Effect of water chemistry on the planktonic communities and relationships among food web components across a freshwater ecotone

Most ecological research on the food web has been focused more on the pelagic zone than on the transitional zone - ecotones between lentic and lotic habitats. The specific goals of this study were to determine whether the contact zone of waters differs in hydrochemical and biological terms from the waters of the canal and the open water zone, and to evaluate the influence of particular macro-habitats on the interactions between components of the planktonic food web. The distribution of samples in ordination space led us to conclude that the studied habitats are distributed along the rising gradient of total organic carbon and nutrients. Assemblages of all investigated groups showed a strong compositional gradient correlated with conductivity and total phosphorus, while a second strong gradient in species composition was explained by nitrate nitrogen and/or phosphate concentrations. The analysis of trophic relationships in the system bacteriaciliates- crustaceans reveals a clear differentiation and strength of mutual relations between the analyzed zones. The highest number of significant correlations was determined in the contact zone. It can also be a place of very efficient matter and energy flow in freshwater ecosystems