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

PORCEL, MARÍA SOL; SAAD, JUAN FRANCISCO; SABIO GARCÍA, CARMEN; SARACENO, M.; ROESLER, IGNACIO; JULIO, LANCELOTTI; IRINA, IZAGUIRRE

Bariloche

Simposio; IAL-IPA joint meeting ?Lagos, Memorias del Territorio?; 2022

This study focused on the analysis of the limnological changes associated to water level fluctuations 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 clear-vegetated state, being more suitable for waterbird nesting. In 2016, the water level dropped by half (approx. 1m), in 2017 lakes dried completed, and next year, lakes were filled again due to winter snowfall. Environmental and plankton samples were collected in three summer campaigns (2015, 2016 and 2018) to answer, “how lakes change their abiotic characteristics and their planktonic communities with interannual hydrological variations”. Phyto- and zooplankton were analyzed by microscopy, while picoplanktonassemblages were studied by flow cytometry and high-throughput sequencing. Principal component analysis ordinated samples of 2016 towards higher values of dissolved organic 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 higher bacteria concentrations in 2016 than 2015. In 2018, Chapu presented 96% of Proteobacteria, while Cervecero showed 52% of Verrucomicrobiota. Photosynthetic picoplankton showed the highest concentration in 2018 dominating phycocyanin-rich picocyanobacterial in both lakes. Regarding phytoplankton, both lakes showed high diversity groups in 2015. In 2016, diatoms and chlorophytes dominated in Chapu and chlorophytes dominated in Cervecero. In 2018, chlorophytes dominated in Chapu and the 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. This study revealed a differential response of the planktonic communities of the lakes to anabrupt interannual hydrological shift, that may have implications for conservation of these ecosystems.