Current state and vegetation history of spring-fed fens in Western Pomerania (Northern Poland): a case study of the Chociel River valley

Alkaline spring-fed fens are a rare type of soligeneous wetlands, characterised by an alternating arrangement of layers of peat and calcareous tufa, defined as the peat-tufa rhythmite. They are known, for example, from the strongly undulating young glacial landscapes of Central Europe, where many of them are protected by law. These include sites located in the Chociel River valley, in Western Pomerania (Northern Poland). One such spring-fed fen (Bobolice site) was investigated in detail using multiple methods (phytosociological, plant macrofossils, sedimentological and geochemical) for the current state of vegetation, reconstruction of its long-term development and, eventually, the identification of management strategies for its effective protection. Six developmental phases reflecting changes in the natural environment at the end of the Late Glacial and in the Holocene, as well as changes caused by human impacts in recent centuries, were identified for the investigated site. In the past, the dominant role in the formation of the spring-fed fen was attributed to sedge and sedge-moss communities, also with an admixture of Sphagnum in the last phase of the fen’s development. For about 300 years increased human activity has been recorded in the Chociel Valley, resulting in a modification of the water regime and a strong transformation of vegetation. Today, the real vegetation is therefore the result of both the presence of various mire habitats and various types of agricultural use. The current state of spring-fed fens in the Chociel River valley points to the urgent need for the implementation of various active protection measures.