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Evaporation and land surface energy budget at the Salar de Atacama, Northern Chile
Abstract
Playa systems are driven by evaporation processes, yet the mechanisms by which evaporation occurs through playa salt crusts are still poorly understood. In this study we examine playa evaporation as it relates to land surface energy fluxes, salt crust characteristics, groundwater and climate at the Salar de Atacama, a 3000 km2 playa in northern Chile containing a uniquely broad range of salt crust types. Land surface energy budget measurements were taken at eight representative sites on this playa during winter (August 2001) and summer (January 2002) seasons. Measured values of net all-wave radiation were highest at vegetated and rough halite crust sites and lowest over smooth, highly reflective salt crusts. Over most of the Salar de Atacama, net radiation was dissipated by means of soil and sensible heat fluxes. Dry salt crusts tended to heat and cool very quickly, whereas soil heating and cooling occurred more gradually at wetter vegetated sites. Sensible heating was strongly linked to wind patterns, with highest sensible heat fluxes occurring on summer days with strong afternoon winds. Very little energy available at the land surface was used to evaporate water. Eddy covariance measurements could only constrain evaporation rates to within 0.1 mm d−1, and some measured evaporation rates were less than this margin of uncertainty. Evaporation rates ranged from 0.1 to 1.1 mm d−1 in smooth salt crusts around the margin of the salar and from 0.4 to 2.8 mm d−1 in vegetated areas. No evaporation was detected from the rugged halite salt crust that covers the interior of the salar, though the depth to groundwater is less than 1 m in this area. These crusts therefore represent a previously unrecorded end member condition in which the salt crusts form a practically impermeable barrier to evaporation.
... The spatiotemporal evolution of evaporation has also been investigated in the Altiplano region of the Atacama Desert. These studies aimed to understand the complex diurnal land-atmosphere turbulent transport over different surfaces (Kampf et al., 2005;de la Fuente and Meruane, 2017;Lobos-Roco et al., 2021), characterizing the larger-scale influence on the local evaporation Lobos-Roco et al., 2021), or simply to assess daily evaporation from bare soils in order to develop relationships that can be used to relate evaporation with the water-table depth (Johnson et al., 2010). These investigations mainly focused on shortterm field experiments based on either daily measurements (Kampf et al., 2005;Suárez et al., 2020) or applied models used to predict potential evaporation (de la Fuente and Meruane, 2017). ...
... These studies aimed to understand the complex diurnal land-atmosphere turbulent transport over different surfaces (Kampf et al., 2005;de la Fuente and Meruane, 2017;Lobos-Roco et al., 2021), characterizing the larger-scale influence on the local evaporation Lobos-Roco et al., 2021), or simply to assess daily evaporation from bare soils in order to develop relationships that can be used to relate evaporation with the water-table depth (Johnson et al., 2010). These investigations mainly focused on shortterm field experiments based on either daily measurements (Kampf et al., 2005;Suárez et al., 2020) or applied models used to predict potential evaporation (de la Fuente and Meruane, 2017). Even with these studies, long-term evaporation observations at a local scale are still lacking, especially when trying to construct conceptual models that can be used for water resource management. ...
... This terminal lake shows significant seasonal changes in its surface, ranging between ∼ 0.5 to 5 km 2 , with a measured depth of ∼ 15 cm . These types of groundwater-fed wetlands are commonly found in the Alti-plano region (Kampf et al., 2005), and result in unique ecological habitats for endemic flora and fauna (Dorador et al., 2013). ...
We investigate how evaporation changes depending on the scales in the Altiplano region of the Atacama Desert. More specifically, we focus on the temporal evolution from the climatological to the sub-diurnal scales on a high-altitude saline lake ecosystem. We analyze the evaporation trends over 70 years (1950–2020) at a high-spatial resolution. The method is based on the downscaling of 30 km ERA5 reanalysis data at hourly resolution to 0.1 km spatial resolution data, using artificial neural networks to analyze the main drivers of evaporation. To this end, we use the Penman open-water evaporation equation, modified to compensate for the energy balance non-closure and the ice cover formation on the lake during the night. Our estimation of the hourly climatology of evaporation shows a consistent agreement with eddy-covariance (EC) measurements and reveals that evaporation is controlled by different drivers depending on the time scale. At the sub-diurnal scale, mechanical turbulence is the primary driver of evaporation, and at this scale, it is not radiation-limited. At the seasonal scale, more than 70 % of the evaporation variability is explained by the radiative contribution term. At the same scale, and using a large-scale moisture tracking model, we identify the main sources of moisture to the Chilean Altiplano. In all cases, our regime of precipitation is controlled by large-scale weather patterns closely linked to climatological fluctuations. Moreover, seasonal evaporation significantly influences the saline lake surface spatial changes. From an interannual scale perspective, evaporation increased by 2.1 mmyr-1 during the entire study period, according to global temperature increases. Finally, we find that yearly evaporation depends on the El Niño–Southern Oscillation (ENSO), where warm and cool ENSO phases are associated with higher evaporation and precipitation rates, respectively. Our results show that warm ENSO phases increase evaporation rates by 15 %, whereas cold phases decrease it by 2 %.
... Because of its location and geographical features, the SdA is characterized by climatic conditions that are among the most arid of the world, with an annual average precipitation of 20 mm/year and an actual evaporation rate of about 1,000 mm/year in vegetated areas. This value rapidly decreases when approaching the rugged halite nucleus, where aquifer brine evaporation is almost absent (Kampf et al., 2005). ...
... Finally, production wells operating from July 1, 2013, to November 18, 2016, are modeled as point extractions whose flow rates change over time. In accordance with Mardones (1998) and Kampf et al. (2005), evaporation can be neglected within the SdA nucleus because the capillary fringe is insignificant and vertical vapor transport is limited by a thick dry salt crust. ...
... Here, recharge is mainly controlled by the halite near-surface conditions, which consist of a fractured and cavity-rich dry salt crust that favors rapid percolation during rainfall events of relatively high intensity. Core samples suggest that the size of pore structures in the near surface can be as large as 1 cm (Kampf et al., 2005). Note also that the surface is flat preventing run-off, and there is no vegetation. ...
Understanding groundwater flow involves characterizing the spatial variability of aquifer attributes and possible hydraulic connectivity structures. The latter are of crucial importance because high permeability channels may control groundwater flow and contaminant transport. In evaporitic aquifer systems, these preferential channels can consist of karst conduits, developed at different scales, as well as fault zones. These features condition the economic development of salt flats at the Central Andes. Hydraulic connectivity may affect exploitation efficiency by enhancing the inflow of less evaporated brine thus diminishing its mineral content (i.e., concentration of Li and K). In this context, we investigate if it is possible to use (tomographic) stochastic inversion (regularized pilot point method) in order to characterize the presence of connectivity structures in an evaporitic aquifer of great extension (some 1,500 km²) from head response measured at numerous observation points during a year long sequence of three hydraulic tests. Results show that, even though the solution is nonunique, the main preferential flow zones are identified. Numerous inversions yield similar fits to observed drawdowns with maximum errors of few centimeters. Preferential flow is identified not only by elongated high permeability regions, but also by a marked scale effect (model transmissivities are some 30 times larger than their local tests counterparts). The main high conductivity zones are consistent with independent information based on geophysics, isotopes, mixing ratios, piezometric data, and the expected dissolution processes.
... This study also introduced the first investigations of a long-term evaporation (1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991) analysis and its relationship with the ENSO phenomenon. At a more local scale, Kampf et al. (2005) measured turbulent fluxes from heterogeneous surfaces in the Salar de Atacama, analysing their diurnal cycles in a seasonal campaign. de la Fuente & Meruane (2017) developed a thermodynamic model to predict potential evaporation in Salar del Huasco using meteorological reanalysis data. ...
... The surface energy balance describes the energy partitioning (radiation), where evaporation is one of the main components. Here, variables such as albedo, soil moisture, and surface roughness characteristics play key roles in evaporation (Kampf et al., 2005). Groundwater upwelling (light blue dashed line in Fig. 1.3a-Box VI) determines the water availability on each surface type (Uribe et al., 2015). ...
... These rainstorms are the source of aquifer recharge and thus they sustain wetlands that are formed in the basins due to surface discharge and groundwater upwelling. The high Andean wetlands sustain unique ecological habitats, being home to the most threatened bird species (Kampf et al., 2005;Johnson et al., 2010). The wetlands act as highly evaporative environments and thus, it is where nearly all the water of the basin is lost to the atmosphere (Johnson et al., 2010). ...
... The spatiotemporal evolution of evaporation has also been investigated in the Altiplano region of the Atacama Desert. These studies aimed to understand the complex diurnal land-atmosphere turbulent transport over different surfaces (Kampf et al., 2005;de la Fuente and Meruane, 2017;Lobos-Roco et al., 2021), characterizing the larger scale influence on the local evaporation Lobos-Roco et al., 2021) or simply to assess daily evaporation from bare soils in order to develop relationships that can be used to relate evaporation with the water table depth (Johnson et al., 2010). These investigations mainly 70 focused on short-term field experiments based on either daily measurements (Kampf et al., 2005;Suárez et al., 2020) or applied models used to predict potential evaporation (de la Fuente and Meruane, 2017). ...
... These studies aimed to understand the complex diurnal land-atmosphere turbulent transport over different surfaces (Kampf et al., 2005;de la Fuente and Meruane, 2017;Lobos-Roco et al., 2021), characterizing the larger scale influence on the local evaporation Lobos-Roco et al., 2021) or simply to assess daily evaporation from bare soils in order to develop relationships that can be used to relate evaporation with the water table depth (Johnson et al., 2010). These investigations mainly 70 focused on short-term field experiments based on either daily measurements (Kampf et al., 2005;Suárez et al., 2020) or applied models used to predict potential evaporation (de la Fuente and Meruane, 2017). Even with these studies, long-term evaporation observations at a local scale are still lacking, especially when trying to construct conceptual models that can be used for water resource management. ...
... This terminal lake shows significant seasonal changes in its surface ranging between ∼0.5 to 5 km 2 , and has a measured depth of ∼15 cm . These types of groundwater-fed wetlands are commonly found in the Altiplano region 115 (Kampf et al., 2005), and result in unique ecological habitats for endemic flora and fauna (Dorador et al., 2013). ...
We investigate how evaporation changes depending on the scales in the Altiplano region of the Atacama Desert. More specifically, the temporal evolution from the climatological to the sub-diurnal scales on a high-altitude saline lake ecosystem. We analyse the evaporation trends over 70 years (1950–2020) at a high-spatial resolution. The method is based on the downscaling of 30-km hourly resolution ERA5 reanalysis data to 0.1-km spatial resolution data, using artificial neural networks to analyze the main drivers of evaporation. To this end, we use the Penman open water evaporation equation, modified to compensate for the energy balance non-closure and the ice cover formation on the lake during the night. Our estimation of the hourly climatology of evaporation shows a consistent agreement with eddy-covariance measurements and reveals that evaporation is controlled by different drivers depending on the time scale. At the sub-diurnal scale, mechanical turbulence is the primary driver of evaporation, and at this scale, it is not radiation-limited. At the seasonal scale, more than 70 % of the evaporation variability is explained by the radiative contribution term. At the same scale, and using a large-scale moisture tracking model, we identify the main sources of moisture to the Chilean Altiplano. In all cases, our regime of precipitation is controlled by large-scale weather patterns closely linked to climatological fluctuations. Moreover, seasonal evaporation influences significantly the saline lake surface spatial changes. From an interannual scale perspective, evaporation increased by 2.1 mm per year during the entire study period, according to global temperature increases. Finally, we find that yearly evaporation depends on the El Niño Southern Oscillation (ENSO), where warm and cool ENSO phases are associated with higher evaporation and precipitation rates, respectively. Our results show that warm ENSO phases increase evaporation rates by 15 %, whereas cold phases decrease it by 2 %.
... Since brines can remain liquid across a broader range of environmental conditions than fresh waters (sustained liquid in low humidity and pressure conditions and from -100 to 300 °C) and evaporites can host and preserve microbial ecosystems, saline pans are increasingly studied as Martian analogs (Benison & Bowen, 2006;Benison & Karmanocky, 2014;Jones et al., 2011;Schreder-Gomes et al., 2022). Regional micrometeorology can be improved by studying and describing saline pans, which can be very extensive (>1000 km 2 ) (Craft & Horel, 2019;Kampf et al., 2005;Tyler et al., 2006). ...
... Uncertainties in our estimated evaporation models rely upon uncertainty in the albedo-water availability relationship and uncertainty in measured evaporation values; random and systematic data acquisition timing errors can lead to measured flux underestimations of 10% (Fratini et al., 2018). Differences between cumulative evaporation estimates across models appear to capture estimated evaporation uncertainty over annual timescales and are comparable in scale to prior evaporation uncertainty measurements from similar settings (3 to 4 cm/year Garcia et al., 2015;Kampf et al., 2005). ...
