Hyper-arid Areas Research Articles

Sun exposure drives Antarctic cryptoendolithic community structure and composition

The harsh environmental conditions of the ice-free regions of Continental Antarctica are considered one of the closest Martian analogues on Earth. There, rocks play a pivotal role as substratum for life and endolithism represents a primary habitat for microorganisms when external environmental conditions become incompatible with active life on rock surfaces, allowing life to spread throughout these regions with extreme temperatures and low water availability. Previous research concluded that altitude and distance from sea do not play as driving factors in shaping microbial abundance and diversity, while sun exposure was hypothesized as significant parameter influencing endolithic settlement and development. With this in mind, eight localities were visited in the Victoria Land along an altitudinal transect from 834 to 3100 m a.s.l. and 48 differently sun-exposed rocks were collected. We explored our hypothesis that changes in sun exposure translate to shifts in community composition and abundances of main biological compartments (fungi, algae and bacteria) using Denaturing Gel Gradient Electrophoresis and quantitative PCR techniques. Major changes in community composition and abundance occurred between north and south sun-exposed samples. As Antarctic endolithic ecosystems are extremely adapted and specialized but scarcely resilient to external perturbation, any shifts in community structure may serve as early-alarm systems of climate change; our findings will be of wide interest for microbial ecologists of extreme environments such as arid and hyper-arid area.

Utilizing Landsat-8 and ASTER data in geologic mapping of hyper-arid mountainous region: case of Gabal Batoga area, South Eastern Desert of Egypt

Landsat-8 and ASTER images were utilized to derive geological information and mapping of a hyper-arid mountainous region. Principal component analyses and band rationing techniques in conjunction with petrography and field investigations enabled to produce a modified new geologic map of Gabal Batoga area, along the Red Sea coast of Egypt. The area is built by non-consanguineous diverse Pan-African basement rock units. These rock units are widely distributed in the Arabian-Nubian Shield. ASTER principal component images (PC2, PC5, PC7) and (PC2, PC3, PC8) as well as band ratio images (b4/b7, b3/b4, b2/b1) were effective in accurate lithological discrimination of the exposed rock units in the study area. The process was also enhanced and emphasized by Landsat-8 principal component images (PC2, PC4, and PC7) and band ratio (b6/b2, b6/b7, b6/b5 × b4/b5). The used methodology and techniques can be applicable in many similar arid and hyper-arid areas in the Arabian-Nubian Shield and elsewhere.

Groundwater Origin in Qanats, Chemo-Isotopic, and Hydrogeological Evidence.

A systematic study of the chemo-isotopic characteristics and origin of the groundwater was carried out at six major qanats in the hyper-arid Gonabad area, eastern Iran. These qanats as a sustainable groundwater extraction technology have a long history, supporting human life for more than a thousand years in this region. The Gonabad qanats are characterized by outlet electrical conductivity (EC) values of 750 to 3900 µS/cm and HCO3 -Na-Mg and Cl-Na water types. The Gonabad meteoric water line (Gn MWL) was drawn at the local scale as δ2 H = 6.32×δ18 O + 8.35 (with R2 = 0.90). It has a lower slope and intercept than the global meteoric water line due to different water vapor sources and isotope kinetic fractionation effects during precipitation in this arid region. The altitude effects on isotopic content of precipitation data were derived as δ18 O = (-0.0031 × H(m.a.s.l) )-1.3). The δ2 H and δ18 O isotopes signatures demonstrate a meteoric origin of the groundwater of these qanats. The shift of the qanat's water samples from the local meteoric water line (LMWL) in a dry period with higher temperatures is most probably due to evaporation during the infiltration process and water movement in qanat gallery. Based on the isotopic results and mass balance calculations, the qanats are locally recharged from an area between 2000 to 2400 m.a.s.l of nearby carbonate formations and coarse alluvial sediments. The dissolution of evaporate interlayers in Neogene deposits deteriorates the groundwater quality, especially in Baidokht qanat.

