Areas In Arid Regions Research Articles

Random forest classification of land cover information of urban areas in arid regions based on TH-1 data

Random forest classification of land cover information of urban areas in arid regions based on TH-1 data

Quantification of Environmental Flow Requirements to Support Ecosystem Services of Oasis Areas: A Case Study in Tarim Basin, Northwest China

Recently, a wide range of quantitative research on the identification of environmental flow requirements (EFRs) has been conducted. However, little focus is given to EFRs to maintain multiple ecosystem services in oasis areas. The present study quantifies the EFRs in oasis areas of Tarim Basin, Xinjiang, Northwest China on the basis of three ecosystem services: (1) maintenance of riverine ecosystem health, (2) assurance of the stability of oasis–desert ecotone and riparian (Tugai) forests, and (3) restoration of oasis–desert ecotone groundwater. The identified consumptive and non-consumptive water requirements are used to quantify and determine the EFRs in Qira oasis by employing the summation and compatibility rules (maximum principle). Results indicate that the annual maximum, medium, and minimum EFRs are 0.752 × 108, 0.619 × 108, and 0.516 × 108 m3, respectively, which account for 58.75%, 48.36%, and 40.29% of the natural river runoff. The months between April and October are identified as the most important periods to maintain the EFRs. Moreover, the water requirement for groundwater restoration of the oasis–desert ecotone accounts for a large proportion, representing 48.27%, 42.32%, and 37.03% of the total EFRs at maximum, medium, and minimum levels, respectively. Therefore, to allocate the integrated EFRs, focus should be placed on the water demand of the desert vegetation’s groundwater restoration, which is crucial for maintaining desert vegetation to prevent sandstorms and soil erosion. This work provides a reference to quantify the EFRs of oasis areas in arid regions.

Effects of nearshore evaporation rates on the design of seabed gallery intake systems for SWRO facilities located along the Red Sea shoreline of Saudi Arabia

Feed water to seawater reverse osmosis desalination systems should have a constant salinity with minimal variation. Intake systems that extract water from shallow nearshore areas in arid regions can exhibit significant fluctuations in salinity caused by high rates of evaporation and lack of circulation. Such fluctuations in salinity could inhibit the design, construction, and operation of seabed gallery intake systems located in shallow nearshore areas, such as the Red Sea inner shelf. Water depths range from 0 to 2 m between the beach and the edge of the fringing reef in the optimal locations for the development of seabed gallery intakes along the coast of the Red Sea of Saudi Arabia. The evaporation rate in this area is between 2 and 3 m per year. The bottom consists of mostly a marine hardground containing a thin veneer of unlithified sediment and no significant cover of corals or seagrass. The rather barren nature of the bottom suggests that periodic hypersalinity may contribute to the formation of hardgrounds on the bottom by causing supersaturation of the seawater with calcium carbonate and may limit the growth of corals and grasses. To assess the changes in salinity, a conceptual model was developed which assumes that a shallow circulation cell develops between the shoreline and deeper water offshore. Lower salinity seawater should migrate landward to replace water loss caused by evaporation with seaward moving of high-salinity water occurring along the bottom to balance the flow with ultimate mixing before the reef tract. To test this circulation pattern, a series of sensors were deployed to continuously monitor the water temperature, conductivity, and salinity at the surface and at the bottom during several periods of high air temperature. Surprisingly, the results show very little variation in salinity, despite the very high evaporation loss. The water salinity ranged between 39,000 and 40,000 mg/L with no diurnal variations of significance. Based on the monitoring and weather station data collected nearby, it appears that the predominant strong onshore wind, particularly during the afternoon and early evening, causes near-continuous mixing of the water between the reef tract and the shoreline. Therefore, the development of seabed gallery intake systems within the shallow water between 1 and 2 m of depth is feasible based on the measured salinity which is similar to that occurring further offshore in water depths between 2 and 20 m.

An evapotranspiration product for arid regions based on the three-temperature model and thermal remote sensing

