Abstract. The aim of the paper was to evaluate the structure of macrozoobenthos in acid, oligotrophic Jasne Lake. The basic abiotic parameters of water and bottom sediments were also studied. The samples were taken on five dates: 25.11.1997 and 13.05., 01.07., 07.08. and 21.10. in 1998. The sampling sites were located in four clearly different zones of the lake bottom at depths: 5 m, 10 m, 15 m and 19 m.The water transparency was very high (11 m) and water pH was extremely low (4.3). The oxygenation of the water near bottom was quite good up to a depth of 10 m. Generally both the water content (75.9% -96.1%) and organic matter content (17.5% -76.5%) in the bottom sediments were relatively high and increased with the depth.The taxonomic composition of the macrozoobenthos was similar to that of other acid water bodies, i.e. common, ubiquitous taxa dominated. Its species richness, diversity, and the density decreased as the depth increased but it is worth noting that the zone colonized by diverse and abundant macrozoobenthos extends to a depth of at least 10 m. The dominant group of benthic fauna at a depth of 5 m were Chironomidae larvae (almost 80% of the total macrozoobenthos density). At this station Ceratopogonidae and Sialis sp. larvae were also relatively numerous. In turn, at depths of 10 m and 15 m Asellus aquaticus (Isopoda) (43% and 57%, respectively) and Trichoptera larvae (37% and 21%, respectively) dominated. Among the chironomids Pseudochironomus sp. and Chironomus sp. larvae prevailed. The only taxa characteristic of acidic waters were Stylodrilus heringianus (Oligochaeta) and Ablabesmyia monilis (Chironomidae).

The aim of our study was to compare the macrozoobenthos structure as well as water and organic matter content of the bottom sediments of two hydrologically different zones of a strongly fluvial the Włocławek Dam Reservoir. Samples were collected from the Włocławek Dam Resevoir at six sites. Three of them were located in the upper, rheolimnic part (URP) of the reservoir and three others in its lower, limnetic part (LLP). Water transparency, sediment water content and organic matter content in the sediments were higher in the LLP. The higher number of taxa and diversity of macrozoobenthos were found in the URP of the reservoir. The density of bottom fauna was slightly higher in the LLP (90,990 ind. m−2) than in the UPR (73,486 ind.  m−2), while the significantly higher biomass of macrozoobenthos was found in the URP of the reservoir (2314 g · m−2) than in the LLP (336 g · m−2). The dominant taxa of Oligochaeta and Chironomidae larvae did not show significant differences in the density between both zones. Some taxa were found only in the URP. In this zone, significantly higher densities of other taxa were observed. The only species with greater abundance in the LLP was Potamothrix hammoniensis (Oligochaeta). Due to the very short water residence time, the differences in the parameters under study between the URP and the LLP of the reservoir were smaller as well as the abundance of the macrozoobenthos was distinctly higher than in other reservoirs.

Abstract. The aim of the study was to determine the impact of the increase in the organic matter content in the bottom sediments on the benthic fauna structure. The research was carried out in a strongly rheolimnic the Włocławek Dam Reservoir (Poland). The samples were taken on eight dates from March 1988 to February 1989. The sampling sites were located at the following depths: 1 m, 2 m, 5 m, 8 m and 10 m.The organic matter content in the bottom sediments increased with depth from 0.6% at a depth of 1 m to 13.2% at a 10 m depth. To a depth of 8 m, the bottom fauna was relatively rich in quality. The significant decline in the diversity and, above all, the number of taxa of the macrozoobenthos groups, only at a depth of 10 m were found. In turn, the abundance (density and biomass) of the bottom fauna increased with depth of the site.The analysis of the increase in Oligochaeta abundance with depth suggests that at the level of about 4% of the organic matter content in the bottom sediments, the food conditions are no longer a factor limiting the Oligochaeta occurrence.

The aim of the study was to indicate the abiotic parameters of water and bottom sediments, which significantly affect the reproduction of Potamothrix hammoniensis in 9 shallow eutrophic lakes, of which 5 were dominated by macrophytes and 4 – by phytoplankton. Samples were collected once a month from January to December 2012. The percentage of Potamothrix hammoniensis individuals with a developed reproductive system varied in individual lakes and ranged from 14 to 72%. There was no correlation between the distinguished lake types and the proportion of sexually mature individuals. The reproductive activity was not observed in summer and early autumn. Among the measured parameters, the highest values of the Pearson correlation coefficient were found between the percentage of individuals with a developed reproductive system and the conductivity (r = 0.69; p < 0.001), pH (r = 0.51; p = 0.002) and the organic matter content in the sediments (r = −0.42; p = 0.012). It is worth noting that there was no correlation between the percentage of sexually mature specimens and the water temperature (r = −0.22, p = 0.204) and the oxygen concentration (r = −0.08; p = 0.648).

The main objective of this study was to characterize the muddy bottom sediments of three hydrologically different old river beds of the lower Vistula, located in the vicinity of Toruń: Port Drzewny, Martwa Wisła and Przybysz. Samples were taken at monthly intervals from April to November 2015 from two (Martwa Wisła and Przybysz) or three sampling sites (Port Drzewny) located in the central parts of the reservoirs. The bottom sediments of these water bodies were characterized by a low water content and organic matter content expressed as a percentage of dry weight, high organic matter content expressed in units of weight, as well as a high sediment oxygen demand. The most distinct reservoir was Martwa Wisła, most likely due to the lack of a connection with the River Vistula.