Past climatic changes and their effects on the phylogenetic pattern of the Gondwanan relict Maindronia (Insecta: Zygentoma) in the Chilean Atacama Desert

Abstract The silverfish family Maindroniidae (Insecta: Zygentoma) consists of three described species from desert biomes in Sudan, the Arabian Peninsula and Chile. This distribution is remarkable for closely related arthropods, suggesting a Gondwanan relict group. Extensive collecting efforts in Chile show a surprisingly widespread distribution in the Atacama. These insects were even found in hyperarid areas where no other metazoans could be observed. Maindronia can thus be considered as the most adapted desert animal in the Atacama, which in turn is one of the driest deserts in the world. The common habitat preference in the Chilean Atacama, and evidently also in Sudan, suggests that hyperarid environments have always been present, at least locally, in South America over the past 120 million years. Likely, Chilean Maindronia have evolved with and within the Atacama Desert. This scenario clearly differs from that shown for other animals or plants that have more recently migrated into suitable environments in the Atacama. Phylogenetic analyses show the presence of at least five clades derived from a single ancestor and diverging in the last 15 million years. The divergence times of the clades can be attributed to palaeoclimatic changes; mostly periods of extreme hyperaridity.

Atmospheric deposition across the Atacama Desert, Chile: Compositions, source distributions, and interannual comparisons

Hyper-arid areas such as the Atacama Desert accumulated significant amounts of insoluble dust and soluble salts from the atmosphere, providing minable salt deposits as well as mimicking the surface processes on Mars. The deposition rates, compositions and sources, however, were poorly constrained. Especially, the variabilities of atmospheric deposition in the Atacama Desert corresponding to a changing climate were unassessed. In this work, the atmospheric depositions collected using dust traps across a west-east elevation gradient in the Atacama (~23°S) from 1/2/2010 to 12/31/2011 were analyzed and compared to previous results in 2007–2009. The insoluble dust deposition rates in our sampling period were significantly higher than those of 2007–2009 in most dust traps, which was attributed to the changes in wind, highlighting the importance of long-term monitoring of insoluble dust fluxes. Soluble salts, instead, showed less distinct interannual variations in deposition rates, geochemical compositions or source contributions. At the coastal site (T1), soluble salts were originated from both primary sea-salt (SS) aerosols and non-sea-salt (NSS) sources such as anthropogenic emission, marine biogenic emission and biomass burning; the deposition rates of these salts largely depended on the wind speed and the amount of anthropogenic emissions. Sulfur isotopic evidence further showed that NSS sulfate at T1 was mainly originated from local SO2 emission from local power plants. The inland sites (T2-T8) displayed much lower soluble salts deposition rates, and the salts were primarily sourced from entrainment of local surface minerals, including Na(Cl, NO3), CaSO4, and nitrate formed via atmospheric oxidation of anthropogenic NOx. Sulfur isotopic compositions of sulfate deposited at T2-T8 were similar to those in local surface soil; however, three sites near the Chuquicamata mine showed slightly lower δ34Ssulfate values, indicating the presence of secondary sulfate originated from mining activities. The soluble salts deposited at the Andean site (T10) were dominantly from wet deposition that incorporated local lake salts, and therefore, the deposition rates were mainly controlled by the amount of precipitation.

The archaeology and ethnoarchaeology of rain-fed cultivation in arid and hyper-arid North Africa

Abstract

Drylands climate response to transient and stabilized 2 °C and 1.5 °C global warming targets

