Arid Zone Research

Changes of pollen taxa diversity in the arid Central Asia under the Holocene Westerlies Mode: A case study of the Altai Mountains

ZHANG Dongliang

2022, 39 (3): 667-675. doi: 10.13866/j.azr.2022.03.01

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Modern climate change poses a huge threat to plants in the arid Central Asia. Due to the short instrumental interval, we are unable to better understand the long time-scale relationship between plant diversities and climate change in this region. However, pollen records in the geological archives provide us an opportunity to understand the existence, distribution and diversity of plants in the past. In this study, we selected three pollen sequences from different elevations (Halasazi Peat, Narenxia Peat and Kanas Lake) in the Altai Mountains to investigate the characteristics of plant diversities and their response patterns to Holocene climate change. The results revealed that the changes of pollen taxa diversity in the Altai Mountains showed a unique pattern. As the climate was warming in the early Holocene, the upper forest limits began to migrate upward, leading to an increase in pollen taxa diversity at high elevations. In the middle Holocene, the climate was warm and wet, and the upward and downward migration of the upper and lower forest limits resulted in higher diversities at high and low elevations, but the lower diversities in the taiga-dominated forest belt mainly resulted from a decreasing species evenness. In the late Holocene, the climate became cooler and wetter, and the upper forest limits moved downward, leading to a significant increase in diversities at middle elevations. The largest changes of plant diversities were observed in the forest belt during the Holocene, which means this belt is the most sensitive and vulnerable area for climate response. This study not only helps us understand the response model of mountain vegetation belt to Holocene climate change, and also provides key evidence for exploring the history of mountain vegetation migration in the arid Central Asia.

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Temporal reconstruction of alpine glacier surface elevation variation in Central Asia

DU Weibing,ZHANG Shiqiong,LI Junli,BAO Anming,WANG Shuangting,SHI Ningke,XU Linjuan,GAO Xin,MA Dandan,ZHENG Yanchao

2022, 39 (3): 676-683. doi: 10.13866/j.azr.2022.03.02

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The topography of the alpine glacier area in Central Asia is complex. Satellite laser altimetry technology can be used to monitor large-scale glacier surface elevation change. This study used ICESat laser altimetry data from 2003 to 2009, and shuttle radar topography mission (SRTM) elevation data and Randolph glacier inventory (RGI) 6.0 cataloging data for 2000 to monitor the surface elevation change of alpine glaciers in Central Asia. The glacial region of Central Asia is divided into three regions according to geographical form. First, the data were tested for normality to eliminate error. When a normal distribution was not observed, outlier values from the standard deviation of the linear regression were selected as abnormal. Point cloud denoising and its accuracy optimization algorithm and a multi-scale analysis model of temporal and spatial variation in surface elevation in the glacier area were established. A cubic polynomial model was used to fit the glacier surface elevation data for different scales across the whole area and sub regions of the high Asian mountains. A time series reconstruction of changes in alpine glacier surface elevation in Central Asia was carried out based on the data for each region from 2003. Temporal changes in glacier surface elevation from 2003 to 2009 were analyzed. The results showed that the average elevation for the whole region decreased, with clear regional differences. From 2003 to 2009, the surface elevation of high Asian glaciers decreased by 9.59 ± 1.89 m. The glacier surface elevation in Areas I (i.e., Tibet and southern Qinghai), II (i.e., Xinjiang, Northern Qinghai, and some parts of Gansu), and III (i.e., outside China and some countries in Central Asia) decreased by 6.51 ± 2.9 m, 7.87 ± 5.03 m, and 9.81 ± 5.1 m, respectively. The glacier surface elevation increased from 2004 to 2005. Area I showed the slowest decline in glacier elevation, followed by Area II; Area III showed the fastest decline. This research method has universal application potential for monitoring point cloud elevation in glacier areas. The model evaluation parameter (R²) was >0.98, indicating that the cubic polynomial relationship between ICESat data and SRTM elevation data showed strong universality in this area. However, this will make the point cloud data more sparse, and the model is highly dependent on the benchmark DEM.

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Assessment of CRU, ERA5, CMFD grid precipitation data for the Tibetan Plateau from 1979 to 2017

WEN Tingting,GUO Yingxiang,DONG Shaorui,DONG Yuanzhen,LAI Xiaoling

2022, 39 (3): 684-697. doi: 10.13866/j.azr.2022.03.03

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In this paper, CRU, ERA5, and CMFD precipitation data for the Qinghai-Xizang Plateau were evaluated on annual and seasonal scales and compared with observed precipitation data from 131 weather stations. (1) The three data types all showed a strong ability to describe total annual precipitation on the plateau, and their correlation coefficients with the observed values were all >0.9. Results from all three models were generally higher than observed precipitation. CRU and CMFD results were closest to observed values in spring, while CMFD results were closest to the observed values in summer and fall; all three models showed the weakest correlations with observed values for winter precipitation. (2) In terms of precipitation distribution, CMFD data had the best ability to simulate plateau precipitation annually, and in spring, summer, and winter. The models showed regional differences in describing fall precipitation. CRU and CMFD results were closest to observed values on the western plateau. (3) Plateau precipitation increased during spring, summer, and fall, especially in the summer, and decreased in the winter. (4) The annual and seasonal variation (spring, summer, and fall) in the CRU data was consistent with that of the observed data, and the winter precipitation results from ERA5 were consistent with observed values. (5) The deviation between CMFD results and observed annual and seasonal precipitation was the smallest. (6) Time series analysis showed that CMFD annual, spring, summer, and fall precipitation results were closest to the observed values, followed by CRU. CMFD winter precipitation results were closest to the observed values, but the correlation coefficient failed the significance test of 95%.

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Study on spatio-temporal dynamics and driving factors of NPP in Central Asian grassland

ZHANG Yunxin,HAO Haichao,FAN Lianlian,LI Yaoming,ZHANG Renping,LI Kaihui

2022, 39 (3): 698-707. doi: 10.13866/j.azr.2022.03.04

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Based on the CASA and Miami models, the net primary productivity (NPP) of five Central Asian countries (Kazakhstan, Tajikistan, Kyrgyzstan, Turkmenistan, and Uzbekistan) was calculated in this study. The purpose was to explore the Spatio-temporal dynamics and driving factors of NPP in Central Asian grassland from 2001 to 2019. The results showed that the average ANPP of grassland in Central Asia from 2001 to 2019 was 118.9 g C·m^-2·a^-1. On the spatial scale, the ANPP of grassland in the plain area increased gradually from south to north with increasing latitude. In contrast, the ANPP of grassland from plain to mountain grassland increased with increasing altitude. On the temporal scale, the overall growth trend of ANPP was not significant, and the future change trend of grassland ANPP in approximately 60% of the region was opposite to that of the past. The trend was not significant in the region of Central Asia with increased grassland ANPP where human activities are dominant and with decreased grassland ANPP, with climate change as the main driving force. A significant positive correlation existed between ANPP and precipitation accounting for 67.8%, with no significant relationship between temperature and the change of ANPP in Central Asian grassland. Therefore, precipitation is the main climatic factor affecting the change of ANPP in Central Asian grassland.

