Plankton communities under water level fluctuations in two lakes of the arid Patagonia

PORCEL, SOL; SAAD, JUAN F.; SABIO Y GARCÍA, CARMEN A.; SARACENO, MARTÍN; ROESLER, IGNACIO; LANCELOTTI, JULIO; IZAGUIRRE, IRINA

Bariloche

Encuentro; IAL IPA 2022 joint meeting; 2022

This study focused on the analysis of the limnological changes associated to water levelfluctuations in two shallow lakes (Cervecero and Chapu) of the Buenos Aires plateau,and the effects on their planktonic communities. In 2015, both lakes were in a clearvegetatedstate, being more suitable for waterbird nesting. In 2016, the water leveldropped by half (approx. 1m), in 2017 lakes dried completed, and next year, lakes werefilled again due to winter snowfall. Environmental and plankton samples were collectedin three summer campaigns (2015, 2016 and 2018) to answer, “how lakes change theirabiotic characteristics and their planktonic communities with interannual hydrologicalvariations”. Phyto- and zooplankton were analyzed by microscopy, while picoplanktonassemblages were studied by flow cytometry and high-throughput sequencing. Principalcomponent analysis ordinated samples of 2016 towards higher values of dissolvedorganic carbon, total nutrients, and conductivity, compared to samples of 2015 and 2018.In 2015 and 2016, both lakes showed similar patterns of bacteria, the most abundantphyla were Proteobacteria and Bacteroidota. However, both lakes showed higherbacteria concentrations in 2016 than 2015. In 2018, Chapu presented 96% ofProteobacteria, while Cervecero showed 52% of Verrucomicrobiota. Photosyntheticpicoplankton showed the highest concentration in 2018 dominating phycocyanin-richpicocyanobacterial in both lakes. Regarding phytoplankton, both lakes showed highdiversity groups in 2015. In 2016, diatoms and chlorophytes dominated in Chapu andchlorophytes dominated in Cervecero. In 2018, chlorophytes dominated in Chapu andthe cyanobacteria Dolichospermum flos-aque developed a bloom in Cervecero.Zooplankton also showed interannual variations in both lakes; particularly in 2018,Keratella kostei dominated in Cervecero, while in Chapu the groups were even. Thisstudy revealed a differential response of the planktonic communities of the lakes to anabrupt interannual hydrological shift, that may have implications for conservation of theseecosystems.