Institute of Earth Environment
Institutional Repository of Institute of Earth Environment, CASNot a member yet
7120 research outputs found
Sort by
Predicting long-term hydrological change caused by climate shifting in the 21st century in the headwater area of the Yellow River Basin
No full textThe Qinghai-Tibetan Plateau (QTP) is one of the amplifiers of global climate change. The headwater area of the Yellow River Basin (HYRB) on the QTP is the dominant water source region for the whole Yellow River Basin. However, the sensitive responses of hydrological processes to the intensifying climate change are exerting high uncertainties to the water cycle in the HYRB. The aim of this study was to investigate the potential climate change under three Representative Concentration Pathways (RCP 2.6, 4.5, and 8.5) and their hydrological impacts in this region using the ensemble climate data from eight general circulation models (GCMs) and the Soil and Water Assessment Tool (SWAT). Compared to the baseline (1976-2015), the projected climate indicated a rise of 7.3-7.8% in annual precipitation, 1.3-1.9 degrees C in maximum air temperature, and 1.2-1.8 degrees C in minimum air temperature during the near future period (2020-2059), and an increment of 9.0-17.9%, 1.5-4.5 degrees C, and 1.3-4.5 degrees C in precipitation, maximum and minimum temperature, respectively, during the far future period (2060-2099). The well-simulated SWAT modeling results suggested that due to a wetter and warmer climate, annual average actual evapotranspiration (AET) would increase obviously in the future (31.9-35.3% during the near future and 33.5-54.3% during the far future), which might cause a slight decrease in soil water. Water yield would decrease by 16.5-20.1% during the near future period, implying a worsening water crisis in the future. Till the end of this century, driven by the increased precipitation, water yield would no longer continue to decrease, with a decline by 15-19.5%. Overall, this study can not only provide scientific understanding of the hydrological responses to the future climate in both semi-arid and alpine areas, but also contribute to the decision support for sustainable development of water resources and protection of eco-environment in the HYRB
Patterns of diversity and community assembly change across local to regional scales: An evidence of deterministic assembly processes along resource availability gradient at temperate forest
No full textDiversity and its maintaining mechanism (community assembly) shift along resource availability gradients at local and regional levels. It is necessary to identify key natural factors shaping community assembly or diversity patterns, so that understanding the patterns of diversity and assembly along these factors across local to regional scales. In this study, we investigated the six local sites of plant community in Qinling Mountains region. Based on the relative importance of environmental factors in shaping the phylogenetic diversity, a complex resource availability gradient was established to assess taxonomic and phylogenetic diversity and assembly patterns along it at local or regional scale separately. Phylogenetic analyses and the biodiversity index were estimated along environmental gradients as well, to assess the difference between change tendencies along natural environmental and resource availability gradients. We found that 1) elevation was the most important regional-scale environmental predictor of phylogeny of community; 2) taxonomic and phylogenetic diversity studies showed similar patterns along both resource and elevational gradients at regional scale, and that diversity at local scale may differ regardless of gradients; 3) at the regional level, phylogenetic structures revealed convergent tendencies along the elevational gradient across different species pools. Phylogenetic assembly patterns along the elevation gradient at the local scale differed from the patterns at the regional scale, with consistent clustering tending to overspread along the resource availability gradient. In conclusion, resource availability shaped community assembly at the regional level. Local patterns of diversity influenced regional patterns differently because of variation in the colonization history or assembly process. Owing to varying assembly patterns along simple environmental gradients, it is vital to establish a complex resource availability gradient to dissect the real assembly mechanism or biodiversity patterns operating in local to regional-scale processes. These findings may provide valuable reference about forest restoration and management
Hydrological Changes Related to ENSO-Like States During the Last Deglaciation in Central Eastern China
