Desert Sites Research Articles

Modelling Soil Moisture in Hyper-Arid Conditions

In most land-surface models, the evolution of soil moisture is governed by soil-hydraulic processes. In hyper-arid soils, these processes break down, but soil moisture continues to show clear temporal variations, suggesting that other processes may be at work. We hypothesize that moisture in such soils varies due to evaporation in the soil and to vapour fluxes at the air–soil interface. To test this, we include vapour exchange between the air and soil in a land-surface model, apply the model to a desert site, and compare the simulated and observed soil moisture. The good agreement between the simulations and observations confirms our hypothesis. Using the model results, we examine the interactions between the soil-moisture and soil-vapour phases and influences of the soil-vapour phase on the surface energy balance.

Impact of dust events on the optimization of photovoltaic-wind hybrid system in desert

Reliable optimization of renewable energy systems has to be adapted to the installation site and its environmental factors. In dust event sources, the impact of dust on solar irradiance or on system’s production is not usually taken into consideration during optimization of photovoltaic (PV) or PV-wind hybrid systems. The first objective of this paper was to make observatory studies on wind velocity and lifting of Saharan dust that characterize Algerian desert which allowed us to extract a wind threshold for each event in our desert site. The second objective was to quantify this dust suspension and its negative impact, up to 47.46% on global solar irradiance (GSI) and 48.95% on photovoltaic yield effects were observed. The third and main objective of this paper was evaluating changes in optimized system when the dust impact was taken into account. To achieve that we adjusted GSI satellite data on HOMER software to dust presence, and then we run an optimization on HOMER with its GSI database and the new data, this data adjustment leads to a significant expansion of 13.70% on the size of PV generator, also 7.66% and 7.68% increase on the investment expenses and cost of energy respectively. Results obtained on this paper can be used to make PV-hybrid system’s technical and financial optimization in the main Algerian dust source trustworthy.

BRDF feature observation method and modeling of desert site based on UAV platform

BRDF feature observation method and modeling of desert site based on UAV platform

Patterns of nitrogen and phosphorus stoichiometry among leaf, stem and root of desert plants and responses to climate and soil factors in Xinjiang, China

Nitrogen (N) and phosphorus (P) play essential roles in plant growth and deserve more attention in desert ecosystems. Nutrients stoichiometry patterns across various plant organs can reflect the plants' trade-offs to obtain resources and their growth strategy. However, it is still unclear how these nutrients are allocated among desert plant organs and how they are related to the arid climate conditions. This study aimed to examine how plant N and P stoichiometry varies among the organs of desert plants, and how they respond to climate and soil factors. Therefore, we analyzed N and P stoichiometry of leaves, stems, and roots collected from 29 desert sites in Xinjiang, China, to achieve this goal. Our studies indicated that the mean N and P concentrations in the stems (17.5 ± 0.2 and 1.0 ± 0.02 mg g−1, respectively) and roots (10.3 ± 0.2 and 0.7 ± 0.01 mg g−1, respectively) were significantly lower than those in leaves (21.4 ± 0.3 and 1.2 ± 0.02 mg g−1, respectively); the N:P ratio in stems (19.1 ± 0.3) was significantly higher than those in roots (17.6 ± 0.4), but N:P in leaves (18.2 ± 0.3) was not significantly different from those in stems and roots. Across plant life forms, N and N:P of both leaves and roots were respectively higher in shrubs than those in trees and herbs, P in three organs were significantly lower in trees than those in shrubs and herbs. Moreover, our results demonstrated that most soil factors had direct influences on N and P stoichiometry among different organs, and climate factors had indirect effect on N and P stoichiometry by affecting soil factors. This study provided the N and P stoichiometric characteristics of desert plant organs and explored their relationships with environmental variables, which can help understand nutrient stoichiometry patterns and utilization strategy of N and P and their potential responses to global climate changes in the desert ecosystems of central Asia.