An accurate estimation of evapotranspiration (ET) is crucial to better understand the water budget and improve related studies. Satellite remote sensing provides an unprecedented opportunity to map the spatiotemporal distribution of ET. However, ET values from barren or sparsely vegetated areas in arid regions are often assumed to be zero in typical ET products because of their low values. In addition, separating ET into soil evaporation (E-s) and vegetation transpiration (E-c) is difficult. To address these challenges, we developed an ET product (MOD3T) based on a three-temperature model and thermal remote sensing, specifically Moderate Resolution Imaging Spectroradiometer (MODIS) data. MOD3T has a spatial resolution of 1 km and a temporal resolution of 8 days. All input parameters except air temperature were obtained from MODIS datasets. Validation in two adjacent arid river basins in northwestern China showed that the mean absolute errors (mean absolute percent errors) between the MOD3T and flux tower ET were 0.71 mm d(-1) (18.5%) and 0.16 mm d(-1) (24.9%) for a densely vegetated area and sparsely vegetated sandy desert, respectively. The error between the MOD3T and water balance ET was 24 mm y(-1) (8.1%). The E-c/ET or E-s/ET of MOD3T was comparable to the observed stable oxygen and hydrogen isotopes. Unlike the MODIS ET (MOD16), MOD3T could not provide continuous ET values (as 70% of the MOD16 area lacked data) but exhibited relatively low uncertainty, particularly in cold seasons. Therefore, MOD3T can provide ET, E-s and E-c estimates for arid regions within acceptable ranges. (C) 2015 Elsevier B.V. All rights reserved.

The disastrous effects of salt dust deposition on cotton leaf photosynthesis and the cell physiological properties in the Ebinur Basin in Northwest China.

Salt dust in rump lake areas in arid regions has long been considered an extreme stressor for both native plants and crops. In recent years, research on the harmful effects of salt dust on native plants has been published by many scholars, but the effect on crops has been little studied. In this work, in order to determine the impact of salt dust storms on cotton, we simulated salt dust exposure of cotton leaves in Ebinur Basin in Northwest China, and measured the particle sizes and salt ions in the dust, and the photosynthesis, the structure and the cell physiological properties of the cotton leaves. (1) Analysis found that the salt ions and particle sizes in the salt dust used in the experiments were consistent with the natural salt dust and modeled the salt dust deposition on cotton leaves in this region. (2) The main salt cations on the surface and inside the cotton leaves were Na+, Ca2+, Cl- and SO4 2-, while the amounts of CO3 - and HCO3 - were low. From the analysis, we can order the quantity of the salt cations and anions ions present on the surface and inside the cotton leaves as Na+>Ca2+>Mg2+>K+ and Cl->SO4 2->HCO3 ->CO3 -, respectively. Furthermore, the five salt dust treatment groups in terms of the total salt ions on both the surface and inside the cotton leaves were A(500g.m-2)>B(400g.m-2)>C(300g.m-2)>D(200g.m-2)>E(100g.m-2)>F(0g.m-2). (3)The salt dust that landed on the surface of the cotton leaves can significantly influence the photosynthetic traits of Pn, PE, Ci, Ti, Gs, Tr, WUE, Ls, φ, Amax, k and Rady of the cotton leaves. (4)Salt dust can significantly damage the physiological functions of the cotton leaves, resulting in a decrease in leaf chlorophyll and carotenoid content, and increasing cytoplasmic membrane permeability and malondialdehyde (MDA) content by increasing the soluble sugar and proline to adjust for the loss of the cell cytosol. This increases the activity of antioxidant enzymes to eliminate harmful materials, such as the intracellular reactive oxygen and MDA, thus reducing the damage caused by the salt dust and maintaining normal physiological functioning. Overall, this work found that the salt dust deposition was a problem for the crop and the salt dust could significantly influence the physiological and biochemical processes of the cotton leaves. This will eventually damage the leaves and reduce the cotton production, leading to agricultural economic loss. Therefore, attention should be paid to salt dust storms in the Ebinur Basin and efficient measures should be undertaken to protect the environment.

Designing slanted soil system for greywater treatment for irrigation purposes in rural area of arid regions

To solve the unpleasant disposal of greywater in rural area and allow its collection for reuse in gardening, a slanted soil treatment system (SSTS) was designed and installed in two households. Granitic gravel of 1–9 mm size was used as the filter medium. The aim of this study was to design a SSTS and assess its suitability as a treatment system allowing greywater reuse in gardening. The efficiency of the SSTS was assessed based on organic matter and bacterial pollution removal. The developed SSTS allowed the collection of greywater from three main sources (shower, dishwashing and laundry) in rural area. The SSTS is efficient in removing at least 50% of suspended solids, chemical oxygen demand and biological oxygen demand. The study highlighted that, contrary to the common perception, greywater streams in rural area are heavily polluted with faecal indicators. The removal efficiency of faecal indicators was lower than 2 log units, and the bacteriological quality of the effluents is generally higher than the WHO reuse guidelines for restricted irrigation. Longer retention time is required to increase the efficiency. The possibility of reusing the treated greywater as irrigation water is discussed on the basis of various qualitative parameters. The SSTS is a promising greywater treatment system for small communities in the rural area in the Sahelian region. To increase the treatment efficiency, future research will focus on the characteristics of the SSTS, the grain size and the establishment of a pretreatment step.

