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Li, J.; He, Z.; Du, J.; Zhao, L.; Chen, L.; Zhu, X.; Lin, P.; Fang, S.; Zhao, M.; Tian, Q.
© 2018 by the author
. Increasing diffuse nitrate loading of groundwater has long been a major environmental and health concern in China, but little is known about the spatial and temporal variability of nitrate concentrations in groundwater at regional scales. The aim of this study was to assess the spatial distribution and variation of nitrate-nitrogen (NO 3 - -N) concentrations in groundwater. We used groundwater quality monitoring data and soil physical characteristics from 21 agro-ecosystems in China for years 2004 to 2014. The results indicated that NO 3 - -N concentrations were highly variable in shallow groundwater across the landscape. Over the study period, most of the NO 3 - -N concentrations were below the World Health Organization permissible limit for drinking water ( < 10 mg N•L). NO 3 - -N concentrations in groundwater neither significantly increased nor decreased in most agro-ecosystems, but fluctuated with seasons. In addition, groundwater NO 3 - -N under purple soil (6.81 mg•L -1 ) and Aeolian sandy soil (6.02 mg•L -1 ) were significantly higher (p < 0.05) than that under other soil types, and it was medium-high (4.49 mg•L -1 ) under aquic cinnamon soil. Elevated nitrate concentrations occurred mainly in oasis agricultural areas of northwestern China, where farmlands with coarse-textured soils use flood irrigation. Therefore, arid and semi-arid areas are expected to sustain high NO 3 - -N concentrations in groundwater. Mitigation strategies can prevent this problem, and include control of N fertilizer input, balanced fertilization, proper rotation system, adoption of improved irrigation methods, and establishment of environmental policies
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The cryosphere reacts sensitively to climate change, as evidenced by the widespread retreat of mountain glaciers
. Subsurface ice contained in permafrost is similarly affected by climate change, causing persistent impacts on natural and human systems. In contrast to glaciers, permafrost is not observable spatially and therefore its presence and possible changes are frequently overlooked. Correspondingly, little is known about permafrost in the mountains of the Hindu Kush Himalaya (HKH) region, despite permafrost area exceeding that of glaciers in nearly all countries. Based on evidence and insight gained mostly in other permafrost areas globally, this review provides a synopsis on what is known or can be inferred about permafrost in the mountains of the HKH region. Given the extreme nature of the environment concerned, it is to be expected that the diversity of conditions and phenomena encountered in permafrost exceed what has previously been described and investigated. We further argue that climate change in concert with increasing development will bring about diverse permafrost-related impacts on vegetation, water quality, geohazards, and livelihoods. To better anticipate and mitigate these effects, a deepened understanding of high-elevation permafrost in subtropical latitudes as well as the pathways interconnecting environmental changes and human livelihoods are needed
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Rock glaciers are widespread in the high mountains of western China
. However, they have not been systematically investigated for more than two decades. In this study, we propose a new method that combines SAR interferometry and optical images from Google Earth to map active rock glaciers (ARGs) in the Northern Tien Shan (NTS) in China. We compiled an inventory that includes 261 ARGs and quantitative information about their locations, geomorphic parameters, and down-slope velocities. Our inventory shows that most of the ARGs are moraine-derived (68 %) and facing north-east (56 %). The altitude distribution of ARGs in the western NTS is significantly different from those located in the eastern part. The down-slope velocities of the ARGs vary significantly in space, with a maximum of about 114 cm yr−1 and a mean of about 37 cm yr−1. Using the ARG locations as a proxy for the extent of alpine permafrost, our inventory suggests that the lowest altitudinal limit for the presence of permafrost in the Northern Tien Shan is about 2500–2800 m, a range determined by the lowest ARG in the entire inventory and by a statistics-based estimation. The successful application of the proposed method would facilitate an effective and robust effort to map rock glaciers over major mountain ranges and provide important datasets to improve mapping and modeling permafrost distribution in vast western China
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The evolutionary diversifications of many taxonomic groups, especially those with limited dispersal ability, are often driven by key geological events, such as tectonic drift, continental collisions, and uplifts of mountains
. Here, we use full range geographic sampling to create a dated molecular phylogeny for two genera of alpine gingers (Cautleya and Roscoea) in the Pan-Himalaya, and test the correlations between evolutionary diversification of this group and major geological events in the studied region. Our results revealed that the origination of their common ancestor and evolutionary split between the two genera occurred during the middle Eocene and the late Eocene to the early Oligocene, corresponding well to the proposed two early uplifts of the Himalayan–Tibetan Plateau. Roscoea species, the highest elevation gingers known, were then divided into distinct Himalayan and Indochinese clades, simultaneous with the rapid extrusion of Indochina and accompanied by the third Himalayan uplift around the Oligocene/Miocene boundary. This study highlights the importance of evolutionary diversification of plants as an independent line of evidence to reflect tectonic events in the Himalayan–Indochinese region