The bacterial communities of surface soils from desert sites in the eastern Utah (USA) portion of the Colorado Plateau

Desert-like areas located in the eastern portion of the state of Utah (USA) have geographic features that can resemble the surface of the planet Mars, characterized by red-colored hills, soils and sandstones. We examined the bacterial biodiversity of surface soil samples from several sites from the Colorado Plateau Desert in eastern Utah using pyrosequencing of PCR amplified bacterial 16S rRNA genes from total extracted soil DNA. The sample sites cover the Great Basin, Goblin Valley State Park and nearby regions on the Colorado Plateau. We also examined several physicochemical parameters of the soil samples to investigate any possible correlations between bacterial community structure and environmental drivers. The predominant bacterial phyla present in the samples were found to belong to members of the Proteobacteria, Actinobacteria, Bacteroidetes, and Gemmatimonadetes. The most abundant genera in our samples were found to belong to the Cesiribacter, Lysobacter, Adhaeribacter, Microvirga and Pontibacter genera. We found that the relative abundance of Proteobacteria and Gemmatimonadetes were significantly correlated with soil pH and a low concentration of organic matter, suggesting that, in these relatively high-altitude desert soils, these two parameters may be of primary importance to influence bacterial community composition.

The use of ANN and conventional solar-plant meteorological variables to estimate atmospheric horizontal extinction

In the search to optimize electricity generation systems based on renewable energy sources, solar power plants are a clear alternative for reducing pollution on the planet. In particular, concentrating solar power plants with central tower technology supply energy to large population centers and they are generally located at desert sites. Production in these plants drops due to the presence of particles in the environment. These particles are complex to measure and doing so usually requires the use of dedicated, expensive instrumentation. In this work, we present a methodology called Extinction that estimates this attenuation phenomenon utilizing meteorological variables, along with the use of artificial neural networks (ANN). Direct normal irradiance, relative humidity, temperature and pressure have been the only meteorological variables needed to estimate the Extinction. The results from the estimations presented a correlation coefficient value (R) of 0.88 (between the measured and estimated atmospheric horizontal extinction with ANN), a normalized Mean Bias Error (nMBE) of 0% and a normalized Root-Mean Square Deviation (nRMSD) of 7%.

Three questions about the eco-physiology of overwintering underground.

In cold environments ectotherms can be dormant underground for long periods. In 1941 Cowles proposed an ecological trade-off involving the depth at which ectotherms overwintered: on warm days, only shallow reptiles could detect warming soils and become active; but on cold days, they risked freezing. Cowles discovered that most reptiles at a desert site overwintered at shallow depths. To extend his study, we compiled hourly soil temperatures (5 depths, 90 sites, continental USA) and physiological data, and simulated consequences of overwintering at fixed depths. In warm localities shallow ectotherms have lowest energy costs and largest reserves in spring, but in cold localities, they risk freezing. Ectotherms shifting hourly to the coldest depth potentially reduce energy expenses, but paradoxically sometimes have higher expenses than those at fixed depths. Biophysical simulations for a desert site predict that shallow ectotherms have increased opportunities for mid-winter activity but need to move deep to digest captured food. Our simulations generate testable predictions to eco-physiological questions but rely on physiological responses to acute cold rather than to natural cooling profiles. Furthermore, natural-history data to test most predictions do not exist. Thus, our simulation approach uncovers knowledge gaps and suggests research agendas for studying ectotherms overwintering underground.

Agriculture induces isotopic shifts and niche contraction in Horned Larks (Eremophila alpestris) of the Colorado Desert

Agriculture can dramatically alter community composition, food webs, and resource availability, yet the impacts of agriculture on many ecosystems and their constituents remain unstudied. Here, we examined the effect of agriculture on the isotopic ecology of Horned Larks (Eremophila alpestris) in the Colorado Desert. Over the last century, the Imperial Valley in southeastern California has transformed from desert scrub into agricultural land, while breeding Horned Larks have persisted in the area. We compared the isotopic composition of nitrogen (δ15N), carbon (δ13C), and hydrogen (δ2H) from feathers of lark specimens from two time periods in the Imperial Valley: a historical series collected between 1916 and 1923 and more recent vouchers collected between 1984 and 2014. We also quantified δ15N and δ13C values from plants and soil samples in contemporary agricultural land and adjacent desert scrub to estimate isotopic baseline changes associated with agricultural intensification. Contemporary larks had lower δ15N and δ13C ratios compared to historical larks, while plant and soil δ15N ratios were higher at agricultural sites compared to adjacent desert sites. These opposing trends suggest temporal change in isotope values that cannot be explained by shifting baselines alone. Furthermore, isotopic niche breadth (‰2; δ15N and δ13C) was lower among contemporary larks. Thus, contemporary larks in the Imperial Valley may capitalize on seeds and phytophagous insects that are abundant among crops, possibly representing an opportunistic change in diet over time in response to agriculture. Finally, δ2H values did not differ between historical and contemporary larks, but contemporary larks had δ2H values that differed from historical ground water, suggesting intake of water introduced by irrigational canals. Collectively, these findings highlight the power of stable isotope analyses combined with natural history collections to examine ecological change in the Anthropocene.