... We observed low measured evaporation rates when the surface was desiccated, regardless of evaporative potential, indicating evaporation from desiccated saline pans is limited by water availability. Our observations corroborate previous work demonstrating negligible groundwater evaporation from desiccated saline pans and playas (Jackson et al., 2018;Kampf et al., 2005). We observed tens of cm of seasonal groundwater change and several cm of diurnal groundwater change when the saline pan was desiccated. ...
... These rainstorms are the source of aquifer recharge and thus they sustain wetlands that are formed in the basins due to surface discharge and groundwater upwelling. The high Andean wetlands sustain unique ecological habitats, being home to the most threatened bird species [2][3][4]. The wetlands act as highly evaporative environments and thus, it is where nearly all the water of the basin is lost to the atmosphere [4]. ...
... Evaporation is strongly influenced by the connection between the land surface and the atmosphere [19], but there is few of this information in the Altiplano region [2]. In the open waters of the high Andean wetlands, de la Fuente and Niño [3] used a thermodynamic model to estimate mean daily evaporation rates of~8 mm day −1 , with peaks reaching values of~40 mm day −1 . ...
... However, for water resources management, observation of the surface energy balance fluxes is relevant in the bofedales and in zones with shallow groundwater (in the lake's downwind direction, i.e., towards the north of the lake) [4]. In the case of the dry salt-crust surface, we expect low evaporation rates, in a similar way to what was observed by Kampf et al. [2] in the Salar de Atacama. Second, the month in which the observations were performed was defined to have the more optimal conditions to study advection episodes, i.e., near the end of the dry season. ...
In the endorheic basins of the Altiplano, water is crucial for sustaining unique ecological habitats. Here, the wetlands act as highly localized evaporative environments, and little is known about the processes that control evaporation. Understanding evaporation in the Altiplano is challenging because these environments are immersed in a complex topography surrounded by desert and are affected by atmospheric circulations at various spatial scales. Also, these environments may be subject to evaporation enhancement events as the result of dry air advection. To better characterize evaporation processes in the Altiplano, the novel Evaporation caused by Dry Air Transport over the Atacama Desert (E-DATA) field campaign was designed and tested at the Salar del Huasco, Chile. The E-DATA combines surface and airborne measurements to understand the evaporation dynamics over heterogeneous surfaces, with the main emphasis on the open water evaporation. The weather and research forecasting model was used for planning the instruments installation strategy to understand how large-scale air flow affects evaporation. Instrumentation deployed included: meteorological stations, eddy covariance systems, scintillometers, radiosondes and an unmanned aerial vehicle, and fiber-optic distributed temperature sensing. Additional water quality and CO2 fluxes measurements were carried out to identify the link between meteorological conditions and the biochemical dynamics of Salar del Huasco. Our first results show that, in the study site, evaporation is driven by processes occurring at multiple spatial and temporal scales and that, even in the case of available water and energy, evaporation is triggered by mechanical turbulence induced by wind.
... Saline-pan-environmental fluxes and surface properties change between dry and wet periods (Nield et al. 2015;Craft and Horel 2019). Application and understanding of micrometeorological processes can be improved by studying and describing saline pans (Craft and Horel 2019;Kampf et al. 2005;Tyler et al. 2006;Zeppetello et al. 2023). A comprehensive methodology for delineating groundwater fluctuations in saline pans is lacking, and the controlling mechanisms still need to be clarified (e.g., Liu 2023). ...
... During measurement periods, data gaps in days with evaporation measurements were filled with values generated with an artificial neural network (Kang et al. 2019; section "Estimated evaporation"). Evaporation uncertainty was not determined here, but eddy covariance evaporation measurements from similar settings had uncertainties of 0.1 mm/day (~3-4 cm/year; Kampf et al. 2005;Garcia et al. 2015). ...
Saline pans are environments with ephemeral to persistent evaporite crusts, surface and groundwater brine, little to no vegetation, and low topographic gradients. These characteristics make them sensitive to diverse hydrological processes. This research provides guidance on assessing and interpreting fluctuations in saline pan groundwater levels. Observations from the center of the Bonneville Salt Flats, Utah, USA, focused on meteorological and groundwater level fluctuations and were used to quantify evaporation and identify natural environmental controls on saline pan groundwater level variation. Primary water fluxes consist of precipitation and evaporation. Eddy-covariance evaporation measurements, spanning over 1.5 years and capturing diverse surface conditions, were collected. An artificial neural network, trained on meteorological measurements and eddy-covariance-measured evaporation, estimated evaporation over a 6-year period. The saline pan has two states: (1) dry, when water availability rather than evaporative potential limits evaporation, and (2) wet, when evapora- tive potential limits evaporation. In dry conditions, characterized by evaporation rates of ~0.1 mm/day, groundwater levels with daily average depths ≥5 cm below the surface, demonstrated daily variations >6 cm during summer and seasonal fluctuations >50 cm in response to temperature changes. Groundwater levels did not respond to temperature changes when there was surface water. Groundwater levels rose to the surface under wet conditions. Over multiple years, the system is in balance, with evaporation equaling precipitation.
... The aforementioned legal dispute provided the opportunity to carry out scientific studies with the aim of quantifying evapotranspiration in the basin, and in wetlands in Chile similar to those occurring in the Bolivian part of the catchment. Kampf et al. (2005) performed one of the first studies that investigated ET a in the Altiplano using micrometeorological methods. They used the eddy covariance (EC) technique to observe ET a in a vegetated wetland, as well as in different salt crusts of the Salar de Atacama basin ($150 km south from the Silala River basin). ...
... And with regard to variation after precipitation events, ET a measured at EC1 seems to be fairly unresponsive in comparison to the other two stations. In general, these results are consistent with previous studies that investigated evapotranspiration in the Altiplano (Blin & Su arez, 2023;Johnson et al., 2010;Kampf et al., 2005;Lobos-Roco et al., 2021Mosre & Su arez, 2021;Su arez et al., 2020). ...
Evapotranspiration has been poorly characterized in the Altiplano, and the legal dispute over the status and use of the waters of the Silala River provided an opportunity for improving knowledge of this hydrological process, in a remote area with a lack of hydrometeorological data. Actual evapotranspiration (ET a ) measurements using eddy covariance (EC) were performed in the riparian wetland (EC1) and over the alluvial deposits (EC2) of the Silala River basin, and in the Putana River wetland (EC3), with similar characteristics to the Silala River headwaters. The portable chamber method was used to characterize soil and plant evaporation near EC2. Satellite‐derived ET a estimates were evaluated with the in‐situ data, and used to investigate spatiotemporal dynamics of the wetland vegetation cover. At EC1 and EC3, annual ET a values were 703 and 841 mm, respectively; and satellite‐derived ET a showed differences of 5% and −35% from these values. ET a exhibited strong seasonal variations at EC1 and EC3, and was sensitive to precipitation at EC2. ET a did not follow the temporal evolution of the reference evapotranspiration at EC2, suggesting that lateral subsurface flow supports ET a in dry periods. Portable chamber measurements revealed that bare soil evaporation is the main component of ET a in the alluvial deposits. ET a data collected within the basin, as described in other papers of this special issue, allowed validation of a hydrological model used to estimate the basin's groundwater recharge, and estimation of the surface flow increase due to river channelization, which were important scientific evidence provided in the legal dispute.
This article is categorized under: Science of Water > Hydrological Processes
Science of Water > Methods
... In particular, experimental and field research consistently show that continuous crusts reduce evaporation rates on playa surfaces by an order of magnitude compared to climate-derived estimates [8,29,[35][36][37]. As a result, the observed groundwater evaporation rates at sites with active and continuous salt crusts tend to lie in the relatively low range of 0.2-0.7 mm=day, including seasonal variations [29,[37][38][39][40][41]. ...
... At Owens Lake, we also directly measure density differences of Δρ ¼ 210 AE 10 kg m −3 between pore water samples taken from close to the surface and at approximately 1 m depth (data in Ref. [84]). The annual average evaporation rates of groundwater are taken as E ¼ 0.4 AE 0.1 mm=day [29,37] for Owens Lake, 0.3 AE 0.1 mm=day [38] for Badwater Basin, and E ¼ 0.7 AE 0.5 mm=day for Sua Pan [35,39], with further details reviewed in Appendix D. These low levels of groundwater evaporation are characteristic of salt pan environments, and similar rates are seen in active playa of the Atacama desert (E ¼ 0.5 AE 0.1 mm=day [40]) and sabkhas near Abu Dhabi (E ¼ 0.2 AE 0.05 mm=day [41]). Finally, we assume the dynamic viscosity of the groundwater to be a constant μ ¼ 10 −3 Pa s. ...
From fairy circles to patterned ground and columnar joints, natural patterns spontaneously appear in many complex geophysical settings. Here, we investigate the origins of polygonally patterned crusts of salt playa and salt pans. These beautifully regular features, approximately a meter in diameter, are found worldwide and are fundamentally important to the transport of salt and dust in arid regions. We show that they are consistent with the surface expression of buoyancy-driven convection in the porous soil beneath a salt crust. By combining quantitative results from direct field observations, analog experiments, and numerical simulations, we further determine the conditions under which salt polygons should form, as well as how their characteristic size emerges.
... Soil water content (SWC) has an important impact on rainfall runoff, transpiration, and vegetation ecosystems in ecological environments [1]. Furthermore, SWC is one of the most significant factors influencing soil physical qualities, pH, plant growth, and biomass [2][3][4], and it has a key effect on soil organic deposition by providing proper water for root respiration and soil microbial activities, especially under dry conditions [5][6][7]. ...
... Soil water content is a key factor that limits crop growth and soil organic matter deposition [1,3]. In the cropland system, the roots of most crops, including wheat, maize, and beans, are distributed at depths of 0-20 cm. ...
Soil water content (SWC) is a vital parameter for understanding crop growth and the soil nutrient water cycle. Monitoring SWC without inserting sensors into the soil, which can break the soil structure, has previously been a significant challenge for scientists. In this study, we developed a non-inserted portable frequency domain reflection (NIP-FDR) instrument to monitor SWC continuously and automatically. The working technique of this instrument was based on the improved adjustable high-frequency oscillation method originating from the frequency domain reflection principle. Compared to the control SWC measurement instrument, the difference in SWC at 0–10 cm, 10–20 cm, and 20–30 cm depth was within 1%, 3%, and 15%, respectively, and the mean variation of SWC was less than 5% in the indoor measurements. In the field verification experiment conducted in the summer of 2020, the mean error of SWC measurements at a depth of 0–20 cm was 5%, while we failed to compare SWC at a depth of 20–30 cm due to low variability in the SWC measurement at this depth during the summer measurement period. This pioneer NIP-FDR was able to effectively monitor surface SWC, especially at depths of 0–20 cm.
... In this study we focus on a particular ∼ 15 cm deep saline lake, the Salar del Huasco (SDH) located in the Altiplano of the Atacama Desert in the NE region of Chile. The dynamics of the E process of SDH can be regarded as exemplifying all the saline lakes in the region (Kampf et al., 2005). Figure 1 shows the dramatic change in the size of the SDH lake from the rainy season in the summer to the dry season in late spring. ...
... Furthermore, the roles of H and L v E are reversed; i.e. it is H that suddenly increases when the afternoon regime commences (water and wet-salt surface Bowen ratio of 0.2 and 4, respectively). The salt crust reduces the soil evaporation of the wet-salt surfaces, in addition to the salt lowering E in general (Kampf et al., 2005) (Fig. 3b). In the desert, L v E is zero all day and R n is balanced between G and H (Fig. 3c). ...
We investigate the influence of regional atmospheric circulation on the evaporation of a saline lake in the Altiplano (also known as the Andean Plateau) region of the Atacama Desert. For that, we conducted a field experiment in the Salar del Huasco (SDH) basin (135 km east of the Pacific Ocean), in November 2018. The measurements were based on surface energy balance (SEB) stations and airborne observations. Additionally, we simulate the meteorological conditions on a regional scale using the Weather Research and Forecasting Model. Our findings show two evaporation regimes: (1) a morning regime controlled by local conditions, in which SEB is dominated by the ground heat flux (∼0.5 of net radiation), very low evaporation (LvE<30 Wm-2) and wind speed <1 ms-1; and (2) an afternoon regime controlled by regional-scale forcing that leads to a sudden increase in wind speed (>15 ms-1) and a jump in evaporation to >500 Wm-2. While in the morning evaporation is limited by very low turbulence (u*∼0.1 ms-1), in the afternoon strong winds (u*∼0.65 ms-1) enhance mechanical turbulence, increasing evaporation. We find that the strong winds in addition to the locally available radiative energy are the principal drivers of evaporation. These winds are the result of a diurnal cyclic circulation between the Pacific Ocean and the Atacama Desert. Finally, we quantify the advection and entrainment of free-tropospheric air masses driven by boundary layer development. Our research contributes to untangling and linking local- and regional-scale processes driving evaporation across confined saline lakes in arid regions.
