Hyper-arid Region Research Articles

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.

Evaluation of Gridded Precipitation Datasets over Arid Regions of Pakistan

The rough topography, harsh climate, and sparse monitoring stations have limited hydro-climatological studies in arid regions of Pakistan. Gauge-based gridded precipitation datasets provide an opportunity to assess the climate where stations are sparsely located. Though, the reliability of these datasets heavily depends on their ability to replicate the observed temporal variability and distribution patterns. Conventional correlation or error analyses are often not enough to justify the variability and distribution of precipitation. In the present study, mean bias error, mean absolute error, modified index of agreement, and Anderson–Darling test have been used to evaluate the performance of four widely used gauge-based gridded precipitation data products, namely, Global Precipitation Climatology Centre (GPCC), Climatic Research Unit (CRU); Asian Precipitation Highly Resolved Observational Data Integration towards Evaluation (APHRODITE), Center for Climatic Research—University of Delaware (UDel) at stations located in semi-arid, arid, and hyper-arid regions in the Balochistan province of Pakistan. The result revealed that the performance of different products varies with climate. However, GPCC precipitation data was found to perform much better in all climatic regions in terms of most of the statistical assessments conducted. As the temporal variability and distribution of precipitation are very important in many hydrological and climatic applications, it can be expected that the methods used in this study can be useful for the better assessment of gauge-based data for various applications.

Responses of vegetation to climatic variations in the desert region of northern China

Global climate change is expected to impact vegetation dynamics. However, differences in the responses of vegetation in desert regions remain poorly understood. We analysed trends in normalised difference vegetation index (NDVI) and its correlations with climatic factors (temperature and precipitation) for typical vegetation in dry sub-humid, semi-arid, arid, and hyper-arid regions of northern China over the past three decades (1982–2015). We also evaluated the effects of climatic variations on vegetation using the vegetation sensitivity index (VSI). Over the study period, NDVI in the dry sub-humid and semi-arid regions showed a significant increasing trend, but no marked trend was noted in the arid region. Both precipitation and temperature had positive effects on NDVI, but that of the latter on NDVI decreased with increasing aridity. The VSI of vegetation dominated by Pinus sylvestris var. mongolica, Ulmus spp., and Caragana spp. was higher than that of vegetation dominated by Artemisia desertorum, A. ordosica, Haloxylon persicum, and H. ammodendron. Our analysis provides two important insights into the responses of vegetation to climatic variations: Firstly, vegetation in the different desert regions of northern China showed diverse responses to climatic variations. Secondly, vegetation dominated by trees (P. sylvestris var. mongolica and Ulmus spp.) and tall shrubs (Caragana spp.) was more sensitive to climatic variations than that dominated by drought-tolerant dwarf shrubs (e.g. A. desertorum and A. ordosica).

Improved constraints on open-system processes in fossil reef corals by combined Th/U, Pa/U and Ra/Th dating: A case study from Aqaba, Jordan

Here we present 230Th/U, 231Pa/U as well as 226Ra/230Th isotope ratios from five fossil reef corals of Last Interglacial origin from the Gulf of Aqaba, Northern Red Sea. The results show clear evidence for open-system behaviour with strongly elevated δ234U values and U concentrations indicating post-depositional U addition. The combined application of all isotope systems enables us to better constrain the nature and timing of the open-system processes than only based on the 230Th/U data.Quantitative modelling of the diagenetic processes allowed us to reproduce the trends in the isotope ratios. Two of the five corals were probably affected by two separate phases of U addition with different δ234U values. The trends observed for two other corals can be explained by U addition followed by U loss. The fifth coral shows signs of both U gain and loss at the same time in the more recent past. The timing of the diagenetic processes is remarkably similar for the five corals and can be constrained to approx. 1 and 6 thousand years (ka) and 100 and 102 ka after coral growth, respectively.Based on the modelling results, we suggest that conventional 231Pa/230Th ages provide the best estimate for the true age of four of the five corals, which range from 109.1 to 114.1 ka. This implies a late Last Interglacial time of deposition. For the fifth coral, the most reliable age estimate is the conventional 230Th/U age of one of the subsamples (117.3 ka), based on a concordia diagram for all subsamples.The timing of the modelled open-system processes suggests that the early event of U addition was associated with interaction of the corals with 234U-enriched seawater or saline groundwater. The later open-system event can be described as U redistribution within the coral reef, since some corals apparently lost U while others gained U. The timing of the second event is broadly consistent with the Bølling-Allerød interstadial, which was probably characterised by enhanced wetness in this typically hyper-arid region.

