No abstract

The zooplankton community structure and diversity were analysed against the gradient of floodplain lakes connectivity and water level under different flood-pulse dynamics in the Vistula River. The lakes differed in terms of hydrology, among others in the degree/type of their connection with the river (permanent, temporary and no connection). The study was conducted during the growing seasons in the years 2006–2013 and involved the lower Vistula River and three floodplain lakes: isolated, transitional and connected. Water samples were collected biweekly from April to September. Zooplankton was the most diverse and abundant in the transitional lake (the highest Shannon α-diversity index H’ and Pielou’s evenness index J’). The gentle washing of the lakes might have stimulated the development of zooplankton in accordance with the Intermediate Disturbance Hypothesis. The diversity and density of zooplankton were higher in the connected lake compared to the isolated one. We confirmed the hypothesis that zooplankton should be more abundant and diverse in floodplain lakes connected with the river (or transitional) than in isolated ones. Zooplankton analyses indicated that hydrological conditions (flood-pulse regime) contributed most substantially to zooplankton diversity and density in the floodplain lakes of the lower Vistula valley.

The present study investigates the responses of zooplankton (including changes in their structure and diversity) to physicochemical and biological parameters in two artificial waterways. Water samples were collected monthly from the Bydgoszcz Canal, the Noteć Canal, and the Brda River during the growing season of April–October 2019. We analyzed how selected parameters (including water temperature, Secchi disk visibility, oxygen concentration, conductivity, and pH, as well as nitrate, phosphate, and chl-a concentrations) affected seasonal variations in zooplankton diversity (T) and density (N). In total, we recorded 98 species, and average zooplankton density was 320 ind/L. At all sites, the same zooplankton species were dominant: Keratella cochlearis among rotifers and the Cladocera Bosmina longirostris among crustaceans. Rotifers dominated qualitatively and quantitatively over crustaceans. Zooplankton density and biomass, as well as the number of zooplankton species, were higher in the Bydgoszcz Canal than in the Brda River or the Noteć Canal. This may be connected to the locks on the Bydgoszcz Canal slowing down water flow, thereby increasing macrophyte vegetation, which creates ecological niches supporting zooplankton development.

Zooplankton indicators based on rotifers (TSIROT) and an indicator based on Secchi disk visibility (TSISD) were used to assess trophic state changes in artificial, slow-flowing, and stagnant canal waters. The study was conducted in the summers of 2019, 2021, and 2022 in the Bydgoszcz Canal and the Noteć Canal (Poland). Water samples were taken from five sites once in the month of July and once in August. In terms of the species number and density, rotifers dominated among zooplankton (at almost all sites), which reflected the high trophic state. Our results showed statistically significant correlations between TSIROT and TSISD as well as between the individual indicators TSIROT1 (Rotifer numbers), TSIROT2 (Rotifer biomass), TSIROT3 (bacterivorous numbers of rotifers), TSIROT6 (rotifers indicating high trophic state), and TSISD. According to our study, the presented indices most likely determine the trends between TSIROT cumulative and TSISD in the studied canals. Similarly to previous studies performed on lakes and small reservoirs, zooplankton constituted a useful indicator of trophic state. It seems that, for stagnant and slowly flowing waters of canals such as the Bydgoszcz Canal and the Noteć Canal, the method of zooplankton trophic status indicators based on rotifers may be applied.

The Bydgoszcz Channel is an important artificial channel connecting two of the largest rivers and their catchments in Poland and in central Europe, the Vistula and Odra. It is also the main vector connecting the Noteć River from the East and near the mouth to Brda river from the West. Except for hydrography the Bydgoszcz Channel is also an interesting artificial river from the ecological point of view. In present study we identified and compared the zooplankton community along with physico-chemical and biological properties. Water samples were collected on Bydgoszcz Channel and Noteć Channel monthly during the spring (April 2019 to June 2019). We investigated how the flow of the channel and its tributary affected the various physico-chemical and biological conditions (including water temperature, water transparency, dissolved oxygen, saturation, conductivity, pH, nitrate, phosphate and Chl-a concentration). These analysed parameters in turn affected the seasonal variations of zooplankton diversity (T) and density (N). The zooplankton community was dominated by rotifers and crustaceans. During May we recorded the highest rotifer density (N Rot) 2090 ind/L in Bydgoszcz Channel with an average 1256 ind/L and highest rotifer diversity (T Rot) of 20 species. The most dominant were Keratella cochlearis, Keratella quadrata, Polyarthra dolichoptera. The highest crustacean density (N Crust) was recorded during June on Bydgoszcz Channel 1420 ind/L with an average of 564.5 ind/L and diversity (T Crust) of 8 species recorded from Noteć Channel. The most dominant species among crustaceans was the cladoceran Bosmina longirostris. We assume that the crustacean diversity, density and biomass increased due to increasing temperature. On the contrary, the rotifers species decreased. It follows that adult copepods and their larval stages copepodites could eat small rotifers causing a decline in the number of rotifers. It is also possible that the decline in rotifer numbers could have been caused by competition for food with the Cladocera.