... The adjacent Andean highlands receive precipitation more often but are still arid to hyperarid (Strecker et al., 2007). Evaporation at the elevation of the salar varies between 0 to 2.8 mm/d, depending on the surface characteristics (Kampf et al., 2005); relative to an estimated mean annual precipitation of 39 mm, the P/E ratio (aridity index) is ~0.033. Interestingly, no evaporation was measured by Kampf et al. (2005) from the rough halite nucleus of Salar de Atacama that comprises approximately half of the surface area and hosts the Li-rich brine at 30-m depth. ...
... Evaporation at the elevation of the salar varies between 0 to 2.8 mm/d, depending on the surface characteristics (Kampf et al., 2005); relative to an estimated mean annual precipitation of 39 mm, the P/E ratio (aridity index) is ~0.033. Interestingly, no evaporation was measured by Kampf et al. (2005) from the rough halite nucleus of Salar de Atacama that comprises approximately half of the surface area and hosts the Li-rich brine at 30-m depth. ...
... La nature des sols est donc une considération importante pour l'estimation de l'évaporation. Dans les playas, l'ETR est généralement faible par rapport à l'ETP (Allison et Barnes, 1985 ;Jacobson et Jankowski, 1989 ;Malek et al., 1990 ;Tyler et al., 1997) voir même nulle occasionnellement (Kampf et al., 2005). Les raisons sont multiples et exposées plus en détails en annexe 4.2. ...
... Ce phénomène permet d'ailleurs d'expliquer pourquoi le niveau de la mer morte ne descend pas aussi vite que le taux d'évaporation potentielle pourrait le suggérer (Stanhill, 1994 ;Yechieli et al., 1998), ou pourquoi une playa humide peut être observée en été malgré un taux d'évaporation potentielle élevé (Fan et al., 1997). Ensuite, lorsqu'un lac est présent, une couche d'évaporite peut se former en surface et peut : 1) limiter l'évaporation en réfléchissant une partie du rayonnement solaire (Malek et al., 1990 ;Tyler et al., 1997) ; voire même 2) bloquer complétement cette évaporation en ayant des propriétés d'étanchéité vis-à-vis de l'eau et de la vapeur (Kampf et al., 2005). Le type de sel présent va aussi influer sur le taux d'évaporation réel (Langbein, 1961). ...
Le bassin crétacé de Tsagaan Els est situé dans le désert de Gobi en Mongolie. L’objectif de cette thèse est de mieux comprendre le fonctionnement hydrogéologique et hydrochimique de ce bassin endoréique afin de faciliter l’implantation de futurs projets miniers. Dans cette optique, un modèle hydrogéologique régional 3D a tout d’abord été développé sous MODFLOW. La calibration à partir des niveaux piézométriques mesurés sur les ouvrages présents au sein des licences et quelques puits nomades, aboutit à plusieurs solutions. Elles présentent chacune des conductivités hydrauliques en accord avec les tests de pompages, et des taux de recharge entre 0.6 et 3.1 mm/an, cohérents avec le climat actuel. Ce modèle a ainsi permis d’étendre nos connaissances piézométriques au-delà des licences et d’effectuer un bilan hydrique régional. Ensuite, l’âge des eaux a été estimé numériquement via ce modèle puis par des datations 14C. Une comparaison des résultats de ces méthodes a indiqué que les solutions présentant des taux de recharges élevés étaient plus probables que celles en présentant de plus faibles à conditions que les écoulements soient restés les mêmes durant les trente derniers milliers d’années. En parallèle, une étude hydrochimique portant sur les ions majeurs, le brome et les isotopes stable de l’eau (18O et 2H) a montré que l’origine de la salinité des eaux était principalement liée à la dissolution d’évaporites superficielles. En dernier lieu, un modèle 3D local, centré sur la playa terminale du bassin a permis de mieux comprendre le fonctionnement actuel et passé du bassin en s’appuyant sur l’évolution spatiotemporelle de la salinité.
... Morning wind speeds throughout the year are generally <2 m s −1 , and wind speeds typically increase in the aernoon, reaching up to 15 m s −1 . 47 The low precipitation and high solar insolation make this place favourable for evaporation technology. Overall, producing lithium from brine at arid region is cost-effective. ...
The exponentially growing market for lithium-ion batteries (LIBs) is driving the development of more environmentally benign processes for producing lithium carbonate, a key precursor. Extracting lithium(i) from brine is a cost-effective method, particularly in the Lithium Triangle in South America, including the Atacama Desert in Chile. Life cycle assessment (LCA) was used to assess the environmental impacts of lithium(i) production by establishing a comprehensive life cycle inventory (LCI) with data from modelling, literature, technical reports and the Ecoinvent database. Information about evaporation rates from Atacama salars, the performance of the northern Chile electrical grid fuel mix and present waste management processes were analysed to establish the water balance, water footprint (WF), water scarcity footprint (WSF) and to estimate in Aspen Plus and Sphera the environmental performance of the battery-grade lithium carbonate production process. The results predicted significant environmental impacts associated with production of input chemicals such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3), as well as with energy conversion from the carbon intensive electrical supply in northern Chile. The waste dumps and surface impoundments required for the production process did not result in significant leachate infiltration, although considerable land areas are occupied. The modelling and analysis results highlighted the importance of accurate brine evaporation rates on the process water balance estimation and on the conventional manufacturing process emissions; insufficient evaporation rates increased the water footprint of chemical production processes. The water resource stress in the arid Atacama region was evident from predicted water balances, WFs and WSFs, emphasising the necessity to innovate less time-consuming and water-conserving processes to increase sustainability.
... Brine lithium deposits in the Andean Plateau of South America are typically characterized by high elevations, numerous salt lakes, high lithium grades, and low Mg/Li ratios (Kampf SK et al., 2005;Vinante D and Alonso RN, 2006;López-Steinmetz RL et al., 2018;Liu CL et al., 2021). Except for Atacama, which has a lower elevation of 2305 m, all salt lakes had elevations above 3300 m. ...
... The evaporation rate in the Salar de Atacama is extremely high, with an annual potential value of approximately 2130 mm [13,26]. This high evaporation rate is attributed to a combination of factors, such as the high temperatures, the intense solar radiation reaching the surface, the wind speed, and the low relative humidity in the region [25,27]. During the summer, when temperatures are higher, evaporation reaches its peak [1,3]. ...
A hydrogeological study of the shallowest part of the halite nucleus of the Salar de Atacama is presented, focusing on the isotopic variability in δ¹⁸O and δ²H (SMOW) in the brine. It is observed that intensive brine extraction has induced upward vertical flows from the lower aquifer, which presents with a lighter isotopic composition (δ¹⁸O: −0.87‰ to −2.49‰; δ²H: −26.04‰ to −33.25‰), toward the upper aquifer, which has more variable and enriched isotopic values. Among the possible explanations for the lighter isotopic composition of the lower aquifer waters is the influence of paleolakes formed during the wetter periods of the Late Pleistocene and Holocene that recharged the underlying aquifers. The geological structure of the Salar, including faults and the distribution of low-permeability layers, has played a determining role in the system’s hydrodynamics. This study emphasizes the need for continuous and detailed monitoring of the isotopic composition to assess the sustainability of the water resource in response to brine extraction and future climate changes. Additionally, it suggests applying this methodology to other salt flats in the region for a better understanding of hydrogeological processes in arid zones. The research provides an integrative view of the relationship between resource extraction, water management, and ecosystem conservation in one of the most important salars in the world.
... Then, if the absolute value of the calculated 'Z' statistic is above the critical value, the trend is considered statistically significant. In this study, Meyer's formula was used to estimate the evaporation of Lake Abiyata due to its simplicity and the requirement of fewer input parameters compared to the Penman equation and other models (Brutsaert, 2013(Brutsaert, , 2017Kampf et al., 2005;Winter, Rosenberry, and Sturrock, 1995). Meyer's formula is particularly suitable for shallow and small-sized lakes( (Meyer, 1942). ...
The study aims to investigate the spatiotemporal change in lake water surface extents over 35 years (1986–2020) and identify potential causes. Three alternative multispectral water indices-Normalized Difference Water Index (NDWI), Automatic Water Extraction Index (AWEI), and Modified Normalized Difference Water Index (MNDWI)—derived from Landsat sensors (TM, ETM+, OLI) were utilized to extract and analyze the lake surface area. The Mann-Kendall correlation was applied to examine whether hydro-meteorological and anthropogenic variables are possible causes for changes. New Hydrological Insights for the Region: MNDWI outperforms other indices with over 96 % accuracy in mapping lake surface area. Lake Abiyata experienced the most significant reduction in surface area from 1986 to 2020 (>50 %), followed by Lake Ziway (<2 %) while Lake Langano remained relatively stable. This significant reduction positively correlates to alterations in lake water depth (R 2 =0.92). Factors such as increased temperature, evaporation, and water abstraction for soda ash production negatively correlated with lake surface area, while inflow from Bulbula River and mean annual rainfall showed positive correlations. Abiyata Lake's decrease in surface area is primarily attributed to water abstraction for soda-ash manufacturing and incoming river flow. If the current trends in water abstraction from the Lake and income water diversion continue, there is a high possibility that Lake Abiyata will change into a terminal lake shortly.
... The combined use of surface water and groundwater is good ecological sustainability [8] [21]. High evapotranspiration accelerates groundwater depletion in the dry season in arid/semi-arid regions [22], negatively affecting well productivity [23] [24] [25]. ...
... However, increased inflow would require an additional constant outflow term, which is not currently supported by available data from either groundwater levels or surface water inundation to downgradient transitional surface water systems. The calculated evaporation rates required to create the seasonal volume variability in surface water inundation were within estimates for brackish surface waters in this environment (Kampf et al., 2005). Volume fluctuations from inflow that resulted from precipitation runoff was within 80% accuracy within the first 5 days for all precipitation events except the first 2017 event, which may indicate that the area of precipitation for this event in particular was spatially distinct from the other events in the record. ...
In water‐stressed hyperarid basins, questions mount over the impacts of anthropogenic groundwater extraction and climate‐driven perturbations on groundwater‐surface water interactions and the resilience of ecosystem‐critical surface water. Coupling groundwater with surface water observations from Sentinel‐2 data provides an unprecedented opportunity to evaluate surface water connectivity with local aquifers following intense precipitation events in arid basins. Surface water area and groundwater level data were analyzed for trends following precipitation, including peak lag time, post‐peak recession rates, and changes in hydraulic gradients. Results indicate variable connectivity following large precipitation events between surface water change and groundwater level fluctuations in the upgradient freshwater aquifer, whereas the downgradient brine‐to‐brackish area of the aquifer indicated virtually no connectivity with the aquifer. Comparison between precipitation and surface water response indicate distinct responses based on the physical relationship of the surface water body with the brine‐to‐brackish area of the aquifer. Lumped parameter modeling of surface water inundation also constrains the possible hydrologic dynamics of the post‐precipitation response. While modeled influx to surface water seems primarily controlled by watershed hydraulics rather than direct hydraulic connectivity of the aquifers, the relationship between surface water and adjacent groundwater levels coupled with surface water area indicates that local aquifers are primarily connected to the surface water bodies through discharge via subsurface infiltration. Modeling results imply that the existence of brine‐adjacent surface water in arid basins relies on upgradient discharge from freshwater aquifers. Our results further support that marginal surface water systems can serve as a critical recharge mechanism to local aquifers.
... In general, ET is an important hydrological parameter in a basin that connects water, surface energy exchanges, and carbon cycles. [8,9]. As it is argued by [10], ET is an important hydrological parameter in water resource management since it aids in a variety of tasks, such as simulation of the catchment soil-water balance, water resource management, and planning [11], design of irrigation systems [6], and climatological studies [12]. ...
In river basins such as the Olifants, the evapotranspiration has been documented as the biggest water user and therefore one of the most important hydrological processes in the basin. Thus, using the Soil and Water Assessment Tool (SWAT) model, this study attempted to assess the hydrological responses of evapotranspiration (ET) to climate change in the Olifants River basin over a period of six decades, focusing mainly on the upper catchment (UC) of the basin. The study showed, on average, a general decline of seasonal ET with a decrease of 10.5% in spring, 29.8% in summer and 17.3% in winter. However, autumn ET showed an average increase of 12.5%. With (1960 – 1970) decade considered as the baseline, the study also found that annual ET in the UC, has been on the decline consistently since the 1960s with the most recent decade (2010 – 2018) taking the biggest share of the drop (12.8%). Here, the average annual decline of ET of 1.75 mm/yr was observed with most of the decline happening in the last decade. This general decadal trend of annual ET mortality in the area coincides with the temperature rise and precipitation decrease of the area, signifying the impact climate change may have had on the evapotranspiration for the past six decades.
