Human activity as a factor causing the biomass, structure and seasonal dynamics of phytoplankton in adjacent fishponds.

The role of phytoplankton as one of the main sources of energy entering the water food network is especially evident in fish-rearing ponds. Indeed, in these comparatively small ponds (unlike many lakes), variations in the abundance of phytoplankton can be extremely sensitive to the action of external factors, including human activity. Here, we present results of the analysis of the phytoplankton dynamics in adjacent fishponds and in supplying/recipient river courses upstream and downstream of the ponds during a growing season. In the grow-out ponds, phytoplankton biomass is shown to reach maximums in spring and in early autumn, while in the nursery pond, the phytoplankton dynamics is characterized by one long peak. The specificity of fish-rearing ponds as the human-regulated reservoirs clearly manifests itself under comparison of phytoplankton biomass of ponds with the biomass of phytoplankton inhabiting a nearby river. The averaged phytoplankton biomass in the ponds was 6.2–10.1 times higher than in the river. Besides, we show here that the taxonomic composition of phytoplankton in the river differs significantly from the composition of phytoplankton in the fish-rearing ponds. In particular, Cyanobacteria and Chlorophyta were revealed as the major portion of the phytoplankton in the fish-rearing ponds, while in the river their abundances were low. [ABSTRACT FROM AUTHOR]