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  • Temporal and spatial variations of net primary productivity and its response to groundwater of a typical oasis in the Tarim Basin, China

    分类: 地球科学 >> 地理学 提交时间: 2021-12-03 合作期刊: 《干旱区科学》

    摘要: Net primary productivity (NPP) of the vegetation in an oasis can reflect the productivity capacity of a plant community under natural environmental conditions. Owing to the extreme arid climate conditions and scarce precipitation in the arid oasis regions, groundwater plays a key role in restricting the development of the vegetation. The Qira Oasis is located on the southern margin of the Taklimakan Desert (Tarim Basin, China) that is one of the most vulnerable regions regarding vegetation growth and water scarcity in the world. Based on remote sensing images of the Qira Oasis and daily meteorological data measured by the ground stations during the period 2006–2019, this study analyzed the temporal and spatial patterns of NPP in the oasis as well as its relation with the variation of groundwater depth using a modified Carnegie Ames Stanford Approach (CASA) model. At the spatial scale, NPP of the vegetation decreased from the interior of the Qira Oasis to the margin; at the temporal scale, NPP of the vegetation in the oasis fluctuated significantly (ranging from 29.80 to 50.07 g C/(m2•month)) but generally showed an increasing trend, with the average increase rate of 0.07 g C/(m2•month). The regions with decreasing NPP occupied 64% of the total area of the oasis. During the study period, NPP of both farmland and grassland showed an increasing trend, while that of forest showed a decreasing trend. The depth of groundwater was deep in the south of the oasis and shallow in the north, showing a gradual increasing trend from south to north. Groundwater, as one of the key factors in the surface change and evolution of the arid oasis, determines the succession direction of the vegetation in the Qira Oasis. With the increase of groundwater depth, grassland coverage and vegetation NPP decreased. During the period 2008–2015, with the recovery of groundwater level, NPP values of all types of vegetation with different coverages increased. This study will provide a scientific basis for the rational utilization and sustainable management of groundwater resources in the oasis.

  • Effects of drip and flood irrigation on carbon dioxide exchange and crop growth in the maize ecosystem in the Hetao Irrigation District, China

    分类: 农、林、牧、渔 >> 农业基础学科 提交时间: 2024-02-21 合作期刊: 《干旱区科学》

    摘要: Drip irrigation and flood irrigation are major irrigation methods for maize crops in the Hetao Irrigation District, Inner Mongolia Autonomous Region, China. This research delves into the effects of these irrigation methods on carbon dioxide (CO2) exchange and crop growth in this region. The experimental site was divided into drip and flood irrigation zones. The irrigation schedules of this study aligned with the local commonly used irrigation schedule. We employed a developed chamber system to measure the diurnal CO2 exchange of maize plants during various growth stages under both drip and flood irrigation methods. From May to September in 2020 and 2021, two sets of repeated experiments were conducted. In each experiment, a total of nine measurements of CO2 exchange were performed to obtain carbon exchange data at different growth stages of maize crop. During each CO2 exchange measurement event, CO2 flux data were collected every two hours over a day-long period to capture the diurnal variations in CO2 exchange. During each CO2 exchange measurement event, the biological parameters (aboveground biomass and crop growth rate) of maize and environmental parameters (including air humidity, air temperature, precipitation, soil water content, and photosynthetically active radiation) were measured. The results indicated a V-shaped trend in net ecosystem CO2 exchange in daytime, reducing slowly at night, while the net assimilation rate (net primary productivity) exhibited a contrasting trend. Notably, compared with flood irrigation, drip irrigation demonstrated significantly higher average daily soil CO2 emission and greater average daily CO2 absorption by maize plants. Consequently, within the maize ecosystem, drip irrigation appeared more conducive to absorbing atmospheric CO2. Furthermore, drip irrigation demonstrated a faster crop growth rate and increased aboveground biomass compared with flood irrigation. A strong linear relationship existed between leaf area index and light utilization efficiency, irrespective of the irrigation method. Notably, drip irrigation displayed superior light use efficiency compared with flood irrigation. The final yield results corroborated these findings, indicating that drip irrigation yielded higher harvest index and overall yield than flood irrigation. The results of this study provide a basis for the selection of optimal irrigation methods commonly used in the Hetao Irrigation District. This research also serves as a reference for future irrigation studies that consider measurements of both carbon emissions and yield simultaneously.

