Monitoring tools and early warning system for harmful cyanobacterial blooms: Río Uruguay and Río de la Plata

Abstract

Potentially hazardous cyanobacterial blooming constitutes one of the most widespread problems experienced by aquatic systems worldwide. However, there are not any monitoring methods sensitive enough to be directly applicable to predict and manage blooming events. In order to fulfill this goal, both ecological and genetic concepts were combined to generate cyanobacteria monitoring tools. Two approaches were used: grouping organisms into functional groups and utilizing molecular analysis (real time quantitative PCR) as indicators of the presence of genes that encode the expression of cyanotoxins (mcy). Six bi-monthly sampling campaigns were performed to evaluate the suitability of these tools (2013-2014) at six locations composed of two sites each one, ranging downstream from Salto Grande, at the River Uruguay, to Punta del Este, at the Estuary River Plate. A remarkable gradient was observed in the meteorological, physical and chemical variables, as well as higher abundances in planktonic organisms both in Salto Grande and in Punta del Este. The most abundant population of toxic species in the whole gradient were found in Salto, and in particular those belonging to the Microcystis aeruginosa complex (MAC). The most relevant environmental variables to determine the gradient and the variation in biological variables were: salinity, temperature, wind and turbidity. The results of the new indicators (presence of MAC in the plankton net and mcy genes) were in agreement with the traditional ones (v.g. chlorophyll-a) demonstrating being much more sensitive in cases of the most severe blooming events than in the low abundance situations. The conjunction of results was applied to the construction of a monitoring and early warning system protocol.