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Effect of environmental conditions on the populations of Luronium natans (L.) RAF

Bazydło E.

Polish Journal of Ecology

2004

Vol. 52, nr 2

181-189

The structure (aggregations distribution, density, age structure) of Luronium natans L. (Raf.) populations has been studied in 21 lakes in the Pomeranian Lakeland (NW Poland), where the highest population density of this species is found in slightly acid (pH 6-7) waters, poor in DOC (<6.0 mg C dm^-3) and phosphorus (<30.0 [mi]g TP dm^-3). Luronium natans reproduces mainly vegetatively and prefers shallow (1-2 m), mineral-organic (5.1-10% C) substrates. Seedlings represent about 10% of a population. High levels of pH (pH>8.0), concentration of carbon (>6.0 mg C dm^-3) and phosphorus (>30.0 [mi]g TP dm^-3) impede the population growth. Under such conditions population densitymay be lower by as much as 80-90%, aggregation size smaller, and the proportion of generative stems higher. Luronium natans aggregation size depends on the depth: the deeper the location - the larger and denser the aggregation, the shallower the location - the larger the fraction of generative individuals (up to 98% of the population).

Temporal and spatial changes in the horizontal distribution of planktonic crustacea between vegetated littoral zone and the zone of open water

Rybak J., Węgleńska T.

Polish Journal of Ecology

2003

Vol. 51, nr 2

205-218

The research concerned the density, dominance structure and species composition of planktonic Crustacea community, as well as their diel horizontal migrations between aggregations of vegetation and open water in the littoral zone of two lakes. The Cladocera communities of sparse beds of submerged macrophyte showed a sharp domination (70%) of individuals of large-sized tycholimnetic species. In the Cladocera community in a dense beds of macrophyte also individuals of littoral species occured in greater numbers. The filamentous algal mats were mainly dominated by Copepoda and small tycholimnetic species of Cladocera. We observed a sharp daily gradient of Crustacea density across macrophyte beds and open water. The greatest diel changes were found near the edge of the macrophyte beds (ecotone zone). Daytime density of Cladocera was several times greater in the macrophyte beds than in the open zone, while during the night-time density differences were not so marked. In contrast, in the case of filamentous algal mat, the sharp gradient of abundance remained constant by both day and night. An inverse relationship between chlorophyll a concentration and Cladocera density was noted in the transect between beds of submerged macrophytes and open water, provide to effective control of phytoplankton biomass by Cladocera during their diel migrations.