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

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

Bariloche

Congreso; Congreso de la International Association of Limnogeology (IAL) y la Internacional Paleontology Association (IPA); 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, andthe effects on their planktonic communities. In 2015, both lakes were in a clearvegetatedstate, 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 dueto winter snowfall. Environmental and plankton samples were collected in three summercampaigns (2015, 2016 and 2018) to answer, ?how lakes change their abiotic characteristicsand their planktonic communities with interannual hydrological variations?. Phyto- andzooplankton were analyzed by microscopy, while picoplankton assemblages were studiedby flow cytometry and high-throughput sequencing. Principal component analysis ordinatedsamples of 2016 towards higher values of dissolved organic carbon, total nutrients, andconductivity, compared to samples of 2015 and 2018. In 2015 and 2016, both lakesshowed similar patterns of bacteria, the most abundant phyla were Proteobacteria andBacteroidota. However, both lakes showed higher bacteria concentrations in 2016 than2015. In 2018, Chapu presented 96% of Proteobacteria, while Cervecero showed 52% ofVerrucomicrobiota. Photosynthetic picoplankton showed the highest concentration in 2018dominating phycocyanin-rich picocyanobacterial in both lakes. Regarding phytoplankton, bothlakes showed high diversity groups in 2015. In 2016, diatoms and chlorophytes dominatedin Chapu and chlorophytes dominated in Cervecero. In 2018, chlorophytes dominated inChapu and the cyanobacteria Dolichospermum flos-aque developed a bloom in Cervecero.Zooplankton also showed interannual variations in both lakes; particularly in 2018, Keratellakostei dominated in Cervecero, while in Chapu the groups were even. This study revealeda differential response of the planktonic communities of the lakes to an abrupt interannualhydrological shift, that may have implications for conservation of these ecosystems.