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During the years 2006–2009, lakes in the Qinghai-Tibetan Plateau (QTP) were investigated using satellite remote sensing strategies
. We report the results of this investigation as well as follow-up research and expanded work. For the investigation, we mainly focused on lakes whose areas are more than 1 km2. The remote sensing data that we used included 408 scenes of CBERS CCD images and 5 scenes of Landsat ETM+ images in Qinghai Province and Tibet Autonomous Region. All these data were acquired around years 2005–2006. Besides remote sensing images, we also collected 1,259 topographic maps. Numbers and areas of lakes were analyzed statistically, which were then compared with those coming from the first lake investigation (implemented between the 1960s and 1980s). According to our investigation, up to and around year 2005–2006, the total number of lakes in the QTP was 1,055 (222 in Qinghai and 833 in Tibet), accounting for more than 30 % of that of China. Thirty newborn lakes with area >1 km2 were found, and 5 dead lakes with initial area >1 km2 were also found. Among those 13 big lakes (>500 km2), Yamzhog Yumco had seriously shrunk, and it has continued to shrink in recent years; Qinghai Lake had shrunk during the period, but some new researches indicated that it has been expanding since the year 2004; Siling Co, Nam Co, and Chibuzhang Co had expanded in the period. We divided the newborn lakes into six categories according to their forming reasons, including river expansion, wetland conversion, etc. The changes of natural conditions led to the death of four lakes, and human exploitation was the main reason for the death of Dalianhai Lake in Qinghai. We picked out three regions which were sensitive to the change of climate and ecological environment: Nagqu Region, Kekexili Region, and the source area of the Yellow River (SAYR). Lakes in both Nagqu and Kekexili have been expanded; meanwhile, most lakes in the SAYR have obviously been shrunk. These regional patterns of lake changes were highly related to variations of temperature, glacier, precipitation, and evaporation. Our investigation and analysis will provide references for researches related to lake changes in the QTP and the response to climate fluctuations
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The Himalaya mountains along the southern edge of the Tibetan Plateau act as a natural barrier for the transport of atmospheric aerosols from the polluted regions of South Asia to the main body of the Tibetan Plateau
. In this study, we investigate the seasonal and diurnal variations of aerosol optical properties measured at two Aerosol Robotic Network (AERONET) sites on the southern side of the Himalaya (Pokhara, 812 m above sea level (a.s.l.) and EVK2-CNR, 5079 m a.s.l. in Nepal) and one on the northern side (Qomolangma (Mt. Everest) station for Atmospheric and Environmental Observation and Research, Chinese Academy of Sciences (QOMS_CAS) in Tibet, 4076 m a.s.l. in China). While observations at QOMS_CAS and EVK2-CNR can generally be representative of a remote background atmosphere, Pokhara is a lower-elevation suburban site with much higher aerosol load due to both the influence of local anthropogenic activities and to its proximity to the Indo-Gangetic Plains. The annual mean aerosol optical depth (AOD) during the investigated period was 0.05 at QOMS_CAS, 0.04 at EVK2-CNR and 0.51 at Pokhara, respectively. Seasonal variations of aerosols are profoundly affected by large-scale atmospheric circulation. Vegetation fires, peaking during April in the Himalayan region and northern India, contribute to a growing fine mode AOD at the three stations. Dust transported to these sites, wind erosion and hydrated/cloud-processed aerosols lead to an increase in coarse mode AOD during the monsoon season at QOMS_CAS and EVK2-CNR. Meanwhile, coarse mode AOD at EVK2-CNR is higher than at QOMS_CAS in August and September, indicating that the transport of coarse mode aerosols from the southern to the northern side may be effectively reduced. The effect of precipitation scavenging is clearly seen at Pokhara, which sees significantly reduced aerosol loads during the monsoon season. Unlike the seasonal variations, diurnal variations are mainly influenced by meso-scale systems and local topography. The diurnal pattern in precipitation appears to contribute to diurnal changes in AOD through the effect of precipitation scavenging. AOD exhibits diurnal patterns related to emissions in Pokhara, while it does not at the other two high-altitude sites. At EVK2-CNR, the daytime airflow carries aerosols up from lower-altitude polluted regions, leading to increasing AOD, while the other two stations are less influenced by valley winds. Surface heating influences the local convection, which further controls the vertical aerosol exchange and the diffusion rate of pollution to the surrounding areas. Fine and coarse mode particles are mixed together on the southern side of the Himalaya in spring, which may lead to the greater inter-annual difference in diurnal cycles of Ångström exponent (AE) at EVK2-CNR than that at QOMS_CAS
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