The Morava River floodplain sediments – a signigicant archive of climate and human impact on landscape

The floodplain sediments of the Morava River deposited in the Strážnické Pomoraví area located in the Lower Moravian Basin have been recording the river history controlled by climate oscillations and human activities. History of erosions and accumulation events has been starting about 14 ka ago in the Late Glacial warm oscillation called Allerød Interstadial. This climate change followed the Last Glacial Maximum caused a permafrost thawing and precipitation rise. These processes triggered river discharge increase in the Morava River catchment. The river has been modified to the wide meandering channel. Analyses of pollen and diatom assemblages extracted from a paleomeander fill show that small lakes (similar like modern Alpine lakes) existed in the Morava River floodplain at the Allerød/Younger Dryas transition. Following climatic change at the glacial/interglacial transition increased the river erosion continuing in the Early Holocene (11.5−9 ka). The river channel has moved from the floodplain edges to its centre. The Holocene climatic optimum (9−5.5 ka) is characteristic by sediment accumulation in the Morava River floodplain. The river has been modified to the anastomous fluvial system with a channel net which is partly preserved and visible at present close the modern river channel. New climatically controlled river incision has started since the end of Subboreal (2.5 ka). The new created channel was filled by meandering river deposits exposed in the modern Morava River banks today. Fine overbank floodplain deposits including channel fills and point bar sequences dominate in this facies. About 70% of radiocarbon ages with the maximum between 11th and 17th century AD have obtained  from these deposits indicating an increase of landscape and river dynamics since the end of first millennium. The probable cause of this feature was a combination of climatic conditions (the end of the Medieval Warm Epoch and following Little Ice Age) and increased human activities in the river catchment. Forest clearance, pasture and agriculture have increased since 12th century AD as indicated by higher charcoal concentration in the floodplain deposits. An anthropogenic concentration of the Morava River to the one straighten channel in the early 20th century triggered a twice increased lateral erosion rate of the river meanders as documented by air-born photograph analyses.