... The second was a shallow (0-30 cm) evaporite crust closed system. Because evaporation from a desiccated saline crust is minimal (Kampf et al., 2005), evapoconcentration of a halite crust brine was considered negligible, making temperature the dominant control on brine salinity in the shallow saline crust. Diurnal brine samples were collected to coincide with maximum and minimum brine temperatures (~6 am and 6 pm), as was determined by a shallow soil temperature probe (Bernau and Bowen, 2021). ...
Knowledge of brine density and mineral saturation states under different temperatures contributes to understanding Earth systems, including dissolution and crystallization of chemical sediments, mixing water bodies with variable density, and mineral resource development and evolution. However, these interpretations often rely on geochemical measurements with low accuracies at high salinities. Here, we test the utility of density measurments to advance understanding of brine geochemistry. We demonstrate the accuracy and limits of determining a brine's density and halite saturation state at multiple temperatures with rapid and relatively inexpensive portable density meter measurements. Density measurements at different temperatures are used to create samples' equations of state, which are used to extrapolate measurements. This methodology presents multiple opportunities. We use brine samples from around the world to show that density and equation of state data provide semi-quantitative information about sample composition and temperature-sensitive mineral precipitation. Importantly, density measurements can be used to evaluate error-prone geochemical measurements. We illustrate example applications with brine samples from the Bonneville Salt Flats, a landscape in Utah, USA, that is valued for mineral resources and recreation opportunities. We developed system-scale equations of state for these saline pan samples and their halite-saturated counterparts. We evaluated methodological limitations with duplication tests and by determining if diurnal fluctuations in salinity and halite saturation in a shallow pool's brine and shallow groundwater in contact with a halite crust were detectable. Average daily changes in halite saturation of shallow pool brine of approximately 3 kg m⁻³ were clearly detected, while diurnal halite saturation fluctuations in the shallow halite crust brine of 0.4 to 0.7 kg m⁻³ were near method limits. Because of their accuracy, low cost, and applications, portable density meter measurements of brines are invaluable in studying brine systems.
... The geological and climatic settings of the SDA contribute to this extreme enrichment, leading to active evaporite deposition (Boschetti et al., 2007;Houston et al., 2011;Bradley et al., 2013;Munk et al., 2016), as a consequence of high evaporation rates (0-2.8 mm/day) and scarce annual precipitation (39 mm) reported for the SDA (Kampf et al., 2005). The large area enclosed by the SDA, estimated at 3.000 km 2 , comprises a massive halite nucleus filled by interstitial brines, and a clastic and evaporitic marginal zone (Houston et al., 2011). ...
The Atacama region in Northern Chile hosts the driest desert on Earth and provides the second highest global Li production, containing the largest reported lithium reserves in the world. The occurrence of extremely elevated Li concentration is restricted to brine deposits contained in the halite nucleus of the Salar de Atacama (SDA). The origin of Li and other solutes in the Andean salt flats has been attributed to different processes, where weathering of Neogene and Quaternary volcanic rocks has been considered to be the most important. Despite recent advances, there is still limited geochemical and isotopic Li data in ignimbrites, particularly surrounding the SDA, hence the potential of these units as a source has remained elusive. In this study, we provide new Li concentration and isotopic data in ignimbrites from the Western Cordillera, fine sediments from the marginal zone of the SDA, and suspended load in shallow groundwater. A moderate enrichment (between 20 and 50 ppm) is recorded in volcanic rocks, averaging 33 ppm, while fine sediments present Li contents one order of magnitude higher, with a mean concentration of ~290 ppm. Due to the Li contents recorded in ignimbrites, which is slightly higher than the upper crust average (24–30 ppm; Rudnick and Gao, 2004), we propose that the potential of these units as the main source of Li resides in their large areal extent, volume, and hydraulic gradient with respect to the SDA. The δ⁷Li values in ignimbrites vary from −1.5 ‰ to +12.8 ‰. In contrast, marginal zone sediments show negative values of δ⁷Li (from −1.9 ‰ to −5.3 ‰), except for fine sediments from the Peine Block where a δ⁷Li is +4.4 ‰. Our results reveal that the measured δ⁷Li in ignimbrites would indicate volatile exsolution as the main syn-eruptive factor controlling the isotope Li distribution. Regarding post-eruptive processes, water-rock interactions trigger partition of ⁷Li from ignimbrite to water. Both syn-eruptive and post-eruptive proposed were tested by numerical modeling, supporting our interpretation. We propose that the predominant constituent in ignimbrites, crystals or glass, impacts the subsequent distribution and fractionation of Li in inflowing waters and fine sediments covering the marginal zone. The analysis presented here allows us to define three subzones where different processes are controlling Li fractionation. These factors together with the geological, hydrologic, and climatic history of the region have led to the world-renowned accumulation of Li in the SDA.
... For example, Tejeda et al. (2003), Vá squez et al. (2013) and Marazuela et al. (2019a) modeled the whole groundwater system within the salt flat through numerical simulations. Kampf et al. (2005) and Kampf and Tyler (2006) assessed the land surface energy fluxes and evaporation processes within the basin by using field measurements and ASTER satellite images, respectively. Marazuela et al. (2019b) studied the relationship between water table fluctuations and evaporation. ...
The Salar de Atacama in northern Chile hosts the biggest lithium reserves globally. However, concerns have arisen regarding the environmental impact of lithium extraction on its basin; in particular, the possible drought of its lagoons that sustain unique natural ecosystems. This investigation implemented an image processing and statistical methodology to assess the area evolution and dynamic behavior of these main water bodies between 1986 and 2018. Results showed that these lagoon systems have not presented significant changes despite increasing lithium production, even for the years of large brine extraction. The analysis indicated that the total surface area of the lagoons varied within a restricted range at 95% confidence level: on average, of the total area covered by these systems 0.03% could have been lost or 0.01% could have been gained per year. Moreover, a multivariate analysis indicated that brine extraction did not have a negative impact on the evolution of the surface areas of the lagoons during the last three decades.
... Petrosalic layer at the salt crust geomorphological surface was found as salt polygons together with egg-shaped and salt strains at the surface. Kampf et al. (2005) believe that evaporation rate is not constant through time. They reported that subsurface water evaporation in playa has increased the thickness of salt crust layer at the surface, gradually. ...
Lut Desert with a warm and arid climate is a suitable environment for evaporites and palygorskite to be formed. The objective of the research is to identify the role of environmental factors using spatial and vertical distribution patterns of evaporitic minerals (halite, anhydrite, and gypsum) and palygorskite related to landscape positions in soils of Lut Desert. Fifteen representative pedons along transversal (A–Aʹ) and longitudinal (B–Bʹ) transects in central (hyper-arid regime) and marginal (arid regime) parts of Lut were studied. Continued long time hyper-arid climate has caused petrosalic layer to be formed in central Lut. Results of the sulfate minerals showed that gypsum dissolution, its re-precipitation, and anhydrite formation have been affected by increase of temperature and salt concentrations, but accumulation and distribution patterns of anhydrite were not a function of temperature and salt concentration. Besides, the source of hydrated illite and hydrous salts in anhydrite accumulations was attributed to the variations in the water table. Distribution pattern of palygorskite showed that hyper-arid climate, erosion and sedimentary processes, poor drainage, erodibility of surface soil (sandy loam and sandy clay loam textural classes), and presence of strong winds were among the most important factors controlling lack of formation and destruction of palygorskite in central Lut. Besides, the decrease of aridity gradient, development of pedogenic processes, and formation of secondary calcite provided ideal conditions for authigenic formation of palygorskite. Therefore, distribution and accumulation patterns of evaporitic minerals and palygorskite in Lut Desert are of great importance for understanding environmental interactions, also soil management purposes.
... The ways in which water moves across landscapes has been of interest to NREL researchers dating back to the first years of the US IBP and research conducted on microwatersheds. Work in that regard expanded greatly following the joining of watershed scientists with the NREL in the last decade (e.g., MacDonald et al., 1991;Kampf et al., 2005;Covino and McGlynn, 2007;Kampf and Burges, 2007;Fassnacht et al., 2017). For example, MacDonald and Huffman (2004) described patterns of decline in water repellency after a fire in northern Colorado. ...
Fundamental knowledge about the processes that control the functioning of the biophysical workings of ecosystems has expanded exponentially since the late 1960s. Scientists, then, had only primitive knowledge about C, N, P, S, and H2O cycles; plant, animal, and soil microbial interactions and dynamics; and land, atmosphere, and water interactions. With the advent of systems ecology paradigm (SEP) and the explosion of technologies supporting field and laboratory research, scientists throughout the world were able to assemble the knowledge base known today as ecosystem science. This chapter describes, through the eyes of scientists associated with the Natural Resource Ecology Laboratory (NREL) at Colorado State University (CSU), the evolution of the SEP in discovering how biophysical systems at small scales (ecological sites, landscapes) function as systems. The NREL and CSU are epicenters of the development of ecosystem science. Later, that knowledge, including humans as components of ecosystems, has been applied to small regions, regions, and the globe. Many research results that have formed the foundation for ecosystem science and management of natural resources, terrestrial environments, and its waters are described in this chapter. Throughout are direct and implicit references to the vital collaborations with the global network of ecosystem scientists.
... The temperature and groundwater depth at BSF and other saline pans vary throughout the day, causing periodic wetting and drying of the crust, and likely thermally-driven dissolution and crystallization of halite (Fig. 5;Turk, 1973;Macumber, 1991). Little removal of water from evaporation occurs from a desiccated crust, making it behave like a hydrologically closed system (Kampf et al., 2005). Halite becomes slightly more soluble as temperatures increase. ...
The Bonneville Salt Flats form a saline pan in western Utah, USA. This modern saline pan has a unique history of land‐speed racing and potash mining. Multi‐decadal measurements record decreasing evaporite volume and extent, spurring multiple environmental studies. The goal of this work is to describe saline pan evaporite morphologies within the context of environmental measurements. Environmental data include field observations, groundwater and dust trap samples, precipitation, albedo, time‐lapse photography, groundwater level, and temperature measurements of air, groundwater and the shallow evaporite crust. Petrographic data include thick sections, evaporite slabs and sediments, and X‐ray computed tomography of evaporites. Diverse halite morphologies are formed at the surface, vadose and phreatic zones. The presence and preservation of these morphologies are influenced by spatially heterogenous natural and anthropogenic processes, including daily to seasonal changes in brine salinity, mineral saturation states, and water level within and across saline pan stages. In addition to hydrological balances delineated by the saline pan stages of flooding, evapoconcentration and desiccation, changes in vertical brine movement, temperature and surficial sedimentary structures influence evaporite morphologies. These results are transferable to the interpretation of altered evaporites and enhancing saline pan depositional models.
... This flat is the third largest saline pan in the world with a surface area of 3,100 km 2 (Marazuela et al., 2020) that has formed through cycles of irregular dry and wet periods. The latter of these cycles, lasted for tens of thousands of years (Bobst et al., 2001) and the phenomenon of solar evaporation has played a major role not only on its formation process (Kampf et al., 2005), but as it is, and has always been, the biggest source of evaporation in the entire Atacama Desert (Finstad et al., 2016). ...
... Natural vegetation cover is governed by sequences of precipitation and evapotranspiration (Sepúlveda et al. 2018a, b). In the large northern endorheic basins, evaporation from the salt flats accounts for most of the water demand (Hernández- Johnson et al. 2010;Kampf et al. 2005). Evaluation of evapotranspiration and its relationship with agricultural and environmental demands and its effect on the water balance of the basins is needed (DGA MOP 2017). ...
This chapter presents the status of groundwater resources in Chile focusing on two relevant aspects. First, the geological and climatic aspects that shape the country’s hydrogeological configuration. These, in turn, provide the context for the hydrogeological configuration within the country. Then, based on the official information provided by the Dirección General de Aguas, DGA, a quantification of groundwater resources in the different hydrogeological administrative units is presented. To illustrate the different typologies of aquifer encountered in the country, some examples of relevant hydrogeological basins are described. Through these examples, we also display different problems that are foreseen in terms of groundwater knowledge, overexploitation, restricted areas, water quality, and climate change, among other factors. Finally, based on the information found, future challenges related to groundwater resources are presented.
... In particular, it is necessary to account for all the transport mechanisms that mobilize water vapor from the evaporative surface toward the land surface and the surface roughness, from which the water vapor diffuses toward the atmosphere according to Equation 1. In this context, laboratory and field studies have shown that the water table depth below the surface (d) is a key parameter that determines the evaporation from unsaturated soils (Kampf et al., 2005;Or et al., 2013;Shokri & Salvucci, 2011;Wang, 2015), where the actual evaporation decreases with d Or et al., 2013). Lehmann et al. (2008) identified two different stages in evaporation as a function of d (see also Or et al., 2013). ...
