the input of organic detritus, and a release from the soils by leaching processes. In particular, reservoirs impounding relatively small water bodies with forested catchments are expected to be enriched by Cd, Mn, Ni, and Zn in RS and sediments of their inlets. On the one hand, the element release from CS is supposed to be particularly intensive in small water bodies due to a relatively high contact area between water and channel bed. On the other hand, the catchment areas of drinking water reservoirs usually have high proportions of forested areas, where under humid climatic conditions and poorly acid-buffering parent rocks a majority of acidified CS may enlarge the release of elements to running water. Impoundments of larger water bodies should be much less affected by this process. Investigations of the mobilizable element fractions in the field-fresh RS show that, with the exception of Mn, no relevant negative influence on the element concentrations of the water column can be assumed from the sediments. In the case of the investigated reservoirs, a deterioration in drinking water quality due to metal enrichments is not to be assumed as long as the bottom sediments remain undisturbed and covered by the water column. However, the apparently quite significant proportions of enriched metals that enter RS from CS due to leaching processes lead to the assumption that the enrichment of potential contaminants in RS will continue in the future, even if metal(loid) emissions from point sources are further reduced. Due to the increasing need for renovation resulting from the increasing age of reservoirs, the management of RS will be a future challenge, for which sufficient options of landfilling and recycling must be provided. For dam operators, synergy effects could arise if these options are developed together with other service providers involved in the management of dredged material, such as watercourse maintenance facilities. The following are available online at [[https://www.mdpi.com/article/10.3390/app12052277/s1](https://www.mdpi.com/article/10.3390/app12052277/s1)]([https://www.mdpi.com/article/10.3390/app12052277/s1](https://www.mdpi.com/article/10.3390/app12052277/s1)), Table S1. Precationary values according to the German Federal Soil Protection Ordinance (mg kg\({}^{-1}\)). Table S2. Rotated component matrix of the three analyzed components. Table S3. Percentage of easily extractable trace metal concentrations on the aqua regia soluble concentrations of air-dried reservoir sediments (RS). Table S4. The element-specific enrichment factors (EF) of reservoirs with different catchment sizes. Conceptualization, J.H. and C.O. ; methodology, J.H. and C.O; sample acquisition T.B., M.K., T.B., J.H., C.J.W., C.O. ; chemical analyses J.H., T.B., M.K., A.M.; grain size analysis M.T. ; element analyses, data validation, software, J.H. ; writing--original draft preparation, J.H., C.O., C.J.W. ; writing--review and editing, J.H., C.O., C.J.W. All authors have read and agreed to the published version of the manuscript. We thank the Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Production for funding the costs necessary to publish this article. Not applicable. The data presented in this study are available on request from the corresponding author. Our sincere thanks go to the operators of the investigated dams (Wasserverband Siegen-Wittgenstein; Wasserzweckverband Landkreis Birkenfeld, Landestalsperrenverwaltung Sachsen) for enabling and supporting the sampling campaigns.