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30 June 2023, Volume 15 Issue 6 Previous Issue    Next Issue
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Research article
Seasonal variations in glacier velocity in the High Mountain Asia region during 2015-2020
ZHANG Zhen, XU Yangyang, LIU Shiyin, DING Jing, ZHAO Jinbiao
Journal of Arid Land. 2023, 15 (6): 637-648.   DOI: 10.1007/s40333-023-0016-5
Abstract ( 100 )   HTML ( 300 )     PDF (4417KB) ( 190 )  

Velocity is an important component of glacier dynamics and directly reflects the response of glaciers to climate change. As a result, an accurate determination of seasonal variation in glacier velocity is very important in understanding the annual variation in glacier dynamics. However, few studies of glacier velocity in the High Mountain Asia (HMA) region were done. Along these lines, in this work, based on Sentinel-1 glacier velocity data, the distribution of glacier velocity in the HMA region was plotted and their seasonal variations during 2015-2020 were systematically analysed. The average glacier velocity in the HMA region was 0.053 m/d, and was positively correlated with the glacier area and slope. Glaciers in the Karakoram Mountains had the fastest average flow velocity (0.060 m/d), where the glaciers exhibited the largest average area and average slope. Moreover, glaciers in the Gangdisê Mountains had the slowest velocity (0.022 m/d) and the smallest average glacier area. The glacier flows were the fastest in spring (0.058 m/d), followed by summer (0.050 m/d), autumn (0.041 m/d), and winter (0.040 m/d). In addition, the glacier flows were the maximum in May, being 1.4 times of the annual average velocity. In some areas, such as the Qilian, Altun, Tibetan Interior, Eastern Kunlun, and Western Kunlun mountains, the peak glacier velocities appeared in June and July. The glacier velocity in the HMA region decreased in midsummer and reached the minimum in December when it was 75% of the annual average. These results highlight the role of meltwater in the seasonal variation in glacier flows in late spring and early summer. The seasonal velocity variation of lake-terminating glaciers was similar to that of land-terminating ones, but the former flowed faster. The velocity difference close to the mass balance line between the lake- and land-terminating glaciers was obviously greater in spring than in other seasons. In summer, the difference between the lake- and land-terminating glaciers at a normalized distance of 0.05-0.40 from the terminus was significantly greater than those of other seasons. The velocity difference between the lake- and land-terminating glaciers is closely related to the variable of ice thickness, and also to the frictional force of the terminal base reduced by proglacial lakes. Thus, it can be concluded that in addition to the variation of the glacier thickness and viscosity, the variation of glacier water input also plays a key role in the seasonal variation of glacier velocity.

Aeolian activity in the southern Gurbantunggut Desert of China during the last 900 years
LI Wen, MU Guijin, YE Changsheng, XU Lishuai, LI Gen
Journal of Arid Land. 2023, 15 (6): 649-666.   DOI: 10.1007/s40333-023-0057-9
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The mineral dust emitted from Central Asia has a significant influence on the global climate system. However, the history and mechanisms of aeolian activity in Central Asia remain unclear, due to the lack of well-dated records of aeolian activity and the intense wind erosion in some of the dust source areas (e.g., deserts). Here, we present the records of aeolian activity from a sedimentary sequence in the southern Gurbantunggut Desert of China using grain size analysis and optically stimulated luminescence (OSL) dating, based on field sampling in 2019. Specifically, we used eight OSL dates to construct chronological frameworks and applied the end-member (EM) analysis for the grain size data to extract the information of aeolian activity in the southern Gurbantunggut Desert during the last 900 a. The results show that the grain size dataset can be subdivided into three EMs (EM1, EM2, and EM3). The primary modal sizes of these EMs (EM1, EM2, and EM3) are 126.00, 178.00, and 283.00 μm, respectively. EM1 represents a mixture of the suspension components and saltation dust, while EM2 and EM3 show saltation dust transported over a shorter distance via strengthened near-surface winds, which can be used to trace aeolian activity. Combined with the OSL chronology, our results demonstrate that during the last 900 a, more intensive and frequent aeolian activity occurred during 450-100 a BP (Before Present) (i.e., the Little Ice Age (LIA)), which was reflected by a higher proportion of the coarse-grained components (EM2+EM3). Aeolian activity decreased during 900-450 a BP (i.e., the Medieval Warm Period (MWP)) and 100 a BP-present (i.e., the Current Warm Period (CWP)). Intensified aeolian activity was associated with the strengthening of the Siberian High and cooling events at high northern latitudes. We propose that the Siberian High, under the influence of temperature changes at high northern latitudes, controlled the frequency and intensity of aeolian activity in Central Asia. Cooling at high northern latitudes would have significantly enhanced the Siberian High, causing its position to shift southward. Subsequently, the incursion of cold air masses from high northern latitudes resulted in stronger wind regimes and increased dust emissions from the southern Gurbantunggut Desert. It is possible that aeolian activity may be weakened in Central Asia under future global warming scenarios, but the impact of human activities on this region must also be considered.