Drylands are one of the most sensitive areas to climate change. Many previous studies assessed the impact of 1.5 °C and 2 °C warming targets using transient warming scenarios by representative concentration pathways of CMIP5. Here we compared the climate changes over global drylands in transient and stabilized 1.5 °C and 2 °C warmer worlds using Community Earth System Model simulations. The projections indicate a warming of 2.3 °C (1.6 °C) over drylands could occur in a stabilized 2 °C (1.5 °C) warmer world by the end of this century. The warming in drier regions is higher and the hyper-arid areas would experience warming of 2.4 °C (1.8 °C). Comparing the 2 °C to 1.5 °C warming targets, the additional 0.5 °C warming will lead to ~ 1.0 °C warming in drylands of Eurasia and North America. Responding to the 2 °C warming, the increased precipitation (21.8–42.6 mm/year) is not enough to offset the increased PET (88.3–101.7 mm/year) over drylands, resulting in the drylands expansion, and the additional 0.5 °C global warming will aggravate the drought in drylands in southern North America and North Africa. Compared to the stabilized 2 °C warming target, controlling the global warming to within 1.5 °C will reduce the warming in drylands by 0.7 °C, and reduce the drylands expansion relative to 1961–1990 by ~ 44%. Compared to the stabilized warming scenarios, the temperature response and drylands area coverage increase are higher in the transient warming scenarios, but the difference of temperature caused by additional 0.5 °C global warming and the precipitation increase in drylands are lower.

Responses of two desert riparian species to fluctuating groundwater depths in hyperarid areas of Northwest China

AbstractIn the hyperarid region of Northwest China, frequent variations in hydrological environments present challenges to the persistence of riparian plants. The main objective of this study was to determine whether two desert riparian species (Populus euphratica and Tamarix ramosissima) differed in their water uptake patterns and ecophysiological responses to fluctuating groundwater depths (GWDs). This study was conducted in typical desert riparian ecosystems in the downstream Heihe River basin, Northwestern China, where the GWD continuously increases during growing season. Stable oxygen composition (δ18O) in xylem water, soil water, and groundwater, as well as leaf water potential and gas exchange were monitored. Results showed that P. euphratica used a higher ratio of soil water, whereas T. ramosissima relied more on groundwater and deep soil water. As the GWD increased during the growing season, both species modified their water use patterns, but they did so differently, P. euphratica extracted an increasing proportion of deep soil water and groundwater, whereas T. ramosissima took an increasing ratio of groundwater at critical growth stages. P. euphratica exhibited decreases in its daily maximum photosynthetic rate (Amax) and stomatal conductance (gmax) as the GWD increased, whereas those of T. ramosissima changed little. In summary, both species shift to use greater ratio of more reliable water sources with the increasing GWD, but the switching of water sources could not sufficiently compensate for the impact of drought stress on gas exchange for P. euphratica.

Coupled influence of precipitation and vegetation on millennial-scale erosion rates derived from 10Be.

Water is one of the main agent of erosion in many environmental settings, but erosion rates derived from beryllium-10 (10Be) suggests that a relationship between precipitation and erosion rate is statistically non-significant on a global scale. This might be because of the strong influence of other variables on erosion rate. In this global 10Be compilation, we examine if mean annual precipitation has a statistically significant secondary control on erosion rate. Our secondary variable assessment suggests a significant secondary influence of precipitation on erosion rate. This is the first time that the influence of precipitation on 10Be-derived erosion rate is recognized on global scale. In fact, in areas where slope is <200m/km (~11°), precipitation influences erosion rate as much as mean basin slope, which has been recognized as the most important variable in previous 10Be compilations. In areas where elevation is <1000m and slope is <11°, the correlation between precipitation and erosion rate improves considerably. These results also suggest that erosion rate responds to change in mean annual precipitation nonlinearly and in three regimes: 1) it increases with an increase in precipitation until ~1000 mm/yr; 2) erosion rate stabilizes at ~1000 mm/yr and decreases slightly with increased precipitation until ~2200 mm/yr; and 3) it increases again with further increases in precipitation. This complex relationship between erosion rate and mean annual precipitation is best explained by the interrelationship between mean annual precipitation and vegetation. Increased vegetation, particularly the presence of trees, is widely recognized to lower erosion rate. Our results suggest that tree cover of 40% or more reduces erosion rate enough to outweigh the direct erosive effects of increased rainfall. Thus, precipitation emerges as a stronger secondary control on erosion rate in hyper-arid areas, as well as in hyper-wet areas. In contrast, the regime between ~1000 and ~2200 mm/yr is dominated by opposing relationships where higher rainfall acts to increase erosion rate, but more water also increases vegetation/tree cover, which slows erosion. These results suggest that when interpreting the sedimentological record, high sediment fluxes are expected to occur when forests transition to grasslands/savannahs; however, aridification of grasslands or savannahs into deserts will result in lower sediment fluxes. This study also implies that anthropogenic deforestation, particularly in regions with high rainfall, can greatly increase erosion.

