El fitoplancton como indicador de calidad de masas de agua muy modificadas en la DMA. El lago artificial de As Pontes (A Coruña. España)

Abstract

According to the Water Framework Directive of the EU (WFD), artificial lakes larger than 0.5 km2 have to be monitored and managed in order to establish or maintain a state of the so-called good ecological water quality. Lake As Pontes is the deepest and largest man-made lake in Spain after the controlled flooding of the open pit left by the mine after 30 years of operations. The extraction of brown lignite led to the formation of a big mining lake (8.76 km2 surface and up to 206 m depth). The main objective of this study is the analysis of changes in phytoplankton communities and trophic status, in order to assess water quality overlooking the adaptation in its recreational and sporting use and obtaining a sustainable ecosystem. Samples were collected from 2009 to 2014 for evaluation of its ecological potential within the framework of the implementation of the Water Framework Directive (WFD) in Galicia. We have identified a total of 126 taxa: 22 Cyanophyta, 47 Heterokontophyta of which 42 are Bacillariophyceae, 3 Chrysophyceae, 1 Xantophyceae y 1 Synurophyceae, 6 Dinophyta, 2 Cryptophyta, 4 Euglenophyta, 14 Charophyta and 31 Chlorophyta. None of them is recognized as toxic, although it has been detected a high concentration of cysts that we have associated with Mallomonas sp., found at the end of August 2013. The current lake trophic state corresponds to a situation of oligotrophy, resulting in a decrease in phytoplankton biomass and productivity factors throughout the sampling period. According to the qualitative and quantitative composition of phytoplankton and the variables that define the trophic status, we can conclude that the lake is in good ecological conditions, according to the WFD criteria.