Dew Formation and Water Availability at High Elevation in the Atacama Desert, Chile By Zachary R. Schubert Ecology and Evolutionary Biology, University of Colorado Boulder Defense Date April 3, 2014 Thesis Advisor: Prof. Steven Schmidt, Ecology and Evolutionary Biology Defense Committee: Prof. Steven Schmidt, Ecology and Evolutionary Biology Prof. Barbara Demmig-Adams, Ecology and Evolutionary Biology Prof. Paul Strom, Honors Program Schubert 1 Abstract The Atacama Desert, Chile, is among the least habitable environments on the planet largely because of its extreme aridity; nevertheless, ecosystems continue to function in many locations there, at least intermittently when water is available. This study addresses the question of whether dew could ever form at high-elevation sites in the Atacama region. Two distinct modeling approaches were used to model dew formation on volcanoes using data from climate stations at 2950, 4720, and 5820 meters above sea level (m.a.s.l.) to help explain the presence of a recently discovered simple microbiological ecosystem existing in soils from 5200 to over 6000 m.a.s.l. on other volcanoes in the region. The first model uses field data for air temperature and relative humidity to calculate dew point (temperature at which dew would form) and compares it with field soil temperatures at different depths as well as with air temperature. The second model calculates and compares the maximum amount of water vapor that air of the respective air temperature at each elevation could hold (saturation vapor pressure) to the actual amount of water vapor present (actual vapor pressure) at the time of measurement. Both models show that dew formation would not occur regularly at any of the elevations or months measured in the field. However, given that there are times just before sunrise when conditions are close to allowing for dew, it is possible that a rare and atypical weather event may result in dew formation. Given the known ability of organisms adapted to arid environments to survive long periods of no water availability, it is possible that this intermittent access to liquid water is sufficient to sustain the ecosystem found on high elevation volcanoes in the Atacama region. Schubert 2 Introduction Life as we know it cannot exist without access to liquid water (O’Malley-James et al. 2013). It follows that wherever life exists there must be liquid water in some quantity, although this may be very small and infrequently available. Therefore, the discovery of a “low diversity, low energy ecosystem of unique and previously uncharacterized microbes” at sites above 6000 meters above sea level (m.a.s.l., 19,600 ft. above sea level) in the soil of volcanoes in the Atacama Desert, northern Chile (Lynch et al. 2012), leads directly to the question of where such an ecosystem gets water in the driest environment on the Earth and, on a larger scale, how life adapts and survives in such extreme environments. Ultimately, answering this question could lead to a more complete understanding of the limits to life on Earth, as the complexities allowed by abundant resources are stripped away, leaving the organisms that remain at their most basic. This is also one of the defining goals of the field of astrobiology, which considers the question of whether and where life could exist on planets other than our own. Sites in the Atacama are considered to be some of the best extraterrestrial analog locations on Earth and therefore may give insight into the potential for life to survive or even to have developed outside the bounds of our planet (Heldmann et al. 2013). The Atacama Desert region is located in northern Chile around 24° South, 69° West, west of the Chilean Andes. This desert is divided into elevational zones with different meteorological and biological features, which arise from prevailing wind patterns (Halloy 1991, D. Schmidt 1999). The effect of these zones on the distribution of vegetation is presented in Figure 1, which has been reproduced from Richter and D. Schmidt (2002). These mountains follow a standard pattern of increased moisture availability, and therefore plant life, in middle elevations from air masses being forced upwards by the slope of the mountain, creating a vegetation belt (Arroyo et al. 1988). Across the Atacama region, the span of this band of vegetation is at its maximum Schubert 3 from 2800 to 5000 m.a.s.l. (Richter and D. Schmidt 2002), with the width of the band varying among individual mountains (Costello et al. 2009, Lynch et al. 2012). Above and below these elevations there is no plant life except for that found at uniquely sheltered and resource-rich locations such as those explored by Costello et al. (2009), where water, carbon dioxide, methane, and heat are provided by geothermal processes. The lower elevation desert scrub band leads down into the Atacama Desert proper (Arroyo et al. 