Monitoring cyanobacteria and cyanotoxins in Alqueva Reservoir, Portugal

Abstract

Alqueva is nowadays the most important water reservoir in Portugal. Additionally, it is becoming an important agronomic and touristic region. These facts bring the questions of the water quality use. During the Alqueva hydro-meteorological experiment (ALEX) campaign, the team of the Water Laboratory from the University of Évora investigated the biological quality indicators of the Alqueva water. Among biological communities investigated, such as Chironomid pupal exuvia, benthic diatoms and phytoplankton, a special attention was given to the presence of cyanobacteria since cyanobacterial blooms are associated with the production of cyanotoxins that pose a health risk to human and livestock water consumers. Polymerase chain reaction (PCR) was used to corroborate microscopic identification and to verify the presence of toxic genes associated with cyanobacteria. Field campaign in Alqueva reservoir took place from June to September 2014. An additional campaign was performed in October due to a bloom situation. Water samples were monthly collected from three fixed platforms placed in the lacustrine zone and selected sites in the margins. Results show that in the integrated phytoplankton samples analyzed, a total of 62 taxa were identified, 15 corresponded to cyanobacteria. Even when Chlorophytes was the richest group, cyanobacteria dominated in abundance in all sampling sites and throughout the whole sampling period, being Cylindrospermopsis, Aphanizomenon and Aphanocapsa the most frequent and abundant genera. The observation of the phytoplankton samples collected at discrete depths revealed the presence of cyanobacteria in the bottom samples collected in Alcarrache and Alqueva-Mourão platforms (20 m) and in Alqueva-Montante (50 m). Given the abundance of cyanobacteria, molecular techniques confirmed also the presence of Microcystis species and microcystin-producing genes (hepatotoxins). It was not possible to confirm the presence of cylindrospermopsin. More primers are being tested to complete the list of microscopic identification of species and cyanotoxins.