En paleoekologisk och paleohydrologisk studie av fuktängar i Bräkneåns dalgång, Bräkne-Hoby, Blekinge

Sammanfattning: The objective of the present investigation was to study how climatic changes and human impact may have affected fluvial wetlands in a river system. There are few earlier investigations in Scandinavia of that kind. Palaeoecological and palaeohydrological investigations were carried out in two fluvial wetlands located in the valley of the river Bräkneån. The main site Björkeryd is situated somewhat below the highest coastline. The primary objective was to study the land use history and how this has affected the river. The palaeohydrological changes recorded in the wetlands were compared with the earlier reconstructed climatic lake-level changes in South Sweden. The sampling was made by use of a Russian chamber corer. The samples were analysed with respect to pollen, plant macrofossils, loss on ignition and magnetic susceptibility. The human impact started with grazing as late as 2300 BP. Around 1000 AD a more obvious change in the landscape began when the forest was cleared to increase the area used for grazing and cultivation. Swamp forests with alder were replaced by open, wet meadows. In the sediment this change is recorded by a distinct increase of the minerogenic content. This increase is found also at Örseryd somewhat further north in the river valley. But there the indications of human impact is missing, which means that the minerogenic increase must have been caused by a rise of the water level in the river, resulting in a flooding of the wetland. In the main the palaeohydrological changes found in the studied wetlands seem to agree with the general climatic lake- level changes established in South Sweden. Some occurring differences can be explained by conditions connected with the local river environment.