3.1.2. Sediments

Surface sediments were generally muddy, with a prevalence of silt at all sites (Figure 4). However, spatial differences included higher sand content at sites A and B, compared to C, D, and E (Figure 4). The median particle diameter (Md) varied similarly to the variation in the silt content among sites, with the highest Md values at sites C, D, and E. The water content (Wc) varied less markedly among sites, with the largest within−site variation at site A. Finally, the TOC content did not show marked differences among sites, except at site F. In particular, TOC varied from 1.7% to 2.3% at sites A and B, respectively, but was up to 5.0 ± 0.01 at site F, providing an additional evidence of its hypertrophic condition (Figure 4). Similar to the water variables, the ordination model of the PCA carried out on the sediment variables revealed a clear separation of site F along the *y*-axis (Figure 5). Along the *x*-axis, sites A and B were located on the negative pole, opposite to sites C, D, and E. The observed pattern is consistent with the variation in sediment grain-size among sites A–E, with higher loadings for sand (negative values) and silt, clay and Md (positive values) on the *x*-axis. On the contrary, factors related to organic enrichment, found at site F, were mostly correlated with the *y*-axis where Wc (a proxy of mud

content) and TOC showed a positive and a negative correlation, respectively (Table 3). Overall, these results were consistent with those obtained from the water variables, indicating that both water and sediment components provide consistent data helpful in assessing the environmental heterogeneity and the trophic features of the Yundang Lagoon.

**Figure 4.** Box-plots of sediment sand, silt and clay content, and median particle diameter (Md) and water content (Wc) at each site (n = 9), as well as the mean value of total organic carbon (TOC) content of sediments at each site (n = 3, ±SE standard error not visible when <0.01).

**Figure 5.** Principal component analysis (PCA) of sediment variables, including sand, silt, and clay content, median particle diameter (Md), and water and total organic carbon content. PC1 = 67.6% of variance, PC2 = 23.9% of variance.

**Table 3.** Component correlation coefficients in the principal component analysis (PCA) of the sediment variables and the first two components (PC1 and PC2 = 67.6% and 23.9% of variance, respectively).


In bold, the highest loadings.
