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1 2006

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Zmiany żyzności trofii w ekosystemach miękkowodnych jezior Borów Tucholskich

Milecka K., Bogaczewicz-Adamczak B.

Przegląd Geologiczny

2006

Vol. 54, nr 1

81-86

Soft water lakes are mostly acid, poor in minerals and have a lot of free CO2 in their water and bottom sediments. So called Lobelia lakes, containing Lobelia dortmanna L., Isoëtes lacustris L., and Littorella uniflora (L.) Ascherson, are a type of soft water lakes. These species are rare in Poland and in Europe mainly because of eutrophication and anthropopression. Lobelia lakes and ecology of isoetids were described in many scientific articles, but their history is poorly recognised. Thus, for some years palaeoecological research has been done in the Tuchola Pinewoods to reveal the time of migration, spreading and development of Lobelia lakes. Pollen analysis and diatom analysis were done for the sediments of lakes: Nierybno, Okoń Duży, Linowskie, Moczadło and Nawionek (Fig. 1). Content of plant remains of Lobelia dortmanna nad Isoëtes lacustris, fossil diatoms and Pediastrum indicates phases of low and high trophy of Lake Nierybno (Fig. 5). The highest trophy was found in the Younger Dryas, in the middle Boreal Period and the oldest time of Subboreal Period. The lowest trophy was observed at the beginning of the Holocene, in the Atlantic Period and in modern times. Low trophy of the lake is related to acid or neutral pH of the water. Reconstruction of the lake history based on diatom analysis shows two main phases of the Nierybno ecosystem existence. In the early stages of the lake’s development it was an eutrophic basin with elevated pH. At the beginning of the Atlantic Period the pH decreased and content of nutrients in the water was reduced. Navicula radiosa, N. leptostriata and N. heimansioides, species typical for Lobelia lakes have been present since then. Generally Lobelia lakes are well preserved in the Tuchola Pinewoods due to low anthropopression and conservation activity of the Tuchola Pinewoods National Park and the Zaborski Landscape Park.