A theoretical framework for computing the evaporation from unsaturated soils is presented and validated based on laboratory experiments that were conducted in an uncontrolled environment where forcing variables vary in time according to diurnal meteorological cycles. This theory introduces a dimensionless number that controls the ratio between the actual and potential evaporation from unsaturated soils. The dimensionless number depends on the transfer velocity, which characterizes evaporation into the atmosphere, the diffusion coefficient of water vapor in the soil, and the water table depth. We show that depending on the value of the dimensionless number, evaporation can be limited by either the air‐side or the soil‐side of the land surface. For large transfer velocity values, evaporation is controlled by water vapor diffusion in the soil, while for shallow water tables, evaporation is controlled by water vapor transport from the land surface into the atmosphere. Despite the good agreement between the shape of the observed and predicted evaporation rates, a fitted dimensionless parameter is required to match the predicted evaporation rates. Possible explanations for this disagreement are given in the discussion.
... Finally, the role that the size of the terminal wetland plays in closing the hydrological cycle is not only restricted to the high Andean wetlands studied in this article. In fact, high Andean wetlands are also known as playas or salt flats landscapes, which can be widely found in the World in places were the annual evaporation exceeds the annual precipitation (Yechieli and Wood, 2002;Kampf et al., 2005). In these type of terminal lakes whose size is dynamically determined by the complete evaporation of the inflow, the long-term monitory of their sizes can be a valuable remote perception tool that would reflect changes in surface and groundwater extraction for human activity, as well as reflecting the impact of climate change on precipitation or evaporation rates. ...
High Andean wetlands of the elevated plateaus of the Andes Mountains of Chile, Argentina, Perú and Bolivia are true oases that sustain life in this arid region. Despite their ecological value, they have been rarely studied and are vulnerable to climate change and human activities that require groundwater resources. One such activity that may be intensified in the near future is mining for nonmetallic minerals such as lithium, whose worldwide demand is expected to increase with the rise of electric vehicles that need batteries. To determine a baseline of the natural dynamics of these systems, which allows sustainable management, it is essential to understand the spatiotemporal dynamics of these wetlands. In this article, we studied the temporal and spatial dynamics of high Andean wetlands of Chile, with the aim of identifying the key processes that govern their dynamics. To do this, we used time series of Landsat data from 1984 to 2019 to study 10 high Andean wetlands. Furthermore, to characterize the climate variability in these systems, we studied the long-term relation between the changes in water and vegetation areas with rainfall and evaporation variability. It was found that the groundwater reservoir plays a key role in sustaining the high Andean wetlands. Wet years with a period of occurrence of 20-30 years are the years in which the groundwater reservoirs are actually recharged, and in between wet years, the groundwater reservoirs gradually release the water that sustains the aquatic ecosystems. Hence, groundwater exploitation should be carefully designed from a long-term perspective, as groundwater levels could take decades to recover.
... The level of the puquı́os is mainly controlled by the balance between the incoming groundwater flow and the local evaporation rate, which is seasonally controlled. 18,21,27,28 The evaporation rate has a much larger impact. Water slowly migrates southwards, globally sweeping the Puquı́os de Huatacondo area, 17 but locally this flow gets more complex NW of Cerro Soledad, where puquı́os are located. ...
The study of extreme evaporitic environments is a subject of increasing interest in sedimentary petrology and planetary geology. We report here the evaporitic precipitation in the shallow, small lakes (puquíos) at the Salar de Llamara (Atacama Desert, northern Chile). We have used a combination of in-situ/laboratory/modeling methodologies allowing the definition of a detailed, in-depth model for the sequence of evaporitic precipitation in the puquíos. The in-situ measurements in these ponds reveal that brines are density-stratified, with important gradients in salinity, temperature and other properties of the solution. These vertical gradients, along with the lateral and seasonal variations, are the main factors of chemical variability controlling the precipitation processes. The evaporation of these brines drives the chemical evolution of the different ions and produces two distinct mineral assemblages: large structures made of millimetric to centimetric-size crystals of gypsum, often forming thrombolite-like or stromatolite-like morphologies, in the ponds; and salt crusts made of mainly gypsum, eugsterite, halite, and thenardite, surrounding the ponds. Evaporation experiments in the laboratory monitored by in-situ X-ray diffraction and optical videomicroscopy reveal a precipitation sequence in accordance with field observations, but distinct from the thermodynamically predicted precipitation. The actual formation of eugsterite - rather than glauberite - and the observed delay in gypsum dissolution are explained using kinetic evaporation models.
... Further, the data obtained from the lysimeters could allow the calibration and validation of numerical models that solve the flow and transport equations, as well as the prediction of atmospheric variables (Boulet, Braud & Vauclin, 1997;Braud, Dantas-Antonino, Vauclin, Thony & Ruelle, 1995;Gowing, Konukcu & Rose, 2006;Gran, Carrera, Olivella & Saaltink, 2011;Novak, 2010;Saravanapavan & Salvucci, 2000 Consultores, 2007;GP Consultores & Collahuasi, 2008;Johson, 2009;Johson et al., 2010;Kampf et al., 2005;Mardones, 1986;1998;Sociedad Minera Salar de Atacama [MINSAL], 1988;Ugarte, 2007) carried out near the salt flats (depths of the water table of 1 m to 2 m) of the endorheic basins of the Chilean Altiplano, where it was identified that evaporation constitutes the main discharge of the water system, and may even consume all the resources that come in the form of precipitation. ...
In this research an estimation of the evaporation discharges from shallow groundwater in the Salar de Pedernales basin is made, using the lysimeter methodology. The analysis performed shows values between 1400 L·s-1 and 1900 L·s-1 with an uncertainty of error of 5% with respect to the average and between 11% and 47% in relation to the minimum and maximum values which can be compared by other studies where different tools have been used to calculate evaporation, such as: chamber, numerical model, water balance, Bowen relationships, Eddy correlations, and evaporation curves vs. altitude. The results confirm that lysimeters are appropriate tools for the determination of soil evapotranspiration and evaporation from shallow groundwater, whose components are key in the hydrology of endorheic basins, arid and semi-arid zones, for the management of protected natural spaces such as salt flats, waterholes, fertile plains, and bofedales.
... Because rainfall recharge can be considered undisturbed by the effects of mining, the focus in terms of brine pumping impacts on the water balance should be the evaporation rate. Evaporation occurs mainly from the water table, which is very close to the land surface and tends to rise by capillarity (Grilli, 1985;Grilli and Vidal, 1986;Houston, 2006;Kampf et al., 2005;Kampf and Tyler, 2006;Muñoz-Pardo et al., 2004). ...
Salt flats are hydrogeological systems with highly valuable wetland and lake ecosystems. The brine pumping carried out to extract lithium is modifying the natural evaporation discharge of salt flats. A methodology to evaluate the impacts caused on water table and evaporation discharge by brine exploitation in salt flats is proposed and applied to the Salar de Atacama. The methodology included field measurements of water table and evaporation rate, followed by its spatio-temporal analysis and the application of the results to a numerical model to improve the brine exploitation design. The spatio-temporal analysis of the water table depth and evaporation rates measured in the field concluded that the evaporation discharge decreased from 12.85 to 10.95 m3·s-1 between 1986 and 2018, that is around 15%. This reduction compensated part of the extractions and could contribute to the preservation of the mixing zone ecosystems. At present, this damping capacity is already amortized in the nucleus and the marginal zone is beginning to be affected by the brine pumping. The sensitivity of the phreatic evaporation on the water table depth justified the great uncertainty of the previous evaporation discharge estimations. Thus, an average error lower than 0.5 m was enough to modify the evaporation by >60%. Therefore, considerable effort should invested to faithfully quantify the discharge by evaporation which is critical in water balance of salt flat basins. The numerical model pointed out that the total pumping outflow should be distributed in the largest possible area. This minimizes the water table drawdown and maximizes the capacity of the evaporation decline to compensate the extractions. The results of this work serve as guidelines to improve the efficiency of future salt flat exploitations.
... The sampling site area (23 • 18 16.668 S and 68 • 8 16.835 W), located about 60 km from San Pedro de Atacama, was distinguished by rugged salt crusts composed almost exclusively of NaCl that covered the soil surface (Kampf et al. 2005). These salts of athalassohaline origin were formed by the continuous evaporation of shallow groundwater due to the hyper-arid climate (Finstad et al. 2016). ...
Considering that most industrial processes are carried out under harsh physicochemical conditions which would inactivate enzymes from commonly isolated mesophilic organisms, current studies are geared towards the identification of extremophilic microorganisms producing enzymes resistant to extreme salt concentrations, temperature and pH. Among the extremophiles, halophilic microorganisms are an important source of salt-tolerant enzymes that can be used in varying biotechnological applications. In this context, the aim of the present work was to isolate and identify halophiles producing hydrolases from the Atacama Desert, one of the harshest environments on Earth. Isolates were recovered from halite samples, and screened for the presence of seven different hydrolase activities (amylase, caseinase, gelatinase, lipase, pectinase, cellulase and inulinase) using agar plate based assays. From a total of 23 halophilic bacterial isolates, most showed lipolytic (19 strains) and pectinolytic (11 strains) activities. The molecular identification of eight selected isolates showed a strong similarity to members of the Halomonas and Idiomarina genera. Therefore, the present study represents a preliminary, but essential, step to identify novel biological sources of extremozymes in an environment once thought to be devoid of life.
... Nevertheless, the sequential study of continental salt flats is equally relevant for several research areas. Playas or dry salt lakes, as zones of groundwater discharge, act as important sources of water in cold arid regions, such as South American salt flats, where playa groundwater and brines support the mining industry and local flora and fauna [41]. Information about hydrology and groundwater table changes in continental salt flats are of substantial importance in monitoring local aquifer changes e.g., [42] and salt losses from the crust e.g., [43]. ...
Understanding extraterrestrial environments and landforms through remote sensing and terrestrial analogy has gained momentum in recent years due to advances in remote sensing platforms, sensors, and computing efficiency. The seasonal brines of the largest salt plateau on Earth in Salar de Uyuni (Bolivian Altiplano) have been inadequately studied for their localized hydrodynamics and the regolith volume transport across the freshwater-brine mixing zones. These brines have recently been projected as a new analogue site for the proposed Martian brines, such as recurring slope lineae (RSL) and slope streaks. The Martian brines have been postulated to be the result of ongoing deliquescence-based salt-hydrology processes on contemporary Mars, similar to the studied Salar de Uyuni brines. As part of a field-site campaign during the cold and dry season in the latter half of August 2017, we deployed an unmanned aerial vehicle (UAV) at two sites of the Salar de Uyuni to perform detailed terrain mapping and geomorphometry. We generated high-resolution (2 cm/pixel) photogrammetric digital elevation models (DEMs) for observing and quantifying short-term terrain changes within the brines and their surroundings. The achieved co-registration for the temporal DEMs was considerably high, from which precise inferences regarding the terrain dynamics were derived. The observed average rate of bottom surface elevation change for brines was ~1.02 mm/day, with localized signs of erosion and deposition. Additionally, we observed short-term changes in the adjacent geomorphology and salt cracks. We conclude that the transferred regolith volume via such brines can be extremely low, well within the resolution limits of the remote sensors that are currently orbiting Mars, thereby making it difficult to resolve the topographic relief and terrain perturbations that are produced by such flows on Mars. Thus, the absence of observable erosion and deposition features within or around most of the proposed Martian RSL and slope streaks cannot be used to dismiss the possibility of fluidized flow within these features.
... 尽管存在能量不闭合现象 [23] 和 EC 自身的随机 误差 [35] , 然而 EC 仍被视为测量生态系统蒸散发最为 准确的手段之一 [36] , 并在森林 [37] 、 草原 [38,39] 、 农田 [26] 、 荒漠 [40,41] Xu 等人 [42] 基于矩阵分布式蒸渗仪的观测结果指出, 河西沙漠地区至少 91%的降水会被蒸发出地表, 剩 余部分则保存于沙层中. 毛乌素沙地的蒸发入渗实 验显示, 10 mm 的降水可于 15 d 内蒸发出地表 [43] . ...
... Geographically, the salt flat is an intramontane endorheic basin (i.e. an alluvium-filled valley within mountainous ranges with a closed drainage system) bounded by high mountains to each side (Fig. 3a). Unlike other salt flats, the topography is of a high level of roughness and seldom covered by shallow water due to the rapid evaporation process (Kampf et al., 2005). Four sectors of the Los Flamencos National Reserve (Fig. 3)-Soncor (S.4), Laguna de Aguas de Quelana (S.5), Valle de La Luna (S.6), Tambillo (S.7) -located in our studied area were created in 1990 and is governed by the Chile National Forest Corporation (CONAF). ...