The CAMELS-CL dataset: catchment attributes and meteorology for large sample studies – Chile dataset

Abstract. We introduce the first catchment dataset for large sample studies in Chile. This dataset includes 516 catchments; it covers particularly wide latitude (17.8 to 55.0∘ S) and elevation (0 to 6993 m a.s.l.) ranges, and it relies on multiple data sources (including ground data, remote-sensed products and reanalyses) to characterise the hydroclimatic conditions and landscape of a region where in situ measurements are scarce. For each catchment, the dataset provides boundaries, daily streamflow records and basin-averaged daily time series of precipitation (from one national and three global datasets), maximum, minimum and mean temperatures, potential evapotranspiration (PET; from two datasets), and snow water equivalent. We calculated hydro-climatological indices using these time series, and leveraged diverse data sources to extract topographic, geological and land cover features. Relying on publicly available reservoirs and water rights data for the country, we estimated the degree of anthropic intervention within the catchments. To facilitate the use of this dataset and promote common standards in large sample studies, we computed most catchment attributes introduced by Addor et al. (2017) in their Catchment Attributes and MEteorology for Large-sample Studies (CAMELS) dataset, and added several others. We used the dataset presented here (named CAMELS-CL) to characterise regional variations in hydroclimatic conditions over Chile and to explore how basin behaviour is influenced by catchment attributes and water extractions. Further, CAMELS-CL enabled us to analyse biases and uncertainties in basin-wide precipitation and PET. The characterisation of catchment water balances revealed large discrepancies between precipitation products in arid regions and a systematic precipitation underestimation in headwater mountain catchments (high elevations and steep slopes) over humid regions. We evaluated PET products based on ground data and found a fairly good performance of both products in humid regions (r>0.91) and lower correlation (r<0.76) in hyper-arid regions. Further, the satellite-based PET showed a consistent overestimation of observation-based PET. Finally, we explored local anomalies in catchment response by analysing the relationship between hydrological signatures and an attribute characterising the level of anthropic interventions. We showed that larger anthropic interventions are correlated with lower than normal annual flows, runoff ratios, elasticity of runoff with respect to precipitation, and flashiness of runoff, especially in arid catchments. CAMELS-CL provides unprecedented information on catchments in a region largely underrepresented in large sample studies. This effort is part of an international initiative to create multi-national large sample datasets freely available for the community. CAMELS-CL can be visualised from http://camels.cr2.cl and downloaded from https://doi.pangaea.de/10.1594/PANGAEA.894885.

Potentials for expanding dry-land agriculture under global warming in water-stressed regions: a quantitative assessment based on drought indices

Agricultural sustainability under the warming climate highly depends on limiting the extreme use of the blue water resources within the irrigated lands, and instead, optimally applying green water resources within the expanded rainfed lands. In this research, potentials for expanding dry farming under climate change were analyzed in five climatic zones of Iran, based on the future projections of basic weather data and drought indices under 20 general circulation models (GCMs) and four emission scenarios, including RCP2.6, RCP4.5, RCP6.5, and RCP8.5. Drought indices included aridity index (AI), expressed as precipitation divided by evapotranspiration, and green water deficit (GWD), expressed as precipitation minus mines evapotranspiration. While annual predictions show a general increase in both precipitation and air temperature over the 2041–2070 period, given results at the monthly scale well revealed the spatial and temporal non-uniformity in the climate change projections. Such heterogeneities, together with those presented for different GCMs and RCPs, well indicated the importance of undertaking a wide range of uncertainties when implementing long-term planning. Based on GWD and AI, the arid and semi-arid regions, the backbone of the rainfed agriculture in Iran, are the most vulnerable to global warming. In these regions, green water availability will reduce by 0.8–167.5% especially within the wet seasons, and drought severity will increase by 0.1–33.2% through the rainfed cropping cycles. On the other hand, future climate may provide new opportunities for expanding dry farming within the hyper-arid region, which is now the most water-stressed region of the country. In this region, global warming projections show a positive increase of 0.3–146.2% in green water availability, and a reduction of 5.1–266.4% in drought severity. However, the humid region remained as the most suitable region for producing rainfed crops, although being widely allocated to irrigated-rice production under current condition. Based on the results, achieving sustainable dryland agriculture highly depends on regionally prioritizing susceptible area for dry farming, since the criteria indices showed an extreme spatial and temporal variability over the mid twenty-first century.

