Floraciones de cianobacterias y valores de microcistina-LR sestónica y disuelta en embalses de la cuenca hidrográfica del Miño-Sil (NW-España)

Abstract

Between October 2012 and February 2015, 181 water samples from nine reservoirs (As Conchas, Cachamuíña, Castadón, Faramontaos, Os Peares, Prada, Salas and Vilasouto), all belong- ing to the catchment area of Miño-Sil, were analyzed. 64 samples, from Vilasouto reservoir, were considered for a more detailed study. The cyanobacteria species were identified and quantified, and the concentration of the microcystin-LR (MC-LR) was determined, both the sestonic and the dis- solved fraction. The cyanobacteria were identified and quantified according to the UNE-EN15204 standard, using a settling chamber combined under an inverted microscope Nikon Eclipse TE 2000-S. The detection and determination of both fractions of MC-LR were conducted by means of an enzyme immunoassay, with the EnviroGard Microcystins QuantiTube kit. In all the reservoirs, except in Salas reservoir in which any cyanobacteria or MC-LR were detected, ten species of potentially toxic cyanobacteria were identified: Anabaena circinalis, Anabaena crassa, Anabaena flos-aquae, Anabaena planctonica, Aphanizomenon flos-aquae, Gomphosphaeria sp., Microcystis aeruginosa, Planktothrix agardhii, Planktothrix rubescens and Woronichinia naegeliana. However, MC-LR found out only in five of these reservoirs (Vilasouto, Castadón, Cachamuíña, Os Peares and Faramontaos). The species that emerged were: A. planctonica, Gomphosphaeria sp. and P. rubescens in Vilasouto; M. aeruginosa in As Conchas, Cachamuíña and Castadón; A. circinalis in Prada and Faramontaos; W. naegeliana in Os Peares, A. flos-aquae in Faramontaos and Aph. flos-aquae in Lindoso. As Conchas and Lindoso reservoirs, in spite of being one after the other in the Lima river, had different non-toxic blooms of M. aeruginosa and Aph. flos-aquae respectively; while Cachamuíña and Castadón reservoirs, which are located in the same way that the previous, these in the Lonia river, showed toxic outcrops of M. aeruginosa. The cyanobacte- rial species identified in Vilasouto reservoir were Anabaena planctonica, Gomphosphaeria sp., Planktothrix agardhii and Planktothrix rubescens; all potentially toxic. P. rubescens was the dom- inant specie in the early months of 2013 and 2014. The bloom of 2013 was the most intense (with a maximum abundance of 257550 cel./ml in February and of 1448000 cel./ml in April), extending even until July. The concentration of sestonic and dissolved MC-LR in Vilasouto exceeded the limit value proposed by WHO (1 μg/l) in different periods: October of 2012, from January to July of 2013 and in March and May of 2014; all showing a significant Spearman correlation (α = 0,05) with the abundance of A. planctonica and P. rubescens.