Abstract
The influence of a thermal discharge caused by the cooling system of a nuclear power station on benthic diatom communities was assessed at the lower Ebro River (in Spain), and the information generated could be useful to understand the effects of increasing temperature on large Mediterranean rivers. Surveys conducted at sites before and after the effluent and collected from natural and artificial substrate were analyzed and, Non-metrical Multidimensional Scaling (NMDS), Similarity Percentage Analysis (SIMPER) and 1-way Analysis of Similarities (ANOSIM) were performed to assess changes in community structure. The relationship between diatom assemblages and environmental variables was assessed with a multivariate distance-based linear regression model (DISTLM) and the model was visualized through a redundancy analysis (dbRDA). NMDS ordination was obtained with a stress of 0.18 and 0.17 for natural and artificial substrates, respectively. ANOSIM showed significant differences between Control and Impacted sites (p < 0.05). Simper analysis showed that the mean dissimilarity between Control and Impacted sites was of 42.22% for natural substrate and of 39.97% for artificial substrate. DISTLM selected a set of explanatory variables (dissolved oxygen, To difference, total phosphorus, pH and chlorophyll) with a 67.24% of fitted variation. Diatoms showed sensitivity to thermal changes, even though when these did not exceed 3℃. The factors that seemed to influence benthic assemblages the most were seasonal variation and the thermal increase caused by the nuclear power station.
Highlights
Diatoms are unicellular algae with a wide spectrum of responses to seasonal and environmental variation, and with optimum ranges of temperature to grow [1] [2] [3]
The influence of a thermal discharge caused by the cooling system of a nuclear power station on benthic diatom communities was assessed at the lower Ebro River, and the information generated could be useful to understand the effects of increasing temperature on large Mediterranean rivers
The relationship between diatom assemblages and environmental variables was assessed with a multivariate distance-based linear regression model (DISTLM) and the model was visualized through a redundancy analysis
Summary
Diatoms are unicellular algae with a wide spectrum of responses to seasonal and environmental variation, and with optimum ranges of temperature to grow [1] [2] [3]. Each species has different tolerances and preferences, and some have been used as indicators of environmental changes and conditions [4] [5] [6]. The importance of temperature in rivers has been widely recognized [9] [11] [12], and the effects of its alteration on aquatic species cover a wide spectrum of direct and indirect effects that range from minor importance to lethal effects [13]. Changes in community structure as response to thermal disturbances have been detected even with a temperature alteration of a few degrees [14] and depend on the preference and tolerance of species to different temperatures as well as on the level of heating
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