## 2 Study Area
Chotts Merouane and Melrhir in Algeria are located within the Northwestern Sahara Aquifer System (NWSAS), which is one of the largest transboundary aquifer systems in the world, and is shared between Algeria, Tunisia, and Libya. With a size of over 1 M km\({}^{2}\), the NWSAS largely contributes to the water supply of chotts through groundwater [81]. Another water supply source of Chotts Melrhir and Merouane is occasional rainfall. The third type is derived from spring thaw waters and wadi flows from the Atlas mountains. Thus, the water levels in Chotts Melrhir and Merouane are supported by three different types of water: occasional rainfalls, spring thaw, and groundwater [82; 83; 84]. A crystallized salt layer forms on the surface of the lake during the periods when the lakes remain dry due to fluctuations in the hydrology of the lake [85]. The chotts in Algeria receive water intermittently; the lake level is subject to frequent shrinkages and a high evaporation rate, which leads to the accumulation of a salt layer on the surface of the sediment at the ground level of the lakes. The distribution of the salt differs within the salt pan, with gypsum- and halite-rich deposits occupying the centers of the depressions and carbonate outliers found at the medium level, as well as lacustrine calcareous deposits located on the aeolian sands [86]. Soil types are largely controlled by the geologic structures  
Figure 2: (**a**) Chott Melrhir and Chott Merouane (also known as Melrhir Chott) enlarged on the Google Maps (2023); (**b**) Chott Melrhir and Chott Merouane on the Google Earth aerial scene (2023). in sedimentary basins, which include large and deep reservoirs of the Sahara contoured by chotts filled by water during rainy periods [87]. Specific soil properties and salinity gradients in chotts in Algeria largely affect the distribution of flora and vegetation types around the saline lakes [88]. For instance, the contents of gypsum affect the variation of the vegetation cover of halophyte plants. Other geochemical parameters of soil in chotts, such as pH, Na, and Cl concentrations, control the distribution of plants in moderately to low saline soils within chotts [89]. The biogeochemical cycles of carbon, nitrogen, sulfur, and other elements within the arid lands of chotts, result in specific types and distributions of species populations and microbial communities [90; 91]. Further details on geochemical settings and soil salinity are discussed in existing papers on the chotts in Algeria [92], with details on hydrogeological evaluations of geothermal resources [93; 94; 95], analysis of mineralogy in desert alluvial soils in wadis of the northern Sahara [96], brine geochemistry and mineralogy of the Algerian play [97; 98], and hydrological and environmental modeling in chotts [99]. The salt pans of Chott Merouane and Chott Melrhir serve as examples of sensitive wetlands within the arid climate of Algeria. The agricultural and vegetation potential of chotts is largely controlled by soil in the northern Sahara which lacks organic carbon. As a result, the vegetation of chotts is characterized by a specific type of flora that has adapted to the highly depleted and dry soil of the semi-arid climate [100]. While most areas of chotts are devoid of vegetation due to high salt concentrations in soil, there are occasional types distributed over the moist areas and edges of wetlands. Such plants are mostly composed of halophytic, succulent, and perennial species, e.g., the _Chenopodiaceae_ family adapted to droughts and salty soils [69]. The social advantages of such unique landscapes include three types of benefits: (1) salt mining in the pan; (2) palm inter-cropping and palm monoculture; (3) grazing areas in a palm oasis on the border of the lake [101]. Despite the ecological importance, special geochemical settings, unique landscapes, and specific biodiversity of the saline lakes, studies on the chotts in Algeria remain scarce.