## 2 Material and Methods  
The study area is located in the southeast coast of Spain (province of Alicante), with an approximate location at coordinates 38.14 N and 0.73 W (Figure 1). It comprises of a coastal floodplain that, centuries ago, was a large coastal marsh and a lagoon (Elche lagoon) [21]. After the progressive implementation of drainage infrastructures for centuries, especially in the 18 th century, the current landscape developed a mixture of irrigated agricultural areas and wetlands, with scattered urban areas.  
The study area was developed over quaternary sediments, mainly transported by two rivers (Segura River in the south and Vinalopo River in the north), whose flow converged into the ancient lagoon. That lagoon was separated from the sea by a sand dune barrier. The resulting topography of the study area is very flat (Figure 1, upper), with an altitude lower than 20 m a.s.l. (excluding El Molar hill with 76 m a.s.l.), with a median ground elevation of 6.8 m and average slope below 1%. Dominant soils were calcaric fluvisols, although anthrosols, due to profoundly modifications through long-term cultivation (i.e., years), and Solonchaks, because of the high soil salinity, are well represented in the area [22]. In  
Figure 1: Descriptive maps of the study area: (**upper**) location of the study area showing the main populated areas (e.g., Almoradi); the digital elevation model (DEM), main water courses (natural and artificial, e.g., azarbes, which is the drainage network) and the location of the sampling points. (**Lower**) agricultural land covers at the study area; irrigation channels associated to each river are shown with different colors.  
fact, previous edaphic research [23] evidenced large variability of soil electrical conductivity values, from low average electrical conductivity values for permanent crops areas (0.423 dS/m) to high values close to saltmarshes (4.5 dS/m). Homogeneous pH values (from 8.1 to 8.4) and soil organic matter content (1.9 to 2.6%) were also observed in our previous study [23].  
In regard to the climate, the Koppen-Geiger climate class is _BSh_ (hot semi-arid climate), with an annual average temperature reaching above 18 \({}^{\circ}\)C, and average precipitation lower than 300 mm [24]. Additionally, high temporal variability in precipitation promotes periods of severe drought, contrasting with periods of very intense and dramatic flood events.  
The agriculture is possible due to the presence of a large network of drainage channels (called azarbes) that allow draining the water, reducing groundwater level to desiccate wetlands and marshes, increasing the arable land (Figure 1, lower). Based on the Corine Land Cover 2018 cartography [25], 74% of the study area is agriculture land cover classes, mainly permanently irrigated land (CLC2018 level 3 code 212 ; 39% of the study area), and fruit trees and berry plantations (CLC2018 level 3 code 222 ; 21% of the study area. However, some wetland areas persisted and were transformed into water reservoirs to be used for irrigation and, nowadays, form the Natural Park of \"El Hondo\" [21]. Two sectors within the irrigation systems can be distinguished: (_a_) the northern sector of the Vinalopo river (pours its water into the channels instead of directly into the sea), and associated channels that finally converge for a single water flow into the Mediterranean Sea. (_b_) The southern sector of the Segura River (larger water flow than the Vinalopo River) and associated channels (also converge for a single water flow into the Mediterranean Sea).