Do aeolian deposits and sand encroachment intensity shape patterns of vegetation diversity and plant functional traits in desert pavements?
M'hammed BOUALLALA, Souad NEFFAR, Lyès BRADAI, Haroun CHENCHOUNI
Journal of Arid Land. 2023, 15 (6): 667-694.   DOI: 10.1007/s40333-023-0014-7
Abstract ( 69 )   HTML ( 31 )     PDF (7273KB) ( 151 )  

The effects of sand encroachment on composition, diversity, and functional patterns of vegetation in drylands are rarely studied, and yet addressing these aspects is important to deepen our understanding of the biodiversity conservation. This study aimed to investigate the effect of sand encroachment on plant functional biodiversity of desert pavements (gravel deserts) in the Sahara Desert of Algeria. Plants were sampled and analyzed in three desert pavements with different levels of sand encroachment (LSE) and quantity of aeolian deposits (low, LLSE; medium, MLSE; and high, HLSE). Within the sample-plot area (100 m2), density of every plant species was identified and total vegetation cover was determined. Plant taxonomic and functional diversity were analyzed and compared between LSE. Result showed that 19 plant species in desert pavements were classified into 18 genera and 13 families. Asteraceae and Poaceae were the most important families. The species Anabasis articulata (Forssk) Moq. characterized LLSE desert pavements with 11 species, whereas Thymelaea microphylla Coss. & Durieu ex Meisn. and Calobota saharae (C&D) Boatwr. & van Wyk were dominant species of desert pavements with MLSE (14 species) and HLSE (10 species), respectively. The highest values of species richness and biodiversity were recorded in desert pavements with MLSE, while low values of these ecological parameters were obtained in desert pavements with HLSE. Desert pavements with LLSE were characterized with the highest values of species abundances. Plant communities were dominated by chamaephytes, anemochorous, arido-active, and competitive stress-tolerant plants. The increase in LSE along the gradient from LLSE to HLSE induced significant changes in plant community variables including decreases in plant density, plant rarity, lifeform composition, morphological type, and aridity adaptation. Desert pavements with HLSE favor the degradation of vegetation and trigger biodiversity erosion.

Estimation of aboveground biomass of arboreal species in the semi-arid region of Brazil using SAR (synthetic aperture radar) images
Janisson B de JESUS, Tatiana M KUPLICH, Íkaro D de C BARRETO, Fernando L HILLEBRAND, Cristiano N da ROSA
Journal of Arid Land. 2023, 15 (6): 695-709.   DOI: 10.1007/s40333-023-0017-4
Abstract ( 39 )   HTML ( 5 )     PDF (2327KB) ( 203 )  

