A Case Study on Fog/Low Stratus Occurrence at Las Lomitas, Atacama Desert (Chile) as a Water Source for Biological Soil Crusts

Abstract

The Atacama Desert is well known for the high occurrence of large-scale fog (spatial extents: hundreds of kilometers) emerging as low stratus (LST) decks over the Pacific Ocean. By contrast, the small-scale and heterogeneous occurrence of small-scale fog (hundreds of meters) particularly during summers is widely unconsidered. However, these events are important for the local vegetation and particularly for the biological soil crusts (BSC) that are widely distributed in this extreme ecosystem. Consequently, a case study in a typical fog oasis in the Pan de Azúcar National Park was conducted to test the feasibility combining field measurements, drone profiling, remote sensing and numerical modeling (i) to investigate fog-type specific differences regarding dynamics, physical properties and formation, (ii) to test the applicability of remote sensing technology for fog monitoring based on existing low-resolution and a proposed new high-resolution product and (iii) to estimate the related fog water input to BSCs. Two types of fog were observed. The well-known fog/LST deck emerging from the Pacific Ocean with high water path and large spatial extent was the first type. Fog of the second type was patchier, small-scale and not necessarily connected to the LST over the ocean. Instead, fog formation of the second type was related to thermal breeze systems, which produced shallow clouds containing less water than those of type 1. In general, such small-scale fog events were not captured well by existing remote sensing products but could be detected with the proposed new high-resolution product which provided promising results. Both fog types were important water resources for the BSCs, with approximately 8% to 24% of the fog water flux available to the BSCs at the surface. The results indicated the feasibility of the proposed methods' pool to estimate the water budget of BSCs with a high spatial resolution in the future.

Desert breath—How fog promotes a novel type of soil biocenosis, forming the coastal Atacama Desert’s living skin

“…In contrast, cyanobacterial lichens (cyanolichens) and cyanobacteria can only be activated by liquid water (Büdel & Lange, ; Lange, Kilian, & Ziegler, ). Interestingly, in contrast to our second hypothesis, cyanobacteria were part of the grit–crust community as well, probably because the two main liquid water sources, fog and dew, were frequently available at Las Lomitas (Lehnert, Thies, et al, ). We noticed that cyanobacterial presence in the arid and hyperarid zone of the Atacama Desert (e.g., Warren‐Rhodes et al, , Wierzchos, Ascaso, & McKay, ) is apparently directly related to microhabitats that provide a condensation surface large enough for dew and fog to precipitate.…”

“…Additionally, rainfall is measured at another AWS (AWS main, Lat: 25.984372°S, Lon: 70.61528°W) directly at the Pacific coast. The setup, calibration, and first results are described in Lehnert, Thies, et al, 2018b.…”

Annual net primary productivity of a cyanobacteria-dominated biological soil crust in the Gulf Savannah, Queensland, Australia

“…Dew formation determined for an inland dune biocrust community in Germany ranged from 0.04 and 0.18 kg m 2 over 2 days (Fischer et al, 2012). Even fog was identified as a major source of non-rainfall water driving biocrust productivity in the Atacama Desert of Chile, where approximately 8 to 24 % of the fog water flux was available to the biocrusts at the soil surface (Lehnert et al, 2018).…”

Effect of changing vegetation on denudation (part 1): Predicted vegetation composition and cover over the last 21 thousand years along the Coastal Cordillera of Chile

“…Most distinct regional discrepancy can be observed at coastal areas between 30° S to 36° S, which might be attributed to the lack of fog-precipitation in our model. Fog precipitation is strongly dependent on distance to the coast, local topography, wind fields, and stratification of the 30 troposphere (Lehnert et al, 2018) and can potentially contribute significant amounts of precipitation (Garreaud et al, 2008). However, a model representation in LPJ-GUESS is difficult due to the scale mismatch and a lack of required input variables to determine the occurrence of fog.…”