Blooms of toxic Raphidiopsis raciborskii in Laguna del Sauce (Uruguay): environmental drivers and impacts

GONZALEZ MADINA, LUCIA; LEVRINI, PAULA; DE TEZANOS PINTO, PAULA; BURWOOD, M; CRISCI, CAROLINA; CARDOZO, A; LAGOMARSINO, JUAN JOSÉ; PACHECO, JUAN PABLO; FOSALBA, CLAUDIA; MENDEZ, G; GARRIDO, LIDIA; MAZZEO, NESTOR

NATAL

Conferencia; 10th International Shalow Lakes Conference; 2021

Laguna del Sauce (34° 43? S, 55° 13? W) is an eutrophic shallow lake and the second drinking water source in Uruguay. This ecosystem suffers recurrent blooms of nitrogen fixing cyanobacteria which are potentially toxic, mostly during summertime. The phytoplankton of this ecosystem has been monitored since 2015, as part of a vigilance monitoring program. In this study we analyze the impacts and environmental drivers linked to the occurrence, persistence, and toxicity of blooms of Cylindrospermopsis raciborskii in Laguna del Sauce from 2015-2020. During this period, two massive, persistent, and toxic blooms of C. raciborskii were recorded. The first bloom occurred in 2015 (104 mm3.L-1), and lasted from the end of summer until autumn, with high concentrations of saxitoxin (9.8 μg.L-1). Saxitoxin concentrations remained high even after the bloom collapsed. This was the first time that saxitoxin was registered in the environment, and its high concentrations caused several interferences linked to water supply. In 2020 a second massive bloom occurred which lasted from summertime until winter. Despite this bloom was of high magnitude and persistence, its biovolume (6,3 mm3.L-1) and toxin content (0,9 μg L-1) were much lower than the ones recorded in 2015. At this time, we were able to implement adjustments in the water plant facility which avoided a crisis in the water supply. Both blooms were associated with similar environmental conditions: low rainfall, low water level, high-residence time, and high-water transparency, with high irradiance in the water-sediment interface. Bloom collapse occurred in similar ways in 2015 and 2020 and was linked to low temperatures and strong precipitation events. Knowing the climatic and limnological characteristics associated with the massive and persistent blooms of C. raciborskii allows anticipating the onset of blooms and adapting the water treatment facilities to decrease the potential risks due to saxitoxin presence in water.