1988). The upper band (above the vegetation zone) receives more precipitation, but the sheer aridity and solar energy input result in rapid and near-complete loss of water due to sublimation (the process of ice transitioning directly into water vapor without passing through a liquid water stage) of ice and snow (Lynch et al. 2012, Arroyo et al. 1988, D. Schmidt 1999). Figure 1: Distribution of vegetation by elevation on Llullaillaco, the second highest active volcano on Earth (Richards and Villeneuve 2004) at 6740 m.a.s.l. (22,100 ft). (reproduced from Richter and D. Schmidt 2002) In their biogeochemical and microbiological studies, Lynch et al. (2012) investigated water, carbon, and nitrogen content of soils from high in the upper elevation band (>6000 m.a.s.l.), finding extremely low values for these parameters, which are necessary for life. Water was found to constitute only about 0.25% of the soil and nitrogen was extremely scarce (below the detection limit of 25 µg N / g soil). Coupled with the enormous daily amplitude of soil temperature of 66.4°C observed at 5500 m.a.s.l. (Lynch et al. 2012) and the high frequency of Schubert 4 freeze-thaw cycles, which D. Schmidt (1999) reports as occurring 350 days per year, it is not surprising that the Lynch study discovered only a very rudimentary ecosystem at these sites. However, given the discovery of extremely well-preserved mummies (which are rich in carbon and nitrogen) above 6000 m.a.s.l. on Llullaillaco (Wilson et al. 2007), it would seem that water is much more of a limiting factor than either of the latter two nutrients because the quality of their preservation indicates that bacteria that cause decay are either not present or not functioning. The question then arises again of how the soil microorganisms discovered by Lynch et al. (2012) obtain water. It has been shown for other arid and semi-arid environments, including in low elevation reaches of the Atacama Desert (Azúa-Bustos et al. 2011), that where the amount or frequency of precipitation is insufficient to sustain the life forms present, non-precipitation water sources such as fog, water vapor adsorption, and dew provide enough water to sustain complex ecosystems (Agam and Berliner 2006, Jacobs et al. 2002, Kidron et al. 2002, Matimati et al. 2013). As fog seemed unlikely given the meteorological conditions of the area, which normally include high wind (D. Schmidt 1999), and because water vapor adsorption (the process of water vapor adhering directly to the surface of soil particles, forming an extremely thin film of liquid water) has been little studied and there is currently no method to calculate its contribution to water in the soil without knowing how much water there was in total (Agam and Berliner 2006), the present study examined whether and when dew formation could occur in this environment. Materials and Methods The climatological data used in the present study came from the only identifiable study that had measured relative humidity, soil temperatures, and air temperatures at elevations above 5000 m.a.s.l. in the Atacama Desert region. These data are contained in a dissertation written by D. Schmidt and published by the Technical University of Dresden in 1999, titled “Das Schubert 5 Extremklima der nordchilenischen Hochatacama unter besonderer Berücksichtigung der Höhengradienten” (“The extreme climate of the north Chilean high Atacama under particular consideration of elevational gradients”). Data tables and figures from this dissertation were translated from German into English and entered into spreadsheets for further processing. The numerical data presented in figures, particularly those displaying average daily time courses of air temperature by season, soil temperature at varying depths by season, and relative humidity for three different mountains at three different elevations, were extracted using Adobe Photoshop before entry into a spreadsheet. Soil depths at which the temperature was measured by D. Schmidt (1999) were 0, 5, 10, 20, and 50 cm. The names of the volcanoes on which D. Schmidt collected his data and their elevations are Volcán Pelón at 2950 m.a.s.l., Jorquencal at 4720 m.a.s.l., and Sairécabur at 5820 m.a.s.l. The studies by D. Schmidt (1999) and Lynch et al. (2012) did not take place on the same mountains. The weather stations of the former were set up on mountains to the north and east of the Salar de Atacama (the salt plain at the hyper-arid core of the Atacama Desert; there are many such salars in the region) near or on the Chile-Bolivia border, while the soil samples taken by the latter are from mountains to the south of the Salar de Atacama on the Chile-Argentina border (named Volcán Socompa and Llullaillaco), at varying elevations. The approximate locations of all sites relevant to the current study are given in Figure 2, below, using a map reproduced from Costello et al.