Abstract

The coast of the Atacama Desert is characterized by regular presence of fog, which provides water and nutrients to unique ecosystems well-adapted to extreme arid conditions. The spatial variation in the availability of resources transported in fog water and their potential role in terms of well-being in fog ecosystems are poorly known. In this context, our hypothesis is that the resource concentrations vary along the coast, among seasons, and fog water inputs. This study was carried out at three different fog oases in the coastal Atacama Desert, hyper-arid (20°S), arid (26°S), and semi-arid (30°S) to determine differential input of compounds and fog water into ecosystems. Particularly we characterize compounds such as Nitrate (NO3-), Ammonia (NH4+), Nitrite (NO2-), Phosphate (PO4-3), and conditions such as pH, Alkalinity, and Hardness. In addition, we assessed the temporal variability of fog water collection (L/m2) across all sites. Samples were collected by using a CASCC (active strand water collector), and the analysis were in situ. The fog water was collected with a standard fog collector (SFC). Fog water composition showed large spatial variation of Nitrate (3-84ppm), followed by Ammonia (0.1 – 2.8 ppm), Phosphate (0– 1.2 ppm), and Nitrite (0 – 0.3 ppm). Concerning chemical conditions, fog water was soft (hardness between 6 – 146 ppm), buffer capacity was lower (alkalinity between 5-40ppm), and pH varies from acid to neutral (4.4<pH<7.2). Our analysis reveals that pH increases with latitude but PO4-3 and NO3- decreases. Fog water collected indicates the highest collection rate at the hyper-arid site (6 L/m2/día) but more marked temporality (fog presence from May to November) than the other places (26°S and 30°S). The relationship between compounds and fog water collected is negative, the season with more water collected, the nutrient concentrations are lower. In conclusion, the nutrient concentrations are closely related to the latitude and volume of fog water collected. Thus, changes in fog water variability due to global warming may affect nutrient input at fog oases. Finally, this work expands our knowledge of the distribution of nutrients, main chemical characteristics, and the temporal variability of fog water along the coastal Atacama Desert. The latter helps us to understand the impact of fog on the ecosystems and continue to research it as a reservoir and transport vector of nutrients, microorganisms, pollutants, microplastics, and more.