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Changing precipitation characteristics in the Yellow River Basin in the last 60 years and tendency prediction for next 30 years

WANG Chenghai,YANG Jintao,YANG Kai,ZHANG Feimin,ZHANG Shengning,LI Kechen,YANG Yi

2022, 39 (3): 708-722. doi: 10.13866/j.azr.2022.03.05

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The climate of the Yellow River Basin has distinctly changed in the past 60 years, which significantly impacts its surface hydrological and ecological processes. In this study, the spatial and temporal characteristics of precipitation in the Yellow River Basin in the past 60 years (1961-2018) were analyzed using in-situ precipitation observations in this basin. Future precipitation trends for the next 30 years (2018-2047) in the Yellow River Basin were projected using outputs from the SSP245 scenario in the CMIP6 model and statistical methods. Results show that there are significant annual, inter-annual, and inter-decadal variations in precipitation in the Yellow River Basin, with a significant oscillation cycle of 2-4 years. For the whole basin, annual and seasonal precipitation is basically isotropic at an inter-annual scale but significant areas of inter-annual variability anomalies are different. Spatial anomalies of precipitation are opposite in the cold season (winter-spring) and the warm season (summer-autumn), with a decrease in precipitation influenced by summer monsoon activity and an increase in precipitation influenced by the winter monsoon. There has been an increasing trend of 20.96 mm·(10a)^-1 in annual precipitation in the Yellow River source area for the past 60 years, and expected annual precipitation will continue to increase at 11.53-17.62 mm·(10a)^-1 over the next 30 years. Annual precipitation in the Hetao area of the Yellow River Basin has continued to increase in the past 60 years at a rate of 2.71 mm·(10a)^-1, but the rate of future increase has slowed to approximately 0.52 mm·(10a)^-1. In lower reaches of the Yellow River, a decreasing trend in precipitation in the past 60 years is presented and will continue to decrease at a rate of 5.46 mm·(10a)^-1.

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Analysis of multi-scalar characteristics of dry and wet conditions in the Yellow River Basin based on SPEI

GAO Bingli,GONG Jie,LI Yan,JIN Tiantian

2022, 39 (3): 723-733. doi: 10.13866/j.azr.2022.03.06

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Based on daily data from 70 meteorological stations in the Yellow River Basin from 1960 to 2020, the Standardized Precipitation Evapotranspiration Index (SPEI) based on precipitation and potential evapotranspiration was calculated. Then, the evolution and persistence characteristics of dry-wet change of the Yellow River Basin from 1960 to 2020 were studied and their influence on meteorological factors was analyzed. Results showed the following: (1) There were differences in dry and wet grades and frequencies among the SPEI at different time scales and dry and wet levels were dominated by normal and light conditions. There was an insignificant wetness trend in summer and an insignificant dryness trend annually, and during spring, autumn, and winter from 1960 to 2020 in the Yellow River Basin. Geographically, the summer climate was mainly wet and 64.29% of meteorological stations showed an increased SPEI. The annual, spring, autumn, and winter climate in the Yellow River Basin was mainly dry and 51.43%, 62.86%, 64.29%, and 51.43% of meteorological stations showed a decrease SPEI, respectively. (2) For the different time scales of dry and wet events, 1970-1979 was a partial dry period, whereas 1960-1969 was a partial wet period, and the frequency of dry and wet events was as follows: autumn > summer > spring > winter. (3) From persistent characteristics of dry and wet events, the intensity of ongoing drought events increased and occurred mainly in autumn and winter, whereas the intensity of persistent wet events increased and occurred mainly in autumn. (4) A decreasing trend in the SPEI from 1960 to 2020 was mainly due to combined effects of a decrease of precipitation, average wind speed and relative humidity.

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Applicability of the LSTM and ARIMA model in drought prediction based on CEEMD: A case study of Xinjiang

DING Yan,XU Dehe,CAO Lianhai,GUAN Xiangrong

2022, 39 (3): 734-744. doi: 10.13866/j.azr.2022.03.07

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The frequent occurrence of droughts seriously affects normal agricultural production and economic development. Accurate prediction of drought occurrence is of great importance in reducing drought losses. Nevertheless, drought occurrences have not been well predicted. Drought indices can be used to quantitatively evaluate the intensity, duration, and influence range of drought. Thus, on the basis of daily precipitation data from 1960 to 2019 in the Xinjiang Uyghur Autonomous Region, the standardized precipitation index (SPI) at timescales of 1, 3, 6, 9, 12, and 24 months were calculated. Aiming for the nonlinear and nonstationary characteristics of SPI, a new drought prediction method was proposed combining the single model and the complementary ensemble empirical mode decomposition (CEEMD), which can process nonlinear and nonstationary signals. In this paper, the autoregressive integrated moving average (ARIMA) model, the long short-term memory (LSTM) network, the CEEMD-ARIMA combined model, and the CEEMD-LSTM combined model were constructed to predict a multiscale SPI. The validity of prediction models was determined using root mean square error, mean absolute error, and coefficient of determination (R²). Kriging interpolation was used to demonstrate the predicted results of the four models. The results revealed that the forecast accuracy of the four models increases with the increase of SPI timescales, and the highest accuracy is obtained at SPI24. CEEMD decomposition can effectively stabilize the time series. Drought prediction based on the CEEMD provides a stable premise for the single model. At each timescale, combined models obtain higher prediction accuracy than single models, which indicates that combined models are more suitable for drought prediction. The forecast accuracy of the four models in order from the lowest to highest accuracy is the LSTM model, followed by the ARIMA, CEEMD-LSTM, and CEEMD-ARIMA models (the maximum R² values are 0.8882, 0.9103, 0.9403, and 0.9846, respectively). The CEEMD-ARIMA model shows the best ability to forecast SPI values. This study explored the applicability of four drought prediction models and provided a basis for meteorological disaster prevention and mitigation efforts.

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Analysis of change and causes of evaporation for the Shiyang River Basin during the past 60 years

LI Xiaoqin,RAN Chen,ZHANG Xiaoxia,RAN Xinmin

2022, 39 (3): 745-753. doi: 10.13866/j.azr.2022.03.08

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Evaporation is an essential component in hydrological processes, and understanding the change and causes of evaporation is of importance for sustainable management of water resources. Based on the four selected meteorological stations, Wushaoling, Yongchang, Wuwei and Minqin, of which ranged along the altitudinal gradient from 1958 to 2017, the study analysed the change of evaporation and its causes based on the modified PenPan model for the Shiyang River Basin. The results shown that (1) the spatially variation of evaporation can attribute to the altitude effects, namely the evaporation decreased with a rate of 38 mm for every 100 m elevation increase, and temporally change has the significant stage differentiation features, i.e. decreased in 1958-1970, whereas increased after 1970, that particularly obvious in the plain areas of low elevation but not in mountainous area; (2) there was a good agreement with the R² greater than 0.85 between the observed evaporation and calculated by the modified PenPan model whether in daily or monthly time-scale, however, the wind speed function need amend further in order to obtain the robust performance; and (3) the yearly change of radiative component was relatively stable, but the aerodynamic component of evaporation increase fluctuated, of which was in consistent with the change of temperature and vapor pressure deficit, suggest that the rised temperature is the major reason for the increase of evaporation in Shiyang River Basin after 1970. The result means that the evaporation will increased under climate warming, it will impose more stress on the water resource sustainable management in the future.

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Precipitation gradient influence on daily greenhouse gas emission fluxes from a Qinghai Lake wetland

YANG Ziwei,CHE Zihan,LIU Fumei,CHEN Kelong

2022, 39 (3): 754-766. doi: 10.13866/j.azr.2022.03.09

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Moisture is the main limiting factor affecting the growth and development of alpine ecosystems. To explore effects of different water conditions on characteristics of greenhouse gas emissions from wetlands, wetlands at the source of the Wayan Mountain in Qinghai Lake Basin were selected. Box-gas chromatography monitored 24-hour greenhouse gas emission characteristics of wetlands and explored effects of control treatment (CK), +25% (precipitation increase 25% treatment), -25% (reduction in the daily change trend of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) under conditions of 25% rain treatment), +75% (precipitation increaseo of 75% treatment), and -75% (precipitation reduction of 75% treatment). The results showed that: (1) CO₂ emission ranged from 47.52 to 123.71 mg·m^-2·h^-1, CH₄ flux ranged from -8.50 to 6.74 µg·m^-2·h^-1, and N₂O flux ranged from -15.82 to 6.90 µg·m^-2·h^-1. (2) The diurnal variation of CO₂, CH₄ and N₂O in CK, +25% and +75% treatments showed emission status, and the diurnal variation of CO₂ in -25% treatment showed emission status, while CH₄ and N₂O showed absorption status; The diurnal changes of CO₂ and N₂O under -75% treatment were emission state, while CH₄ was absorption state, and there were significant differences among different precipitation treatments (P<0.05). (3) CO₂ had a significant positive correlation with soil temperature (P<0.05) and a significant negative correlation with soil moisture (P<0.05); There was a significant negative correlation between CH₄ and soil temperature (P<0.05) and between CH₄ and soil moisture (P<0.05); There was a positive correlation between N₂O and soil temperature (P<0.05), while there was a negative correlation between N₂O and soil moisture in CK treatment and a positive correlation in rain reduction treatment (P<0.05), and there was no obvious regularity. (4) Small succession of plant communities occurred under different water treatments. The balance of soil moisture and temperature has a significant impact on the greenhouse gas emission flux in this area, and the imbalance should be avoided to lead to the increase of greenhouse gas emissions.