  • Monitoring the impact of climate change and human activities on grassland vegetation dynamics in the northeastern Qinghai-Tibet Plateau of China during 2000–2015

    分类: 环境科学技术及资源科学技术 >> 环境科学技术基础学科 提交时间: 2019-10-26 合作期刊: 《干旱区科学》

    摘要: Climate change and human activities can influence vegetation net primary productivity (NPP), a key component of natural ecosystems. The Qinghai-Tibet Plateau of China, in spite of its significant natural and cultural values, is one of the most susceptible regions to climate change and human disturbances in the world. To assess the impact of climate change and human activities on vegetation dynamics in the grassland ecosystems of the northeastern Qinghai-Tibet Plateau, we applied a time-series trend analysis to normalized difference vegetation index (NDVI) datasets from 2000 to 2015 and compared these spatiotemporal variations with trends in climatic variables over the same time period. The constrained ordination approach (redundancy analysis) was used to determine which climatic variables or human-related factors mostly influenced the variation of NDVI. Furthermore, in order to determine whether current conservation measures and programs are effective in ecological protection and reconstruction, we divided the northeastern Qinghai-Tibet Plateau into two parts: the Three-River Headwater conservation area (TRH zone) in the south and the non-conservation area (NTRH zone) in the north. The results indicated an overall (73.32%) increasing trend of vegetation NPP in grasslands throughout the study area. During the period 2000–2015, NDVI in the TRH and NTRH zones increased at the rates of 0.0015/a and 0.0020/a, respectively. Specifically, precipitation accounted for 9.2% of the total variation in NDVI, while temperature accounted for 13.4%. In addition, variation in vegetation NPP of grasslands responded not only to long- and short-term changes in climate, as conceptualized in non-equilibrium theory, but also to the impact of human activities and their associated perturbations. The redundancy analysis successfully separated the relative contributions of climate change and human activities, of which village population and agricultural gross domestic product were the two most important contributors to the NDVI changes, explaining 17.8% and 17.1% of the total variation of NDVI (with the total contribution >30.0%), respectively. The total contribution percentages of climate change and human activities to the NDVI variation were 27.5% and 34.9%, respectively, in the northeastern Qinghai-Tibet Plateau. Finally, our study shows that the grassland restoration in the study area was enhanced by protection measures and programs in the TRH zone, which explained 7.6% of the total variation in NDVI.

  • Effects of grazing on net primary productivity, evapotranspiration and water use efficiency in the grasslands of Xinjiang