Cryostratigraphical studies of ground ice formation and distribution in a High Arctic polar desert landscape, Resolute Bay, Nunavut1

Ground ice distribution and abundance have wide-ranging effects on periglacial environments and possible impacts on climate change scenarios. In contrast, very few studies measure ground ice in the High Arctic, especially in polar deserts and where coarse surficial material complicates coring operations. Ground ice volumes and cryostructures were determined for eight sites in a polar desert, near Resolute Bay, Nunavut, chosen for their hydrogeomorphic classification. Dry, unvegetated polar desert sites exhibited ice content close to soil porosity, with a <45 cm thick ice-enriched transition zone. In wetland sites, suspended cryostructures and ice dominated cryofacies (ice content at least 2× soil porosity values) were prevalent in the upper ∼2 m of permafrost. Average ground ice saturation at those locations exceeded porosity values by a factor between 1.8 and 20.1 and by up to two orders of magnitude at the ∼10 cm vertical scale. Sites with the highest ice contents were historically submerged wetlands with a history of sediment supply, sustained water availability, and syngenetic and quasi-syngenetic permafrost aggradation. Ice enrichment in those environments were mainly caused by the strong upward freezing potential beneath the thaw front, which, combined with abundant water supply, caused ice aggradation and frost heaving to form lithalsa plateaus. Most of the sites already expressed cryostratigraphic evidence of permafrost degradation. Permafrost degradation carries important ecological ramifications, as wetland locations are the most productive, life-supporting oases in the otherwise relatively barren landscape, carrying essential functions linked with hydrological processes and nutrient and contaminant cycling.

Evapotranspiration Partitioning at Field Scales Using TSEB and Multi-Satellite Data Fusion in The Middle Reaches of Heihe River Basin, Northwest China

Daily evapotranspiration (ET) and its components of evaporation (E) and transpiration (T) at field scale are often required for improving agricultural water management and maintaining ecosystem health, especially in semiarid and arid regions. In this study, multi-year daily ET, E, and T at a spatial resolution of 100 m in the middle reaches of Heihe River Basin were computed based on an ET partitioning method developed by combing remote sensing-based ET model and multi-satellite data fusion methodology. Evaluations using flux tower measurements over irrigated cropland and natural desert sites indicate that this method can provide reliable estimates of surface flux partitioning and daily ET. Modeled daily ET yielded root mean square error (RMSE) values of 0.85 mm for cropland site and 0.84 mm for desert site, respectively. The E and T partitioning capabilities of this proposed method was further assessed by using ratios E/ET and T/ET derived from isotopic technology at the irrigated cropland site. Results show that apart from early in the growing season when the actual E was reduced by plastic film mulching, the modeled E/ET and T/ET agree well with observations in terms of both magnitude and temporal dynamics. The multi-year seasonal patterns of modeled ET, E, and T at field scale from this ET partitioning method shows reasonable seasonal variation and spatial variability, which can be used for monitoring plant water consumption in both agricultural and natural ecosystems.

Results of comparisons of the predictions of 17 dense gas dispersion models with observations from the Jack Rabbit II chlorine field experiment