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Characteristics and causes of climate change in hail in occurrence Shaanxi Province

MA Rongjun,LI Xiaofei,MAO Yanlin,XUE Yutong,WU Zhanhao

2022, 39 (3): 767-773. doi: 10.13866/j.azr.2022.03.10

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Numerous studies have shown that the number of hailstorms in Shaanxi Province (northern China) has been significantly decreasing from the late 1990s to the present, but studies on the characteristics of hailstorm changes within more specific provincial regions are lacking. To investigate the hail occurrence patterns in Shaanxi Province and to better predict and prevent hail, this paper analyzes the characteristics of hail variability in Shaanxi Province on the basis of hail data recorded at 99 ground stations from 2000 to 2019 provided by the Meteorological Center of the Shaanxi Provincial Meteorological Bureau. For the analysis of different regions in the province, the stations were divided into three regions, namely northern Shaanxi (Yan’an and Yulin), central Guanzhou (Xi’an, Baoji, Xianyang, Tongchuan, and Weinan), and southern Shaanxi (Hanzhong, Ankang, and Shangluo) according to the administrative divisions of the cities where the stations are located. The climatic characteristics of hail in each region were analyzed separately. We found that the number of hailstorms in Shaanxi Province increases from south to north; a linear fit of elevation to the mean annual hailstorm number revealed a significantly positive correlation between elevation and mean annual hailstorm number at low elevations, with each 1 m increase in elevation within 1.5 km of elevation increasing the mean annual hailstorm number by 0.0007. Furthermore, hail occurrence in Shaanxi Province increases from south to north with seasonal differences; hailstorms in northern Shaanxi occur more frequently in the summer and less frequently in the winter. The region with the next-highest number of hailstorms is Guanzhong, and an average number of hailstorms occurs in southern Shaanxi. A 5 year sliding average of the interannual hail counts was fitted linearly, and results show a decreasing trend in the overall interannual hail counts in Shaanxi Province, with the fastest decline in northern Shaanxi, followed by Guanzhong; there was no significant interannual variation in southern Shaanxi. Using monthly averages of ERA5 parameters provided by the ECMWF and considering the physical mechanisms of the hail process, eight indicators were selected and fitted to the 5 year sliding average: (1) convective effective potential energy (CAPE); (2) the K-index; (3) 2 m temperature (i.e., air mass temperature 2 m from the ground); (4) 2 m dew point (i.e., air mass dew point temperature 2 m from the ground); (5) 0 ℃ layer height; (6) convective precipitation; (7) total precipitation; and (8) cloud base height. A linear fit was made to the hail counts; results show that CAPE played a dominant role in the interannual trend of hail in Shaanxi Province, and the K-index played a dominant role in the summer in northern Shaanxi and in the spring in Guanzhong. Furthermore, the 0 ℃ layer height played a dominant role in the trend of hail counts during the summer and autumn in Guanzhong and during the spring and summer in southern Shaanxi.

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An automatic method for delineating lake surfaces in Qaidam Basin using Landsat images

WEN Guangchao,LI Xing,WU Bingjie,WANG Xiaohe,XIE Hongbo

2022, 39 (3): 774-786. doi: 10.13866/j.azr.2022.03.11

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Lakes in the Qaidam Basin maintain regional ecological balance, supply production and domestic water consumption, and protect the ecological environment. These lakes have undergone a series of changes in response to enhanced regional climate change and human activities. To analyze characteristics of lake changes and investigate casual factors, an automatic method for lake surface delineation based on Landsat remote sensing images with a different series of sensors (the Lake Water Differential Model) was proposed by understanding TOA (top-of-atmosphere) reflectance differences between water and non-water surfaces in the Koruk Lake Basin. This model is applied to extract lake information at varying times or locations. Model performance is evaluated using overall accuracy, the Kappa coefficient, and user’s accuracy, and the derived lake surfaces were compared to those from the NDWI (Normalized Difference Water Index) and MNDWI (Modified Normalized Difference Water Index) methods. These results show the following: (1) target and non-target objects are distinguished by a TOA reflectance difference. (2) Based on a stable threshold, the Lake Water Differential Model can delineate lake surfaces. Compared with the NDWI, MNDWI, and other water body information extraction methods, the Lake Water Differential Model can more effectively suppress interference factors, such as surface rivers, ice, snow, shadows, swamps, and wetlands. In areas of model application, our proposed method can achieve a performance of 99.48% of the average OA, 99.66% of user accuracy, and 0.9877 of Kappa. (3) Input data of the model can be either TOA or Landsat (level-2) surface reflectance data. (4) The model is suitable for extracting lake water information in a large area of Qaidam Basin and provides technical support for the study of lake surface dynamics.

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Evaluation of groundwater resource sustainability based on GRACE and GLDAS in arid region of Northwest China

RUAN Yongjian,WU Xiuqin

2022, 39 (3): 787-800. doi: 10.13866/j.azr.2022.03.12

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The arid region of Northwest China is a groundwater-dependent ecosystem. Groundwater resources are a strategic support for developing the arid region in Northwest China. It is important to understand the significance of groundwater changes in real time to reveal change characteristics of groundwater and regional economic development. Previously, traditional groundwater monitoring research was artificial and expensive and large-scale and long-term analyses were difficult. Research based on satellite information also lacks quantitative evaluations of groundwater sustainability. To explore recent groundwater sustainability in arid areas of Northwest China, GRACE gravity satellite and GLDAS data were used to invert groundwater storage changes and determine trend changes for 200 months from April 2002 to September 2020 in arid areas of Northwest China. The groundwater drought index, which is based on GRACE, was calculated to obtain the groundwater drought situation in the arid region of Northwest China. Finally, the GGDI was further combined with the sustainability index to quantify the reliability, resilience, and vulnerability of groundwater to evaluate the recent groundwater sustainability in the arid region of Northwest China. Results show that from 2002 to 2020, groundwater reserves were greatly reduced in the arid area of Northwest China, and the drought degree of groundwater has deepened. The average reliability, resilience, and vulnerability of groundwater is 0.495, 0.470, and 0.404, respectively, and the regional groundwater sustainability index (SI) is 0.28, which indicates a low groundwater sustainability level. This study reveals a temporal and spatial distribution and the evolution trend of groundwater sustainability in arid regions of Northwest China, which provides theoretical and supporting data for the protection and management of regional groundwater resources.