... The output is water table evaporation produced in the nucleus and marginal zone, where the mean surficial water evaporation rate is 4.3 mm/d. Evaporation decreases as the depth of the water table increases, and it depends on the soil composition (Kampf et al., 2005;Kampf and Tyler, 2006;Muñoz-Pardo and Ortiz-Astete, 2004). ...
Over the past two decades, considerable attention has been focused on lithium as a critical mineral resource. This is driven primarily by the unprecedented need for this element in moving the energy transition forward because of its utility in lithium-ion batteries for electric vehicles and energy storage. Lithium resources are found in three main types of deposits, but closed-basin brines are known to currently contain most of the global resources. Lithium resources are also present in sedimentary-basin (oil field) and geothermal-basin brines, although these are emerging and not yet produced at a commercial scale. Here we provide an update on the global state of lithium brine resources by type but with a focus on updating the ore deposit model for closed-basin lithium brines and introducing a seventh important characteristic for the formation of closed-basin lithium brines. This characteristic is hydro(geo)ology, which refers to the coupled role of hydrological basin characteristics and subsurface hydrogeological properties and their structure and distribution. Emerging lithium brine types are incorporated into our updated conceptual model, and case studies of two globally important lithium brine systems are also presented. Pegmatite and volcano-sedimentary lithium deposits are compiled to complete the lithium resource picture. Lastly, we consider lithium production over time and some guidelines for the exploration of closed-basin brines.
Lithium brine deposits are mainly distributed in the three major plateaus of the world: the Qinghai‐Tibet Plateau in China, the Andean Plateau in South America and the Western Plateau in North America, forming the three major lithium ore‐forming regions in the world. The lithium‐rich salt lakes on the Qinghai‐Tibet Plateau in China include Zabuye Salt Lake, Nam Co Salt Lake and Da Qaidam Salt Lake. The lithium‐rich salt lakes on the Andean Plateau in South America mainly include Uyuni Salt Lake and Atacama Salt Lake, while the lithium‐rich salt lakes on the Western Plateau in North America mainly include the Salton Sea and Clayton Valley. Based on a large amount of data collection, this article analyses the characteristics of the lithium‐rich salt lakes on the three plateaus, and concludes that the tectonic background of the lithium‐rich salt lakes is mostly associated with subduction‐collision orogenic belts, surrounded by abundant igneous rocks. The main source of lithium is deep‐seated hydrothermal fluids leaching lithium from rocks and bringing it to the surface in the form of hot springs, replenishing the salt lakes.
This work firstly presents a newly compiled literature-based database of global playas (Part 1) and later reviews geomorphological aspects of lake margin calcium carbonate (CaCO 3) landforms (CCLs) and recommends research priorities (Part 2). In Part 1 literature data reveal that playa occurrence is not limited by topography per se but is mainly constrained by climatic factors and the excess of evaporation over total inflow. Playa evaporation rates vary between ∼4200 mm/yr and ∼760 mm/yr. Evapo-concentration effects take place along with increasing salinity or Total Dissolved Solids (TDS). pH values vary between pH 2 to pH 10, although globally most playas comprise carbonate and soda lakes. Part 2 compiles CCL data from large bioherms to crusts, marginal calcretes, tufa pinnacles and mounds. The literature shows that, for example, while playa marginal calcretes occur most dominantly in southern Africa and Australia, further research is required to establish the role of groundwater incursions in relation to the land-palustrine-playa interface. In contrast, work on mostly biogenic carbonate precipitation resulting in bioherm and crust formation is more advanced. Nonetheless the review highlights the need for more research to establish direct links between (micro) textural fabrics and mound or crust building processes as similar carbonate fabrics may result from different pathways of precipitation and diagenetic replacement. ARTICLE HISTORY
Isotopic composition modelling is a key aspect in many environmental studies. This work presents Isocompy, an open source Python library that estimates isotopic compositions through machine learning algorithms with user-defined variables. Isocompy includes dataset preprocessing, outlier detection, statistical analysis, feature selection, model validation and calibration and postprocessing. This tool has the flexibility to operate with discontinuous inputs in time and space. The automatic decision-making procedures are knitted in different stages of the algorithm, although it is possible to manually complete each step. The extensive output reports, figures and maps generated by Isocompy facilitate the comprehension of stable water isotope studies. The functionality of Isocompy is demonstrated with an application example involving the meteorological features and isotopic composition of precipitation in N Chile, which are compared with the results produced in previous studies. In essence, Isocompy offers an open source foundation for isotopic studies that ensures reproducible research in environmental fields.
Wormholes are highly conductive channels that develop in high solubility rocks. They are especially important for environmental and industrial sustainability in saline karst aquifers (e.g. Salar de Uyuni, Salar de Atacama). Wormholes dynamics (i.e., the space and time evolution of these preferential flow paths) depends on the hydrodynamic and geochemical conditions during formation, as well as on wormholes competition for flow. Despite the importance of wormholes interaction for their development, experimental efforts have focused on the evolution of a single flow-path. Direct observation and quantification of wormholes dynamics is still lacking. We propose an experimental set-up to visualize and characterize the dynamics of multiple wormholes, which may help to understand the changes in flow and transport behaviour of aquifers. We performed a dissolution experiment in a 2D synthetic evaporitic aquifer, and simultaneous fluorescent tracer tests before and during wormhole growth. We visualized the growth by sequential photographs, with the fluorescent tracer highlighting the evolving structures. We quantified wormholes dynamics by measuring pressure and mass changes of the aquifer, and by image analysis. On the one hand, results show that wormholes tend to form along areas where flux was fastest prior to dissolution. They also show clear evidence of competition for water between wormholes and represent the first quantitative evidence of the amplifying factor that drives the self-organization in wormhole growth. On the other hand, we found that the competition is slower than predicted by current analytical and numerical theories, but consistent with other laboratory results. We conjecture that the discrepancy between theory and experiments can be attributed to the combined effect of non-linear kinetics and particle dragging during dissolution. We then compared experimental tracer breakthrough curves before and during the formation of preferential flow paths. They reflect wormhole growth by an accentuated non-Fickian behaviour, with reduced first arrival and increased tailing.
The Bonneville Salt Flats is a vast dynamic landscape that has been the focus of diverse activities ranging from land speed racing, recreation, potash mining, and an experimental salt crust restoration project. Over the past century, this site has been the focus of several studies, primarily on decadal changes in salt crust thickness and extent. Despite past research, much remained unknown about the origin of the Bonneville Salt Flats’ evaporite sediments, how the evaporite textures of these sediments have changed over time, and the unique hydrology of this system over daily to seasonal timescales. Furthermore, long-term studies demonstrated brine geochemical measurements were imprecise; therefore, an accurate and precise brine salinity measurement methodology was needed. To address these problems, this dissertation: makes paleoenvironmental interpretations of sediment cores; uses petrography of thick sections to determine how evaporite texture changed over time; analyzes several years of environmental measurements, including water level, evaporation, meteorological measurements, and surface time-lapse observations; and lastly, it demonstrates a methodology using brine density measurements at different temperatures to estimate salinity. Sediment deposits show the Bonneville Salt Flats is much younger than previously believed, first forming approximately ~8,300 years ago. Persistent halite accumulation first occurred ~5,400 years ago, not 13,000 years ago, with the desiccation of Lake Bonneville, as was commonly believed. Halite evaporite sediments at the Bonneville Salt Flats show a diversity of morphologies, demonstrating a complex record of post-depositional alteration. Environmental measurements reveal two groundwater states. During the sealed or flooded state, groundwater levels rise rapidly, bringing groundwater to the surface following precipitation. Groundwater level fluctuations are muted during this state. Under desiccated state conditions, groundwater levels primarily vary in response to seasonal and daily temperature changes. Finally, brine density measurements can be used for high-precision measurements of small changes in salinity and provide a valuable evaluation tool in saline systems.
https://www.proquest.com/dissertations-theses/spatial-temporal-scales-water-salt-movement-at/docview/2780150115/se-2?accountid=57447
Compaction and salinization of soils reduce croplands fertility, affect natural ecosystems, and are major concerns worldwide. Soil compaction alters soil structure and affects the soil's hydraulic properties, and it therefore may have a significant impact on evaporation and solute transport processes in the soil. In this work, we investigated the combined processes of soil compaction, bare soil evaporation, and salt precipitation. X-ray computed microtomography techniques were used to study the geometrical soil pore and grain parameters influenced by compaction. The impact of compaction on evaporation and salt precipitation was studied using column experiments. We found that compaction reduced the average grain size and increased the number of grains, due to the crushing of the grains and their translocation within the compacted soil profile. Changes in pore and grain geometry and size were heterogeneously distributed throughout the soil profile, with changes most apparent near the source of compaction, in our case, at the soil surface. The column experiments showed that the presence of small pores in the upper layer of the compacted soil profile leads to higher evaporation loss and salt precipitation rates, due to the increase of hydraulic connectivity to the soil surface and the prolongation of the first stage of evaporation.
Past environments on Mars contained abundant water, suggesting certain regions may have been conducive to life as we know it and implying the potential for microbial inhabitants. Gale and Jezero craters, home of the Perseverance and Curiosity rovers, hosted ancient lakes that experienced periods of active hydrologic cycling and prolonged drying intervals. Exploration of these basins (and future operations on Mars) will benefit from detailed characterizations of analogous environments on Earth, where life detection strategies at various spatial scales (i.e., rover to orbiter) can be tested and validated. Investigations of terrestrial analogs are critical for understanding (1) how microorganisms generate chemical biosignatures in environments characterized by multiple extreme conditions; (2) the impact of environmental conditions and mineralogy on biosignature preservation; and (3) what technologies and techniques are needed to detect biosignatures remotely or in situ. Here, we survey five terrestrial sites analogous to climate conditions proposed for Late Noachian to Early Hesperian Mars, when craters are thought to have hosted active lakes. We review the geologic setting, environmental conditions, microbial habitability, extant microbial communities, and preserved biomarkers at each analog and discuss their relevance to the search for signs of life in Martian craters with in situ and remote instrumentation. The analogs range from active to desiccated lake systems, temperate to hyper-arid climates, and have acidic to neutral-pH and hypo- to hyper-saline waters. Each analog hosts microorganisms adapted to multiple extremes (polyextremophiles), including aspects of water availability (i.e., surface waters versus shallow subsurface water versus groundwater) and physiochemistry (e.g., water activity, salinity, temperature, alkalinity, pH, and redox potential) that can form macrobiological features such as microbial mats. Comparing the expected achievable spatial resolution of several key Mars instruments to the spatial extent of macrobiological features at each analog reveals that most features are unlikely to be resolved from orbit and require rover-scale instruments for detection. We recommend that future studies at these analogs use multi-scale remote sensing surveys to determine thresholds for detecting macrobiological features and map how patterns in mineralogy or physical characteristics of environments correlate to modern-day microbial communities or preserved biomarkers. It will also be critical to determine how the characteristics of macrobiological features, such as areal extent, percent cover, thickness, pigments, etc., impact detectability thresholds. These findings can provide vital information on potential topographic or spectroscopic signatures of life, and at what scales they are detectable. This research is critical to guide sample collection locations within craters like Jezero, and for selecting landing sites for future missions in evaporative Martian basins and other rocky bodies.
Water-related challenges involve aspects of scientific hydrology and water resources management. We studied research projects funded by the State of Chile through different institutional funds in the last 20 years to identify scientific challenges for hydrology in Chile, which are mainly related to the understanding of the water cycle and infrastructure design. Then, the recent evolution of the challenges in hydrology and water resources are analyzed, as they have been faced by several research, innovation, and development centers recently created. We also present the challenges in water resources management identified by many of these research centers and institutions, which deal mainly with eco- and socio-hydrological issues and integrated water resources management. Finally, some challenges related with water resources policy in Chile are commented as well.
Playas may form in both hydrologically open and closed systems. Several previous
classification schemes of playas rely heavily on geomorphic features rather
than the groundwater hydrology of the system and the degree to which the basin is
hydrologically open or closed. This paper presents a review of the literature on
playa classifications and their hydrologic characteristics, which can be used to better
define the hydrology of playas. A modification of the original hydrologically
based classification schemes of Meinzer (1922) and Snyder (1962) illustrates the importance
of groundwater in playa systems.
In this paper a playa is defined as an intracontinental basin where the water
balance of the lake (all sources of precipitation, surface-water flow, and groundwater
flow minus evaporation and evapotranspiration) is negative for more than half
the year, and the annual water balance is also negative. The playa surface must act
as a local or regional discharge zone. Evidence of evaporite minerals will generally
be present in parts of the basin. This includes carbonate minerals that can be
demonstrated to have been formed through evaporative processes. A recharge playa
is defined as above, except the playa surface acts as a means for recharging water to
the aquifer. In this case, evaporite minerals are absent. Although evaporite formation
is an important part of a playa sequence, significant accumulations of subaqueously
deposited evaporites are only possible when saline water bodies are partially
maintained by a constant inflow of groundwater.
