Effect of surrounding trees and dry rush presence on spring zooplankton community in an urban pond complex

The role of both natural and artificial ponds in supporting biodiversity and as an infrequent habitat for aquatic organisms in urban areas may be greater than that in more rural landscapes. Moreover, biological succession and the dynamics of zooplankton can differ in urban ponds where we may observe a specific combination of environmental factors (e.g., an increase of eutrophication and pollution) compared to other water ecosystems. Therefore, ten urban artificial ponds were examined and the type of direct catchment area was established as the most important factor in the determination of zooplankton distribution. Different environmental factors structured zooplankton distribution between forest and meadow ponds. Low concentrations of oxygen as well as lack of fish, which was an effect of high concentrations of ammonium nitrogen, were responsible for the occurrence of littoral species and large crustacean species (e.g., Daphnia hyalina and Megacyclops viridis) in the case of forest ponds. Fish predation on large crustaceans and favourable food conditions (high concentration of chlorophyll a) created suitable conditions for the occurrence of pelagic species (e.g., Keratella cochlearis and K. quadrata) in the case of meadow ponds. Moreover, soon after the ice cover melted and before new macrophytes developed, previous-year dry rush stems created valuable refuge conditions for zooplankton in this type of pond. Despite anthropogenic pollution resulting from the close vicinity of the agglomeration of Poznan and unfavourable conditions attributed to the spring season a diverse zooplankton community occurred, reaching the level of 119 species in total.