Influence of Temperature Stress in Arid Conditions on Protein Degradation Enzymes in Rodent Digestive Organs

The activity of protein degradation enzymes in rodents under temperature stresses caused by a body temperature rise (hyperthermia) up to 42°С is studied under the conditions of hyperarid regions of arid territories. The heat stress was induced in a special chamber; water at a temperature necessary to raise or lower the body temperature passed through the chamber casing. Regardless of body temperature, the activity of neutral proteases (ANPs) of the liver decreases in both cases. The mechanisms leading to a decrease in ANP with an increase in body temperature are different, since the degree of decreased enzyme activity in this case is several times higher than with low-temperature stress. With hyperthermia, the ANP of all grades of thermal regime is significantly reduced, both in comparison with the control and with hypothermia, except for the incubation temperature of 10°C. The changes occurring in the rodent (in the liver) are evidence of the degree of influence of arid climatic conditions on the adaptability of the considered animals to climate warming.

Dalangtan Saline Playa in a Hyperarid Region on Tibet Plateau: I. Evolution and Environments.

Since 2008, we have been studying a saline lake, Dalangtan (DLT) Playa, and its surroundings in a hyperarid region of the Qaidam Basin on the Tibetan Plateau as a potential Mars analog site. We describe the evolution of saline deposits in the Qaidam Basin (including DLT), based on investigative findings accumulated over the course of 60 years of geological surveys. In addition, we report regional meteorological patterns recorded for the past 32 years along with meteorological station recorded data at DLT since 2012. Overall, the DLT area on the Tibetan Plateau has low atmospheric pressure, high ultraviolet radiation, low annual mean temperatures (T) but large seasonal and diurnal T cycles, and extremely low relative humidity, all of which bear some similarities with the equatorial region on Mars. In addition, salt types similar to those found on Mars, such as magnesium-sulfates, chlorides, and perchlorates, are found at the surface and subsurface in the DLT area (and the other two playas in the Qaidam Basin), thus supporting DLT as a Mars analog in terms of mineralogy and geochemistry.

A Late Pleistocene-Holocene multi-proxy record of climate variability in the Jazmurian playa, southeastern Iran

We present a multi-proxy record from a 5-m long sediment core from the Jazmurian playa in southeastern Iran to provide insights into globally-recognized major climatic events since the Last Glacial Maximum (LGM). In particular, we examined how variability in the Indian Ocean Summer Monsoon (IOSM) and Mid-Latitude Westerlies (MLW) contribute to distinct environmental changes in this arid to hyper-arid region in the interior of West Asia. While interior West Asia showed cold windy conditions during the LGM and post-LGM, southeast Iran experienced quiescent conditions similar to south Asia. The presence of fine-grained sediments, low magnetic susceptibility, and a decrease in aeolian inputs from ca. 21 to 14 cal kyr BP, suggests that effects of both wind and precipitation were minimal during these quiescent conditions. Increased fluvial inputs, coupled with a low abundance of evaporite minerals in Jazmurian sediments, indicated a greater influence of the IOSM between 14 and 13.2 cal kyr BP. In contrast, the Jazmurian playa was dry and dusty between 13.2 and 11.4 cal kyr BP, as reflected by an increase in aeolian sands, and the presence of evaporite minerals. This was followed by a period of strong IOSM activity during the early Holocene, coinciding with higher fluvial input ca. 11.4 cal kyr BP. The early Holocene in southeast Iran was wetter than other analogs in south Asia because of inputs from both IOSM and MWL. Several intense dry periods with sharp increases in aeolian inputs occurred after the early Holocene, due to the southward migration of the Intertropical Convergence Zone. Precipitation sources changed from a monsoon-dominated regime to one influenced mainly by the MLW during the late-Holocene. These results show that palaeoenvironmental changes in the Jazmurian playa, located at the border of IOSM and MLW zones, were primarily governed by global and regional paleoclimatic changes.

