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Sustainability of eco-environment in semi-arid regions: Lessons from the Chinese Loess Plateau
No full textThe eco-environment of semi-arid regions is extremely sensitive and vulnerable to climate change and human activities. The realization of sustainability of eco-environments has long been a key issue. Consequently, we analysed the Chinese Loess Plateau (CLP) to identify solutions to the sustainable development of such regions. We first reviewed the eco-environmental changes in the CLP and discussed the impacts of human activities over the past 3000 years, and then summarized previous experiences on the protection and restoration of degraded eco-environments. Our study indicates that the increasing demand for cultivated land has led to the destruction of vegetation and subsequent worsening of soil erosion on the CLP, which in turn, has led to an increase in floods in the Yellow River basin. However, many positive measures, such as slope cropland abandonment and afforestation have been demonstrated to be effective in improving the eco-environment via reducing soil erosion, and decreasing sediment input and flood disasters in the Yellow River in recent decades. Nonetheless, emerging problems such as water shortage, food insecurity, rapid urban development, and over-exploitation of energy resources hinder the sustainable development of the eco-environment in the CLP. Given the historical and present eco-environmental situations of the CLP, we provide suggestions for the sustainable development of both the eco-environment and social economy, which could serve as guidelines for eco-environmental design and government policy-making in semi-arid regions globally
Sustainability of eco-environment in semi-arid regions: Lessons from the Chinese Loess Plateau
No full textThe eco-environment of semi-arid regions is extremely sensitive and vulnerable to climate change and human activities. The realization of sustainability of eco-environments has long been a key issue. Consequently, we analysed the Chinese Loess Plateau (CLP) to identify solutions to the sustainable development of such regions. We first reviewed the eco-environmental changes in the CLP and discussed the impacts of human activities over the past 3000 years, and then summarized previous experiences on the protection and restoration of degraded eco-environments. Our study indicates that the increasing demand for cultivated land has led to the destruction of vegetation and subsequent worsening of soil erosion on the CLP, which in turn, has led to an increase in floods in the Yellow River basin. However, many positive measures, such as slope cropland abandonment and afforestation have been demonstrated to be effective in improving the eco-environment via reducing soil erosion, and decreasing sediment input and flood disasters in the Yellow River in recent decades. Nonetheless, emerging problems such as water shortage, food insecurity, rapid urban development, and over-exploitation of energy resources hinder the sustainable development of the eco-environment in the CLP. Given the historical and present eco-environmental situations of the CLP, we provide suggestions for the sustainable development of both the eco-environment and social economy, which could serve as guidelines for eco-environmental design and government policy-making in semi-arid regions globally
Coral perspective on temperature seasonality and interannual variability in the northern South China Sea during the Roman Warm Period
No full textFew reconstructions of sea-surface temperature (SST) have focused on seasonal and interannual variability, two major components of the global climate system, due to the limited temporal resolution of proxies. This study presents a combined 228-year-long, monthly resolved strontium to calcium ratios (Sr/Ca) record covering the period of 2070-1740 a BP (years before 1950 CE (Common Era)) extracted from three U-series-based sub-fossil Porites corals located on the Xisha Islands, northern South China Sea (SCS). The composite time series allowed for accurate assessment of the natural range of SST variations during snapshots of the Roman Warm Period (RWP). Reconstructed SST revealed that the RWP was characterized by cooler conditions compared with the 20th century, consistent with climatic variations in the western Pacific and East Asia. The amplitude of SST seasonality was within the modern range, except for a lower value at 1980-1928 a BP. Interannual variability associated with El Nino-Southern Oscillation (ENSO) activity was enhanced by 39% relative to 1980-2014 CE. The results of the sliding window demonstrate that ENSO variability persistently strengthened during 2070-2010 a BP, followed by an overall fluctuating attenuation during 1980-1928 a BP. Then, the trends of rising first before descending twice during 1852-1800 a BP appeared. Furthermore, ENSO activity played a leading role in steering short-term changes in SST seasonality in the northern SCS, manifested as stronger ENSO activity with more frequent El Nino events and decreased SST seasonality. Considering that the frequency of extreme ENSO events may strengthen in the future under global warming, the climate in the northern SCS might become more variable and complex
Sensitive Groups of Bacteria Dictate Microbial Functional Responses to Short-term Warming and N Input in a Semiarid Grassland
