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15 November 2020, Volume 37 Issue 6 Previous Issue    Next Issue

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Evapotranspiration in the Jinghe River Basin based on the surface energy balance system ZHENG Qian-qian, DAI Peng-chao, ZHANG Jin-yan, WU Zhao-peng 2020, 37 (6):  1378-1387.  doi: 10.13866/j.azr.2020.06.02 Abstract ( 636 )   PDF (3577KB) ( 632 )   The arid ecological fragile area of Jinghe Basin was selected as the research area. Daily meteorological observation data from 1990 to 2016 and six scenes of corresponding Landsat series images were investigated. The results show that under the context of global warming, evapotranspiration in the study area as a whole has increased over the past 26 years and Morlet wavelet analysis shows that there are 5 a, 7 a, 13 a scale change cycles. Additionally, evapotranspiration in the study area is spatially high in the south and low in the north. The evapotranspiration was reduced in the unused land in the northeast and significantly increased in the northwestern part of Lake Aibi and the southern mountainous area. Evapotranspiration under different land-use types followed the pattern from high to low of forest land > water body > grassland > cultivated land > construction land > unused land. Among the measured meteorological factors, wind speed was highly positively correlated with surface evapotranspiration, along with elevation and specific surface emissivity. The meteorological factors that show a highly negative correlation with surface evapotranspiration were near-surface air relative humidity, and the surface parameters were temperature vegetation drought index and surface temperature. References | Related Articles | Metrics

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Spatiotemporal variation of albedo of four representative glaciers in the Heihe River Basin based on multi-source data WANG Jun-yao, HUAI Bao-juan, WANG Ye-tang, SUN Wei-jun, ZHANG Wu-ying 2020, 37 (6):  1396-1405.  doi: 10.13866/j.azr.2020.06.04 Abstract ( 653 )   PDF (2644KB) ( 636 )   Glacier albedo is a critical parameter that controls the process of radiation budget, the fluctuation of which directly affects the change in glacier energy-mass balance. By remote sensing, studies on the characteristics of glacier albedo and its spatiotemporal distribution can be taken as an important reference for estimating glacier melting and downstream river runoff. In this study, albedo dataset retrieved from Landsat TM/ETM+ images and MOD10A1 daily albedo product were used as the main data sources, and Landsat TM/ETM+ images and MOD10A1 data’error were analyzed by field measurements. Then, the spatiotemporal variations of albedo were investigated on four representative glaciers in Heihe River Basin of MOD10A1 from 2000 to 2018. The results showed that there was a certain bias between albedo value derived from MOD10A1 products and ground measured, but the time series was similar; there is a difference in inversion results between MOD10A1 and Landsat TM/ETM+, suggesting a good applicability of glacier albedo in Heihe River Basin. On the interannual scale, the albedo of four glaciers was decreasing. Among the spatial scale, the annual average albedo of Bayi glacier was the highest, followed by Yanglonghe glacier No. 5, Qiyi glacier, and Shiyi glacier; the average albedo of Yanglonghe glacier No. 5 was the highest in the ablation season, followed by the Qiyi glacier, Bayi glacier, and Shiyi glacier. References | Related Articles | Metrics

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Spatial and temporal variations in sand dune soil moisture content and groundwater depth ZHANG Yuan-hao, Ala Musa, YIN Jia-wang, JIANG Shao-yan 2020, 37 (6):  1427-1436.  doi: 10.13866/j.azr.2020.06.07 Abstract ( 2388 )   PDF (2779KB) ( 729 )   In arid and semi-arid dune areas, precipitation is scarce and evaporation occurs quickly; thus, the status of water resources is the key factor for the operation of these ecosystems. Soil water content and groundwater in the dune area are the main water resource measurement indicators. Based on vegetation cover gradients, the typical sand dune types (mobile dunes, semi-fixed dunes, fixed dunes) were selected in the dune study area, and changes in soil moisture content and groundwater depth were measured in the dunes under different vegetation coverage and slope positions. The results revealed that vegetation coverage was the main factor affecting dune soil moisture content. As the vegetation coverage increases, the soil moisture content gradually decreases. The sequence of soil moisture content in each of the dune types was highest in the mobile dune, followed by the semi-fixed dune, and finally the fixed dune. Differences in soil moisture content were also observed at different slope positions, showing the trend of windward slope bottom > leeward slope bottom > middle windward slope > hilltop > leeward slope. The temporal variation characteristics of dune soil moisture were consistent with the occurrence characteristics of rainfall and mainly controlled by the rainfall process. In addition, the seasonal change in the groundwater level in the dune area showed a marked rise in the non-growing season and a gradual decline in the growing season, with an annual variation range of -0.21-0.18 m. Vegetation coverage also affected the groundwater level in the dune area. The coefficient of variation from large to small was fixed dunes > semi-fixed dunes > mobile dunes. The groundwater level is influenced by rainfall; when the cumulative rainfall in a short time or single rainfall exceeds 30 mm, the groundwater level in the dune area shows a corresponding rise. The rise amplitude is influenced by the vegetation coverage and slope position on the dune surface. Furthermore, groundwater may recharge the deep soil water at the bottom of the dune slope, but has no obvious replenishment effect on the soil water in the middle and top of the dune slope. References | Related Articles | Metrics