Clones or no clones: genetic structure of riparian Populus euphratica forests in Central Asia

Many riparian (Tugai) forests growing along rivers in arid and hyper-arid regions of Central Asia are dominated by the Euphrates poplar (Populus euphratica). Besides generative reproduction, which is only possible upon flooding events and at a distance to the groundwater of less than 2 m, this phreatophytic tree species also reproduces vegetatively by forming clones that can cover land surface areas of several hectares. Along a gradient of groundwater distances, we investigated whether the fraction of clones in P. euphratica stands (1) increases with increasing distance to the water table; (2) is higher if supplied with water via river cut-offs; and (3) approaches 100% at a short distance to the groundwater, but at high salt concentrations in the upper soil layers, which would prevent germination and establishment of seedlings. AFLP (Amplified Fragment Length Polymorphism) analyses were conducted on leaf samples taken from mature P. euphratica trees growing at the fringes of the Taklimakan Desert in stands with different distances (2–12 m) to the groundwater at two plots at the middle and the lower reaches of the Tarim River and in a stand close to Ebinur Lake, Xinjiang, China. Genetic diversity was large among plots, but considerably smaller within plots. We found the highest genetic diversity (caused by regeneration from seeds) at plots that have a short distance to the groundwater or are supplied with additional water. There was no significant relationship between groundwater distance and clonal fraction. All investigated trees at the saline Ebinur Lake site belonged to one single clone. Our results demonstrate that the genetic pattern of this widespread species is not easily predictable even over small distances as it is a result of a complex interplay of stand history and dispersal of propagules (pollen, seeds, and vegetative diaspores) by wind and water. In conservation and restoration schemes, P. euphratica stands with a high genetic diversity and stands that grow at short distances to the water table and are regularly subjected to flooding (which favors generative over clonal reproduction) should be prioritized.

Transitioning to low-carbon suburbs in hot-arid regions: A case-study of Emirati villas in Abu Dhabi

The continued and global popularity of single-family homes indicates that a scalable, yet regionally appropriate strategy for achieving zero-carbon suburban development is needed in the coming decades. This need is especially critical in the hyper-arid region around the Arabian Gulf where per-person carbon emissions are among the highest in the world. Using geometrically sensitive simulation models for a household's building energy, water, and automobile use, this paper uses Emirati neighborhoods in Abu Dhabi, UAE as a case study to estimate emissions for a baseline and set of future possible scenarios towards transitioning single-family households in the region to low, and eventually near-zero operational carbon emissions. An analysis of the combined impact of energy efficiency gains through (1) technology adoption and better design, (2) carbon intensity reduction from renewable energy transitions, and (3) carbon sequestration from parcel scale tree planting is presented. From a baseline CO2 emissions of 64.3 tons per household per year for new construction, the study finds future emissions potential reductions of 33.7%–49.0% from improved house design, 98.1% from electrification and solar energy sourcing, and 99.4% from combined design and technology improvements. This study also finds that if the water-energy nexus in Abu Dhabi transitioned to solar-powered, reverse-osmosis desalination, trees would become net carbon sinks (0.6–1.9 kg CO2/m2/yr). As a result, in the future, low-density neighborhoods with dense areas of tree planting may become a sustainable housing typology when measured by net operational emissions. This fact would upend multiple current assumptions by Western planners about sustainable transitions for arid regions.

Rock-water interaction processes based on geochemical modeling and remote sensing applications in hyper-arid environment: cases from the southeastern region of Egypt

