*3.2. Exhanges in the DESCR Framework*

The exchanges and the characteristics of the drivers will eventually be affected by the changes in the state of the environment [4]. The main exchanges in the study area are shown in Figure 8.

**Figure 8.** Main physical exchanges in La Mancha.

3.2.1. Hydrodynamics and SLR

In August (the rainy season), the values of pH, salinity and density are affected by the amount of freshwater available. In April (the dry season), these parameters depend only on the sea water, and this is also when the greatest spatial variability of the temperature is observed.

Under normal conditions, the salinity in the lagoon is stratified from south to north: the Caño Gallegos stream provides freshwater, with values of less than 0.5 PSU, while in the north of the lagoon, the salinity is higher, since it is connected to the sea [12]. As it was mentioned previously, the opening of the lagoon inlet by local fishermen also affects the salinity of the lagoon. From the results of the numerical model implemented by Rivera [36], it is seen that if the inlet is open continuously for more than three months, the residence time of the water in the lagoon increases. This increase is directly related to eutrophication in coastal waters [37].

Regarding coastal flooding, storm surge levels near the study area were reported by Silva et al. [38], where the values of the storm surge caused by the atmospheric pressure gradient, wind and waves were calculated for different return periods using climate data from 1948 to 2010. These values are shown in Table 2.

**Table 2.** Storm surge levels in La Mancha area, data from Silva et al. [38].


The relative rise in the sea level has a range of effects on the morphological changes in this area at different scales [19]. Sea level rise affects the flood levels, which are related to the geographic location, coastal orientation and beach slope [24]. According to Pérez et al. [19], in Veracruz, the trend of sea level rise is +1.89 mm/year. This is in line with global IPCC reports and is conditioned by the subsidence of the natural deltaic surface [39]. The geodynamics of the Gulf of Mexico are regulated by the movements of the North America, Circum-Pacific Kula, Farallón, Cocos and Caribbean tectonic plates. These tectonic plates cause continental and oceanic movements that intermittently induce the continental accumulations of deep marine sediments in the continental marginal accretional prism of the Gulf of Mexico [40].