Temporal and spatial variability of soil organic matter and total nitrogen in a typical oasis cropland ecosystem in arid region of Northwest China

Soil degradation resulted from unreasonable land use has been a serious problem in the arid region of Northwest China. This paper seeks to understand the relationship between topsoil properties and farming practices for land management targeting at improving soil quality in this region. The temporal and spatial variation of soil organic matter (SOM), total nitrogen (STN) were analyzed with classical statistics and geostatistics methods in Linze County, Gansu Province, an typical oasis agricultural area in arid region of northwest China, as affected by farming practices using the data from 1982 to 2008. The results of classical statistics indicated that the average SOM and STN concentrations were 12.78 ± 4.38 g kg−1 and 0.72 ± 0.21 g kg−1 in 1982, 13.76 ± 4.02 g kg−1 and 0.81 ± 0.20 g kg−1 in 2008, respectively. The net carbon and nitrogen increased at an average rate of 0.104 Mg C ha-1 year−1 (1 Mg = 106g) and 0.014 Mg N ha−1 year−1 in the past 26 years. Geostatistical analyses showed that the spatially related areas of SOM and STN were expanded by effect of farming practices. The spatial distributions of SOM and STN contents were influenced by regional soil parent materials. Temporal variation maps of SOM revealed a change trend was closely related to the amount of the application of organic manures. It was concluded that the applications of chemical fertilizers were effective for increasing of STN, and the continuous applications of chemical fertilizers combining with applications of organic manures (approximately 45 m3 ha−1) every other year were helpful in accumulating soil organic carbon.

Controls on Radial Growth of Mountain Big Sagebrush and Implications for Climate Change

Mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana) covers large areas in arid regions of western North America. Climate-change models predict a decrease in the range of sagebrush, but few studies have examined details of predicted changes on sagebrush growth and the potential impacts of these changes on the commu- nity. We analyzed effects of temperature, precipitation, and snow depth on sagebrush annual ring width for 1969 to 2007 in the Gunnison Basin of Colorado. Temperature at all times of year except winter had negative correlations with ring widths; summer temperature had the strongest negative relationship. Ring widths correlated positively with precipita- tion in various seasons except summer; winter precipitation had the strongest relationship with growth. Maximum snow depth also correlated positively and strongly with ring width. Multiple regressions showed that summer temperature and either winter precipitation or maximum snow depth, which recharges deeper soil horizons, are both important in controlling growth. Overall, water stress and perhaps especially maximum snow depth appear to limit growth of this species. With predicted increases in temperature and probable reduced snow depth, sagebrush growth rates are likely to decrease. If so, sagebrush populations and cover may decline, which may have substantial effects on community com- position and carbon balance.

Tolerance of six Namaqualand pioneer species to saline soil conditions

Saline soils pose a great problem to reclamation of mined areas in arid regions. Experiments were carried out in order to determine the tolerance of six Namaqualand pioneer species to varying levels of salinity. Both perennial and ephemeral species were used and results of all species showed that increased salinity induced a significant decrease in biomass production. With increased salinity, biomass allocation towards the leaves increased, while that towards the stems decreased in both perennial and ephemeral species, but biomass allocation towards the other plant organs varied. Of the six species tested, the perennials seemed to be better suited for rehabilitation purposes under saline soil conditions.

Lithologic mapping in arid regions with Landsat thematic mapper data: Meatiq dome, Egypt

Digital Landsat thematic mapper (TM) data were evaluated for lithologic mapping capabilities over the Meatiq dome area in the hyper-arid Eastern Desert of Egypt. Bi-directional spectral reflectance data (0.4–2.5 µm) for powders of the major rock types exposed in the dome and published spectral reflectance data were used as guides in selecting TM band reflectance ratios that maximize discrimination of individual rock types on the basis of their respective mineralogies. Comparison of TM data with field and petrographic observations shows (1) increasing amounts of magnetite and other opaque minerals, with low, flat spectral reflectances, decrease the ratio of TM band 5 (1.55 to 1.75) to band 1 (0.45 to 0.52 µm); (2) increasing amounts of hydroxyl-bearing minerals, with hydroxyl ion vibrational absorptions in TM band-7 wavelength region (2.08 to 2.35 µm), increase the ratio of TM band 5 to band 7; (3) increasing amounts of Fe-bearing aluminosilicates that absorb in the band-4 wavelength region (0.76 to 0.9 µm) increase the product of the following two TM ratios: band 5 to band 4 and band 3 (0.63 to 0.69 µm) to band 4; and (4) thin (≤5 µm), desert varnish that covers many outcrops modulates, but does not obscure, the spectral reflectance signatures of the Meatiq rocks. The varnish consists of amorphous to poorly crystalline dioctahedral smectite, iron oxides, and/or oxyhydroxides. Serpentinite, mafic mylonite, massive amphibolite, quartzofeldspathic mylonite, biotite schist, and quartz phyllonite were mapped on the basis of their unique values in one or more of the three ratio images, whereas coarse- and fine-grained granites, granite gneiss, and tonalite, with similar mineralogies and TM band ratios, were mapped as a group. Finer subdivisions were made where field traverses provided local verification. Results demonstrate that appropriate processing and presentation of Landsat TM data can significantly augment field observations for lithologic mapping of large areas in arid regions.