BackgroundThe interaction between rocks and groundwater can be considered as multi-faceted processes in hydrogeology where the groundwater chemistry can be resulted from leaching and/or minerals dissolution. The scientific approach of this study based on testing the contribution of remote sensing in providing information related to rock-groundwater interaction along with the outputs of the geochemical model. The current research aims to explore the impacts of lithologic nature and structural geology on the groundwater chemistry. The mentioned objective is significant for the future sustainable development of groundwater in hyper-arid regions. Therefore, both geology and geochemistry of water-bearing formations along the flow path to the studied aquifers were identified. The area was chosen as an example from hyper-arid region to carry out this scientific approach.ResultsThe obtained results indicate the existence of three main aquifers: Quaternary alluvial (salinity 1253 mg/l to 18,854 mg/l), Nubian Sandstone (salinity 311 mg/l to 14,388 mg/l), and fractured basement (salinity 320 mg/l to 19,375 mg/l). The results of speciation modeling showed that studied aquifers are supersaturated with gibbsite, goethite, hematite, magnetite, aragonite, calcite, dolomite, and alunite. Nubian aquifer specifically has homogeneity results due to the similarity of water-bearing and geology of watersheds (ferruginous sandstone and ironstone). Remote sensing data and digital elevation model analyses were used for generation of the thematic layers which is affecting the groundwater occurrences and quality such as geology, geomorphology, structural lineaments, slope, flow direction, drainage lines, and elevations.ConclusionsThe current research concluded that the groundwater chemistry can be a signature of the rock-water interaction. The potential implications of the research are represented through a priority map for groundwater exploration for both hydro-geophysical investigation and testing wells in order to evaluate the groundwater capabilities where the data from the recorded wells were used to calibrate this map.

Dalangtan Saline Playa in a Hyperarid Region on Tibet Plateau: II. Preservation of Salts with High Hydration Degrees in Subsurface.

Based on a field expedition to the Dalangtan (DLT) saline playa located in a hyperarid region (Qaidam Basin) on the Tibet Plateau and follow-up investigations, we report the mineralogy and geochemistry of the salt layers in two vertical stratigraphic cross sections in the DLT playa. Na-, Ca-, Mg-, KCaMg-sulfates; Na-, K-, KMg-chlorides; mixed (K, Mg)-chloride-sulfate; and chlorate and perchlorate were identified in the collected samples. This mineral assemblage represents the last-stage precipitation products from Na-K-Mg-Ca-Cl-SO4 brine and the oxychlorine formation from photochemistry reaction similar to other hyperarid regions on Earth. The spatial distributions of these salts in both stratigraphic cross sections suggest very limited brine volumes during the precipitation episodes in the Holocene era. More importantly, sulfates and chlorides with a high degree of hydrations were found preserved within the subsurface salt-rich layers of DLT saline playa, where the environmental conditions at the surface are controlled by the hyperaridity in the Qaidam Basin on the Tibet Plateau. Our findings suggest a very different temperature and relative humidity environment maintained by the hydrous salts in a subsurface salty layer, where the climatic conditions at surface have very little or no influence. This observation bears some similarities with four observations on Mars, which implies not only a large humidity reservoir in midlatitude and equatorial regions on Mars but also habitability potential that warrants further investigation.

Groundwater Quality Assessment in a Hyper-arid Region of Rajasthan, India

Groundwater is an important source of livelihood in regions where rainfall is scanty, surface water sources are absent, and all domestic and agricultural needs are fulfilled with groundwater. This study deals with groundwater quality assessment in a hyper-arid region using multivariate statistical analysis. A total of 43 samples were collected and analyzed using principal component analysis and hierarchical cluster analysis to model the relationship and interdependence among the various physicochemical variables contributing to groundwater quality in the study area. The results of the statistical techniques showed that the variables are in strong correlation with each other. Cluster analysis proved to be a good tool to ascertain the spatial similarity between the contributing variables. The methodology adopted in the present study has been found to be effective and can be utilized to establish strong water quality monitoring network in similar areas.

Dalangtan Saline Playa in a Hyperarid Region of Tibet Plateau: III. Correlated Multiscale Surface Mineralogy and Geochemistry Survey.

