How Much Is Too Little to Detect Impacts? A Case Study of a Nuclear Power Plant

<div><p>Several approaches have been proposed to assess impacts on natural assemblages. Ideally, the potentially impacted site and multiple reference sites are sampled through time, before and after the impact. Often, however, the lack of information regarding the potential overall impact, the lack of knowledge about the environment in many regions worldwide, budgets constraints and the increasing dimensions of human activities compromise the reliability of the impact assessment. We evaluated the impact, if any, and its extent of a nuclear power plant effluent on sessile epibiota assemblages using a suitable and feasible sampling design with no ‘before’ data and budget and logistic constraints. Assemblages were sampled at multiple times and at increasing distances from the point of the discharge of the effluent. There was a clear and localized effect of the power plant effluent (up to 100 m from the point of the discharge). However, depending on the time of the year, the impact reaches up to 600 m. We found a significantly lower richness of taxa in the Effluent site when compared to other sites. Furthermore, at all times, the variability of assemblages near the discharge was also smaller than in other sites. Although the sampling design used here (in particular the number of replicates) did not allow an unambiguously evaluation of the full extent of the impact in relation to its intensity and temporal variability, the multiple temporal and spatial scales used allowed the detection of some differences in the intensity of the impact, depending on the time of sampling. Our findings greatly contribute to increase the knowledge on the effects of multiple stressors caused by the effluent of a power plant and also have important implications for management strategies and conservation ecology, in general.</p> </div

Asymmetrical univariate analyses of variance of the percentage cover of biofilm on panels submerged in different sites in all sampling times.

<p><i>n</i> = 4. The whole analyses is shown as well as the <i>a priori</i> contrast (i.e. the analyses where the distances to be compared were chosen <i>a priori</i>).</p><p>ns = not significant;</p>*<p> = <i>p</i><0.05;</p>**<p> = <i>p</i><0.01. Eff = Effluent; 600 m and 1400 m = sites 600 and 1400 m away from the effluent, respectively. Factor 1: Distance (Di), fixed, with 2 levels; Factor 2: Sites (Si), random, nested in Distance; Factor 3: Time (Ti), random, with 4 levels (except in comparisons with the Control sites, where there were only 2 levels). Data were arc-sin transformed.</p>+<p>Because the analysis “effluent vs. controls” was only done for two times of sampling, the degrees of freedom of Time is 1, Di (Ti) and Lo(Di) X Ti are 3 and the residual is 42.</p

Mean values (±SE, n = 3) of sea-water temperature (A) and chlorine levels (B) found at different sites at Times 1 (square); 2 (white circle) and 3 (black circle).

<p>Measures were taken every month from July 2002 to April 2003. C1 = control 1 at the intake area; C2 = control 2– located at the East side of Brandão Island. ND = Not detected.</p

Percentage cover (±SE; <i>n</i> = 4 at the Effluent and 8 at the other sites) of Biofilm in the different sites, in each time of sampling.

<p>Note that in times T3 and T4, only one control (C2) was sampled due to losses of replicates. Black bars = T1; White bars = T2; Grey bars = T3; Striped bars = T4.</p

Variability in the assemblages within the Effluent site, the sites 600 m and 1400 m away from the effluent and within the controls.

<p>The deviations from the centroids in each site were calculated within each time. Black bars = T1; White bars = T2; Crossed bars = T3; Striped bars = T4. <i>n</i> = 4 at the Effuent and 8 at the other sites; Note that in Time 3 and 4, only one control site (C2) was analyzed due to losses of replicates.</p

Asymmetrical univariate analyses of variance of the number of taxa on panels submerged in different sites in all sampling times.

<p><i>n</i> = 4. The whole analyses is shown as well as the <i>a priori</i> contrast (i.e. the analyses where the distances to be compared were chosen <i>a priori</i>).</p><p>ns = not significant;</p>*<p> = <i>p</i><0.05;</p>**<p> = <i>p</i><0.01.</p><p>Eff  =  Effluent; 600 m and 1400 m = sites 600 and 1400 m away from the effluent, respectively. Factor 1: Distance (Di), fixed, with 2 levels; Factor 2: Sites (Si), random, nested in Distance; Factor 3: Time (Ti), random, with 4 levels (except in comparisons with the Control sites, where there were only 2 levels).</p>+<p>Because the analysis “effluent vs. controls” was only done for two times of sampling, the degrees of freedom of Time is 1, Di (Ti) and Lo(Di) X Ti are 3 and the residual is 42.</p

Univariate analyses of variance of the number of taxa on panels submerged in different sites in all sampling times.

<p><i>n</i> = 4. The whole analyses is shown as well as the <i>a priori</i> contrast (i.e. the analyses where the distances to be compared were chosen <i>a priori</i>).</p><p>ns = not significant;</p>*<p> = <i>p</i><0.05;</p>**<p> = <i>p</i><0.01.</p><p>600 m and 1400 m = sites 600 and 1400 m away from the effluent, respectively. Factor 1: Distance (Di), fixed, with 2 levels; Factor 2: Sites (Si), random, nested in Distance with 4 levels; Factor 3: Time (Ti), random, with 2 levels.</p

Average dissimilarities among and within the sites sampled at the discharge point (Effluent), 600 and 1400 m away from the discharge areas (600 m and 1400 m, respectively) and control sites (C1 and C2), in each time.

*<p>Note that at times 3 and 4, only one control was sampled (C2).</p

Map of the location of the CNAAA power plant and the sites sampled.

<p>Effluent (Eff) –100 m far from the discharge point of the power plant; 600 m sites (N600 and S600) – one on each side of the bay, 600 m far from the discharge point; 1400 m sites (N1400 and S1400) – one on each side of the bay, 1400 m far from the discharge point; Control 1 (C1) – the intake area of the cooling system, control area; Control 2 (C2) – located on the East side of Brandão Island, control area.</p

Number (± SE; <i>n</i> = 4 at the Effluent and and 8 at the other sites) of taxa found in each time at the Effluent site (squares), the sites 600 m (triangles) and 1400 m away from the effluent (inverted triangles) and at the control sites (circles).

<p>Note that in times T3 and T4, only one control (C2) was sampled due to losses of replicates.</p