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Effects of Caragana intermedia on soil particles in desertified grassland CAO Yuan, YANG Xin-guo, CHEN Lin, WANG Xing, SONG Nai-ping, WANG Lei 2020, 37 (6):  1437-1446.  doi: 10.13866/j.azr.2020.06.08 Abstract ( 359 )   PDF (6825KB) ( 188 )   Introduction of artificial shrubs in arid area is a common ecological restoration measure. Artificial shrubs can stabilize soil surface environment and promote restoration of desertified land through its function of warding off wind and fixing sand. Caragana intermedia is a typical xeric shrub for sand control in desertified land. However, the effect of C. intermedia on desertified grassland after years of introduction is still lacking in terms of regional summary and analysis. By adopting methods of classical statistics and geostatistics, we divided the typical desert steppe located in central Ningxia into 37 spatial grids, sizing 20 km×20 km each and selecting 4 sample plots in each grid, which totals up to 148 sample plots, in accordance with different varieties of vegetation (C. intermedia and desertified grassland) and slope direction (northern and southern slope). With these data, we compared the desertified grassland and grassland with C. intermedia (artificial C. intermedia plantations) in terms of soil particle composition. We then analyzed the effect on soil particle composition and clay enrichment capacity both in desertified grassland and artificial C. intermedia plantations in designated area, with the aim of providing decisionmaking reference for restoration of desertified land of similar type. Preliminary research result shows that there is no significant difference in soil particle composition between artificial C. intermedia plantations and desertified grassland. On the shrub scale, the enrichment capacity of clay is relatively higher at the northern slope of artificial C. intermedia plantations, with a rate of 0.11 on average and maximum rate of 1.09 and with northern slope in the north part of the study area; whereas, the rate in the south part gradually descends and, by contrast, its enrichment capacity at southern slope is mostly in the negative, with an average of -0.08. Compared with shrub scale, enrichment capacity of clay is significantly lower on the patch scale; ratio at the northern slope is still in positive, but decreases sharply, while that of the southern slope is in the negative with an enhancing tendency and an average of -0.17. In conclusion, the introduction of C. intermedia is an important engineering measure for restoring desertified grassland in desert steppe and its effect not only relates to desertified degree of the soil, but also relates to micro-habitat (slope direction). So, far, as the area under study is concerned, C. intermedia’s effect after its introduction, instead of significantly enhancing the area’s clay content, it spatially promoted clay redistribution. To a certain extent, it demonstrated a negative effect as a result of the shrub encroachment; and such negative effect would be strengthened with increases in desertified degree of the soil in desert steppe. References | Related Articles | Metrics

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Spatial-temporal differentiation of near-surface ozone concentration and dominant meteorological factors in Inner Mongolia CHEN Zhi-qing, SHAO Tian-jie, ZHAO Jing-bo, CAO Jun-ji, YUE Da-peng 2020, 37 (6):  1504-1512.  doi: 10.13866/j.azr.2020.06.15 Abstract ( 457 )   PDF (2679KB) ( 275 )   Spatial and temporal ozone (O3) distribution characteristics were examined using air quality monitoring data from 12 leagues and cities in Inner Mongolia in 2017. The impact of meteorological factors on O3 concentration and distribution was explored using a generalized additive model (GAM). Above-standard O3 concentration was ob? served in 12 leagues and cities in Inner Mongolia to varying degrees. The average monthly O3 concentration showed a trend of increasing before decreasing over the span of a year, peaking with the worst pollution from April to Sep? tember and reaching the annual maximum (136 μg·m-3) in July. Regional regularity was as follows: O3 concentration was the highest in central Inner Mongolia, moderate in western Inner Mongolia, and lower in eastern Inner Mongo? lia. The dominant meteorological factors on O3 concentration change in Inner Mongolia were identified by construct? ing a GAM. Temperature was the primary meteorological factor affecting O3 concentration in all areas; relative hu? midity, sunshine duration, and wind speed were the secondary dominant factors in eastern, central, and western In? ner Mongolia, respectively. References | Related Articles | Metrics