The Jack Rabbit II (JR II) chlorine field trials in 2015 and 2016 involved nine 5–20 ton releases of pressurized liquefied chlorine from a tank mounted 1 m above a broad flat desert sand surface. A model comparison study was initiated, where 17 widely-used dense-gas dispersion models were run by scientists in seven countries. Predictions were submitted following specified formats, using specified emissions and meteorology inputs. To compare with the model predictions, sets of observations were defined for the arc-maximum 1–3 s averaged concentrations (arc max C) and for cloud widths and heights (to 20 ppm and 200 ppm contours) at distances from 0.2 to 11.0 km from the release. The initial focus is on the three field trials (1, 6, and 7) that have the highest observed concentrations and that have detailed emissions information. It is found that these models are able to satisfactorily simulate (generally within a factor of two) the observed arc max C's and their variation with downwind distance at this flat desert site. At each downwind distance, the scatter in the arc max C predictions covers about 1 ½ orders of magnitude, but the observed arc max C is within the range of the predictions. The median of the cloud width predictions is about 50% larger than the observed value for the three trials. The median of the cloud height predictions is within about 10% of the observed value. For both cloud width and/or height, there are a few models with large (factor of 3 or higher) overpredictions. Of the 17 models, when compared to observations, there is a core group of 5 or 6 with consistently (across all three trials and all distances) less mean error and scatter in their predictions of arc max C and cloud width and height. However, as a group, the 17 models are performing adequately (using the “factor of two” rule of thumb). An important caveat is that, at the JR II desert site, chlorine deposition is minimal. At a site with vegetation and/or organic-rich soil, the effects of removal of chlorine by deposition are expected to be significant.

Isolation and Characterization of Thermophilic Bacteria Indigenous to Al-Ahsa Desert

Deciphering the biological resources across the Saudi niches is highly recommended for the prosperity. To this end, the aim of the current work was to isolate thermophilic bacteria from unexplored areas of Al-Ahsa region, and investigate their phenotypic characteristics. Three soil samples were collected from different desert sites of Al-Ahsa region. Thermophilic bacteria were isolated directly for soil samples into Thermus medium broth as a standard method. Single colonies of the actively growing bacterial isolates were preserved in 20% glycerol then kept at -80°C. The isolates were screened for production of thermostable enzymes using the commercially available kit API20E strip (bioMerieux, Marcy l’Etoile, France). Incubation were carried out at 50°C. It can be concluded that thermophilic bacteria in Al-Ahsa region harbor novel thermostable enzymes that might have biotechnological applications, in future.

An Operational Split-Window Algorithm for Retrieving Land Surface Temperature from Geostationary Satellite Data: A Case Study on Himawari-8 AHI Data

An operational split-window (SW) algorithm was developed to retrieve high-temporal-resolution land surface temperature (LST) from global geostationary (GEO) satellite data. First, the MODTRAN 5.2 and SeeBor V5.0 atmospheric profiles were used to establish a simulation database to derive the SW algorithm coefficients for GEO satellites. Then, the dynamic land surface emissivities (LSEs) in the two SW bands were estimated using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Emissivity Dataset (GED), fractional vegetation cover (FVC), and snow cover products. Here, the proposed SW algorithm was applied to Himawari-8 Advanced Himawari Imager (AHI) observations. LST estimates were retrieved in January, April, July, and October 2016, and three validation methods were used to evaluate the LST retrievals, including the temperature-based (T-based) method, radiance-based (R-based) method, and intercomparison method. The in situ night-time observations from two Heihe Watershed Allied Telemetry Experimental Research (HiWATER) sites and four Terrestrial Ecosystem Research Network (TERN) OzFlux sites were used in the T-based validation, where a mean bias of −0.70 K and a mean root-mean-square error (RMSE) of 2.29 K were achieved. In the R-based validation, the biases were 0.14 and −0.13 K and RMSEs were 0.83 and 0.86 K for the daytime and nighttime, respectively, over four forest sites, four desert sites, and two inland water sites. Additionally, the AHI LST estimates were compared with the Collection 6 MYD11_L2 and MYD21_L2 LST products over southeastern China and the Australian continent, and the results indicated that the AHI LST was more consistent with the MYD21 LST and was generally higher than the MYD11 LST. The pronounced discrepancy between the AHI and MYD11 LST could be mainly caused by the differences in the emissivities used. We conclude that the developed SW algorithm is of high accuracy and shows promise in producing LST data with global coverage using observations from a constellation of GEO satellites.

Life under quartz: Hypolithic mosses in the Mojave Desert.

