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Plant replacement trend in soft-water lakes with isoetids

Ronowski Rafał P., Banaś Krzysztof, Merdalski Marek, Szmeja Józef

Oceanological and Hydrobiological Studies

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2020

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Vol. 49, No. 2

157--167

EN

A number of small, shallow inland lakes in the Northern Hemisphere are acidic, soft-water water bodies, mostly fed by precipitation. Some of these lakes are home to Lobelia dortmanna and other aquatic macrophytes from the isoetid group. The present study identifies a plant species replacement trend along the main environmental gradient in such lakes, i.e. pH of water. In 70 lakes covered by the study and ordered along the gradient of increasing alkalinity, bryophytes gradually decline. Their decreasing frequency is 86.8% (pH 4.0), 32.5% (pH 6.5) and <10% (pH 6.6–9.5). At the same time, the frequency of vascular plants increases from 13.2% in strongly acidic lakes up to 92.8% in alkaline ones. The majority of isoetids usually occur at pH 5.5–6.7, but one of them (Littorella uniflora) often (frequency 40.5%) occurs also in eutrophic, alkaline lakes (pH 9.0–9.5), where it forms large populations. In lakes ranked according to the decreasing alkalinity gradient, bryophyte populations have been found to be smaller, while vascular plants become more abundant. The decreasing water acidity leads to partial or total elimination of bryophytes, which are replaced by eutrophilic vascular plants, frequently accompanied by some stonewort species.

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Zmiany żyzności trofii w ekosystemach miękkowodnych jezior Borów Tucholskich

Milecka K., Bogaczewicz-Adamczak B.

Przegląd Geologiczny

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2006

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Vol. 54, nr 1

81-86

EN

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.

3

Changes in the vegetation of softwater lakes under the influence of humic substances

Bociąg K., Szmeja J.

Polish Journal of Ecology

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2001

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Vol. 49, nr 4

319-326

EN

The effect of dissolved allochthonous humic substances (aDHS) on submerged aquatic vegetation was studied in softwater lakes. It has been found that with increasing aDHS (in the range of concentrations 1.2 to 20.6 mg C dm^-3) the number of macrophyte species decreases (from 17 to 1), the biomass is reduced considerably (86--> 0 g dw m^-2), especially the biomass of the dominants, and the Shannon-Weaver index changes (up to the concentrations of 4.5 mg C dm^-3 the index increases and then decreases). Population areas become increasingly narrow and shifted towards shallow littoral sites. Plant degeneration begins in deep-water sectors. It is not connected with the appearance of new dominants, and leads on to the elimination of all plants from a lake.