Spatial and temporal variation of phytoplankton in subtropical stabilization ponds/Distribuição espacial e temporal do fitoplâncton em lagoas de estabilização subtropicais

Aim: This study aimed at analyzing the phytoplankton community in two stabilization ponds of a subtropical region regarding spatial and temporal composition, richness, and abundance, as well as the respective relationships with local abiotic factors. For this purpose, we tested the hypothesis that eutrophic discharges of sewage results in the maintenance of high-density phytoplankton community, mainly Cyanobacteria and Chlorophyceae, both spatially and seasonally, as well as the occurrence of a spatial and seasonal similarity between phytoplankton richness and density in stabilization ponds. Methods: We carried out monthly samplings of the phytoplankton community and environmental variables, between March 2011 and February 2012, in two stabilization ponds located in the city of Cascavel, West Paraná State, Brazil. Results: We observed that the sampled months presented a clear distinction regarding environmental variability, which did not occur for the ponds. We identified 39 taxa, with Cyanobacteria as the most representative group both in richness and density. We records low diversity and evenness of species and low phytoplankton spatial and temporal variability without significant differences between the richness and density mean values according to the periods and sampling station. Conductivity, nutrients, dissolved oxygen and turbidity were the major structuring environmental variables of phytoplankton. Conclusion: Our results corroborated our hypotheses considering the similar spatial and temporal phytoplankton distributions because of abiotic conditions behaving similarly, as well as the direct connection of the ponds. This paper points out the importance of such studies to proper management, including cyanobacteria control and operational decisions regarding stabilization ponds and the export of undesirable inoculum for receiving water bodies.