Environmental impacts of a highly congested section of the Pan-American highway in Peru using life cycle assessment

Road construction and transportation generate significant environmental impacts. Hence, it is increasingly important to understand the environmental burdens produced throughout the different stages of road development: construction, maintenance, traffic, and end-of-life. In this study, life cycle assessment (LCA) was used as an environmental management methodology to determine the impacts associated with a 22.4 km stretch of the South Pan-American (PS) highway in the province of Lima, Peru, one of the main access routes for traffic and goods entering Lima, located in a hyper-arid area parallel to the Pacific Ocean. Life cycle modeling included the site-specific estimation of particulate matter emissions due to tire abrasion, brake lining, and road surface dust. In addition, different modeling options for combustion emissions for vehicles were considered. For this, sensitivity and uncertainty analysis were undertaken considering different emission standards and current vehicle fleet characteristics. The impact assessment stage included the calculation of climate change emissions, as well as air quality and abiotic depletion impact categories. Results demonstrate that environmental impacts are mainly attributable to traffic, representing in all impact categories assessed over 97% of burdens. The sensitivity analysis suggests that the use of secondary data from commonly used life cycle databases is a good proxy for the estimation of global warming potential impacts in the transport sector. However, for air quality categories, important variability was detected based on modeling assumptions. This study intends to serve as a reference for the life cycle modeling of controlled access highways in developing countries, particularly in hyper-arid or desert areas.

Probability assessment of vegetation vulnerability to drought based on remote sensing data.

Drought is one of the important factors causing vegetation degradation. Determination of areas with vegetation more sensitive to drought can be effective in drought risk management. Considering the ability to describe vegetation conditions, vegetation health index (VHI) was used to determine the probability of vegetation vulnerability to drought and to provide the map of Iran showing sensitive areas to drought. This study tries to express the probability of vegetation vulnerability to drought in four main climatic classes including hyper-arid, arid, semi-arid and semi-humid, and humid in Iran. Temperature condition index (TCI) and vegetation condition index (VCI) were calculated using land surface temperature (LST) derived from the MOD11A2 product and normalized different vegetation index (NDVI) obtained from MOD13A2 product, MODIS sensor. Combining these two indices, VHI was calculated for late of March, April, May, and June during 2000-2017. VHI was classified into five classes representing the drought intensity. Then, the probability of occurrence (%) of each class was calculated and multiplied with weight of each class, varying from 0 to 40 based on drought intensity. Finally, probability of vegetation vulnerability index (PVVI) was calculated by summing of the values obtained for each class. The results showed that PVVI was higher in arid and hyper-arid areas than that in other areas in the four studied periods. The highest mean values of PVVI in humid as well as semi-arid and semi-humid classes were found in April as 59.87 and 62.4, respectively, while the highest mean values of PVVI in arid and hyper-arid classes were observed in May as 70.98 and 68.13, respectively. In total, our results showed that PVVI is affected by different climatic and topographic conditions, and it suggested that this index be used to determine the probability of vegetation vulnerability.