We report the first multiscale, systematic field-based testing of correlations between orbital scale advanced spaceborne thermal emission and reflection radiometer visible near-infrared (VNIR)/shortwave infrared (SWIR) reflectance and thermal infrared relative emissivity and outcrop scale Raman spectroscopy, VNIR reflectance, X-ray diffraction (XRD), and laser-induced breakdown spectroscopy (LIBS) mineralogy and chemistry in a saline dry lakebed. This article is one of three reports describing the evolution of salt deposits, meteorological record, and surface and subsurface salt mineralogy in Dalangtan, Qaidam Basin, a hyperarid region of the Tibet Plateau, China, as potential environmental, mineralogical, and biogeochemical analogs to Mars. We have successfully bridged remote sensing data to fine scale mineralogy and chemistry data. We have defined spectral end-members in the northwestern Qaidam Basin and classified areas within the study area on the basis of their spectral similarity to the spectral end-members. Results of VNIR/SWIR classification reveal zonation of spectral units within three large anticlinal domes in the study area that can be correlated between the three structures. Laboratory Raman, VNIR reflectance, XRD, and LIBS data of surface mineral samples collected along a traverse over Xiaoliangshan (XLS) indicate that the surface is dominated by gypsum, Mg sulfates, Na sulfates, halite, and carbonates, with minor concentrations of illite present in most samples as well. Our results can be used as a first step toward better characterizing the potential of orbital reflectance spectroscopy as a method for mineral detection and quantification in salt-rich planetary environments, with the benefit that this technique can be validated on the ground using instruments onboard rovers.

Oasis microclimate effects under different weather events in arid or hyper arid regions: a case analysis in southern Taklimakan desert and implication for maintaining oasis sustainability

The vegetation of desert oasis regulates the regional microclimate in arid or hyper-arid regions. A wide range of studies on the oasis microclimate effects have been conducted under sunny conditions. However, less concern has been focused on microclimatic variations of oasis effects caused by the influences of different types and coverage of vegetation in oasis during other different weather events, especially during catastrophic weather conditions. Based on the measurements from 1 August, 2010 to 30 December, 2014 in the Qira oasis, a hyper arid zone of southern Taklimakan desert, Northwest China, this paper investigates the existences and variabilities of the oasis microclimate effects during dust storm, blown sand, floating dust, and rain events and analyzes the impacts of different types of vegetation (bare desert, sparse desert grassland, desert oasis dense shrub grassland and forests, and oasis crops and fruit trees) on desert oasis microclimates. Moreover, the importance of maintaining the oasis sustainability mirrored by the oasis microclimate effects is highlighted and discussed. Results show that the oasis with abundant vegetation exerts cooling and humidifying effects under four weather events relative to bare desert land. As a result of high wind velocities, the oasis microclimatic effects are weakened during catastrophic weather conditions such as dust storm or blown sand events. The type and coverage of vegetation and the topography as well as weather events jointly impact on the oasis microclimate effects. The findings of this work provide an implication for the conservation and restoration of oasis vegetation to maintain both the oasis microclimate environment and the sustainability of desert oasis.

Mining the Genome of Streptomyces leeuwenhoekii: Two New Type I Baeyer-Villiger Monooxygenases From Atacama Desert.

Actinobacteria are an important source of commercial (bio)compounds for the biotechnological and pharmaceutical industry. They have also been successfully exploited in the search of novel biocatalysts. We set out to explore a recently identified actinomycete, Streptomyces leeuwenhoekii C34, isolated from a hyper-arid region, the Atacama desert, for Baeyer–Villiger monooxygenases (BVMOs). Such oxidative enzymes are known for their broad applicability as biocatalysts by being able to perform various chemical reactions with high chemo-, regio-, and/or enantioselectivity. By choosing this specific Actinobacterium, which comes from an extreme environment, the respective enzymes are also expected to display attractive features by tolerating harsh conditions. In this work, we identified two genes in the genome of S. leeuwenhoekii (sle_13190 and sle_62070) that were predicted to encode for Type I BVMOs, the respective flavoproteins share 49% sequence identity. The two genes were cloned, overexpressed in E. coli with phosphite dehydrogenase (PTDH) as fusion partner and successfully purified. Both flavin-containing proteins showed NADPH-dependent Baeyer–Villiger oxidation activity for various ketones and sulfoxidation activity with some sulfides. Gratifyingly, both enzymes were found to be rather robust by displaying a relatively high apparent melting temperature (45°C) and tolerating water-miscible cosolvents. Specifically, Sle_62070 was found to be highly active with cyclic ketones and displayed a high regioselectivity by producing only one lactone from 2-phenylcyclohexanone, and high enantioselectivity by producing only normal (-)-1S,5R and abnormal (-)-1R,5S lactones (ee > 99%) from bicyclo[3.2.0]hept-2-en-6-one. These two newly discovered BVMOs add two new potent biocatalysts to the known collection of BVMOs.

