*3.1. Environmental Variables*

Among the water variables, both salinity and DO showed increasingly higher values from C1 to C3 (Figure 2), most variation found in salinity at C3 due to large di fferences between the summer (27 psu) and winter (3 psu) dates [30]. Di fferently from salinity, the median of DO was significantly higher at C3 than at both C1 and C2. Sediment variables had large within- and between-site variation. In particular, while C1 had low and homogeneous Wc, OM, chlorophyll-*a* (Chl-*a*), and phaeopigment values, C2 was most variable and had the highest peaks and outliers in OM, Chl-*<sup>a</sup>*, and phaeopigments among the three sites. C3 was in an intermediate position, with the medians of all sediment variables between C1 and C2 (Figure 2).

The PCA showed a clear separation of both sites and dates (Figure 3). C1 data-points were located on the left-had side of the ordination model (second and third quadrants), while those of C2 were located on the right-hand side (first and fourth quadrants). C3 was in intermediate position, ye<sup>t</sup> clearly separated from C1 and C2. The two sampling dates were also clearly distinguishable for each site, summer and winter data-point being positioned on the upper and lower portion of the model, respectively. Among the environmental variables, sediment Wc, OM, Chl-*<sup>a</sup>*, and phaeopigments were mostly correlated with PC1, while water temperature and salinity showed the highest correlation with PC2 (Table 1). This indicates that sites were discriminated on the *x*-axis by the sediment variables mostly a ffected by the trophic features, while on the *y*-axis they were distributed in relation to the confinement gradient as indicated by the water variables. The variance explained by the model was 46.1% and 23.5% for PC1 and PC2, respectively.

**Figure 2.** Mean values (n = 4, ±SE) of water salinity and dissolved oxygen (DO) concentration, and mean values (n = 12, ±SE) of sediment water (Wc), phaeopigment (Pha), organic matter (OM), and chlorophyll-*a* (Chl-*a*) contents at the sampling sites C1, C2, and C3 during the study period.

**Figure 3.** Principal component analysis (PCA) on environmental variables.


**Table 1.** Component correlation coefficients in the PCA of the environmental variables and the first two components. 69.6% of variance explained by Principal Components 1 (46.1%) and 2 (23.5%). In bold, the highest loadings.