Assessment of spatial distributions of some climate indices in Iraq

Aridity is one of the main factors which distinguish the climate of a region and has significant influence on human activities. This study investigated the spatial distribution of the aridity indices to determine the climate conditions in Iraq over the period (1981-2015), depending on the data of the air temperature and rainfall which obtained from 28 stations distributed through Iraq. The used aridity indices are: Lang, Erinc, Emberger, UNEP, De Martonne and Thornthwaite. The spatial distribution was determined using inverse distance weighting (IDW) interpolated method. The results of aridity indices analysis shows that the hyper-arid, arid, and semi-arid categories are predominant with almost (91%) to (100%) of the country’s area. Dry sub-humid, moist sub-humid and humid categories occupies less than (10%) with most of indices at stations of (Arbil, Sulaymaniyah, and Salahaddin). To evaluate the seasonal spatial distributions, De Martonne was utilized. During winter, the climate types ranged from semi-arid to very-humid, while at spring season from arid to humid. Autumn season dominated by arid at (97%) of study area. The summer season was the driest compared with the other seasons. The change point for aridity indices was detected by using the cumulative sum charts (CUSUMs), it is found for the most stations in (1997). Consequently, the spatial distribution for the aridity indices were analyzed through two periods (1981-1997 and 1998-2015), this analysis showed that the arid and hyper-arid areas were increased in the second period compared with the first period with obvious extension toward the north of Iraq.

Modeling daily soil temperature over diverse climate conditions in Iran—a comparison of multiple linear regression and support vector regression techniques

The knowledge of soil temperature at different depths is important for agricultural industry and for understanding climate change. The aim of this study is to evaluate the performance of a support vector regression (SVR)-based model in estimating daily soil temperature at 10, 30 and 100 cm depth at different climate conditions over Iran. The obtained results were compared to those obtained from a more classical multiple linear regression (MLR) model. The correlation sensitivity for the input combinations and periodicity effect were also investigated. Climatic data used as inputs to the models were minimum and maximum air temperature, solar radiation, relative humidity, dew point, and the atmospheric pressure (reduced to see level), collected from five synoptic stations Kerman, Ahvaz, Tabriz, Saghez, and Rasht located respectively in the hyper-arid, arid, semi-arid, Mediterranean, and hyper-humid climate conditions. According to the results, the performance of both MLR and SVR models was quite well at surface layer, i.e., 10-cm depth. However, SVR performed better than MLR in estimating soil temperature at deeper layers especially 100 cm depth. Moreover, both models performed better in humid climate condition than arid and hyper-arid areas. Further, adding a periodicity component into the modeling process considerably improved the models’ performance especially in the case of SVR.

Simulation of Pan Evaporation and Application to Estimate the Evaporation of Juyan Lake, Northwest China under a Hyper-Arid Climate

Because of its nature, lake evaporation (EL) is rarely measured directly. The most common method used is to apply a pan coefficient (Kp) to the measured pan evaporation (Ep). To reconstruct the long sequence dataset of Ep, this study firstly determined the conversion coefficients of Ep of two pans (φ20 and E601, each applied to a different range of years) measured synchronously at the nearest meteorological station during the unfrozen period through 1986 to 2001, and then Ep was estimated by the PenPan model that developed to the Class A pan and applied to quantify the EL of the Juyan Lake, located in the hyper-arid area of northwest China. There was a significantly linear relationship between the E601 and φ20 with the conversion coefficients of 0.60 and 0.61 at daily and monthly time scales, respectively. The annual Ep based on monthly conversion coefficients was estimated at 2240.5 mm and decreased by 6.5 mm per year, which was consistent with the declining wind speed (U) during the 60 years from 1957 to 2016. The Ep simulated by the PenPan model with the modified net radiation (Rn) had better performance (compared to Ep measured by E601) than the original PenPan model, which may be attributed to the overestimated Rn under the surface of E601 that was embedded in the soil rather than above the ground similar to the Class A and φ20. The measured monthly EL and Ep has a significantly linear relationship during the unfrozen period in 2014 and 2015, but the ratio of Ep to EL, i.e., Kp varied within the year, with an average of 0.79, and was logarithmically associated with U. The yearly mean EL with full lake area from 2005 to 2015 was 1638.5 mm and 1385.6 mm, calculated by the water budget and the PenPan model with the modified Rn, respectively; the latter was comparable to the surface runoff with an average of 1462.9 mm. In conclusion, the PenPan model with the modified Rn has good performance in simulating Ep of the E601, and by applying varied Kp to the model we can improve the estimates of lake evaporation.

