## 3 Results and Discussion
### Dissolved Phase
#### 3.2.3 Diffusive and Benthic Fluxes at the SWI
At site VN1, not only Cr but also Cu,  
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Site**} & \multicolumn{8}{c}{**Diffusive Fluxes (\(\mathrm{\SIUnitSymbolMicro g}\)/\(\mathrm{m}^{2}\) d)**} & \multicolumn{8}{c}{**(mmol/\(\mathrm{m}^{2}\) d)**} \\ \cline{2-13}  & **Al** & **As** & **Cd** & **Cr** & **Cu** & **Hg** & **Fe** & **Mn** & **Ni** & **Pb** & **V** & **Zn** & **H\({}_{2}\)S** \\ \hline
**VN1** & & & & & & & & & & & & & \\ (this & 13.3 & 240 & 0.04 & 0.99 & 0.24 & 0.44 & 132 & 3415 & \(-\)0.53 & 4.44 & 8.62 & \(-\)23.7 & 28.6 [12] \\ study) & & & & & & & & & & & & \\ \hline
**VN3** & & & & & & & & & & & & \\ (this & 55.1 & 2.06 & 0.04 & 7.01 & 1.79 & 0.08 & 167 & 803 & 6.90 & 5.74 & 11.0 & 345 & 55.5 [12] \\ study) & & & & & & & & & & & & & \\ \hline
**SL** & & & & & & & & & & & & & \\ Lucija (SLO) & & 21.0 & 0.02 & 5.47 & 8.05 & 932 & 0.03 & 499 & 6.36 & \(-\)52.2 & n.d. & \(-\)3.36 & 0.006 \\
[23] & & & & & & & & & & & & & \\ \hline
**SR-1**, & & & & & & & & & & & & & \\ San & & & & & & & & & & & & & \\ Rocco & n.d. & 50.4 & 0.00 & 0.21 & \(-\)17.7 & 283 & 1.47 & 40.9 & \(-\)8.27 & \(-\)62.7 & n.d. & \(-\)90.7 & n.d. \\
[23] & & & & & & & & & & & & \\ \hline
**SR-2**, & & & & & & & & & & & & & \\ San & & & & & & & & & & & & & \\ Rocco & n.d. & 11.7 & \(-\)0.03 & 0.56 & \(-\)157 & 92.6 & 0.97 & 6980 & 1.11 & 4.75 & n.d. & 37.2 & 0.001 \\ (ITA) & & & & & & & & & & & & \\ \hline
**1 E**, & & & & & & & & & & & & & \\ Taranto & & & & & & & & & & & & \\ (ITA) & & & & & & & & & & & & & \\ [22] & & & & & & & & & & & & & \\ \hline
**1 I**, & & & & & & & & & & & & & \\ Taranto & & & & & & & & & & & & & \\ (ITA) & & & & & & & & & & & & & \\ Taranto & & & & & & & & & & & & & \\ (ITA) & & & & & & & & & & & & & \\ Taranto & & & & & & & & & & & &Hg and Mn showed influxes, which could be the consequence of the immobilisation of Mn and, in parallel, of the other involved metal(loid)s. However, the highest benthic effluxes, except As and Pb, were observed at this oxic site, VN1, thus indicating a major release from sediment to water column of Al, Fe, Ni, V, Cd and Zn. These benthic fluxes could be largely governed by the intense bioturbation, mostly by polychaetes [50], occurred at this site as already observed in the Thau Lagoon along the French Mediterranean coast [51]. The effluxes of Cu, Pb and Hg, and especially As and Mn, were estimated as being higher at VN3 than VN1, and they could be related to the association with Mn-oxides. In particular, Mn appears to be very important in the sediment redox processes [48,51] found in a high percentage of the labile fraction as oxide and hydroxide in the thin oxic SWI onto which other metals can be bonded or adsorbed. In anoxic conditions, Mn, which shows a very high efflux, is reduced and released in dissolved form, together with other metal(loid)s, to the overlying water column. Similarly, As, which is known to be involved in the redox processes [52], showed the highest efflux at this anoxic site VN3 (Table 4). Conversely, the lower influx of Cr at VN3 could be due to its lower solubility than in oxic site VN1 [53] and/or complexing with organic ligands [43]. Moreover, the behavior of metal(loid)s also depends on microbial activity [45], which degrades organic matter that acts as a complexing agent for many elements. This can be an additional reason for higher effluxes of other metal(loid)s in oxic conditions at VN1. Moreover, some contribution to the increase of the dissolved metal(loid) concentrations in the benthic chamber could be due to the resuspension of sediment as a consequence of the benthic chamber deployment [54]. In the case of Al, it was not possible to calculate the benthic flux at the anoxic site, VN3, since it is present in sediment and in porewaters but not in the benthic chamber. Aluminum is a conservative element of the sedimentary matrix and was not influenced by the changes of redox conditions.