Several species of dryland cyanobacteria are known to occur as hypoliths under semi-translucent rocks. In the Mojave Desert, these organisms find refuge from intense solar radiation under milky quartz where moisture persists for a longer period of time than in adjacent soil surface habitat. Desert mosses, which are extremely desiccation-tolerant, can also occur in these hypolithic spaces, though little is known about this unique moss microhabitat and how species composition compares to that of adjacent soil surface communities. To address this question, we deployed microclimate dataloggers and collected moss samples from under and adjacent to 18 milky quartz rocks (quartz mean center thickness 26 ± 15 mm) in a western high elevation Mojave Desert site. Light transmission through Mojave quartz rocks may be as low as 1.2%, and data from microclimate loggers deployed for five months support the hypothesis that quartz provides thermal buffering and higher relative humidity compared to the soil surface. Of the 53 samples collected from hypolith and surface microhabitats, 68% were Syntrichia caninervis, the dominant bryophyte of the Mojave Desert biological soil crust. Tortula inermis accounted for 28% of the samples and 4% were Bryum argenteum. In a comparison of moss community composition, we found that S. caninervis was more likely to be on the soil surface, though it was abundant in both microhabitats, while T. inermis was more restricted to hypoliths, perhaps due to protection from temperature extremes. In our study site, the differences between hypolithic and surface microhabitats enable niche partitioning between T. inermis and S. caninervis, enhancing alpha diversity. This work points to the need to thoroughly consider microhabitats when assessing bryophyte species diversity and modelling species distributions. This focus is particularly important in extreme environments, where mosses may find refuge from the prevailing macroclimatic conditions in microhabitats such as hypoliths.

Microbial Diversity of Some Sabkha and Desert Sites in Saudi Arabia.

Several studies isolated fungal and bacterial species from extreme environments, such as Sabkha and hot deserts, as their natural habitat, some of which are of medicinal importance. Current research aimed investigating the microbial (fungi and bacteria) diversity and abundance in Sabkha and desert areas in Saudi Arabia. Soil samples from nine different geographical areas (Al-Aushazia lake, AlQasab, AlKasar, Tabuk, Al-Kharj, Al-Madina, Jubail, Taif and Abqaiq) were collected and cultured for microbial isolation. Isolated fungi and bacteria were identified by molecular techniques (PCR and sequencing). Based on 18S rDNA sequencing, 203 fungal species belonging to 33 genera were identified. The most common fungal genera were Fusarium, Alternaria, Chaetomium, Aspergillus Cochliobolus and Pencillium, while the most common species were Chaetomium globosum and Fusarium oxysporum. By 16S rDNA sequencing 22 bacterial species belonging to only two genera, Bacillus and Lactobacillus, were identified. The most commonly isolated bacterial species were Bacillus subtilis and Lactobacillus murinus. Some fungal species were confined to specific locations, such as Actinomyces elegans, Fusarium proliferatum, Gymnoascus reesii and Myzostoma spp. that were only isolated from Al-Aushazia soil. AlQasab soil had the highest microbial diversity among other areas with abundances of 23.5% and 4.4% of total fungi, and bacteria, respectively. Findings of this study show a higher degree of fungal diversity than that of bacteria in all studied areas. Further studies needed to investigate the connection between some isolated species and their habitat ecology, as well as to identify those of medicinal importance.

Large nitrogen oxide emission pulses from desert soils and associated microbiomes

Nitrogen (N) trace gas emission pulses produced after wetting dry soils may be important pathways of ecosystem N loss. However, the rates and mechanisms controlling these emissions remain unclear. We tested whether changes in microbial community structure and increased rates of atmospheric N deposition could explain N emissions at two desert sites differing in atmospheric N deposition by ~ six fold. We measured peak NOx (sum of nitric oxide and nitrogen dioxide) emissions 12 h post-wetting. NOx emissions remained elevated over 24 h and increased after adding N. In contrast, we measured the highest nitrous oxide (N2O) emissions within only 15 min post-wetting. N2O emissions decreased within 12 h, were insensitive to adding N, and were among the highest reported globally. Microbial communities at the high N deposition site were less diverse with higher 16S nitrifier and bacterial amoA gene abundances relative to the low N deposition site, suggesting an increased capacity for nitrification. Nevertheless, N emissions were lower at the high N deposition site. While microbial communities changed after wetting, these changes were not correlated with N emissions. We conclude that desert soils can produce substantial NOx and N2O emission pulses, but that these emissions do not appear directly governed by changing microbial community characteristics or higher atmospheric N inputs. These findings highlight the importance of gaseous N loss pathways from dryland ecosystems that may contribute to sustained N limitation, with implications for atmospheric chemistry and Earth’s climate.