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Combined weight method based on game theory for flood risk assessment in the Wuwei Region

SU Guangquan,LYU Haishen,ZHU Yonghua,CHEN Tingxing,HUA Jiacheng

2022, 39 (3): 801-809. doi: 10.13866/j.azr.2022.03.13

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Floods are the most frequent natural disasters in the world, and the Chinese region has shown the most significant increase in flood risk worldwide. Based on the frequency of flash floods in Wuwei City, Gansu Province, a flood risk assessment method combined with subjective and objective weights and based on game theory was adopted and GIS technology was applied. Seven indicators were selected to construct a flood risk assessment index system from three aspects: disaster dangers, disaster environment sensitivity, and suffering flexibility. Then, the risk zoning chart of flood disaster in Wuwei was drawn, which showed that the overall flood risk level of Wuwei City is low and flood risk shows a decreasing distribution characteristic from southwest to northeast. The results are in good agreement with historic flood event data in which the highest risk area accounts only for 4.94% of the total area, which is concentrated at the junction of Liangzhou District and Gulang County and southwest of Tianzhu County. The sum of the lowest risk area and the lower risk area accounts for 43.84% of the total area, which is concentrated in the eastern desert area of Minqin County. The main sources of flood risk vary among counties in Wuwei City. The risk of disaster-causing factors presents a belt-like distribution characteristic that decreases from southwest to northeast. The highest risk areas are distributed mainly in the Qilian Mountains of Tianzhu County, and the lowest risk areas are concentrated in lower reaches of the Shiyang River in the northeast. The distribution of the disaster environment sensitivity is relatively uniform except for the Qilian Mountains with higher stability. There are obvious differences in the vulnerability of disaster-bearing bodies, and the vulnerability at the junction of Liangzhou County and Gulang County is much higher than that of other regions. The entropy method and analytic hierarchy process are used for comparison with the game theory combination weighting method, which demonstrates that the combination weighting method of game theory can reduce the subjectivity of the single weighting method, improve the accuracy of the flood risk map, and provide valuable information for flood management.

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Spatiotemporal variations of stable hydrogen and oxygen isotopes in Xinjiang tap water

XIA Yijie,WANG Shengjie,ZHANG Mingjun

2022, 39 (3): 810-819. doi: 10.13866/j.azr.2022.03.14

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Stable hydrogen and oxygen isotopes are natural tracers reflecting the water cycle process, and tap water is an important domestic water source. The variation of stable hydrogen and oxygen isotopes in tap water is useful for tracing sources of domestic water supply and provides a reference for rational water resource management. The measured isotopic data of 352 tap water samples in Xinjiang were applied to analyze the spatiotemporal variation of stable hydrogen and oxygen isotopes as well as deuterium excess (d-excess; d = δ²H - 8δ¹⁸O) in tap water. The results show that the d-excess of the tap water line in Xinjiang is δ²H = 7.67δ¹⁸O + 10.54 (R² = 0.92). The value of δ²H ranges from -105.57‰ to -37.82‰ on a monthly basis, and δ¹⁸O ranges from -14.48‰ to -6.67‰. The d-excess fluctuates from 1.89‰ to 24.38‰. The stable hydrogen and oxygen isotopes, as well as d-excess, exhibit seasonal variation in both northern and southern Xinjiang, and the seasonal difference in southern Xinjiang is greater than that in northern Xinjiang. The BW model is applied to map the stable hydrogen and oxygen isotopes in tap water. Tap water in southern Xinjiang presents higher isotopic values than northern Xinjiang, and water in the mountainous regions shows lower isotopic values than does water in the low-lying basins.

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Hydrogen-oxygen isotope characteristics of water bodies in the Xiangride-Qaidam River Basin and its influencing factors

HE Qixin,CAO Guangchao,CAO Shengkui,CHENG Mengyuan,DIAO Erlong,GAO Siyuan,QIU Xunxun,ZHAO Meiliang,CHENG Guo

2022, 39 (3): 820-828. doi: 10.13866/j.azr.2022.03.15

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In this paper, 59 sets of samples from different water bodies such as lake water, river water, groundwater, well water, and snow in the Xiangride-Qaidam River Basin were used to measure δ²H and δ¹⁸O of indoor samples; analyze their characteristics; and explore their influencing factors, deuterium excess parameter values, and river water variation along the river. Results show that (1) the hydrogen and oxygen isotope characteristics of the water bodies in the Xiangride-Delta River Basin are different. In addition, the enrichment of δ¹⁸O during water cycle is presented in the following order: lake water > ice > groundwater > river water > well water > snow. River water and groundwater are closely linked hydraulically, and the evaporation of river water and lake water is the strongest among the water bodies in the basin. (2) The maximum values of lake water δ²H and δ¹⁸O are observed in Hobson Lake at the bottom of the basin, and the minimum values are observed in the upper east branch of the river water collected from winter to the wrong lake. It shows that the δ²H and δ¹⁸O of lake water in the northern part of the Qinghai-Tibet Plateau are more positive than those in the south, and there is an obvious elevation effect. (3) Moreover, a significant linear relationship is found between river water δ²H and δ¹⁸O: δ²H = 4.93 δ¹⁸O - 29.6 (R²=0.97). The enrichment of hydrogen and oxygen isotope components is primarily controlled by the influence of river evaporation; strong evaporation effect in the upper reaches of the river; and high deuterium excess caused by high altitude, low temperature, and low air humidity. (4) Compared with water, the depletion of hydrogen and oxygen-stable isotopes in ice at the same location results from repeated evaporation and condensation of local water vapor.

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An assessment of groundwater, surface water, and hydrochemical characteristics in the upper valley of the Bortala River

DING Qizhen,LEI Mi,ZHOU Jinlong,ZHANG Jie,XU Dongsheng

2022, 39 (3): 829-840. doi: 10.13866/j.azr.2022.03.16

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This paper examined the hydrochemical characteristics and water quality status of groundwater and surface water in the upper valley of the Bortala River, Xinjiang. The examination was based on 36 groups of water sample data. Hydrochemical characteristics and their influencing factors were studied by Piper diagram, correlation analyses, Gibbs diagram and ion ratio, and the entropy-Bayesian water quality evaluation model, Wilcox and USSL diagrams were used to evaluate water quality. Results of hydrochemical analyses showed the following: (1) the mechanical well water, spring water, and river water in the study area were weakly alkaline fresh water, and total hardness (TH), F^-, $N O 3 -$ and total dissolved solids were aligned as mechanical well water > spring water > river water, whereas $H C O 3 -$ and Ca²⁺ were the dominant anions and cations, respectively. Contents of each component in the upper Bortala River increased along the river. (2) The main hydrochemical types of mechanical well water and spring water in the area were the HCO₃-Ca type, and main hydrochemical types of river water were the HCO₃-Ca and HCO₃·SO₄-Ca·Na types. Hydrochemical characteristics were controlled mainly by rock weathering, and hydrochemical components were mainly from carbonate rock weathering. Evaporation rock dissolution also occurred and it was affected by cation exchange and human activities. The water quality evaluation of drinking water showed that 82.6% of mechanical well water and 100% of spring water were suitable for drinking, basically suitable for drinking, or suitable for drinking after proper treatment. Water sample points that were not suitable for drinking were affected mainly by excessive Fe, F^-, and $N O 3 -$ . River water, well water, and spring water were suitable for the evaluation of irrigation water quality.

