The Elbe River is one of the major rivers in Central Europe. It springs at an altitude of about 1,400 meters in the Giant Mountains in the north of the Czech Republic. It flows through eastern, middle, and northern Bohemia, and its catchment area includes most of Bohemia. The Elbe traverses the northeastern part of Germany and flows into the North Sea. The total river length is 1,094 km. In the Czech Republic, the monitored river length is 371 km and the catchment area includes 49,933 km2. The average flow at the Czech-German borders is 311 m3 s-1. Many weirs dam the watercourse of Elbe River in the Czech Republic. This artificial intervention is crucial for the characteristics of the riverbed, its width, depth, and bottom substrate. The width of the riverbed in the monitored area ranges from approx. 10 m on the upper course to approx. 150 m on the lower course and river sections above the weirs. The depth of the river varies from 0.5 m in the upper parts and below the weirs to more than 5 m in the lower course and above the weirs. The bottom substrate varies from the stony, gravelly, and sandy fractions in shallow and fast-running sections to muddy/silty fractions in slow-running sections above the weirs. The main tributaries of the Elbe in Bohemia are Metuje, Orlice, Jizera, Ploučnice, Vltava, Ohře and Bílina rivers. The catchment area is densely populated. The river is exposed to various sources of pollution (organic, agricultural, and industrial) and hydromorphological pressures (straightening, shortening, regulation of meanders, and fragmentation of river continuity). There are seven permanent monitoring sites on the Elbe River in the Czech Republic: Děčín (river kilometer 747.9), Litoměřice (796.9), Obříství (842.1), Lysá nad Labem (878.8), Valy (954.7), Hradec Králové (994.4) and Vestřev (1051). The Elbe basin long term environmental research has been organised by the Ministry of Environment of the Czech Republic and cooperation institutions since 1993. More than 600 physicochemical parameters, including sensory properties of water, are regularly monitored in at least nine different types of matrices (water, sediment, periphyton, floats, sedimentable floats, benthos, fish tissues, fish fry, and Dreissena polymorpha tissue) and using passive samplers. Among the main monitored characteristics belong balances of macroelements (carbon, nitrogen, oxygen, phosphorus), concentrations of inorganic salts, heavy metals and various organic pollutants such as pesticides, personal care products (including drugs) and other anthropogenic substances in the environment. Characteristics such as abundance and species composition are regularly monitored in fish, macrophytes, macrozoobenthos, phytobenthos and plankton.

How do freshwater ecosystems react to changing environmental conditions and to what extent can these changes be captured in the dynamics of eco-evolutionary processes? The project REES ('Rhine Eco-Evolutionary System') aims at the long-term assessment of eco-evolutionary interactions in the Rhine as a limnic habitat under consideration of diverse associated water bodies. The study area includes the main flow channel of the Rhine (km 845, North Rhine-Westphalia), as well as Rhine oxbows, Rhine water-fed gravel pit lakes in ecological succession and the surrounding floodplain (Rees, district of Kleve). The Ecological Research Station Rees-Grietherbusch of the Institute of Zoology (University of Cologne) and the Nature Conservation Center District Kleve e.V. form the central infrastructure of the study area. In addition, the Ecological Rhine Station of the University under the direction of Prof. Dr. Arndt is also associated to the project, which enables direct sampling and experimental recording of the main Rhine flow channel. The extensive system of standing and flowing freshwater bodies covered in the REES study site allows the investigation of dynamic variations in biodiversity composition at all levels, from species diversity of communities to genomic diversity at the molecular level of individuals and populations. Along a selected trophic cascade, representative species will be long-term observed and analyzed ecologically and especially also (population-)genomically. The incorporation of ecological genomics is the core aspect of this LTER-D project, which is intended to capture the feedback of evolutionary changes on the ecological system. Population genomic approaches can be used to infer both evolutionary and ecological processes from genomic data. To cope with the dimension of this project, REES is designed as an interdisciplinary collaboration project and currently counts seven project partners with corresponding subordinate projects.