Hydrometric network design in hyper-arid areas: example of Atacama Desert (North Chile)

AbstractEfficient water management needs hydrological information provided by hydrometric networks. In arid and mountainous regions, hydrologic models for water resources management and forecasting require a large amount of data due to the temporal and spatial heterogeneity of hydrometeorological variables. The interaction of complex oceanic and atmospheric circulations makes North Chile one of the world's most arid areas. Since the onset of large mining projects in the nineties, constant population and economic growth generates high pressure on water resources. The existing regional scale hydrometric network in Tarapacá allows for the description of general characteristics and trends at national, but not at water basin level and therefore does not meet actual demands. Methods for hydrometric network design were designed for temperate areas in general. Based on a review of existing methodologies, the paper identifies multi-criteria analysis (MCA) as best adaptable to the context. It develops a methodology for hyper-arid areas, complementing MCA with stakeholder and geographic information system (GIS) analysis, as well as optimization. The paper optimizes the existing hydrometric network in the Tarapacá region, characterized by strong constraints regarding access and topography. Three MCA techniques are compared. The result is an optimized network consisting of 36 rainfall and 21 streamflow stations.

Exploring morphology, layering and formation history of linear terrestrial dunes from radar observations: Implications for Titan

Understanding the morphology and internal layering of large aeolian dune fields through radar observations can provide unique insights into the climatic and geophysical conditions that led to their formation. In this study, we perform a large-scale characterization of the morphology and internal layering of linear dunes in hyper-arid areas on Earth, through utilizing multiple complementary radar datasets (SIR-C imaging, SRTM interferometry-derived elevations and radar sounding or Ground Penetrating Radar (GPR)). Linear dune fields in the Egyptian desert are of special interest, due to their significance as planetary analogs to dunes on Mars and Saturn's largest moon, Titan. Satellite radar imagery and elevation data of the region show significant variance in the geomorphology of different dune fields in Egypt. In addition, GPR probing of the first few meters suggests different inner settings in the layering of dunes of different ages in eastern and western Egypt, reflecting different paleo-climatic regimes that led to their formation. Furthermore, our radiometric analysis suggests that dunes with different inner layering arrangement also exhibit different radar backscatter returns as a function of their heights. For relatively younger dunes with a homogeneous inner structure, like the ones in eastern Egypt in the Qattaniya dune field, we observe that sigma0 does not change as a function of the dune height. For relatively older dunes in western Egypt like the Great Sand Sea (Northern (Siwa) and Southern dune fields), we observed a linear correlation between sigma0 and the dune height. Thus, surface properties of dunes like morphology and backscatter variation with height are related to inner characteristics like arrangement of internal layering, relative ages and can be used to infer their depositional history.Linear dunes discovered in the equatorial regions of Titan by the Cassini-Huygens mission are morphologically very similar to these linear dune fields in the Egyptian Sahara. Hence, assessing the variability of morphology and radar backscatter properties of Titan's dunes as a function of their heights can help constrain the ambiguities associated with their internal structure and formation history and provide insights into Titan's paleo-wind regimes.

Development of design storm hyetographs in hyper-arid and arid regions: case study of Sultanate of Oman

The temporal distribution of the design storm is an important input in hydrological models. This research aims to develop design storm profiles representative of arid and hyper-arid areas based on actual storm recordings. Two hundred thirty-six rainfall storms were collected from seventeen rainfall gauges that cover the coastal zone of Oman for the period from 1993 to 2007. Storms were classified into four categories according to their total durations. Design storm hyetographs were derived from raw rainfall records for all four categories using the Alternating Block Method (ABM) and were also computed by ABM applied on the Intensity-Duration-Frequency (IDF) curves. Both design storm profiles were compared and it was found that the ABM_IDF storm profiles were equivalent to the four ABM_Storms profiles from a practical point of view as they produce similar peak discharges. The storm profiles developed in the current research were also compared to the commonly used Soil Conservation Service (SCS) dimensionless distributions and the UK50 storm profiles. The results showed that the most conservative commonly used SCS type II and the UK50 summer profiles are not safe to be used in design purposes in arid and hyper arid regions, despite their wide utilization in many codes of practice in these regions. The study recommends using the newly developed dimensionless storm profiles derived from the actual records.