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Temporal and spatial variation change of groundwater environment in the salinized irrigation districts under the background of water-saving reconstruction

CUI Jiaqi,LI Xianyue,SHI Haibin,SUN Yanan,MA Hongyu,JIAN Wenhao

2022, 39 (3): 841-852. doi: 10.13866/j.azr.2022.03.17

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Groundwater is an important resource in the arid region of Northwest China, and large-scale water-saving transformation projects are bound to cause changes in the groundwater environment. On the basis of the spatial-temporal probability distribution, the spatial-temporal variations of groundwater depth and salinity were explored in the Yongji irrigation area of the Hetao Irrigation District before the Agricultural Water-saving Transformation Project (AWSTP) (1998-2000), at the initial stage (2001-2006), the middle stage (2007-2012), and the late stage (2013-2018). The Kriging method was used to analyze the probability distribution of groundwater depth and salinity under different threshold conditions before and after the AWSTP. The results show that as the AWSTP advanced, both the buried depth of groundwater and groundwater salinity increased. In the late stage of the AWSTP (2013-2018), the average buried depth of groundwater increased by 0.36 m, and groundwater salinity increased by 1.37 g·L^-1 compared with preproject measures (1998-2000). On a spatial scale, 33% of the high-probability area of shallow groundwater (i.e., groundwater depth less than 2.0 m; probability of occurrence above 0.5) transitioned to the high-probability area of deep groundwater (i.e., groundwater depth greater than or equal to 2.0 m). Shallow groundwater has been affected by urbanization (with a large amount of groundwater exploitation), and groundwater depth has increased significantly in the central, southern, and northern parts of the area. The high-probability areas of groundwater salinity less than 2.5 g·L^-1 and greater than or equal to 3.0 g·L^-1 have expanded by 17% and 4%, respectively. In other words, the south-central part of the study area tended to desalinate, whereas the northern and eastern edges tended to mineralize. The 21 year average deep groundwater (i.e., groundwater depth greater than or equal to 2.0 m) with high-probability areas accounted for 39% of the total area and is mainly concentrated in the south-central area. The high-probability areas with salinity less than 2.5 g·L^-1 accounted for 67% on average, and the high-probability areas with salinity greater than or equal to 3.0 g·L^-1 were concentrated in the northern region and accounted for 27% of the total area. The AWSTP has resulted in an increase in groundwater depth (i.e., effectively reduced the groundwater level). Although groundwater salinity is increasing, the mineralized areas are mostly concentrated near the drains. Further improvements to the drainage system are recommended.

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Comparison of phytoremediation effects of Medicago sativa and Coreopsis basalis on crude-oil-contaminated soil in eastern Gansu Province

JING Mingbo,WANG Jincheng,ZHANG Wei,ZHOU Lihui,ZHANG Shaopeng

2022, 39 (3): 853-862. doi: 10.13866/j.azr.2022.03.18

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Phytoremediation is the most eco-friendly, economically sustainable, cost-effective technology available for the biodegradation of soil pollutants, while crude-oil-contaminated soil is susceptible to many factors in the process of phytoremediation, including climatic conditions, landform and soil properties, etc. The main properties of the Loess Plateau are high degree of salinization, an arid, and lack of soil fertility, thereby there are obvious regional vegetation distribution in this area. Compositae have strong drought resistance and tolerance and it is a ubiquitous plant growing wild and widely distributed throughout Northwest China. However, the phytoremediation effect of crude oil contaminated soil by Compositae has not been further studied in the Loess Plateau. Thus, in order to analyze and compare the phytoremediation efficiency of Medicago sativa and Coreopsis lanceolata on oil-contaminated soil in eastern Gansu Province of the Loess Plateau. The indigenous plants M. sativa and C. lanceolata were selected as the test plants, and a five months site remediation experiment was conducted in Changqing Oilfield Company, Qingyang City of Gansu Province. The changes of TPH (Total petroleum hydrocarbon, TPH) removal rate, plant growth index, soil physical-chemical properties and enzyme activities as well as microbial community structure in root-zone soil of M. sativa and C. lanceolata under different crude oil concentrations, i.e., light pollution group (TPH=3%), moderate pollution group (TPH=7%) and heavy pollution group (TPH=9%), were measured. We found that: (1) With the crude oil concentration increase from 3% to 9%, the removal rates of TPH in the root-zone soil of M. sativa were 69.88±4.16%、42.59±3.94%、19.20±2.77% and 2.01±0.19%, while were75.33±2.91%、74.87±2.79%、42.47±1.99% and 2.20±0.51% in the root-zone soil of C. lanceolata, respectively. (2) The emergence rate and chlorophyll a/b value of the two tested plants were not significantly affected by crude oil concentrations at 3%, while the effects of oil concentrations ranged from 7% to 9% on seedling emergence rate, chlorophyll a/b value, aboveground and underground dry weight, root vitality and root-shoot ratio of M. sativa were relatively significant (P<0.05). (3) Oil concentration ranged from 3% to 7% had relatively little inhibition on soil available P content in the root-zone soil of M. sativa (P<0.05), while the soil pH, urease and alkaline phosphatase activities in the root zone of C. lanceolata were significantly higher than those of M. sativa in the concentration ranged from 7% to 9% (P<0.05). (4) High throughput sequencing results showed that the relative abundance of crude oil degrading bacteria, i.e., Alcanivorax, Marinobacter, Halanaerobium, Halomonas and Nocardioides, etc. in the root-zone soil of C. lanceolata were significantly higher than those in the M. sativa (P<0.05). (5) Variance decomposition results indicated that the inhibition of oil concentration on the physiological characteristics of M. sativa was the decisive factor limiting the root zone soil TPH removal rate, while the combined effect of soil physicochemical × microbial characteristics was the main environmental factor determining the root zone soil TPH removal rate of C. lanceolata higher than that in the treatment group of M. sativa (P<0.05). In conclusion, the phytoremediation efficiency of C. lanceolata on crude-oil-contaminated soil in eastern Gansu Province of the Loess Plateau is better than that of M. sativa.

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Distribution pattern and driving mechanisms of the sand plant Leymus racemosus in the Junggar Basin

ZHANG Lin,ZHANG Yunling,MA Songmei,ZHANG Dan,HE Lingyun

2022, 39 (3): 863-871. doi: 10.13866/j.azr.2022.03.19

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Our objective was to simulate and predict ecological suitability, possible suitable distribution range, spatial distribution characteristics, and possible response to future climate change of Leymus racemosus (Lam.) Tzvelev in Xinjiang. The data in this study were based on 24 natural distribution sites and eight environmental factors of Leymus racemosus and were analyzed using GIS spatial analysis and the MaxEnt model. The suitable distribution range and changes in the distribution pattern of Leymus racemosus in Xinjiang under the present climate (1970-2000), the 2050 period (2041-2060), and the 2070 period (2081-2100) for the “Middle of the Road” narrative (SSP2) of the shared socioeconomic pathways were analyzed. We used multivariate environmental similarity surface analysis and the most dissimilar variable to explore the key climatic factors. Under the present climate, the suitable distribution area of Leymus racemosus accounts for 5.57% of the total area of Xinjiang, mainly concentrated in the low-cover grasslands near the Irtysh River. Compared with the present climate, the suitable habitat of Leymus racemosus will be significantly reduced by 0.99% and 1.33% in 2050 and 2070, respectively; its suitable habitat will be highly fragmented, and the center of its suitable habitat will move to the Northwest at higher latitudes and higher elevations. Factors that mainly influence the suitable distribution of Leymus racemosus in Xinjiang are the precipitation of the driest month, precipitation seasonality (C_v), and the standard deviation of seasonal temperature variation.

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A health evaluation of a Haloxylon ammodendron plantation in the Shiyang River lower reaches

LI Xuening,XU Xianying,ZHENG Guiheng,MA Quanlin,ZHANG Yunian,LIU Hujun,ZHAO Peng,YANG Xuemei

2022, 39 (3): 872-882. doi: 10.13866/j.azr.2022.03.20

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A Haloxylon ammodendron forest is a protected ecological forest in a desert area. It not only reduces the impact of wind sand disasters, controls soil erosion, and maintains the ecological stability of desert oasis but also improves soil quality and increases carbon storage of the desert ecosystem. Recently, the H. ammodendron forest has been declining in Minqin. Determining sustainable management of the artificial H. ammodendron forest is critical for the health status and function of wind prevention and sand fixation for this forest over time. In this study, the artificial H. ammodendron forest in the lower reaches of the Shiyang River was selected as the research focus. Through a literature review and expert consultation, a health evaluation system of the artificial H. ammodendron forest with 5 primary indicators and 19 secondary indicators was constructed. Analytic hierarchy process combined with an entropy method was used to determine the weight of each index. Based on the ecological health index (HI) and field survey data, the health status of the artificial H. ammodendron forest was evaluated. Results show the following: the HI value of the artificial H. ammodendron forest in the lower reaches of the Shiyang River is between 0.50 and 0.67; the average comprehensive HI is 0.617, which is in a sub-health state; and to improve the stability of the artificial H. ammodendron forest, we should take measures such as stubble and enclosure.