Palaeohydrology and its impact on groundwater in arid environments: Gebel Duwi and its vicinities, Eastern Desert, Egypt

From ancient times, access to water in arid and hyper-arid regions has been crucial for life. Increased knowledge about groundwater conditions is therefore extremely important for the future development of desert areas. Gebel Duwi, a limestone ridge, sited in the today hyper-arid Eastern Desert of Egypt, was chosen for testing current hypotheses concerning the interdependence of palaeohydrologic features and geologic settings for groundwater investigations. Two sub-basins are identified in affecting Gebel Duwi: Wadi Nakheil and Wadi Sodmein. Both have extraordinary high stream order, indicating the reality of a very old drainage system. Several additional palaeohydrologic features such as wadi terraces, alluvial fans, and playa deposits are also recorded in these sub-basins. These features, as well as finds from an important archaeological site (Sodmein Cave), provide information about palaeoenvironmental changes and wetter climatic periods in the younger geologic past, mainly in the Late Pleistocene and Holocene, which have affected the occurrence of present day groundwater. This study combines new results of geological and geomorphological field studies, examinations of digital elevation models, as well as of rock and water analyses in an integrated approach. Resulting maps comprise landforms, lithology, elevation, drainage lines slope, structural lineaments and flow directions. The hydrogeologic condition indicates suitable locations for groundwater recharge and accumulation. The research presented is interdisciplinary in approach and is recommended for future studies with regard to groundwater exploration, sustainable groundwater use, and the protection of archaeological sites in arid lands.

Characteristics of ecosystem water use efficiency in a desert riparian forest

The Ejin oasis, located on the river sides of a hyper-arid region, represents some of the richest desert ecosystems, populated with riparian forest. Water availability is the main limited factors for the distribution and growth of the forest. Currently, the water–carbon process and mechanisms in the desert riparian forest remain uncertain. The study investigated the seasonal and inter-annual variations in the gross primary productivity (GPP), evapotranspiration (ET) and ecosystem water use efficiency (WUE), and their relationships with the event (e.g., irrigation) and climatic factors. The results showed that the desert riparian forest produced new plant biomass with 0.79 g C kg−1 of water loss during the growing season. In the study period, monthly GPP and ET was tightly coupled, and the mean cumulative GPP and ET from May–October were 676 g C m−2 and 864 mm, respectively. Daily GPP and ET had similar relationships with global radiation (Rg), air temperature (Ta) and vapor pressure deficit at monthly scale. Consequently, the seasonal variations in WUE were not obvious in the growing season, except in September. In September, the value of WUE decreased significantly with an increase in Ta (for Ta > 15 °C) after irrigation, which was attributable to the increased ET and a relatively steady GPP. It is possible that the time of irrigation is able to affect the seasonal course of WUE. The study has implications that enable more rational water management to maintain the the health and activities of the riparian forest in such a hyper-arid region.

Seasonal and diurnal evaporation from a deep hypersaline lake: The Dead Sea as a case study

Evaporation plays a major role in lake systems, as it affects the water, energy and solutes budgets. Water salinity reduces evaporation, and as a result affects the energy budget of the lake, including stored heat. In this study, we explore the seasonal and diurnal variations of evaporation and other energy fluxes over the Dead Sea, the deepest and saltiest hypersaline lake on Earth. We present two consecutive years observations using Eddy Covariance system, meteorological stations and a buoy station measuring the water column properties. These observations reveal the effects of synoptic and mesoscale atmospheric circulation on lake evaporation. The seasonal cycle of evaporation is characterized by two peaks. The summer evaporation peak is related to high radiation inputs. The winter peak stem from the high heat storage of the deep lake, with evaporation driven by high vapor pressure demand, combined with synoptic scale wind systems and thermal instability. In summer, the synoptic circulation is stable, providing a weak background wind velocity (Persian trough), hence, the dominant diurnal wind pattern is induced by the Mediterranean Sea Breeze (mesoscale circulation). The two years of eddy covariance measurements in the hypersaline Dead Sea, located in a hyperarid region, revealed annual evaporation rate of 1.13 ± 0.13 m yr−1. We explored several evaporation models versus the directly measured evaporation, and found that the most reliable is a mass transfer model, that was calibrated here for the Dead Sea.