In hydrologically closed basins, the brine chemistry is influenced by the lithology
of the sediments and bedrock within the playa catchment. In hydrologically
open (through-flow) discharge complexes, the brine composition may be determined
by the rate of groundwater flow through the basin (leakage ratio) relative to the
weathering rate of the surrounding sediments and bed rock. If the groundwater inflow
greatly exceeds the rate of chemical weathering, then the brine composition
may be dominated by the chemical composition of regional or local precipitation.
Extensive accumulations of subaqueous evaporites form in playas when there is
sufficient groundwater to maintain a shallow brine pond for an extended period oftime. This has important implications for paleoclimate reconstructions of closed
basin playa sequences. Extremely arid periods, when there is insufficient water to
maintain a brine, will result in displacive intrasediment growth of evaporites; and
extremely wet periods may be too fresh for a brine to develop. It is only in the intermediate
periods when evaporation is high and water input is balanced by evaporation
that extensive subaqueous evaporites will accumulate in closed basin playas.
Dated subsurface cores, 40 In, 100 In, and 200 In in length, from the Salar de Atacama, Chile, record changes in climate and tectonics over the past 325 ka. These cores were used to assess completeness of the stratigraphic record and how that record was influenced by faulting and climate change. The same basic facies, efflorescent halite crust and cement (subaerial halite), and chevron halite (saline lake) occur in each core. The dominant facies is efflorescent halite formed in a subaerial environment like that in the Atacama basin today. Thick, well-preserved efflorescent crusts in the Salar de Atacama cores illustrate that major sediment aggradation occurred in subaerial environments by growth of efflorescent halite from evaporation of ground-water brines. Similar pedogenically formed evaporites may be preserved in the geologic record. The N-S trending Salar Fault System has downdropped the eastern block of the Salar de Atacama (core 2002) relative to the western block (cores 2005 and 2031). Relative faulting rates over the past 60 ka were determined from stratigraphic offset and uranium-series ages from core 2005. Major faulting along the Salar Fault System occurred between 16.5 and 5.4 ka, with offset of 26.5 m and faulting rates of 2.4 m/kyr. Aggradation of efflorescent halite crusts on the downdropped eastern block served to smooth out topographic variations created by faulting. Although stratigraphic units in core 2002 shifted down > 30 m over the past 60 ka, the thickness and sedimentary features are similar for all but one equivalent stratigraphic unit in all three cores. Faulting along the Salar Fault System, despite significant offset, did not alter the basic stratigraphic record. Temporal completeness of the stratigraphic record, within the limits of the age dates and their errors of greater than 3 ka, was examined qualitatively by comparing long-term sedimentation rates (0.6-0.9 m/kyr) and shorter-term sedimentation rates (0.3-3.6 m/kyr). The similarity of sedimentation rates on the 10 kyr scale and the longer 100 to 300 kyr scale suggests temporal completeness of Salar de Atacama sediments, at least at the 10 kyr scale. Although hiatuses, long periods of subaerial exposure, and dissolution of evaporites may have occurred, the main climate fluctuations at Salar de Atacama over the last 100 ka are recorded in all three subsurface cores. Paleoclimate records obtained from such cores are therefore representative of basin-wide climate change and are valid for regional paleoclimate reconstructions.
A 100 m long salt core (SQM #2005) from the Salar de Atacama, northern Chile (23°S, 68°W), a dry lake bed, contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central Andes of South America. Six U-series disequilibrium dates range sequentially from 106.1±6.4 to 5.4±2.7 ka. Based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments, interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods (saline lakes and expanded mudflats) existed in the Salar de Atacama from 75.7 to 60.7 ka and from 53.4 to 15.3 ka, with the wettest perennial lake interval from 26.7 to 16.5 ka. Short relatively wet periods also occurred in the Holocene from 11.4 to 10.2 ka and from 6.2 to 3.5 ka. These wet periods at Salar de Atacama correspond well with other late Pleistocene climate records from the central Andes that are a function of the net hydrologic budget. The Minchin–Tauca lake sequence from Salar de Uyuni, Bolivia, is synchronous with the 53.4–15.3 ka saline lake wet period at Salar de Atacama. The Tauca phase coincided with the wettest perennial lake interval at Salar de Atacama from 26.7 to 16.5 ka. The Coipasa lake phase from Uyuni was probably contemporaneous with the early Holocene wet period at Salar de Atacama from 11.4 to 10.2 ka. The early Holocene wet interval at Salar de Atacama was also synchronous with the maximum Holocene lake levels of the Chilean Altiplano lakes to the east and with grass-rich rodent middens between 11.8 and 10.5 ka in age from the Atacama basin.
Groundwater evaporation and subsequent precipitation of soluble salts at Owens Lake in eastern California have created one of the single largest sources of airborne dust in the USA, yet the evaporation and salt flux have not been fully quantified. In this study, we compare eddy correlation, microlysimeters and solute profiling methods to determine their validity and sensitivity in playa environments. These techniques are often used to estimate evaporative losses, yet have not been critically compared at one field site to judge their relative effectiveness and accuracy. Results suggest that eddy correlation methods are the most widely applicable for the variety of conditions found on large playa lakes. Chloride profiling is shown to be highly sensitive to thermal and density-driven fluxes in the near surface and, as a result, appears to underestimate yearly groundwater evaporation. Yearly mean groundwater evaporation from the playa surface estimated from the three study areas was found to range from 88 to 104 mm year−1, whereas mean evaporation from the brine-covered areas was 872 mm year−1. Uncertainties on these mean rates were estimated to be ±25%, based on comparisons between eddy correlation and lysimeter estimates. On a yearly basis, evaporation accounts for approximately 47 × 106 m3 of water loss from the playa surface and open-water areas of the lake. Over the playa area, as much as 7.5 × 108 kg (7.5 × 105 t) of salt are annually concentrated by evaporation at or near the playa surface, much of which appears to be lost during dust storms in area.
A study was made of the effect of the watertable, water-conducting properties of the soil, climatic factors and groundwater salinity on the salinization of soils in the Murrumbidgee Irrigation Areas, Australia.
Average daily capillary flow rates were calculated from measured salinization (by sampling) for each month between May 1960 and October 1961. Potential gradients were calculated from suction measurements by tensiometers. Field percentages of available water varied from 8 to 14 % for the soils studied. Good agreement was found between values for hydraulic conductivity measured by the augerhole method and capillary conductivity calculated from chloride accumulation (measured monthly sampling).
The agreement between field data and the theory of steady-state flow through unsaturated soils was satisfactory when no limit was set on evaporation by the moisture-conducting proporties of the soil. Where potential evaporation exceeded the maximum possible flow, evaporation from the soil was equal to, or less than the predicted maximum flow through the profile. Reduction of evaporation under these conditions was caused either by the establishment of a natural mulch or by the appearance of a salt crust at the surface.
It was concluded that 'critical depth' of watertable corresponded to the watertable at which the flow rate through the soil profile was reduced to about 0.1 cm day- 1. Generally the watertable should be kept lower in soils of intermediate texture than in either finely or coarsely textured soils.
In the fine-textured soils of the Murrumbidgee Area the salinity hazard was markedly reduced if the watertable was kept at about 120 cm below the surface (bare soil) far below the root zone.
The nucleus of the Atacama salt plain in Chile is a a brine aquifer that interacts with freshwater aquifers that recharge it from the upper portions of the basin. This interaction originates a saline interface that controls the flow of freshwater entering the salt plain located precisely where a number of different extents and shapes occur, providing habitats for abundant wildlife. The sustainability of this wildlife depends on the size, depth and chemical properties of the lagoons. This paper reports the study and analysis of the hydrogeological behavior of the saline aquifer and the lagoon zone using a Modflow simulation model. Evaporation from the lagoons and from groundwater is estimated on the basis of field measurements, and the recharge of the freshwater aquifer is estimated by means of a hydrological simulation model using 27 years of precipitation and evaporation data in the basin. Results show that the evaporation losses from groundwater in the vicinity of the lagoons exhibit a strong correlation with seasonal variations of groundwater recharge, and this effect reduces the variations in the net freshwater recharge into the lagoons.
The Salar de Atacama in northern Chile is a sedimentary basin containing a 900 m thick salt crust (nucleus), about 1.100 km2 in area, surrounded by a 2.000 km2 fringe of saline muds. The salt crust is filled with a sodium chloride interstitial brine rich in Mg, K, Li, B. The main inflows to the salar drain volcanic formations of the Andean Highlands at the east side of the basin. The salts dissolved in inflow waters have a double origin. The weathering of volcanic rocks supplies K, Li, Mg, B and, to a lesser extent, Na and Ca. The leaching of ancient evaporites beneath the volcanic formations provides additional amounts of Na, Ca, Cl, SO4 in the most saline inflow waters. The mass-balance of the upper nucleus shows a strong excess of NaCl with respect to the bittern solutes Mg, K, Li, B, which suggests that the nucleus did not originate from inflow waters similar to the present ones. The excess of NaCl is likely to be due to NaCl-rich inflow waters that formerly drained the Cordillera de la Sal, a Tertiary evaporitic ridge at the western rim of the salar. The average sedimentation rate of halite has been estimated at 0.1 mm/year from the date of an ignimbrite interbedded in the nucleus. The same rate is obtained from the present inflow waters, which suggests that the halite of the nucleus was deposited from ancient inflows similar to the present ones. This is in contradiction with the mass-balance which indicates that the former inflows were much more concentrated in NaCl. The discrepancy may be solved assuming an intermittent activity of the salar. Long dry periods of inactivity were alternating with short wet periods during which large amounts of salt were deposited. The lack of lacustrine deposits and the high purity of the salt suggest that the nucleus is not the remnant of an ancient deep saline lake, but originated mostly from sub-surface and subterraneous saline inflows.
The rate of capillary rise of moisture in a heavy clay soil was calculated by means of a water balance. This moisture movement supplied about 150 mm in 1953. Under favourable circumstances, a delivery of 3-4 mm per day is possible. The calculated values appeared to be in conformity with the law of unsaturated moisture flow. A graph gives the relationship between height above the water table, pF and capillary rise. (Abstract retrieved from CAB Abstracts by CABI’s permission)
The approximately 20 published data based on isotopic profiles of the unsaturated zone lead us to express the evaporative flux as an inverse power function of the piezometric depth below the soil surface, independently of the soil characteristics. Recent publications report suction values taken at over 1 000 m from the soil surface in arid regions as well as hydraulic conductivities corresponding to these values. These new data allowed us to compute new bounds of the evaporative flux from aquifers in arid regions; they corroborate the weak influence of soil characteristics.
This paper presents the results of numerical simulations of groundwater circulation and solute transport at the Salar de Atacama through use of a numerical model to solve the two-dimensional problem of flow in an aquifer when considering the effects of variable density. The phenomena associated with solute transport are modeled by means of an advection-dispersion equation, and a linear relationship is assumed between fluid density and concentration of the dissolved solids. Simulations considered conditions of high groundwater evaporation, which depends on the depth of the phreatic surface. Results indicate that the discharge of groundwater occurs essentially in freshwater-saline water interface zones, where a number of lagunas begin. Different freshwater recharge scenarios were simulated, while it was verified that the effects of evaporation are important and minimize or buffer the variations in the phreatic surface and the discharges of groundwater that are the source of water supply for the lagunas.
A network of 9-m-tall surface flux measurement stations were deployed at
eight sparsely vegetated sites during the Monsoon '90 experiment to
measure net radiation, Q, soil heat flux, G, sensible heat flux, H
(using eddy correlation), and latent heat flux, λE (using the
energy balance equation). At four of these sites, 2-m-tall eddy
correlation systems were used to measure all four fluxes directly. Also
a 2-m-tall Bowen ratio system was deployed at one site. Magnitudes of
the energy balance closure (Q + G + H + λE) increased as the
complexity of terrain increased. The daytime Bowen ratio decreased from
about 10 before the monsoon season to about 0.3 during the monsoons.
Source areas of the measurements are developed and compared to scales of
heterogeneity arising from the sparse vegetation and the topography.
There was very good agreement among simultaneous measurements of Q with
the same model sensor at different heights (representing different
source areas), but poor agreement among different brands of sensors.
Comparisons of simultaneous measurements of G suggest that because of
the extremely small source area, extreme care in sensor deployment is
necessary for accurate measurement in sparse canopies. A recently
published model to estimate fetch is used to interpret measurements of H
at the 2 m and 9 m heights. Three sites were characterized by undulating
topography, with ridgetops separated by about 200-600 m. At these sites,
sensors were located on ridgetops, and the 9-m fetch included the
adjacent valley, whereas the 2-m fetch was limited to the immediate
ridgetop and hillside. Before the monsoons began, vegetation was mostly
dormant, the watershed was uniformly hot and dry, and the two
measurements of H were in close agreement. After the monsoons began and
vegetation fully matured, the 2-m measurements of H were significantly
greater than the 9-m measurements, presumably because the vegetation in
the valleys was denser and cooler than on the ridgetops and hillsides.