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Effects of deficit irrigation and film mulching on biomass and production of Cyperus esculentus in the southern Xinjiang Basin

DING Ya,YANG Jianming,LI Li,ZHANG Zhihao,ZENG Fanjiang

2022, 39 (3): 883-892. doi: 10.13866/j.azr.2022.03.21

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The effect of drip irrigation and film mulching of Yousha beans in the southern Xinjiang basin and the optimal irrigation system were explored to provide a reference for constructing a water-saving and high-yield management and cultivation mode. A 1-year experiment was conducted under conditions of film mulching (M) and no film mulching (NM). Addtionally, three water control levels were set, the irrigation frequency was 6-10 days, irrigation amounts of T1 and T2 were 3431.40 m³·hm^-2and 4133.85 m³·hm^-2, respectively, and a local common irrigation amount was used as the control (CK, 5316.45 m³·hm^-2) yield and water use efficiency. Results showed that the density of Cyperus esculentus. was significantly affected by water treatment (P<0.05), but the root: shoot ratio was not significantly affected by water treatment (P>0.05). Contents of crude fat, soluble starch, and soluble sugar of grass covered with a plastic film increased by 58.82%, 3.35%, and 17.20%, respectively, on average compared with those without plastic film. Contents of crude fat, soluble starch, and soluble sugar of tubers covered with plastic film were higher than those without plastic film and increased by 7.48%, 2.56% and 2.55%, respectively. Furthermore, there was no significant difference between water treatments (P>0.05) but they reached the maximum in the T2 treatment. The yield and water use efficiency increased first and then decreased with an increased irrigation amount. Under film mulching conditions, the yield of grass and tubers under the T2 treatment were the largest and were 3974.55 kg·hm^-2 and 5253.85 kg·hm^-2 and significantly increased by 6.45% and 36.95%, respectively, compared with the CK treatment (P<0.05). Compared with a condition of no film mulching, the average yield of T2 and CK significantly increased by 29.41% and 34.76%, respectively (P<0.05). The water use efficiency of grass and tubers in the T2 treatment was significantly higher than the CK by 38.63% and 34.33% (P<0.05), respectively. Compared with T2 (film mulching), the water use efficiency of grass and tubers treated with the CK and T2 under no film mulching conditions was significantly increased by 38.91% and 34.33%, respectively (P<0.05). There was no significant difference in the water use efficiency of grass (P>0.05), but there was a significant difference in the water use efficiency of tubers (P<0.05). Therefore, under film mulching conditions, the irrigation quota was 4133.85 m³·hm^-2, which improved not only the quality and yield of Cyperus esculentus but also the water use efficiency and saved water resources, that is, under conditions of film mulching, the irrigation mode with an irrigation quota of 4133.85 m³·hm^-2 showed economic and water-saving benefits.

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Response of drought on water and nitrogen utilization and carbohydrate distribution of Populus × euramericana ‘Biyu’ cuttings

SHANG Jiazhou,ZHAO Yuqi,WANG Weifeng,GAO Tianhui,ZONG Yuzheng

2022, 39 (3): 893-899. doi: 10.13866/j.azr.2022.03.22

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The ecophysiological response of poplar to soil drought and drought resistance strategies among species remained unclear. In this study, Populus×euramericana ‘Biyu’ cuttings grown in pots were used as materials. Changes of leaf gas exchanges, water and nitrogen use traits, growth, and carbohydrate allocation among organs under 2-year drought were investigated. Results showed that the leaves of 1-year-old poplar cuttings became smaller but thicker under drought with stable stomatal conductance, and transpiration rate. The net photosynthesis rate decreased by non-stomatal inhibition, and the transient water and nitrogen use efficiency significantly decreased. In the second year, the leaves became even smaller and thicker with a higher carbon and nitrogen ratio. However, leaf nitrogen contents remained unchanged, which could improve leaf drought resistance. The net photosynthesis rate increased slightly, and transient water and nitrogen use efficiency remained stable. Moreover, moderate drought significantly increased whole-plant nitrogen use efficiency. Under a 2-year drought treatment, the growth significantly decreased. More biomass and non-structural carbohydrates allocated into the stem but not in the root system, and the root and shoot ratio became smaller, which are detrimental to the water and nitrogen uptake in the root and whole-plant drought resistance. Therefore, P.× euramericana ‘Biyu’cuttings can reduce water consumption in smaller but thicker leaves under drought, with high leaf nitrogen content, but this response could reduce the leaf area used for photosynthesis, resulting in decreased growth and smaller roots. These results indicated that P.×euramericana ‘Biyu’ has low drought resistance, which is not suitable for large-scale afforestation in arid and semi-arid areas.

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Straight root tensile properties of Salix psammophila in response to cyclic loading

HU Jinghua,LIU Jing,BAI Luyi,ZHANG Xin,LAN Pengbo,YUAN Yanan

2022, 39 (3): 900-907. doi: 10.13866/j.azr.2022.03.23

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To clarify mechanical properties of straight roots in response to repeated loading and unloading induced by simulated high wind drawing, an axial cyclic load test was applied to straight roots of Salix psammophila. These roots had a diameter of 1-5 mm in the Shendong mining area and a TY8000 servo-type strong force was used to reveal the soil-fixing ability of plants in wind-eroded areas after their roots were repeatedly stressed by strong long-term winds. Results show the following: (1) the tensile force of straight roots after cyclic loading was positively correlated with the diameter based on a power function; the tensile strength after cyclic loading was negatively correlated with root diameter based on a power function, which was similar to the relationship between tensile force, tensile strength, and root diameter under a monotonic load. (2) Compared with the monotonic load, the tensile force and tensile strength after cyclic loading of straight roots of all diameters were significantly enhanced (P<0.05), and the tensile force and tensile strength of 1-2 mm, 2.5-3.5 mm, and 4-5 mm roots increased by 60%, 60%, 48%, 50%, and 31%, 32%, respectively. (3) In the cycle process, the force-displacement curve of straight roots showed obvious cycle characteristics with increasing cycle number; the hysteresis loop spacing is gradually close to closing; and as the area decreases, the capacity of resistance to plastic deformation becomes worse, which tends to be stable. The accumulated elongation of straight roots increases with increasing cycle number, which can be divided into a rapid growth stage and a slow growth stage. (4) The elastic stress, ultimate stress, and elasticity modulus of straight roots was negatively correlated with root diameter after monotonic load and cyclic load, and the accumulated elastic strain and ultimate strain have no relationship with root diameter. The elastic stress, ultimate stress, and accumulated elastic strain after cyclic loading of all diameters was enhanced, the ultimate strain was monotonic load > cyclic load, and the elastic modulus has no relationship under different loads.

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Effect of saline water drip irrigation on salt ions distribution for the Haloxylon ammoedndron-Cistanche deserticola association (H-C association) and quality of Cistanche deserticola Ma

LIU Ling,LUO Jianhong,LI Bingwen,XU Xinwen,FAN Jinglong,MA Zhiguo

2022, 39 (3): 908-915. doi: 10.13866/j.azr.2022.03.24

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The impact of saltwater drip irrigation on salt ion distribution and the quality of Cistanche cistanche Ma and Haloxylon ammodendron-Cistanche deserticola Ma (H-C) association during artificial cultivation in the planting base of C. deserticola on the Taklimakan Desert edge was examined. We selected four sample plots with obvious differences in irrigation mineralization to collect samples of H. ammodendron and C. deserticola. We also collected and analyzed the salt ion content in soil, H-C association, and main medicinal components of C. deserticola from different locations. Results showed the following: (1) The salt content of roots, main stems, and assimilated branches of C. deserticola inoculated by drip irrigation with high salinity brackish water was in the order of assimilating branch>coarse roots>fine roots>stems; the salt content in C. deserticolais was similar to that of the root system. (2) The contents of total salt, Na⁺, and Cl^- in C. deserticola increased with an increase of irrigation salinity and soil salinity; the proportion of K⁺ in C. deserticola accounts for one-third of the total salt and can accumulate K⁺, but there is no significant difference in K⁺ content with irrigation salt concentration. (3) The synthesis of phenylethanol glycosides, which are the main medicinal ingredient in C. deserticola, increased with an increase of irrigation salinity, and salt stress promotes the accumulation of a main pharmacological component in C. deserticola. In consequence, high salinity saline water drip irrigation can improve the quality of C. deserticola. And it is necessary to pay attention to the effect of long-term high salinity stress on the host H.ammodendron, so it is important to develop a reasonable irrigation system.

