## 3 Results and Discussion
### Climate Change Impact on Salt Marsh Composition and Ecosystem Services
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Climate Change Scenario**} \\ \cline{2-5}  & **Atmospheric CO\({}_{2}\) Rise** & **Prolonged Submission** & **Temperature Rise** & **Osmotic Stress** \\ \hline Sado estuary & 14\% & \(-9\%\) & \(-20\%\) & \(-35\%\) \\ \hline Mira estuary & 6\% & \(-14\%\) & \(-15\%\) & \(-31\%\) \\ \hline Tagus estuary & 15\% & \(-10\%\) & \(-22\%\) & \(-32\%\) \\ \hline Mondego estuary & 14\% & \(-25\%\) & \(-15\%\) & \(-34\%\) \\ \hline Aveiro coastal lagoon & 15\% & \(-27\%\) & \(-15\%\) & \(-36\%\) \\ \hline Ria Formosa coastal lagoon & 5\% & \(-1\%\) & \(-9\%\) & \(-8\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Relative salt marsh coverage area changes in the different transitional systems, compared to the present-day conditions. Figure 6: Species relative abundance (%) in the salt mars of the transitional systems analyzed under present-day conditions and in the five climate change scenarios considered. As noted, the climate change scenarios evaluated have differential impacts on the halophyte species according to their physiological characteristics, and thus inevitably differential impacts on the ecosystem services, depending on the transitional system floristic inventory. Being directly connected to the species primary productivity, the blue carbon, nitrogen, and phosphorous stocks will be one of the most affected ecosystem services due to climate change (Figure 7). As noted, for most cases, atmospheric CO2 rise results in higher primary productivity for the majority of species, increasing species ability to allocate carbon, nitrogen, and phosphorous in its biomass and sediments. This is in agreement with the physiological data available for C3 halophyte species, where increased atmospheric CO2 results in an increase in the biomass carbon content [14; 16]. Except for the Ria Formosa coastal lagoon, all the blue carbon stocks will be affected negatively under the remaining climate change scenarios that are considered (Figure 7). The higher percentage of species highly adapted to submersion and underwater photosynthesis [12; 20; 53] allows the Ria Formosa system to have a high blue carbon stock under a prolonged submersion (due to sea level rise) scenario. The same could be observed for blue nitrogen and phosphorous stocks, driven from this strong ability to maintain high primary production rates, even under prolonged submersion periods (Figure 7). Regarding the different stressor effects on the blue stocks, it can be observed that as previously mentioned for the species coverage, osmotic stress will have the most profound impact in the salt marsh stocks. If the whole ecosystem service value is considered, a similar tendency can be observed (Figure 8). Since most of the ecosystem services are evaluated having as a basis a cost per unit of salt marsh area, the value of the transitional systems tends to increase under rising atmospheric CO2, driven from a higher salt marsh coverage (Figure 8). This was also reported by previous studies [63] using modeling approaches, suggesting that the net impact of climate change will be to increase carbon burial rates in the first half of the twenty-first century. Nevertheless, if the value of the ecosystem services is calculated having as a basis a value per square meter of salt marsh, the negative effects of climate change in the salt marsh ecosystem services are exacerbated. The average value per square meter tends to decrease either by a reduction of the colonization area through a reduction of the primary productivity of the species or due to an increased area due to higher productivity of a certain species (e.g., under rising atmospheric CO2) and a consequent dilution of the ecosystem value into a larger area, that does not all benefit from the enhancing stressor. This valuation can be taken into account not only for ecological economics purposes but also to assess the system resilience or susceptibility to climate change.