Insights into heterotrophic protozoa assemblages spatiotemporal distribution in urban-agricultural landscapes streams

This study investigated the environmental variables that influence heterotrophic protozoan assemblages in streams located in urban-agricultural landscapes of Argentina and estimated their potential as water quality indicators through environmental optimum distribution calculations. We sampled nine streams across all four seasons, collecting data on relevant environmental variables and protozoans in the water. For the analysis, we compared richness and total abundance across seasons and among streams and then focused on dominant genera. We performed a canonical correspondence analysis, multiple regression models, and calculations of optimum and tolerance levels. A total of 109 taxa most of them belonging to ciliates were identified. Total density distribution among seasons (spring was different from the other seasons) and streams were variable. Stentor and Zoothamnium were associated with higher water flow and high chlorophyll-a (Chl-a) content. At the same time, Paramecium, Blepharisma, Holophyra, and Litonotus were linked to lower oxygen availability or higher organic matter concentrations. Results showed that Pleuronema and Holophrya had lower optimum temperature values than Difflugia and Arcella. For dissolved oxygen, Holophrya had a higher optimum value than Litonotus while for Chl-a content, Stentor and Zoothamnium had a higher optimum value than Vorticella. The other showed similar optimum values for soluble reactive phosphorus, water temperature, and biochemical oxygen demand (BOD₅), all displaying broad tolerance ranges. Results suggest that protozoa assemblages respond to environmental changes in lowlands streams, and optimum distribution values of some genera suggest that these groups could be used in the future to design water quality indexes.