Abstract
The Water Framework Directive (WFD) is used to evaluate the water quality of aquatic ecosystems. Phytoplankton is the only biological element considered in the reservoirs water quality assessment. In this study, we aimed to assess the use of the bacterioplankton community as an indicator of water quality, using a culture-independent assay (denaturing gradient gel electrophoresis, DGGE). Four Portuguese reservoirs (Miranda, Pocinho, Aguieira and Alqueva) were analysed in four periods (autumn 2018, spring and autumn 2019, and spring 2020). Bacterial total abundance had similar values for Miranda, Pocinho and Aguieira, and generally lower values for Alqueva. Diversity and richness values did not show a clear trend. Negative correlations were observed between some nutrients and the bacterial community. Overall, members of Actinobacteria, Bacteroidetes, Cyanobacteria, Nitrospirae and Proteobacteria were identified in all sampling sites. In Alqueva, no spatial, temporal or water body quality relationships with bacterial community were observed, which may be due to its higher size, low water velocity rate and higher residence times. However, in Miranda, Pocinho and Aguieira, a strong spatial and temporal bacterial community dynamic was observed. Furthermore, the presence of some species (e.g., Acinetobacter sp.) may reflect the poor water quality that was not detected by the WFD approach.
Highlights
Superficial freshwaters, especially reservoirs, are subjected to eutrophication, mainly due to the excessive charge of nutrients, in particular, in the area upstream of the reservoir [1,2]. The occurrence of this phenomenon leads to excessive growth of primary producers, which can disrupt the dynamics of the biological equilibrium in the aquatic ecosystem [3]
According to the physical and chemical parameters used in the Water Framework Directive 2000/60/EC (WFD), for heavily modified and artificial water bodies, only the pH, O2, NO3 − and Ptotal have environmental quality standard (EQS) values established for a good ecological potential (EP) (Table 1)
According to the WFD, the O2 concentration was below the minimum EQS limit in M, Ag1 and Ag2 in autumn of 2019 (Aut19)
Summary
Superficial freshwaters, especially reservoirs, are subjected to eutrophication, mainly due to the excessive charge of nutrients, in particular, in the area upstream of the reservoir [1,2] The occurrence of this phenomenon leads to excessive growth of primary producers, which can disrupt the dynamics of the biological equilibrium in the aquatic ecosystem [3]. The Water Framework Directive 2000/60/EC (WFD), created in 2000 and applied by the European Union, aims to assess the ecological quality of water bodies [4] which, in the case of heavily modified water bodies (reservoirs), is denominated as “ecological potential” This classification allows determining which parameters are in good conditions (similar to reference values) and which parameters are changed and responsible for water degradation. As biological elements only, the phytoplankton community is considered for this water typology
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