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Climate characteristics of day and night precipitation during the growing season in Inner Mongolia from 1961 to 2018 SHEN Lu-ting, ZHANG Fang-min, HUANG Jin, LI Yun-peng 2020, 37 (6):  1519-1527.  doi: 10.13866/j.azr.2020.06.17 Abstract ( 1083 )   PDF (4011KB) ( 347 )   The aim of this study is to provide scientific guidance for agricultural development and ecological restoration projects in Inner Mongolia. The spatial and temporal climate characteristics of day and night precipitation amounts in Inner Mongolia during the growing season from 1961 to 2018 were analyzed based on the daily surface precipitation data collected at 103 meteorological observation stations using trend analysis, Mann- Kendall test, and Morlet wavelet. In the past 58 years, the average annual precipitation amounts in the daytime were more than those at night during the growing season in Inner Mongolia. However, day and night precipitation amounts showed significant monthly variation as well as different oscillation periods. The day and night precipitation amounts did not change obviously, but the number of day and night precipitation days showed decreasing trends. The annual precipitation amount and days had similar spatial distributions, decreasing from the northeast to the southwest. Day precipitation contributed more to the daily total precipitation amount in southcentral and eastern Inner Mongolia, whereas the difference between day and night precipitation amounts (DDNA) and the difference between day and night precipitation days (DDND) were both higher than west Inner Mongolia. The DDNA and DDND were smaller in western Inner Mongolia. In addition, the variation patterns of day and night precipitation were similar, showing decreasing trends in central Inner Mongolia but increasing trends in western and eastern Inner Mongolia. However, the number of day and night precipitation days showed quite different spatial variation patterns. The number of day precipitation days did not change obviously in western Inner Mongolia but decreased in central and northeast Inner Mongolia. The number of night precipitation days increased in western, central, and northeastern Inner Mongolia but decreased from southeast to northeast. References | Related Articles | Metrics

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Effects of extreme drought and nitrogen addition on species diversity,leaf trait, and productivity in a semiarid sandy grassland SUN Yi-mei, TIAN Qing, LYU Peng, GUO Ai-xia, ZHANG Sen-xi, ZUO Xiao-an 2020, 37 (6):  1569-1579.  doi: 10.13866/j.azr.2020.06.23 Abstract ( 511 )   PDF (3374KB) ( 336 )   We examined the effects of extreme drought (rain reduction by 60% and drought for 60 days) and nitrogen addition (20 g·m- 2 ·a- 1) on species diversity, productivity, and leaf trait in Horqin Sandy Land. Results show that changes in water and nitrogen altered important values of dominant species, such that which the important values of Echinops gmelini and Artemisia scoparia increased significantly under short-term extreme drought and nitrogen addition treatment. Short-term extreme drought had a significant effect on plant height (H), leaf nitrogen content (LNC), and aboveground biomass. Following rain reduction by 60%, H decreased, while LNC increased. Aboveground biomass decreased, following rain reduction by 60% and drought for 60 days. There was no significant difference in species diversity, specific leaf area (SLA), leaf day matter content (LDMC), and leaf carbon content (LCC) between drought treatments. Short-term nitrogen addition significantly changed the leaf traits and aboveground biomass. Following the addition nitrogen, SLA, and LNC increased, while LDMC decreased. There was no significant difference in plant diversity. Interaction between extreme drought and nitrogen addition had no significant effect on species diversity, leaf traits, and aboveground biomass. Correlation and regression analysis showed that species diversity, SLA, LDMC, LCC, and LNC did not significantly correlate with biomass, while H was positively correlated with aboveground biomass following nitrogen addition. The annual dominant plant communities in semiarid sandy grassland adapt to extreme drought and nitrogen deposition by changing key traits of dominant species, in which H has a greater impact on grassland productivity References | Related Articles | Metrics

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Estimation of ecological thresholds in plant and soil properties during desertification in an alpine grassland ZONG Ning, SHI Pei-li, SUN Jian 2020, 37 (6):  1580-1589.  doi: 10.13866/j.azr.2020.06.24 Abstract ( 464 )   PDF (4770KB) ( 224 )   Alpine grassland desertification is an important environmental problem, which have an important impact on grassland forage production and residents’living environment. The current studies on grassland desertification are mostly focused on the changes in vegetation and soil properties during desertification process, with no prior knowledge about which variables are more sensitive and can be used to indicate state transition in the desertification process, and how to quantify the ecological threshold of the desertification process. Using the method of space- for- time, five types of communities were selected to represent the different gradients of alpine grassland desertification to systematically study the changes in plants, soil properties, and microorganisms during the desertification process, and to identify the desertification thresholds. The results showed that plant community cover, above- ground, and underground biomass significantly decreased with the increase in desertification. Soil moisture concentration gradually decreased, and soil bulk density gradually increased with the increase in the extent of desertification. Gravel content was significantly higher in severely desertified grassland community than in other desertified community types. Soil total carbon and nitrogen concentrations in the soil surface (0-10 cm) gradually decreased, and the ratio of carbon to nitrogen was significantly higher in severely desertified community than in other types of grassland community. Abrupt changes in vegetation occurred in lightly to moderately desertified communities. Meanwhile, rapid changes in soil properties and soil microorganisms (desertification threshold) occurred in moderately to severely desertified communities. Such results suggest that the response of plants to desertification could be more sensitive than that of soil sub-systems, and plants could be treated as a more direct indicators of the gradients of grassland desertification. Moreover, mildly to moderately desertified communities could be the key stage of grassland desertification. Thus, it is very important to take the right methods to avoid further desertification of the grassland. References | Related Articles | Metrics