Saltation vs. soil stabilization: Two processes determining the character of surfaces in arid regions

In satellite images of sandy areas in arid regions disturbed (crumbled) surfaces appear much brighter than stabilized soil. From observations of Landsat satellite images that show directional surface features along the dominant wind direction, two theses are inferred concerning eolian erosion and transport: (1) transport is dominantly a near-surface phenomenon of saltation rather than of aerodynamic entrainment and later deposition; (2) both the disturbed surface characteristics in the saltating regions (saltation formations in our terminology) and the stability of the crusted soil in the quiescent regions are locally self-perpetuating. Thesis (1) is suggested by the appearance of the zones in the lee of protrusions from the surface, or even a river, that constitute obstacles (across the dominant wind directon) to particle flow. In the lee of a ridge between two “streaks” or in the lee of a protruding outcropping within a “sheet”, one finds darker zones, in contrast to the adjacent bright saltation formation. These darker zones are laterally uniform, and have to be interpreted as stable, quiescent areas of non-deposition and non-erosion. Thesis (2) is inferred from (i) the sharpness of the transition in the reflectivity at the boundaries (parallel to the dominant wind direction) between the bright “streaks” or “sheets” and the darker stable surface, and (ii) the constant width of some long quiescent areas in the wind-shadow of an isolated obstacle. Variability of wind direction, in any season of any strength, should have produced a gradual boundary. The disturbed and the stable surfaces are therefore interpreted as locally a bi-stable situation: an occasional wind will produce no effect over a stable surface, which tends to be “immune” to the oelian influences, whereas the surface in a saltation formation is prone to be disturbed anew by a comparable wind. The bistable situation is linked to positive feedback mechanisms; the most important mechanism appears to be the cohesion of the crusted surface. Such a surface can be broken only by high energy impact. The feedback mechanisms have implications for designing measures to reduce the danger of dust storms.

Saltation vs. soil stabilization: Two processes determining the character of surfaces in arid regions

In satellite images of sandy areas in arid regions disturbed (crumbled) surfaces appear much brighter than stabilized soil. From observations of Landsat satellite images that show directional surface features along the dominant wind direction, two theses are inferred concerning eolian erosion and transport: (1) transport is dominantly a near-surface phenomenon of saltation rather than of aerodynamic entrainment and later deposition; (2) both the disturbed surface characteristics in the saltating regions (saltation formations in our terminology) and the stability of the crusted soil in the quiescent regions are locally self-perpetuating. Thesis (1) is suggested by the appearance of the zones in the lee of protrusions from the surface, or even a river, that constitute obstacles (across the dominant wind direction) to particle flow. In the lee of a ridge between two “streaks” or in the lee of a protruding outcropping within a “sheet”, one finds darker zones, in contrast to the adjacent bright saltation formation. These darker zones are laterally uniform, and have to be interpreted as stable, quiescent areas of non-deposition and non-erosion. Thesis (2) is inferred from (i) the sharpness of the transition in the reflectivity at the boundaries (parallel to the dominant wind direction) between the bright “streaks” or “sheets” and the darker stable surface, and (ii) the constant width of some long quiescent areas in the wind-shadow of an isolated obstacle. Variability of wind direction, in any season of any strength, should have produced a gradual boundary. The disturbed and the stable surfaces are therefore interpreted as locally a bi-stable situation: an occasional wind will produce no effect over a stable surface, which tends to be “immune” to the eolian influences, whereas the surface in a saltation formation is prone to be disturbed anew by a comparable wind. The bistable situation is linked to positive feedback mechanisms; the most important mechanism appears to be the cohesion of the crusted surface. Such a surface can be broken only by high energy impact. The feedback mechanisms have implications for designing measures to reduce the danger of dust storms.