The influence of locks on zooplankton in canals (the Bydgoszcz Canal and the Noteć Canal, Poland)

Artificial waterways are characterized by dams and locks that slow water flow. Such conditions can influence the environment of freshwater organisms, including the zooplankton community. Our research aimed to assess the impact of environmental and hydrological conditions on the zooplankton of sites upstream and downstream of canal locks. The study was carried out in 2021 and 2022. Water samples were collected monthly from two canals during the growing season. We evaluated how water flow velocity and selected environmental parameters (i.e., water temperature, Secchi disk visibility, conductivity, oxygen concentration, saturation, pH and chl-a concentrations) influence the zooplankton diversity (T) density (N) and biomass (B). Our study showed that the zooplankton of the canals was highly diverse. Rotifers dominated over crustaceans in diversity and density at all sites of canals. The statistical analysis revealed differences in environmental and biological conditions between habitats located upstream and downstream of locks. Rotifers density and biomass changed approximately proportionally to changes in chlorophyll at sites upstream of locks. It supports the hypothesis that rotifer communities are defined by the bottom-up effect linked to food supply (phytoplankton). The growth of crustaceans (density and biomass), as well as total zooplankton biomass, was affected by water temperature at sites downstream of the lock.