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The disappearance of stonewort populations in lobelia lakes of the Kashubian Lakeland (NW Poland)

Bociąg K., Rekowska E., Banaś K.

Oceanological and Hydrobiological Studies

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2011

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Vol. 40, No.2

30-36

EN

The subject of this work is a comparative analysis of stonewort populations in 5 lobelia lakes of the Kashubian Lakeland based on literature data from the mid-1970s and the authors' own studies from 2006. In the 1970s 15 sites of 7 stonewort species: Chara delicatula, C. fragilis, C. tomentosa, C. rudis, Nitella flexilis, N. opaca and N. mucronata were recorded in the lakes under study. The populations of C. delicatula and N. flexilis occupied the area from 0.3 to 6 m deep and were characterized by 20% cover on average. Thirty years later, in 2006, the presence of only 6 out of 15 stands was confirmed: 3 of C. delicatula and 3 of N. flexilis. Thus, a total of 9 stands (60%) and 5 species (71%) had disappeared completely. The majority of the preserved populations survived in a vestigial form. Population areas of C. delicatula reached a depth of 2 m and their cover did not exceed 5%. Populations of N. flexilis occupied the littoral up to a depth of 7 m and had 10% cover. The disappearance of stoneworts was probably caused by both anthropogenic factors and natural processes.

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Effect of light competition with filamentous algae on the population dynamics and development of the moss species Warnstorfia exannulata in a softwater lake

Szmeja J., Bociąg K., Merdalski M.

Polish Journal of Ecology

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2010

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Vol. 58, nr 2

221-230

EN

The effect of a massive bloom of filamentous algae on the long-term abundance dynamics of the moss Warnstorfia exannulata (B., S. & G.) Loeske was studied in an acidic lowproductivity lake in NW Poland. Individuals were counted on 4 experimental plots, 1 x 1 m each, at a depth of 2.5 m. The studies were conducted for 36 months, every 30 days, by SCUBA diving. Over the three years the seasonal changes in water pH, conductivity, HCO3 - concentration, sediment hydration and pH were not statistically significant (P> 0.05), and light intensity was higher in winter than in summer. Over the three years 4 consecutive stages of population development were observed: regeneration, stabilisation of abundance (fluctuations), regression and repeated regeneration. These stages appeared and lasted at different temperatures and light intensity. The greatest monthly increase in abundance took place in summer and lasted until the beginning of autumn under conditions of high temperature and relatively low light intensity. Long-term abundance variations were strongly correlated with the appearance of filamentous algae, less strongly with the dynamics of the dominant species (Sphagnum denticulatum), and the least with water temperature, light intensity, water and sediment pH, conductivity and HCO3 - concentration. As a result of a massive bloom of these algae, light intensity decreased in the water, Warnstorfia shed its leaves, and then the entire population disappeared. In winter that year it began to regenerate from vegetative propagules (leafless shoots), which were the remains of individuals growing before the filamentous algae appeared. In softwater lakes such massive algal blooms are a common phenomenon which limits light transmission to the substrate and as a result leads to changes in the submerged vegetation structure, especially that of bryophytes.

3

Morphological variation of oospores in the population of Chara rudis A. Braun in a mesotrophic lake

Boszke P., Bociąg K.

Polish Journal of Ecology

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2008

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Vol. 56, nr 1

139-147

EN

The morphological variation of Chara rudis A. Braun oospores was examined in a local population in a deep (43 m), hardwater (34 mg Ca dm[^-3]) and mesotrophic (P[tot] 0.095 mg P dm[^-3], SD 8 m) lake (NW Poland). Two variants of population density and three variants of depth were taken into account. Oospores are 712.8 [plus or minus] 37.6 (600-817) [mi]m long and 452.6 [plus or minus] 34.2 (350-516) [mi]m wide. They have 8-13 ridges. The outer membrane is slightly granulated. The isopolarity index (length/width x 100) is 158.4 [plus or minus] 9.9 (140-190). The variation coefficient varies from 5% for oospore length to around 10% for fossa width. It was shown that the differences between oospores coming from individual depth and density variants are statistically significant. The biggest (733.21 [plus or minus] 33.3 [mi]m) oospores occurred on individuals growing at a depth of 3 m, while the smallest ones (673.3 [plus or minus] 43.4 [mi]m) at 5 m. The oospores from highly dense aggregations (> 50 individuals x 0.1 m[^-2]) were much longer and wider than oospores from scattered (<10 individuals x 0.1 m[^-2]) individuals. The observed intrapopulation variation of oospores can be regarded as a response to environmental changes along the depth gradient.

4

Population structure and regeneration of Phragmites australis (Cav.) Trin. ex Steud. in flood control ditches in the depression wetland (Żuławy Wiślane, Northern Poland)

Boszke P., Bociąg K., Szmeja J.

Polish Journal of Ecology

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2005

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Vol. 53, nr 1

3-12

EN

The population structure of Phragmites australis (Cav.) Trin. ex Steud. was examined in seven categories of overgrowing flood control ditches, differing on time which had elapsed from the last clean-up. Density, biomass, frequency of development stages, as well as the size and habit of the shoots, were determined in the populations. Site conditions in the ditches and the proportion of the common reed in the total biomass of plants were also examined. The rate at which populations in cleaned ditches regenerate is very quick. Three years after the maintenance works in ditches the reed population is already fully regenerated. Well developed reed rushes, which biomass is about 650 g d.w.m-2, are dominant. Its density amounts to 76 ± 25 shoots m-2. Flowering and fruiting shoots are the most numerous. The first signs of population regression were observed in the ditches left without cleaning for more than 5 years. Population density is gradually lower, the proportion of generative shoots is reduced, and the reed is lighter and has smaller assimilation area. In the 11-year-old and older ditches the reed is replaced by other plant species, mainly grasses and shrubs.

5

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.