Assessing the magnitude of potential environmental impacts related to water and toxicity in the Peruvian hyper-arid coast: A case study for the cultivation of grapes for pisco production

The environmental sustainability of the cultivation of grapes for the production of alcoholic beverages has been extensively analyzed in the literature from a Life Cycle Assessment perspective, although certain impact categories have been repeatedly neglected despite their importance, such as toxic emissions or the depletion of freshwater resources. Hence, the current study provides a detailed assessment of water footprint-related impact categories, including toxicity, for the cultivation of grapes for pisco production, an alcoholic beverage produced in coastal Peru in hyper-arid areas that suffer high levels of water scarcity. Characterization factors at a sub-watershed level were used to calculate water consumption impact assessment of grape production using the AWARE method. Site-specific toxic emissions were modelled using the PestLCI model, considering primary climate and soil data. The USEtox assessment method was then used to compute freshwater eco-toxicity with these data. Results demonstrate the high water footprint of irrigating vineyards in coastal Peru, especially considering the inefficient flooding irrigation process. In terms of water consumption, despite the high variability shown between sub-watersheds, the shift to other irrigation technologies must be analyzed with care due to the high competition for water existing in the area. Eutrophication potential showed particularly high values compared to the literature, whereas freshwater eco-toxicity impacts were relatively low due to the high volatilization of pesticides to air. Nevertheless, the lack of an adequate wastewater management system implies that the estimated potential toxic and eutrophying emissions may constitute a further environmental threat to water bodies.

Desert Vegetation Forty Years after an Oil Spill.

Deserts are the most frequent locations of terrestrial crude oil contaminations. Nevertheless, the long-term effects of petroleum hydrocarbons on desert ecosystems are still unknown, which makes risk assessment and decision making concerning remediation difficult. This study examined the long-term effects of petroleum hydrocarbons on perennial desert vegetation. The study site was a hyper-arid area in the south of Israel, which was contaminated by a crude oil spill in 1975. The contaminated area was compared to uncontaminated reference areas. The composition of perennial plants 40 yr after the oil spill was not significantly affected by the contamination. However, the size distribution of the two most dominant shrub species, Baker and (Moq.) Iljin., and the only tree species, Savi and (Forssk.) Hayne, were different from the reference. These differences can be explained by decreased recruitment. The estimated recruitment of in the last 40 yr post oil spill was 74% less than recruitment in the reference area. Low recruitment of may in the future lead to the loss of tree cover, which would change the entire ecosystem, as are keystone species on which a number of microorganisms, plants, and animals rely. Remediation of oil spills and preventative measures are recommended.

Measurement and analysis of the yearly characteristics of deep-buried phreatic evaporation in a hyper-arid area

Water scarcity is the primary cause of land deterioration, so finding new available water resources is crucial to ecological restoration. We investigated a hyper-arid Gobi location in the Dunhuang Mogao Grottoes in this work wherein the burial depth of phreatic water is over 200m. An air-conditioner was used in a closed greenhouse to condense and measure the yearly amount of phreatic evaporation (PE) from 2010 to 2015. The results shown that the annual quantity of PE is 4.52mm, and that the PE has sinusoidal characteristics. The average PE is 0.0183mmd−1 from March to November. Accordingly, by monitoring the annual changes in soil-air temperature and humidity to a depth of 5.0m, we analyzed the water migration mechanism in the heterothermozone (subsurface zone of variable temperature). The results show that, from March to November, the temperature and absolute humidity (AH) increase. This is due to the flow of solar heat entering the soil — the soil subsequently releases moisture and the soil is in a state of increasing AH so that evaporation occurs. From November to March, the temperature decreases. Now, the soil absorbs water vapor and AH is in a state of decline. Thus, it is temperature alternation in the heterothermozone — due to solar heat transfer — that provides the main driving power for PE. When it drives water vapor to move downwards in the heterothermozone, a small part is reversed upwards and evaporates. Solar radiation intensity dominates the annual sinusoidal PE characteristics.