    分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2018-05-18 合作期刊: 《干旱区科学》

    摘要: Grazing is a main human activity in the grasslands of Xinjiang. It is vital to identify the effects of grazing on the sustainable utilization of local grasslands. However, the effects of grazing on net primary productivity (NPP), evapotranspiration (ET) and water use efficiency (WUE) in this region remain unclear. Using the spatial Biome-BGC grazing model, we explored the effects of grazing on NPP, ET and WUE across the different regions and grassland types in Xinjiang during 19792012. NPP, ET and WUE under the grazed scenario were generally lower than those under the ungrazed scenario, and the differences showed increasing trends over time. The decreases in NPP, ET and WUE varied significantly among the regions and grassland types. NPP decreased as follows: among the regions, Northern Xinjiang (16.60 g C/(m2a)), Tianshan Mountains (15.94 g C/(m2a)) and Southern Xinjiang (3.54 g C/(m2a)); and among the grassland types, typical grasslands (25.70 g C/(m2a)), swamp meadows (25.26 g C/(m2a)), mid-mountain meadows (23.39 g C/(m2a)), alpine meadows (6.33 g C/(m2a)), desert grasslands (5.82 g C/(m2a)) and saline meadows (2.90 g C/(m2a)). ET decreased as follows: among the regions, Tianshan Mountains (28.95 mm/a), Northern Xinjiang (8.11 mm/a) and Southern Xinjiang (7.57 mm/a); and among the grassland types, mid-mountain meadows (29.30 mm/a), swamp meadows (25.07 mm/a), typical grasslands (24.56 mm/a), alpine meadows (20.69 mm/a), desert grasslands (11.06 mm/a) and saline meadows (3.44 mm/a). WUE decreased as follows: among the regions, Northern Xinjiang (0.053 g C/kg H2O), Tianshan Mountains (0.034 g C/kg H2O) and Southern Xinjiang (0.012 g C/kg H2O); and among the grassland types, typical grasslands (0.0609 g C/kg H2O), swamp meadows (0.0548 g C/kg H2O), mid-mountain meadows (0.0501 g C/kg H2O), desert grasslands (0.0172 g C/kg H2O), alpine meadows (0.0121 g C/kg H2O) and saline meadows (0.0067 g C/kg H2O). In general, the decreases in NPP and WUE were more significant in the regions with relatively high levels of vegetation growth because of the high grazing intensity in these regions. The decreases in ET were significant in mountainous areas due to the terrain and high grazing intensity.

  • Spatiotemporal variation in vegetation net primary productivity and its relationship with meteorological factors in the Tarim River Basin of China from 2001 to 2020 based on the Google Earth Engine

    分类: 地球科学 >> 地理学 提交时间: 2022-12-12 合作期刊: 《干旱区科学》

    摘要:Vegetation growth status is an important indicator of ecological security. The Tarim River Basin is located in the inland arid region of Northwest China and has a highly fragile ecological environment. Assessing the vegetation net primary productivity (NPP) of the Tarim River Basin can provide insights into the vegetation growth variations in the region. Therefore, based on the Google Earth Engine (GEE) cloud platform, we studied the spatiotemporal variation of vegetation NPP in the Tarim River Basin (except for the eastern Gobi and Kumutag deserts) from 2001 to 2020 and analyzed the correlations between vegetation NPP and meteorological factors (air temperature and precipitation) using the Sen slope estimation method, coefficient of variation, and rescaled range analysis method. In terms of temporal characteristics, vegetation NPP in the Tarim River Basin showed an overall fluctuating upward trend from 2001 to 2020, with the smallest value of 118.99 g C/(m2•a) in 2001 and the largest value of 155.07 g C/(m2•a) in 2017. Regarding the spatial characteristics, vegetation NPP in the Tarim River Basin showed a downward trend from northwest to southeast along the outer edge of the study area. The annual average value of vegetation NPP was 133.35 g C/(m2•a), and the area with annual average vegetation NPP values greater than 100.00 g C/(m2•a) was 82,638.75 km2, accounting for 57.76% of the basin. The future trend of vegetation NPP was dominated by anti-continuity characteristic; the percentage of the area with anti-continuity characteristic was 63.57%. The area with a significant positive correlation between vegetation NPP and air temperature accounted for 53.74% of the regions that passed the significance test, while the area with a significant positive correlation between vegetation NPP and precipitation occupied 98.68% of the regions that passed the significance test. Hence, the effect of precipitation on vegetation NPP was greater than that of air temperature. The results of this study improve the understanding on the spatiotemporal variation of vegetation NPP in the Tarim River Basin and the impact of meteorological factors on vegetation NPP.

