Different nutrient and light scenarios in human impacted shallow lakes host persistent cyanobacterial harmful blooms

O'FARRELL, I.; IZAGUIRRE I.; YEMA L.; SCHIAFFINO, M. R.; LAGOMARSINO, L.; SÁNCHEZ ML; HUBER, P.

Berlín

Congreso; 36 Congress of the International Association of Limnology (SIL); 2022

SIL

Cyanobacteria Harmful Blooms impair the nutrient enriched, turbid and polymictic shallow lakes spread along the Central Plains of Argentina. A 3-year research indicated that the structure and dynamics of cyanobacterial assemblages driving to bloom prevalence were more prone to be affected by light conditions, nutrient concentrations and water level fluctuations, than by temperature variations. The effect of seasonal temperature was subordinated to the light conditions (highly affected by water level fluctuations) and nutrient concentrations. Species composition and biovolume changed across a gradient of resources and conditions determining unique scenarios in each individual lake. Even the high P lakes differed in the structure and dynamics of their assemblages due to the influence of water depth on inorganic turbidity. Anyhow, the saturating relationship between cyanobacterial biovolume and TP suggested limitation by nitrogen, as increased TKN:TP were related to lakes with highest cyanobacteria biovolume or to peaks of N-fixers and non-fixers in others. The overall responses of taxa to the main drivers responsible for CyanoHABs differed according to the scale used for the analysis: i) at a regional scale Raphidiopsis, Sphaerospermopsisand Anabaenopsisoccurred at lower transparencies and in individual lakes growth was promoted after temporary decreases of inorganic seston; ii) despite pulses of pico-sized cell colonies were observed under poor light conditions in individual lakes, they bloomed in the more transparent waters from other water bodies. The relationship with TP was quite similar at the lake and regional scales, evidencing the preference of P. agardhii, Microcystisand Anabaenopsisfor high P lakes.