Eco-morphological changes and potential salmon habitat suitability since pre-industrial times in the Mulde River system (Germany)

Channel patterns and river connectivity are widely recognised to be representative parameters for the fluvial–geomorphological behaviour and the eco-morphological properties of rivers. They are sensitive to climate and land-use changes and, in turn, can indicate the habitat suitability for aquatic fauna, i.e. expressed by the diversity of channel width, flow velocity, and depositional regimes. Both habitat potential and the overall river connectivity since medieval times have also been influenced by barriers such as weirs and dams. Here we present the results of a multi-temporal study investigating river morphology, river connectivity, and floodplain land use in the Mulde River system. The study is motivated by the local extinction of the Atlantic salmon ( Salmo salar ) within the last 2 centuries and reintroduction endeavours that have met with very limited success. In order to test for salmon presence in relation to waterbody structures, we make use of old maps (Sächsische Meilenblätter, 1780–1821; Von Deckersche Quadratmeilenblätter, 1816–1821) to pinpoint (i) historical barriers and (ii) anthropogenic changes in channel patterns that may have affected migratory fish populations. Furthermore, we evaluate (iii) historical floodplain land use as a pollution proxy, presuming that this also influences salmon habitat suitability. Our initial results point to a negative relation between an increasing number of cumulative barriers, as well as increased floodplain land use, and the presence of salmon populations during past periods. Finally, sinuous and meandering channel patterns correspond to higher probabilities of salmon presence.