  • Estimation of net primary productivity and its driving factors in the Ili River Valley, China

    分类: 地球科学 >> 地球科学史 提交时间: 2018-09-18 合作期刊: 《干旱区科学》

    摘要: Net primary productivity (NPP), as an important variable and ecological indicator in grassland ecosystems, can reflect environmental change and the carbon budget level. The Ili River Valley is a wetland nestled in the hinterland of the Eurasian continent, which responds sensitively to the global climate change. Understanding carbon budget and their responses to climate change in the ecosystem of Ili River Valley has a significant effect on the adaptability of future climate change and sustainable development. In this study, we calculated the NPP and analyzed its spatio-temporal pattern of the Ili River Valley during the period 2000–2014 using the normalized difference vegetation index (NDVI) and an improved Carnegie-Ames-Stanford (CASA) model. Results indicate that validation showed a good performance of CASA over the study region, with an overall coefficient of determination (R2) of 0.65 and root mean square error (RMSE) of 20.86 g C/(m2•a). Temporally, annual NPP of the Ili River Valley was 599.19 g C/(m2•a) and showed a decreasing trend from 2000 to 2014, with an annual decrease rate of –3.51 g C/(m2•a). However, the spatial variation was not consistent, in which 55.69% of the areas showed a decreasing tendency, 12.60% of the areas remained relatively stable and 31.71% appeared an increasing tendency. In addition, the decreasing trends in NPP were not continuous throughout the 15-year period, which was likely being caused by a shift in climate conditions. Precipitation was found to be the dominant climatic factor that controlled the inter-annual variability in NPP. Furthermore, the correlations between NPP and climate factors differed along the vertical zonal. In the medium-high altitudes of the Ili River Valley, the NPP was positively correlated to precipitation and negatively correlated to temperature and net radiation. In the low-altitude valley and high-altitude mountain areas, the NPP showed a negative correlation with precipitation and a weakly positive correlation with temperature and net radiation. The results suggested that the vegetation of the Ili River Valley degraded in recent years, and there was a more complex mechanism of local hydrothermal redistribution that controlled the growth of vegetation in this valley ecosystem.

  • Spatiotemporal characteristics and influencing factors of ecosystem services in Central Asia

    分类: 地球科学 >> 地理学 提交时间: 2023-02-06 合作期刊: 《干旱区科学》

    摘要: Land use/land cover (LULC) change and climate change are two major factors affecting the provision of ecosystem services which are closely related to human well-being. However, a clear understanding of the relationships between these two factors and ecosystem services in Central Asia is still lacking. This study aimed to comprehensively assess ecosystem services in Central Asia and analyze how they are impacted by changes in LULC and climate. The spatiotemporal patterns of three ecosystem services during the period of 20002015, namely the net primary productivity (NPP), water yield, and soil retention, were quantified and mapped by the Carnegie-Ames-Stanford Approach (CASA) model, Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model, and Revised Universal Soil Loss Equation (RUSLE). Scenarios were used to determine the relative importance and combined effect of LULC change and climate change on ecosystem services. Then, the relationships between climate factors (precipitation and temperature) and ecosystem services, as well as between LULC change and ecosystem services, were further discussed. The results showed that the high values of ecosystem services appeared in the southeast of Central Asia. Among the six biomes (alpine forest region (AFR), alpine meadow region (AMR), typical steppe region (TSR), desert steppe region (DSR), desert region (DR), and lake region (LR)), the values of ecosystem services followed the order of AFR>AMR>TSR>DSR> DR>LR. In addition, the values of ecosystem services fluctuated during the period of 20002015, with the most significant decreases observed in the southeast mountainous area and northwest of Central Asia. LULC change had a greater impact on the NPP, while climate change had a stronger influence on the water yield and soil retention. The combined LULC change and climate change exhibited a significant synergistic effect on ecosystem services in most of Central Asia. Moreover, ecosystem services were more strongly and positively correlated with precipitation than with temperature. The greening of desert areas and forest land expansion could improve ecosystem services, but unreasonable development of cropland and urbanization have had an adverse impact on ecosystem services. According to the results, ecological stability in Central Asia can be achieved through the natural vegetation protection, reasonable urbanization, and ecological agriculture development.