No full textEnvironmental change factors can significantly affect the composition and physiology of soil microbes. How the resulting changes in the community composition are related to microbial functions, however, remains poorly understood. We investigated the effects of climate warming (+ 1.4 degrees C of air temperature and + 0.75 degrees C of soil temperature at 10 cm depth) and reactive nitrogen (N) input (12 g N m(-2) year(-1)) on the community composition and physiologies of soil bacteria in a semiarid Loess grassland. Soil bacterial communities were assessed by Miseq sequencing of 16S rRNA gene amplicons while their physiological properties were assessed by microbial metabolic quotients (qCO(2), microbial respiration per unit of microbial biomass) and microbial community-level physiological profiles (CLPPs). Our results showed that N input, but not warming, altered bacterial community structure, although both warming and N input significantly affected the abundances of certain phyla. While phyla Verrucomicrobia and Chloroflexi were sensitive to warming, Saccharibacteria, Bacteroidetes and Actinobacteria were primarily responsive to N input. Both warming and N input increased microbial metabolic quotients, but only warming significantly impacted soil microbial CLPPs with L-cysteine, oxalic acid, oxoglutaric acid and aminobutyric acid being the sensitive C sources. Structural equation modeling showed that warming and N input influenced soil bacterial phyla through soil moisture, soil NO3--N and plant biomass. The sensitive bacterial phyla, not the whole community property, were significantly correlated with qCO(2) and microbial C utilization. Our findings suggest that responses of bacterial groups sensitive to environmental change factors, rather than the whole community, may exert dominant effects on soil microbial functions under future climate change scenarios
Timing of river capture in major Yangtze River tributaries: Insights from sediment provenance and morphometric indices
No full textThe eastern margin of the Tibetan Plateau represents one of the morphologically most active regions on Earth, where the interplay of recent crustal deformation and subsequent fluvial landscape adjustment has affected the course of continental-scale rivers by river piracy events. Based solely on field observations, such an event has been hypothesised for two of the largest tributaries of the Yangtze River: the Jialing and Hanjiang Rivers. To test this hypothesis, we employ a novel combination of independent methods including a provenance study based on age distributions of detrital zircons from both modern riverbeds and river terraces and a morphometric analysis of river channels and drainage divides. We supported the morphometric analysis with a time-dependent numerical model describing the evolution of river channel long profiles and drainage divides in a succession of river capture events. Analysed zircon ages show clearly distinguishable distributions for the modern Jialing and Hanjiang Rivers, but similar distributions for the recent Hanjiang River up to its topmost terraces. This suggests that the capture of the Hanjiang headwaters by the Jialing River is unlikely to have taken place during the last 1.2 million years. However, several knickpoints in the main stem and the tributaries of the Jialing River cluster at an elevation of about 900 m and separate steeper (downstream) from less steep channel segments (upstream), which is consistent with the morphological expression of a major capture event. chi mapping indicates drainage divide asymmetry at catchment scale with on average steeper rivers on the Jialing side, whereas Gilbert metrics show a symmetric divide at hillslope scale. This numerical model explains this apparent contradiction by the travel time of capture-related knickpoints from the capture point towards the watershed, where chi mapping indicates divide asymmetry immediately after the river capture, while Gilbert metrics are only affected as soon as the knickpoints reach the channel heads and the divide effectively starts moving. Based on knickpoint travel distances and constraints on regional incision / uplift rates, we estimate the possible date of river capture to be the Pliocene. This is earlier than the formation of the terraces investigated in the provenance study but recent enough that most of the drainage divides are still unaffected and currently almost stable. Only the wind gap located in the almost dry valley connecting the two competing drainage systems is likely to have shifted towards the Hanjiang side. We suggest that this resulted in the capture of another important tributary of the Hanjiang River (the Heishui River) by the Jialing drainage system. Our results illustrate the complex evolution of drainage networks along the eastern margin of the Tibetan Plateau, and highlight the importance for combining provenance and morphometric analyses in regions of active landscape rejuvenation where river captures are likely to occur. (c) 2021 Elsevier B.V. All rights reserved
Grain size characteristics of the sand silt layers in the ancient delta of the dried Lop Nur lake (east Tarim Basin) and their environmental implications
No full textGrain size characteristics of sediments are an effective index for the depositional environment. However, whether grain size is an accurate indicator for the formation environment is still obscure. In this study, two main types of lithology can be found in the yardang sediments from the Loulan area (Lop Nur): sand-silt layers and clay-silt layers. These two types are common in arid northwestern China. The clay-silt layers were primarily composed of lacustrine-swamp deposits, whereas the sand silt layers were formed under fluvial conditions based on geomorphic and stratigraphic lithologic evidence. However, grain size characteristics of the sand-silt layers, such as grain size distribution, C-M diagram, and grain size parameters, were consistent with that of the aeolian deposits. The study of the field deposition environment indicated that the sand-silt layers were fluvial sediments of materials originating from the aeolian sediments transported over a short distance and deposited by floods. As a result, the fluvial sediments exhibited the grain size characteristics of aeolian sediments. This indicates that some sediments may retain different depositional environment information, having undergone transportation and deposition processes. Therefore, when using grain size characteristics to determine the depositional environment, field deposition environment investigation should be combined with other environmental proxy indicators
Grain size characteristics of the sand silt layers in the ancient delta of the dried Lop Nur lake (east Tarim Basin) and their environmental implications