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Differentiation characteristics and main influencing factors of soil salinization in the West of Hetao Irrigation Area

SU Chunli,JI Qiannan,TAO Yanzhen,XIE Xianjun,PAN Hongjie

2022, 39 (3): 916-923. doi: 10.13866/j.azr.2022.03.25

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As a result of long-term irrigation from the Yellow River, the Hetao Irrigation Area has experienced extensive soil secondary salinization, which seriously affects the development of the regional economy and ecology. The degree, type, and distribution characteristics of soil salinization in the western Hetao Irrigation Area, and the main factors affecting soil salinization are investigated. Results show that more than 50% of the soil samples in the study area were salinized to varying degrees, which is distributed in patches and blocks. The degree of soil salinization in the north and southeast was serious than that of other parts of the study area, especially in the depressions along the Main canal and Huangji canal. The main types of soil salinity were SO₄-Na and SO₄·Cl-Na. The average total dissolved solids (TDS) of groundwater in the study area was 2.13 g∙L^-1, which is classified as brackish water. The average buried depth of groundwater level is 4.65 m, and 65% of the sampled wells were less than 3 m. High TDS groundwater, which is resulted from long-term flood irrigation and strong evaporation, is the direct cause of soil salinization. The main factors affecting soil salinization in alluvial plains include the elevated salinity of groundwater, shallow groundwater levels caused by agricultural irrigation, and strong evaporation of phreatic water.

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Effects of vegetation restoration on soil stoichiometry in the eastern Hobq Desert

LIU Yuan,LI Xiaojing,DUAN Yuxi,LI Bo,WANG Weifeng,LIU Zongqi,FENG Tao

2022, 39 (3): 924-932. doi: 10.13866/j.azr.2022.03.26

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To clarify the impact of vegetation restoration on stoichiometric characteristics, aeolian sandy soil, mobile sandy land, semi-fixed sandy land, Artemisia ordosica-fixed sandy land, and Salix psammophila-fixed sandy land in the eastern part of Kubuqi were selected as research areas. This research analyzed temporal and spatial changes and the correlations among vegetation biomass and soil carbon, nitrogen, and phosphorus stoichiometry at different depths (0-60 cm). Results show the following: (1) the content of soil C and N significantly increased with vegetation restoration, whereas the content of soil P slightly increased and reached a maximum value in Salix cheilophila-fixed sandy land (5.86 g·kg^-1, 0.41 g·kg^-1, 1.74 g·kg^-1), the content of C, N, and P in soil decreased with soil layer depth, and the difference in the P content in the soil layer was small. (2) The soil stoichiometric ratio at different stages or soil layers was significantly different with vegetation restoration. Soil C:N first decreased and then increased, whereas C:P and N:P increased gradually. Soil C:P and N:P decreased gradually with deepening of the soil layer, whereas C:N had no obvious change. (3) Soil C, N, and P were significantly and positively correlated with aboveground and litter biomass and there was no significant correlation between soil C:N and C:P and N:P. However, soil C:P was positively correlated with N:P, and soil C:P and N:P were positively correlated with aboveground, underground, and litter biomass. In conclusion, artificial planting to promote vegetation restoration can significantly affect the content and stoichiometric characteristics of soil C, N, and P to effectively improve soil physical and chemical properties and enhance the carbon and nitrogen sequestration capacity of the desert ecosystem.

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Soil mechanical composition and soil nutrient content of Reaumuria soongorica nebkhas

LI Xiaole,WEI Yajuan,DANG Xiaohong,DAI Yuzhi,ZHAI Bo,CHI Xu,WU Huimin

2022, 39 (3): 933-942. doi: 10.13866/j.azr.2022.03.27

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Understanding the effects of desert shrubs on the soil structure and nutrient spatial heterogeneity of nebkhas is important for maintaining the stability of desert ecosystems and preventing regional desertification. In this study, soil grain-size composition and soil nutrient accumulation of Reaumuria soongorica in the steppe desert transition zone of Baiyinengel Nature Reserve, Hangjin Banner, Ordos City, were analyzed. (1) The soil was mainly fine sand (content ranging from 36.34% to 65.31%); the clay and silt content was less than 7.00%. (2) Reaumuria soongorica protects nebkhas from wind erosion and also plays a role in fixing quicksand. The sediment of nebkhas tended to be refined, and particle sorting became successively worse from the leeward side to the windward side and the open space between nebkhas. The particle distribution peak became wider and flatter, and the fractal dimension became smaller. The distribution of soil particle size composition in the shrub nebkha was more symmetrical than that in the open space between the mounds. (3) The soil organic matter (SOM), alkaline hydrolyzed nitrogen (AN), available phosphorus (AP), and available potassium (AK) contents on the windward and leeward sides of the nebkha increased by 29.37% and 40.63%, 23.49% and 35.12%, 62.72% and 66.45%, 30.10% and 22.75% (P<0.05), respectively, and RII (Relative Interaction Intense) > 0. Under the influence of wind erosion and plant feedback, nutrients were enriched in nebkhas, forming “fertile islands. ”

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Monitoring and prediction of ecological environmental quality in the Yanhe River Basin based on the remote sensing ecological index

WANG Lixia,ZHAO Rui,LIU Zhao,ZHANG Shuangcheng,KONG Jinling,YANG Yun

2022, 39 (3): 943-954. doi: 10.13866/j.azr.2022.03.28

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Based on Landsat remote sensing images of the Yanhe River Basin in 1998, 2004, 2010, and 2016, the remote sensing ecological index (RSEI) was calculated to analyze and evaluate temporal and spatial changes of environmental quality in the Yanhe River Basin. The CA-Markov model was also used to simulate and predict the ecological environment in 2022 and 2028. Results show that (1) the RSEI has good applicability in the Yanhe River Basin and can be used to monitor and evaluate temporal and spatial characteristics of the ecological environment in the basin. (2) For the time scale, the mean RSEI value changed from 0.392 in 1998 to 0.530 in 2016 and showed an increasing trend year by year. On a spatial scale, the RSEI gradually increased from southeast to northwest. RSEI grades were divided by 0.2 intervals and the total area of RSEI grades was mainly poor and moderate. These grades accounted for a total of 62.4%, which was distributed mainly in the valley of the basin, while the high grade area accounted for the least, at approximately 8.1%, which was distributed mainly in the mountainous region of the southern part of the basin. (3) There is a large spatial difference between the effects of natural and human factors on changes in environmental quality in the watershed. In the area with an altitude of 1200-1800 m, the change of eco-environmental quality was affected mainly by natural factors. However, areas below 1200 m are affected mainly by human activities. (4) It is predicted that by 2028, the ecological environment quality of the basin will continue to improve, and the area of good and high grade will account for 66%, but there are still big problems in the northwest of the basin because of the fragile ecological environment background.

