Wetlands and lakes formation and evolution on the Lower Danube Floodplain during Middle and Late Holocene

Abstract

River floodplains are amongst the most dynamic features which are continuously changing their shape and structure in relation to climate, vegetation, human pressure and base-level variability. In this study, we focus on the lower reach of Danube (upstream of its delta) and investigate the formation and transformations of wetlands and lakes during the last 8000 years using a multi-proxy methodology. We identified two main stages of floodplain landscape changes which are divided by a major shift in the regime of the most important controlling factor of this region which is the sea level. The transgressive stage covers the 8000-5500 BP period with sustained sea level rise (6-3 mm/yr) when floodplain dynamics acted to adapt to the ever-changing base level. Consequently, successive transitions between wet and dry conditions have been recorded as intertwined (thick) coarse-grained and (thinner) fine-grained sedimentary units. The latter stage (5500 BP - present) begins once with abrupt sea-level rise deceleration which fostered the expansion of persistent wetlands and lakes within meta-stable floodplain. The depositional evidence of this stage is composed of fine-grained sediments and peat. The transition between the two floodplain stages corresponds to the blooming phase of lakes, marshes and secondary channels which altogether persisted until the 20th century when during the communist period large floodplain areas were subject to drainage and desiccation works and their transformation into arable lands.