## 5 Discussion
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Map/Reference** & **(1)** & **(2)** & **(3)** & **(4)** & **(5)** & **(6)** & **(7)** & **(8)** & **(9)** & **(10)** & **(11)** & \(P_{Hi}\) \\ \hline Anthropic Features (1) & **10.0** & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **100.0** \\ Beach (2) & 0.0 & **13.0** & **6.0** & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **68.4** \\ Embryo Dunes (3) & 0.0 & 0.0 & **4.0** & 0.0 & 0.0 & **2.0** & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **66.7** \\ Estuarine Beaches (4) & 0.0 & 0.0 & 0.0 & **10.0** & 2.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **0.0** \\ Estuarine Dunes (5) & 0.0 & 0.0 & 0.0 & **11.0** & 5.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **0.0** \\ Fixed Dunes (6) & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **8.0** & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **0.0** \\ Flood Tidal Delta (7) & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **10.0** & 0.0 & 0.0 & 0.0 & 0.0 & **0.0** \\ Mudflats (8) & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **23.0** & **4.0** & 0.0 & 0.0 & **0.0** \\ Saltmarshes (9) & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **13.0** & 0.0 & 0.0 & **0.0** \\ Sand Bars (10) & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **2.0** & 0.0 & **6.0** & 0.0 & **0.0** \\ San Flats (11) & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & 0.0 & **10.0** & **0.0** \\ \hline \(P_{Pi}\) & **100.0** & **100.0** & **40.0** & **90.9** & **71.4** & **80.0** & **100.0** & **92.0** & **76.5** & **100.0** & **100.0** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Confusion matrix resulting from classifying training set pixels in the San Vicente de la Barquera estuary. Shaded cells indicate areas with larger confusion coefficients between defined features. Main diagonal, in bold, indicates features confirmed by field inspection (reference points). Final column and row, in bold, show \(P_{Uli}\) and \(P_{Pi}\) for the corresponding feature. Column numbers match with row numbers. into a vast muddy intertidal plain partially covered by seagrasses and macroalgae in some points. The loss of the saltmashes, and their associated communities, will reduce the capacity of the system to retain sediment [60]. One possible cause of this pattern may be the lack of sediment input into the estuary due to the small fluvial supply. Previous studies have shown that the sediment balance of these systems, both internally and externally, may enable the adjustment of the bed elevation to the sea level rise (SLR) [61]. However, if the source of sediment is reduced and the system is unable to make this adjustment, it will cause the migration of the vegetation to higher elevation areas when available [62]. In particular, for this area, [63] described SLR rates of 2.08 \(\pm\) 0.33 mm yr\({}^{-1}\) from 1943 to 2004 for Santander (nearest tidal gauge), with an accelerated rate at the end of the analysed period [14]. This, together with the impossibility of landward migration due to the orography of this area, promotes the squeeze of the saltmarsh, reducing the probability of plant survival [64]. Hence, the persistence over time of the saltmarsh depends on a balance between the supply of sediment and nutrients and external energetic forcing, including wave energy, storm surges and tidal flooding [65; 66; 67; 68]. Doing a similar analysis for the GUA estuary (Figure 8), it can be concluded that the saltmarsh has an equilibrated balance between sediment supplies and hydrodynamic processes. The interaction of external and internal agents favours sediment mobilization [32], resulting in an increment in the surface of around 0.3 ha/year (Figure 8). An equilibrated balance of sediment inputs allows the tidal subsystem to prograde (horizontally) and aggrade (vertically) following a natural behaviour [13]. The large availability of sandy sediments in this comes from the river itself, which erodes deeply weathered granites in its basin, and by the erosion of westward sandy cliffs, transported to the estuary by the prevailing eastward littoral drift [32; 69].