## 2 Study Area  
The study area is located in northern Algeria (Figure 1). A special focus is placed on the ephemeral salt lakes--Chott Merluir and Chott Merouane--in the Maghreb region [46; 47; 48]. The formation of these chotts is caused by complex geologic settings and tectonic developments in northern Algeria. This region belongs to the North African Alpine chain, which is formed by three large mountain domains: Tell, pre-Atlas, and Atlas, which each present the deformed margin of the stable African Craton. The Earth's crust in this area has undergone a complex deformation during the Alpine orogen [49]. To the south and east of the South Atlas Front, the Saharan topography presents a longitudinal asymmetry and decreases in altitude eastwards. In eastern Algeria, the Atlas foreland corresponds to the distribution of chotts and sabkhas, which are located within the active subsiding area with topographic depressions. Chotts are situated within a large asymmetrical syncline of the Northern Sahara Sedimentary Basin, which was formed as a result of complex tectonic movements [50; 51]. Similar to playas, chotts in Algeria are endorhei lakes located at the bottom of a large hydrographic basin [52]. These salt lakes encompass immense areas (nearly 3 M hectares)of shallow topographic depressions in northern Algeria, located in the arid region of the Sahara, characterized by a specific hydrological regime and a high level of salinity [53]. The topographic depression occupied by Chotts Melrhir and Merouane (Figure 2) is located south of the Maghrebian Atlas in the Northern Sahara Sedimentary Basin. Their formation was largely influenced by vertical movements in the Atlas system during the Mesozoic and Cenozoic periods, as well as Triassic-Lower Jurassic faults [54]. The aquifer is composed of Quaternary sediments, such as sand, sandstone, clayey sand, and gypsum; the groundwater flow is predominantly oriented in a northward direction [55; 56], which controls the geochemical content of groundwater [57]. The chotts in Algeria occupy a large area, mainly located in the eastern part of the country. Their geographic situation and extent are largely influenced by a complex combination of topographic and climatic factors: the extent of the depression favors the accumulation of  
Figure 1: Topographic map of Algeria. Software: GMT v. 6.1.1. Data sources: GEBCO and DCW. The rotated red square indicates the study area with Chotts Melrhir and Merouane. Map source: author. water, sediments, and dust [58; 59], while the eastern Sahara experiences a higher level of precipitation and moisture, making it the wettest region in the country [60; 61]. Moreover, the regional environmental setting of eastern Algeria and the northern Sahara is characterized by the contrasting influences of the Mediterranean climate in the north and the arid Sahara in the south [62; 63]. The largest chotts of Algeria include Chotts Merouane and Melrhir (Figure 2) [64]. Moreover, Algeria's large chotts include multiple minor chotts of smaller sizes, including Chott Ech Chergui, which is the second largest chott in North Africa [65; 66; 67; 68], Chott El Beida (Chott El Beida-Hammam Essoukhna), Chott Oum El Raneb [69], Chott El-Gharbi [70], and Chott El Hodna [71]. The specific hydrological setting of chotts exhibits a highly contrasting regime: chotts remain dry for much of the year but collect drainage water in the winter period from the occasional rain, wadi flow, spring thaw water, or groundwater [72; 73]. The level of a chott surface depends on the position of the water table. Overall, sediment deflation occurs during the decline of the water table, and sediment accumulation occurs during the water rise. Such highly specific hydrogeological and hydrochemical settings of the chotts in Algeria are a result of the complex geological development of Algeria [74; 75; 76; 77]. This has led to the formation of saline minerals and lithium in the lake sediments [78; 79; 80].