At one lowland site with little topographic relief, the vegetation was
more uniform, and the two measurements of H were in close agreement
during peak vegetation. Values of λE could only be compared at
two sites, but the 9-m values were greater than the 2-m values,
suggesting λE from the dense vegetation in the valleys was
greater than elsewhere.
The approximately 20 published data based on isotopic profiles of the unsaturated zone lead us to express the evaporative flux as an inverse power function of the piezometric depth below the soil surface, independently of the soil characteristics. Recent publications report suction values taken at over 1 000 m from the soil surface in arid regions as well as hydraulic conductivities corresponding to these values. These new data allowed us to compute new bounds of the evaporative flux from aquifers in arid regions; they corroborate the weak influence of soil characteristics.
Annual evaporation from an area of wetland vegetation in a dampland on a groundwater mound near Perth, Western Australia, was estimated from measurements of daily evaporation using ventilated chambers on thirteen occasions between March 1987 and March 1988. Evaporation over this period was estimated to be 814 mm, which exceeded the annual rainfall (747 mm) by 67 mm of water. Groundwater loss during summer was 266 mm of water (equivalent to 35% of annual rainfall).During summer, estimates of daily evaporation using diurnal water-table fluctuations gave values which were highly correlated (r = 0.90) with the ventilated chamber method. Provided that estimation was restricted to periods when vegetation is drawing mainly on groundwater, the diurnal fluctuation method offers a practical, cheap alternative method of estimating evaporation from wetlands.
Depth profiles of deuterium composition, expressed as delta-values, have been used to make point estimates of evaporation from the floor of the normally “dry” Lake Frome, a salt lake in northern South Australia. Values from five sites, varying between 90 and 230 mm yr.−1, have been used to obtain a relatively crude approximation for mean evaporation rate from the lake of 170 mm yr.−1. Under the assumption that this represents discharge of water from the regional groundwater system, the groundwater inflow into the lake is calculated as ∼ 5 × 108 m3 yr.−1. Two possible models which describe groundwater inflow into the lake are discussed.
Evaporation of water from saturated saline soils or sediments induces gradients of the solutes in the remaining interstitial solution. These gradients lead to a systematic and predictable solute distribution in the soil solution which may be used, in some cases, to estimate the rate of evaporation. Simple one-dimensional transport models for the distribution of Cl− and Br− indicate net evaporation rates from the salt-covered surface of Lake Eyre, South Australia of between 0.9 and 2.8 cm yr−1; the former is a minimum estimate averaged over ∼20 yrs (which includes the major 1974 filling event) while the latter reflects the most recent summer evaporation period.
Annual evaporation from a site within a Banksia woodland on a groundwater mound near Perth, Western Australia, was estimated from measurements of daily evaporation by ventilated chambers on fourteen occasions during a 12-month period. The total evaporation for this period was estimated to be 666 mm (77% of annual rainfall). About two-thirds of the total evaporation came from the ground flora, one-fifth from Banksia trees, and the remainder from the tall shrub Adenanthos cygnorum. Depth to water table, which ranged from 4 to 12 m over the site, had little effect on total evaporation. This work suggests that regular reduction in ground flora foliage, for example, by controlled burning could increase recharge.
An interdisciplinary field experiment was conducted to study the water and energy balance of a semiarid rangeland watershed in southeast Arizona during the summer of 1990. Two subwatersheds, one grass dominated and the other shrub dominated, were selected for intensive study with ground-based remote sensing systems and hydrometeorological instrumentation. Surface energy balance was evaluated at both sites using direct and indirect measurements of the turbulent fluxes (eddy correlation, variance, and Bowen ratio methods) and using an aerodynamic approach based on remote measurements of surface reflectance and temperature and conventional meteorological information. Estimates of net radiant flux density (Rn), derived from measurements of air temperature, incoming solar radiation, and surface temperature and radiance compared well with values measured using a net radiometer (mean absolute difference (MAD ~=50 W/m2 over a range from 115 to 670 W/m2). Soil heat flux density (G) was estimated using a relation between G/Rn and a spectral vegetation index computed from the red and near-infrared surface reflectance. These G estimates compared well with conventional measurements of G using buried soil heat flux plates (MAD ~=20 W/m2 over a range from -13 to 213 W/m2). In order to account for the effects of sparse vegetation, semiempirical adjustments to the single-layer bulk aerodynamic resistance approach were required for evaluation of sensible heat flux density (H). This yielded differences between measurements and remote estimates of H of approximately 33 W/m2 over a range from 13 to 303 W/m2. The resulting estimates of latent heat flux density, LE, were of the same magnitude and trend as measured values; however, a significant scatter was still observed: MAD ~=40 W/m2 over a range from 0 to 340 W/m2. Because LE was solved as a residual, there was a cumulative effect of errors associated with remote estimates of Rn, G, and H.
We set up two automatic weather stations over a playa (the flat floor of an undrained desert basin that, at times, becomes a shallow lake), approximately 65 km east–west by 130 km north–south, located in Dugway (40° 08′N, 113° 27′W, 1124 m above mean sea level) in northwestern Utah, USA, in 1999. These stations measured the radiation budget components, namely: incoming Rsi and outgoing Rso solar or shortwave radiation, using two Kipp and Zonen pyranometers (one inverted), the incoming Rli (or atmospheric) and outgoing Rlo (or terrestrial) longwave radiation, using two Kipp and Zonen pyrgeometers (one inverted) during the year 2000. These sensors were ventilated throughout the year to prevent dew and frost formation. Summation of these components yields the net radiation Rn. We also measured the air temperatures and humidity at 1 and 2 m and the soil moisture and temperature (Campbell Sci., Inc., CSI) to evaluate the energy budget components (latent (LE), sensible (H), and the soil (Gsur) heat fluxes). The 10 m wind speed U10 and direction (R.M. Young wind monitor), precipitation (CSI), and the surface temperature (Radiation and Energy Balance Systems, REBS) were also measured during 2000. The measurements were taken every 2 s, averaged into 20 min, continuously, throughout the year 2000. The annual comparison of radiation budget components indicates that about 34% of the annual Rsi (6937.7 MJ m−2 year−1) was reflected back to the sky as Rso, with Rli and Rlo amounting to 9943.4 MJ m−2 year−1 and 12 789.7 MJ m−2 year−1 respectively. This yields about 1634.3 MJ m−2 year−1 as Rn, which is about 24% of the annual Rsi. Of the total 1634.3 MJ m−2 year−1 available energy, about 25% was used for the process of evaporation (LE) and 77% for heating the air (H). The annual heat contribution from the soil to the energy budget amounted to 2% during the experimental period. Our studies showed that the total annual measured precipitation amounted to 108.0 mm year−1 during the year 2000, but the total evaporation was 167.6 mm year−1, which means some water was extracted from the shallow water table (about 60 cm on the average depth during the year 2000). Copyright © 2003 Royal Meteorological Society.
Bowen ratio meteorological stations have been deployed to measure rates of evaporation from groundwater discharge playas and from an adjacent vegetated bench in the Estancia Basin, in central New Mexico. The playas are remnants of late Pleistocene pluvial Lake Estancia and are discharge areas for groundwater originating as precipitation in the adjacent Manzano Mts. They also accumulate water during local precipitation events. Evaporation is calculated from measured values of net radiation, soil heat flux, atmospheric temperature, and relative humidity. Evaporation rates are strongly dependent on the presence or absence of standing water in the playas, with rates increasing more than 600% after individual rainstorms. Evaporation at site E-12, in the southeastern part of the playa complex, measured 74 cm over a yearlong period from mid-1997 through mid-1998. This value compares favorably to earlier estimates from northern Estancia playas, but is nearly three times greater than evaporation at a similar playa in western Utah. Differences in geographical position, salt crust composition, and physical properties may explain some of the difference in evaporation rates in these two geographic regions. q 2000 Elsevier Science B.V. All rights reserved.
Two long term microclimate measurement stations with Bowen ratio capability have been used to study water cycling in a closed desert basin. Microclimate variables including the temperature and vapor pressure gradients were monitored continuously and were used to estimate the Bowen ratio, sensible and latent heat fluxes during 1986 and 1987. Despite having a water table that varied between the surface and 30 cm below the surface, the playa had little evaporation except after rainfall events. The very high osmotic pressure of the soil and salt crust caused most of the absorbed radiation to be partitioned to sensible heat. In contrast, along the margin the thin grass and brush cover transpired water freely, with the latent heat flux exceeding 60% of available energy for much of the season. The higher air temperatures above the playa raised potential evapotranspiration (ET) significantly higher than along the margin throughout the summer. The annual average actual ET of the playa was only 36% of the margin. During the drier summer period (May–October), this ratio decreased to < 28%. Immediately after a rainfall event, evaporation rates of the two sites were similar, but the playa rate was quickly reduced as the osmotic potential increased. During this study, the playa lost < 229 mm of subsurface water to evaporation annually, while > 638 mm were lost from the margin groundwater supply.The 24-h solar and net radiation correlations were 0.80 and 0.94 for the playa and margin, respectively. The lower correlation for the playa resulted from the wide variation of albedo with surface moisture changes. The annual average albedo values for the playa and margin were 0.64 and 0.46, respectively.
Water balance studies have been undertaken at a groundwater-discharge playa (Spring Lake) near Curtin Springs, in arid central Australia. Hydraulic calculations indicate that the groundwater inflow to the playa is about 2000 m3 d−1. This is equivalent to evaporative discharge, integrated over the playa surface area (15 km2), of about 49 mm yr−1. As the mean annual rainfall is 226 mm the total evaporative discharge is about 275 mm yr−1.Measured water losses from the playa surface during a 3-month dry period, July–September 1985, ranged from 0.28 to 0.45 mm d−1. This is of the expected order of magnitude for the cooler half of the year. The rate of water loss is variable over the playa surface.The playa is surrounded by sand dunes. Monitoring of water level fluctuations indicates that annual rainfall events induce groundwater recharge in the playa-marginal zone where the water table is within 4 m of the ground surface.Evaporation from the playa has resulted in the development of highly saline brines, with density 1.20 or more and containing more than 250 g 1−2 total dissolved solids. The brines are sodium chloride waters with appreciable magnesium and sulphate. At the playa margin, a transition zone has developed between saline regional groundwaters which underlie sand dunes, and the playa hypersaline brines. Salt may be diffusing downwards beneath the regional grounwaters.Gypsum is precipitating in the playa. The effects of seasonal and longer term drought are shown by the development of gypsum fields on the playa bed and playa-marginal gypsum terraces which are later colonised by halophytic plants. Long-term reduction in groundwater head results in the vegetation of playas which, no longer actively discharging groundwater, become susceptible to alluviation or aeolian sand drift. Thus playas migrate by a process, playa capture, analogous to river capture, but induced by groundwater head decay.
Diffuse (evaporative) discharge of ground water is of interest in the management of local or regional ground waters, and soil salinity. However, past studies show that discharge may vary greatly between soils in agricultural areas and salt flats for similar water table depths. Low discharge from salt flats has been previously attributed to the effect of salt crusts, yet possible soil hydrological reasons for those differences have not been examined. Steady-state hydraulic theory describing the relationship between discharge and water table depth is reviewed. The minimum water table depths required for the theory to be applied are defined in terms of soil parameters. Relationships between discharge and water table depth are then used to analyse the results of previous diffuse discharge studies. It is shown that discharge from both bare agricultural soils and salt flats is consistent with this theory. Unsaturated hydraulic conductivity of three salt flat soils, determined from measurements of discharge and soil matric suction, showed that low discharge flexus recorded from the sites were due to low soil permeability. The relationship between discharge flux and water table depth calculated for these sites also described discharge from other salt flats, implying that low hydraulic conductivity caused low discharge from these areas as well. The reasons for the low hydraulic conductivity of salt flat soils are not clear, and need to be investigated to determine if it is a general property of soils in these areas, or results from the high salinity levels.
When the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived.
If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre‐dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required.
If the constituent's density fluctuations or mean gradients are measured directly in the air in situ , then corrections arising from both heat and water vapour fluxes are required.
These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cent.
Compositional zoning within Salar de Atacama and Salar de Llulliallaco has been mapped from Landsat Thematic Mapper (TM) data. The data were enhanced using decorrelation stretching of TM bands 7, 5, and 4, which were considered to possess the majority of the mineralogical information. The resulting 7, 5, 4 (red, green, blue) color composites provide excellent discrimination of evaporite mineral zones within the salar. The interpretation is supported by fieldwork at the Salar de Atacama and spectral considerations. A strong relationship between the mineralogy of a unit and surface roughness was observed in the field, hence there is potential for imaging radar to provide complementary zonal data.
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