The Caatinga biome is an important ecosystem in the semi-arid region of Brazil. It has significantly degraded due to human activities and is currently a region undergoing desertification. Thus, monitoring the variation in the Caatinga biome has become essential for its sustainable development. However, traditional methods for estimating aboveground biomass (AGB) are time-consuming and destructive. Remote sensing, such as optical and radar imaging, can estimate and correlate with vegetation. Nevertheless, radar imaging is still a novelty to be applied in estimating the AGB of this biome, which is an area with little research. Therefore, this study aimed to use Sentinel-1 images to estimate the AGB of the Caatinga biome in Sergipe State (northeastern Brazil) and to verify its influencing factors. Nineteen sample plots (30 m×30 m) were selected, and the stems of individuals with a circumference at breast height (1.3 m above the ground) equal to or greater than 6.0 cm were measured, and the AGB through an allometric equation was estimated. The Sentinel-1 images from 3 different periods (green, intermediate, and dry periods) were used to consider the phenological conditions of the Caatinga biome. All the pre-processing and extraction of attributes (co-polarized VV (vertical transmit and vertical receive), cross-polarized VH (vertical transmit and horizontal receive), and band ratio VH/VV backscatter, radar vegetation index, dual polarization synthetic aperture radar (SAR) vegetation index (DPSVI), entropy (H), and alpha angle (α)) were performed with Sentinel's Application Platform. These attributes were used to estimate the AGB through simple and multiple linear regressions and evaluated by the coefficients of determination (R2), correlation (r), and root mean squared error (RMSE). The results showed that the attributes individually had little ability to estimate the AGB of the Caatinga biome in the three periods. Combined with multiple regression, we found that the intermediate period presented the equation with the best results among the observed and estimated variables (R2=0.73; r=0.85; RMSE=8.33 Mg/hm2), followed by the greenness period (R2=0.72; r=0.85; RMSE=8.40 Mg/hm2). The attributes contributing to these equations were VH/VV, DPSVI, H, α, and co-polarized VV for the green period and cross-polarized VH for the intermediate period. The study showed that the Sentinel-1 images could be used to estimate the AGB of the Caatinga biome in the green and intermediate phenological periods since the SAR attributes highly correlated with the estimated variable (i.e., AGB) through multiple linear equations.

Modelling the dead fuel moisture content in a grassland of Ergun City, China
CHANG Chang, CHANG Yu, GUO Meng, HU Yuanman
Journal of Arid Land. 2023, 15 (6): 710-723.   DOI: 10.1007/s40333-023-0103-7
Abstract ( 167 )   HTML ( 5 )     PDF (4071KB) ( 157 )  

The dead fuel moisture content (DFMC) is the key driver leading to fire occurrence. Accurately estimating the DFMC could help identify locations facing fire risks, prioritise areas for fire monitoring, and facilitate timely deployment of fire-suppression resources. In this study, the DFMC and environmental variables, including air temperature, relative humidity, wind speed, solar radiation, rainfall, atmospheric pressure, soil temperature, and soil humidity, were simultaneously measured in a grassland of Ergun City, Inner Mongolia Autonomous Region of China in 2021. We chose three regression models, i.e., random forest (RF) model, extreme gradient boosting (XGB) model, and boosted regression tree (BRT) model, to model the seasonal DFMC according to the data collected. To ensure accuracy, we added time-lag variables of 3 d to the models. The results showed that the RF model had the best fitting effect with an R2 value of 0.847 and a prediction accuracy with a mean absolute error score of 4.764% among the three models. The accuracies of the models in spring and autumn were higher than those in the other two seasons. In addition, different seasons had different key influencing factors, and the degree of influence of these factors on the DFMC changed with time lags. Moreover, time-lag variables within 44 h clearly improved the fitting effect and prediction accuracy, indicating that environmental conditions within approximately 48 h greatly influence the DFMC. This study highlights the importance of considering 48 h time-lagged variables when predicting the DFMC of grassland fuels and mapping grassland fire risks based on the DFMC to help locate high-priority areas for grassland fire monitoring and prevention.