No full textGrain size characteristics of sediments are an effective index for the depositional environment. However, whether grain size is an accurate indicator for the formation environment is still obscure. In this study, two main types of lithology can be found in the yardang sediments from the Loulan area (Lop Nur): sand-silt layers and clay-silt layers. These two types are common in arid northwestern China. The clay-silt layers were primarily composed of lacustrine-swamp deposits, whereas the sand silt layers were formed under fluvial conditions based on geomorphic and stratigraphic lithologic evidence. However, grain size characteristics of the sand-silt layers, such as grain size distribution, C-M diagram, and grain size parameters, were consistent with that of the aeolian deposits. The study of the field deposition environment indicated that the sand-silt layers were fluvial sediments of materials originating from the aeolian sediments transported over a short distance and deposited by floods. As a result, the fluvial sediments exhibited the grain size characteristics of aeolian sediments. This indicates that some sediments may retain different depositional environment information, having undergone transportation and deposition processes. Therefore, when using grain size characteristics to determine the depositional environment, field deposition environment investigation should be combined with other environmental proxy indicators
Impacts of dynamic and thermal forcing by the Tibetan Plateau on the precipitation distribution in the Asian arid and monsoon regions
No full textThe dynamic and thermal effects of the Tibetan Plateau (TP) on the precipitation in the Asian arid and monsoon regions were investigated using three numerical experiments-one using real topography, one with the whole TP removed, and one with sensible heat turned off over the TP. The results show that there are strong seasonal and regional differences in the dynamic and thermal effects of the TP on the precipitation in the Asian arid regions. The dynamic effect dominated the decrease in winter precipitation by blocking the westerly, while the thermal effect dominated the decrease in summer precipitation due to the TP-induced compensation downdraft in Central Asia and arid East Asia. The thermal effect dominated and accounted for 60% of the decrease in summer precipitation in West Asia. The results also show that both the dynamic and thermal effects of TP exhibit a more salient influence on the East Asian monsoon region than the South Asian monsoon region. The thermal effect dominated and accounted for 40% of the increase in summer precipitation due to intensification of the summer monsoon, while the dynamic effect dominated and accounted for 80% of the decrease in winter precipitation due to the northeast wind anomaly in the northern East Asian monsoon region. The anomalous wind can reach to the coast of South China and form frontal precipitation in the southern East Asian monsoon region in winter. The thermal effect dominated and accounted for 80% of the increase in precipitation in the pre-monsoon period due to intensification of the Asian summer monsoon
Influence of landfill and land use scenario on runoff, evapotranspiration, and sediment yield over the Chinese Loess Plateau
No full textThe Gully Consolidation and Highland Protection (GCHP) project was implemented across the Loess Plateau. Understanding the impacts of the GCHP requires applications of a distributed hydrologic model. The Soil and Water Assessment Tool (SWAT) and Geography Information System (GIS) were used for evaluating the GCHP project's impact on runoff and sediments in the catchment. The correlation coefficient value, the relative error and the Nash-Sutcliffe index are 0.83, -2.30% and 0.89 for the calibration period of our SWAT model in Yanwachuan (YWC) gully by using SWAT Calibration and Uncertainty Programs (SWAT-CUP) software. The distributed hydrological model was used to simulate five scenarios of a typical watershed YWC gully in Longdong Loess Plateau, and analyzed the response of runoff, sediment, and evapotranspiration under different designed scenarios of GCHP project. The results show that gully head landfill (the loess soil were directly transferred and dumped from other places) can reduce the runoff and sediment. The simulated annual average runoff is about 2.5% lower after landfill than that in the natural state, but the evapotranspiration is about 2.4% higher. The grassland plays a more important role in water conservation than forest vegetation in the YWC watershed. The results also show that the SWAT model is useful for the study of the hydrological response of GCHP at the watershed scale. The results of this study are providing scientific information to predict and prevent soil erosion
Effects of atmospheric aging processes on in vitro induced oxidative stress and chemical composition of biomass burning aerosols
No full textBiomass burning (BB) has an important impact on local/regional air quality and human health in China, but most previous studies overlooked the influence of atmospheric aging processes on cytotoxicity and chemical composition of BB aerosols. In this study, we combined a combustion chamber and an oxidation flow reactor to generate fresh and aged BB PM2.5. Human bronchial epithelial BEAS-2B cells were exposed to PM2.5 preparation for 24 h, and then determined for particle-induced reactive oxygen species (ROS) in vitro. The particle-induced ROS production increased by 11 %-64 % after two days of aging, suggesting an enhancement of in vitro-induced oxidative stress (OS) of aged BB particles. Chemical analysis showed that organic matter (OM) was the dominant component with no changes in relative abundance for the fresh and aged BB particles. Organic polycyclic aromatic compounds and some metals showed strong correlations with ROS in fresh particles, indicating the important effects of these harmful components on the OS of fresh BB aerosols. However, such correlations were not found for the aged particles, which is possibly related to the loss of non- or low-toxic semivolatile compounds and the formation of secondary harmful OM (such as some N-containing organic compounds) during the atmospheric aging processes