Stability Assessment of OCO-2 Radiometric Calibration Using Aqua MODIS as a Reference

With three imaging grating spectrometers, the Orbiting Carbon Observatory-2 (OCO-2) measures high spectral resolution spectra ( λ / Δ λ ≈ 19,000) of reflected solar radiation within the molecular oxygen (O 2 ) A-band at 0.765 μ m and two carbon dioxide (CO 2 ) bands at 1.61 and 2.06 μ m. OCO-2 uses onboard lamps with a reflective diffuser, solar observations through a transmissive diffuser, lunar measurements, and surface targets for radiometric calibration and validation. Separating calibrator aging from instrument degradation poses a challenge to OCO-2. Here we present a methodology for trending the OCO-2 Build 8R radiometric calibration using OCO-2 nadir observations over eight desert sites and nearly simultaneous observations from Moderate Resolution Imaging Spectroradiometer (MODIS) with sensor viewing zenith angles of 15 ± 0.5 ∘ . For the O 2 A-band, this methodology is able to quantify a drift of −0.8 ± 0.1% per year and capture a small error in correcting the aging of the solar calibrator. For the other two OCO-2 bands, no measurable changes were seen, indicating less than 0.1% and less than 0.3% per year drift in the radiometric calibration of Band 2 and Band 3, respectively.

Wind energy resource assessment of desert sites in Algeria: energy and reduction of CO<sub>2</sub> emissions

<p><span>This paper presents a statistical analysis of wind potential of four locations in southern Algeria, namely Adrar, In Salah, Illizi and Tamanrasset, using the Weibull distribution. The evaluation the energy production by the CALORIUS 37 wind turbine taking into account the meteorological (wind and temperature and geographical (latitude, longitude and altitude) datas of these locations. The data were collected every 3 hours over 5 years and used to estimate of the annual energy produced, in order to determine the amount of three types of fossil energy (natural gas, gasoil and gasoline) preserved and the quantities of CO<sub>2</sub> that can be avoided. The shape parameter k, varies from 2.0 (Illizi and Tamanrasset) to 2.48 (In Salah), this means that all the distributions are stable, while the scale parameters C varies from 4.6 m/s (Illizi) to 6.3 m/s (In Salah) and mean velocity v varies from 4.1 m/s (Illizi) to 5.5 m/s (Adrar), while the annual energy produced by CALORIUS 37 range from 4467.6 kWh (Illizi) to 8409.6 kWh (Adrar), the equivalent of energies range from 0.38 TEP (Illizi) to 0.72 TEP (Adrar) and the amount of carbon dioxide (CO<sub>2</sub> ) that we can provide varies from 0.90 TE-CO<sub>2</sub> (natural gas power plant in Illizi ) to 2.24 TE-CO<sub>2</sub> (gasoil power plant in Adrar).</span></p>

Wind energy resource assessment of desert sites in Algeria: energy and reduction of CO2 emissions

Wind energy resource assessment of desert sites in Algeria: energy and reduction of CO2 emissions

Orientación de nidos de hornero (Furnarius rufus): Efectos de la vegetación, el viento y la radiación solar en el noroeste de la Argentina

Solar radiation, winds and cover vegetation can affect nest construction decisions in birds; for example, the orientation of their entrance. In this study, the nest entrance orientation of rufous hornero (Furnarius rufus) in a subtropical desert site from Northern Argentina was examined. It was evaluated whether solar radiation and winds influence the mean orientation of nests with abundant upper vegetation cover and of those with little or no upper vegetation cover. Nests with abundant upper vegetation cover showed a randomly defined nest entrance orientation, suggesting that solar radiation and winds are not relevant in nest construction. Nests with little or no upper vegetation cover showed a non-random entrance, southeastern oriented, which would avoid direct solar radiation. Thus, nest with little or no upper vegetation cover were oriented towards prevailing southern humid winds as to increase cooling inside the nest. This work emphasizes the importance of including nest vegetation cover as a variable that may affect nest orientation.https://doi.org/10.25260/EA.20.30.1.0.1019