Effects of drought treatment on photosystem II activity in the ephemeral plant Erodium oxyrhinchum
CHEN Yingying, LIN Yajun, ZHOU Xiaobing, ZHANG Jing, YANG Chunhong, ZHANG Yuanming
Journal of Arid Land. 2023, 15 (6): 724-739.   DOI: 10.1007/s40333-023-0058-8
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Drought is a critical limiting factor affecting the growth and development of plants in arid and semi-arid areas. Photosynthesis, one of the most important physiological processes of plants, can be significantly inhibited by drought. Photosystem II (PSII) is considered the main attack target when photosynthesis is affected by drought. To clarify how PSII components of the ephemeral plant Erodium oxyrhinchum (grown in the Gurbantunggut Desert, China) respond to drought treatment, we evaluated the functional activity of PSII by determining chlorophyll fluorescence and gas exchange parameters under different drought treatment levels (control (400 mL), moderate drought (200 mL), and severe drought (100 mL)). Under moderate drought treatment, significant decreases were found in net photosynthetic rate (Pn), effective quantum yield of PSII (Y(II)), relative electron transfer rate of PSII (rETR(II)), oxygen-releasing complex, probability of an absorbed exciton moving an electron into the electron transport chain beyond primary quinone receptor QA- (Φ(Eo)), probability of a trapped exciton moving an electron into the electron transport chain beyond primary quinone receptor QA- (ψ(Eo)), and performance index of PSII (PIabs). Compared to control treatment, marked increases were observed in water use efficiency (WUE), relative variable fluorescence at the J step (VJ), initial fluorescence (Fo), and dissipated energy per active reaction center (DIo/RC) under moderate drought treatment, but there were no substantial changes in semi-saturated light intensity (IK), active reaction centers per cross-section (RC/CS), and total performance index of PSII and PSI (PItotal, where PSI is the photosystem I). The changes of the above parameters under severe drought treatment were more significant than those under moderate drought treatment. In addition, severe drought treatment significantly increased the absorbed energy per active reaction center (ABS/RC) and trapping energy per active reaction center (TRo/RC) but decreased the energy transmission connectivity of PSII components, RC/CS, and PItotal, compared to moderate drought and control treatments. Principle component analysis (PCA) revealed similar information according to the grouping of parameters. Moderate drought treatment was obviously characterized by RC/CS parameter, and the values of Fo, VJ, ABS/RC, DIo/RC, and TRo/RC showed specific reactions to severe drought treatment. These results demonstrated that moderate drought treatment reduced the photochemical activity of PSII to a certain extent but E. oxyrhinchum still showed strong adaptation against drought treatment, while severe drought treatment seriously damaged the structure of PSII. The results of this study are useful for further understanding the adaptations of ephemeral plants to different water conditions and can provide a reference for the selection of relevant parameters for photosynthesis measurements of large samples in the field.

Improved drought tolerance in Festuca ovina L. using plant growth promoting bacteria
Fateme RIGI, Morteza SABERI, Mahdieh EBRAHIMI
Journal of Arid Land. 2023, 15 (6): 740-755.   DOI: 10.1007/s40333-023-0015-6
Abstract ( 176 )   HTML ( 7 )     PDF (1088KB) ( 457 )  

Numerous ecological factors influence a plant's ability to live and grow, in which dryness is a substantial constraint on plant growth in arid and semi-arid areas. In response to a specific environmental stress, plants can use the most effective bacteria to support and facilitate their growth and development. Today, plant growth promoting rhizobacteria (PGPR) is widely used to reduce drought stress on plant growth. In this study, the effects of drought on Festuca ovina L. germination, growth, and nutrient absorption were investigated using PGPR in a factorial test with a completely random design under four water regimes. Soil water content was kept at 100% FC (field capacity), 70% FC (FC), 50% FC, and 30% FC. The treatments were inoculated with Azotobacter vinelandii, Pantoea agglomerans+Pseudomonas putida, and a mixture of bio-fertilizers. Results showed that the effects of drought stress were significantly reduced (P<0.05) when A. vinelandii and P. agglomerans+P. putida were used separately, however, the combined treatment of bio-fertilizers had a greater influence on seed germination than the single application. P. agglomerans+P. putida under 30% FC condition resulted in higher increases in stem, root length, and plant dry biomass. The highest uptake of nutrients was observed for the combined treatment of bio-fertilizers under 30% FC condition. Therefore, the use of A. vinelandii and P. agglomerans+P. putida, applied separately or combined, increased tolerance to drought stress in F. ovina by increased germination indices, dry weight, stem length, and root length. Because of the beneficial effects of PGPR on the growth characteristics of plants under drought conditions and the reduction of negative effects of drought stress, inoculating F. ovina seeds with Azotobacter and Pseudomonas is recommended to improve their growth and development characteristics under drought conditions. PGPR, as an affordable and environmentally friendly method, can improve the production of forage in water-stress rangelands.