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Analysis of cultivated land’s spatio-temporal changes and influencing factors in Gansu Province in recent 25 years

HOU Qingqing,CHEN Ying,PEI Tingting,JI Zhenxia,XIE Baopeng

2022, 39 (3): 955-967. doi: 10.13866/j.azr.2022.03.29

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Studying the temporal and spatial changes and driving factors of cultivated land resources have important practical significance for improving regional food security, strictly cultivated land protection red lines, and formulating cultivated land protection policies and measures. Based on the land use data of Gansu Province in 1995, 2005, 2015, and 2020, with the support of ArcGIS and GeoDa. This paper comprehensively analyzed the temporal and spatial evolution characteristics of cultivated land resources in Gansu Province in the recent 25 years from the grid, reseau, and county scale using geographic detectors to detect the main driving factors causing cultivated land changes. The results showed that (1) the cultivated land in Gansu Province was 1.6% from 1995 to 2020, increasing from 1995 to 2005 and decreasing from 2005 to 2020. The cultivated land mainly flowed to grassland, forest, and construction land, while the unused land mainly moved to cultivated land and grassland. (2) The spatial distribution of cultivated land showed the typical characteristics of “more in the southeast and less in the northwest.” (3) The spatial distribution of cultivated land was influenced by the interaction of natural and socio-economic factors. The interaction between population and land development intensity was the main reason for the difference in the spatial distribution of cultivated land in Gansu Province in 1995, 2005, and 2015. However, the interaction between temperature and precipitation has become the dominant factor affecting cultivated land in 2020. Findings from this study can serve as a scientific basis for the protection and management of cultivated land in Gansu Province.

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Land-use change and ecological environment effects on Fenhe River Basin

SU Yingqing,ZHANG Enyue,LIU Yuan,LIU Geng,LIN Fei

2022, 39 (3): 968-977. doi: 10.13866/j.azr.2022.03.30

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Research on land-use changes and ecological environment effects is important to understand regional ecological environment changes and promote the coordinated development of regional economy and environment. In this paper, the Fenhe River Basin was selected as the study area. Based on the land use and normalized vegetation index data in five periods (2000, 2005, 2010, 2015, and 2018), land-use changes and ecological effects in the study area in 2000, 2005, 2010, 2015, and 2018 were comprehensively analyzed using land-use dynamic attitude, geological information map, ecological value index, and fractional vegetation cover. Results showed that (1) from 2000 to 2018, the construction land and forest land in the basin showed an increasing trend; the growth areas were 1350.90 km² and 85.50 km², accounting for 92.83% and 0.96%, respectively. The cultivated land and grassland showed a slight downward trend, and the reduction areas were 729 km² and 674.10 km², respectively. The reduction rates were -5.02% and -7.63%, respectively. Waters and unused land maintained a multi-year average of 297 km² and 7.92 km², respectively. The spatial pattern showed that the construction land and cultivated land were concentrated in the core area of the basin, and grassland and forest land were concentrated in the edge area. (2) Comprehensive land-use dynamic degree, land transfer map, and land-use fluctuation trend of each time series were similar, and the evident indigenous change area was primarily located in the basin and its transition zone in the mountainous area. The comprehensive land-use dynamic degree for many years was 4.34%. The single land-use dynamic degree and land-use fluctuation were the highest in construction land and forest land, respectively. (3) Based on the influence of different dominant land-use types, the temporal evolution of the ecological value index showed a wavy “decline-growth-decline” curve; fractional vegetation cover showed “growth-decline-growth” evolution characteristics, and spatial pattern overlapped with spatial patches in land-use change regions. Given the terrain structure, land-use standards, and socio-economic and environmental protection policies, land-use changes in the future basin may increase, and stress on the ecological environment will increase.

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Comprehensive evaluation of drought tolerance of six forage species at the seedling stage

TIAN Xiaoxia,WEI Xiaofeng,WEI Hao,XU Mingshuang,MAO Peichun

2022, 39 (3): 978-985. doi: 10.13866/j.azr.2022.03.31

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Artificial grassland can be planted in arid and semi-arid areas to screen forage species with strong drought resistance at the seedling stage. A water controlling experiment was conducted to determine the effect of drought stress on six forage species by adopting the pot culture method. The plant height (PH), shoot dry weight, root dry weight (RDW), root-shoot ratio (RSR), relative water content (RWC), proline content (Pro), soluble protein content (SP), antioxidant enzyme activity, and other indices of six materials were measured. Based on the drought resistance coefficient of each individual index, correlation analysis, principal component analysis, and subordinate function analysis were performed to comprehensively evaluate the drought resistance of six forage species. Result showed that drought stress had significant effects on the growth and physiological indices of six test materials. Correlation analysis showed that 12 indices such as PH, growth rate, and RDW were positively correlated with one another, but a negative correlation was observed between the 12 indices and malondialdehyde content. Principal component analysis showed that the contribution rate of four principal components could reach 98.40%, which could represent most of the data information of six test materials. The drought resistance (D value) of six test materials was comprehensively evaluated using a subordinate function method and weight coefficients, and the drought resistance ability of test materials was presented in the following order: Elytrigia elongatum > Elymus dahuricus > Astragalus adsurgens > Bromus inermis > Medicago sativa > Agropyron cristatum. Moreover, the D value was found to be significantly and positively correlated with PH (0.984^**), RDW (0.948^**), free proline content (0.971^**), and soluble protein content, indicating that it can be used as a good indicator for screening drought tolerance of similar materials at the seedling stage.

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Compensation effect of nitrogen fertilizer post-shift on water-deficient cotton yield at different stages

DAI Jianmin,HE Qingyu,XIE Ling,DOU Qiaoqiao,ZHANG Jusong

2022, 39 (3): 986-995. doi: 10.13866/j.azr.2022.03.32

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The flowering and boll stages are the most critical periods for the formation of cotton. To explore the compensation effect of nitrogen fertilizer backward shift on the yield of water-deficient cotton at the flowering and boll stages, Xinluzao No. 45 was used as the test material and a split-plot test design was adopted. The drip irrigation amount in two flowering and boll stages was determined as follows: a conventional irrigation amount of 2410 m³·hm^-2 (W1) was the control and the deficit irrigation amount was 1668 m³·hm^-2 (W2). N1 (flowering period fertilizer: boll period fertilizer 3:3), N2 (flowering period fertilizer: boll period fertilizer 2:4) and N3 (flowering period fertilizer: boll period fertilizer 4:2) was explored. Results showed that under the same nitrogen fertilizer conditions, the leaf area index (LAI) and net photosynthetic rate (Pn) of the water deficit were significantly lower than those of the normal irrigation treatment; was prolonged and the accumulation and proportion of dry matter in reproductive organs decreased significantly; the number and weight of bolls per plant decreased by an average of 11.7% and 45.6%, respectively, compared with normal irrigation; and the yield of seed cotton decreased by an average of 17.3%. The water consumption and partial productivity of nitrogen fertilizer decreased by 35.49% and 15.97% on average, respectively, and water use efficiency increased by an average of 16.77%. Compared with normal irrigation and under a water deficit condition at the flowering and boll stages, the LAI and Pn of cotton treated with nitrogen fertilizer (N2) increased compared with that of N1 and N3 and the expression was N2 > N1 > N3. The dry matter accumulation, Δt, and Vm performed best under fertilization, GT was the most coordinated, and the transfer rate from vegetative growth to reproductive growth of cotton was the highest at 68.25%. The number of bolls per plant and weight of single bolls increased by 10.40%, 16.02%, 8.41%, and 11.61%, respectively, and the yield of seed cotton increased by 7.32% and 13.88%, respectively. Water consumption, water use efficiency, and partial nitrogen fertilizer productivity were as follows: N2 > N1 > N3. In summary, a backward shift in nitrogen fertilizer can increase the LAI and Pn of cotton in the flowering stage, slow down the decline of LAI and Pn in the late boll stage, increase dry matter accumulation in the aerial part and increase the proportion of reproductive organs, and regulate the yield and its components to reduce the impact of water stress.

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