## 11 Special Issue \"Floodplains and Reservoirs as Sinks and Sources for Pollutants\"  
**[PERSON]**  
Faculty of Geography, Philipps-Universitat Marburg, D-35032 Marburg, Germany; [EMAIL_ADDRESS]  
Florodplain soils and reservoir sediments are known for their fine-grained structure and rich organic-matter substances; therefore, they are able to sorb metals and other potential pollutants, which is is characteristic of their sink function. Under changing environmental conditions, including climate change effects, such as changing water levels and redox conditions, and during reservoir rehabilitation measures, floodplain soils and reservoir sediments can also be sources of pollutants. This Special Issue aims to collect and present different research approaches and regional case studies from Kazakhstan, the USA, Germany, China, Iraq and Iran to show both the regularities and special peculiarities of such sink and source functions of floodplains and reservoirs, including one case of organic pollutants in the snow cover. A total of nine papers are presented in this Special Issue. [PERSON] et al. [1] identified both heavy metals and microplastics as pollutants in floodplain reservoirs and provided evidence for their special accumulation in the upper 50 cm of the floodplain soils, as well as their migration down to a 200 cm soil depth. [PERSON] et al. [2] reported that the transboundary (Kazakhstan-Russia) Ural River is heavily contaminated with polychlorinated biphenyls, heavy metals, oil contaminants, and pesticides, which also lead to an enrichment in these pollutants in the muscular tissues of fish. Petrolium hydrocarbon enrichments were proven by these authors both in the water of the northeastern Caspian Sea and in muscles of Caspian fish. [PERSON] et al. [3] determined element-specific enrichment factors for arsenic, chromium, vanadium, cadmium, manganese, nickel and zinc in the sediments of six reservoirs. The authors could prove the origin of these elements by leaching processes from catchment soils. [PERSON] and [PERSON] [4] show the catchment origin of pollutants in river sediments by other methods, analyzing different factors such as geology, dams, and land cover, vegetation, rock characteristics (contents of K\({}_{2}\)O, CaO, and SiO\({}_{2}\)) and reservoir drainage area on a basin scale using R.F. models. [PERSON] et al. [5] compared metal (loid) enrichments in two reservoirs with different mining histories and land use characteristics, including analyses of their tributaries and catchment soils. Based on the German Federal Soil Protection Ordinance, the status quo of the metal (loid) contamination of the two reservoirs was evaluated, and recommendations for further management and investigations were made. [PERSON] and [PERSON] [6] combined the revised universal soil loss equation (RUSLE) with remote sensing (RS) and a geographic information system (GIS) to construct a soil erosion hazard map of the Shat Al-Arab basin. Annual soil erosion rates in tons per hecrate were determined. The highest soil loss rates are associated with heavy rainfall, loamy soil predominance, elevated terrains/plateal borders with a steep side slope, and intensive farming. [PERSON] et al. [7] aimed to identify multi-metal distribution patterns in the Sacramento River floodplain, and found 484 significant correlations between metal distribution patterns. The most important factors were the distance to specific streams due to emissions, transport processes in their watersheds, and local soil properties. [PERSON] et al. [8] analyzed and evaluated the polychlorinated biphenyls (PCBs) contamination in snow cover in southeastern Kazakhstan during different winter periods. The snow cover pollution of the study area from up to 25 individual PCB congeners was identified. [PERSON] et al. [9]reported on the water-bottom sediment system of the Kapshagay Reservoir and visualized the processes of metal migration and accumulation within this system. This research received no external funding.