No full textPresent knowledge of hydrological changes in the East Asian summer monsoon region during the last deglaciation lacks precision, most especially for central eastern China. A hydrological reconstruction based on elemental ratios, such as Rubidium/Strontium (Rb/Sr) and Zirconium/Rubidium (Zr/Rb), and grain-size distribution for the period of 22.8-7.4 ka was derived from the Dajiuhu basin in central eastern China. The reconstruction shows that there were some small wet-dry fluctuations within the basin between 22.8 and 17.5 ka, but an abrupt wetting after 17.5 ka, with a maximum occurring around 15.0 ka, then a drying trend until the early Holocene. This pattern parallels the zonal gradient of sea surface temperature (SST) across the tropical Pacific, which suggests that wet conditions in the Dajiuhu basin respond to the decreased SST zonal gradient. A marked decrease in the tropical Pacific SST zonal gradient, seen as an El Nino-like state, could lead to an anomalous anticyclonic circulation at the Western Pacific and a southward excursion of the Western Pacific Subtropical High, which favors the occurrence of wet conditions in central eastern China. Meanwhile, this El Nino-like state could sharpen the SST meridional gradient between the tropics and the extratropics, and then shift the upper tropospheric westerlies southward, which in turn induces a prolonged Mei-yu and more precipitation in central eastern China. Overall, it is concluded that the El Nino-Southern Oscillation-like states might be a major forcing for hydrological changes in central eastern China during the last deglaciation
Effects of Anomalous Arctic Polar Vortex on Vegetation Growth in Northern Eurasia
No full textThe northern Eurasia is a region heavily affected by the Arctic polar vortex (APV). Understanding the vegetation responses to anomalous APV in this region is important for dealing with climate change. In this study, we investigated the impacts and mechanism of the anomalous APV phases on the vegetation dynamics in the northern Eurasia. The larger and smaller APV phases correspond to almost opposite atmospheric circulation patterns which result in opposite vegetation responses. The decreased (increased) solar radiation, the enhanced (weakened) northerly winds, together with the decreased (increased) water vapor divergence, caused the decreasing (increasing) of the air temperature, increasing (decreasing) of the precipitation and soil moisture in the study area during the larger (smaller) APV phase. The response of vegetation growth to the APV depends on climate change and vegetation sensitivity to it. In most parts of the study area, vegetation growth was positively associated with air temperature, and hence, vegetation was suppressed (promoted) during the larger (smaller) APV phase. In the northeast of the Caspian Sea (NCS), vegetation growth was sensitive to precipitation. Therefore, the increased (decreased) soil moisture in summer and autumn were responsible for the promoted (suppressed) vegetation growth during the larger (smaller) APV phase. (Citation: Gong, H., M. Huang, and Z. Wang, 2021: Effects of anomalous Arctic polar vortex on vegetation growth in northern Eurasia. SOLA, 17, 151-157, doi:10.2151/sola.2021-027.
Asymmetric response of short- and long-duration dry spells to warming during the warm-rain season over Eastern monsoon China
No full textChanges in dry spell duration have been analyzed over China and worldwide. However, the asymmetric response (i.e. skewed distribution) of short- and long-duration dry spells to warming temperature and possible mechanisms remain unknown. Here, we investigate this response based on daily weather observations during the warm-rain season (May-September) over 1961-2019 from 1540 quality-controlled stations across Eastern Monsoon China (EMC). Our results show a 1. warming in surface air temperature (SAT) and a considerable elongation of dry spells. Specifically, the regional average, maximum, and total dry spell duration over EMC increased by +7.06%, +6.17%, and +5.16%, respectively over 1961-2019. The areas in EMC with long dry spells and high SAT are also the areas that have experienced faster increases in the duration of dry spells per degree of warming. We find increases in the frequency of long-duration dry spells, but significant decreases in the frequency of short-duration dry spells. The increasing frequency of long-duration dry-spells can be explained by the slight increase in land evaporation (+1.6%/degrees C) over EMC and the decrease in integrated moisture vapor transport (-3.8%/degrees C) with warming, such that atmospheric moisture sources cannot meet the warming-induced demand, resulting in significant decreases in relative humidity (-2.4%/degrees C) and precipitation (-7.0%/degrees C). In contrast, the decreasing frequency of short-duration dry spells during hotter warm-rain seasons occurs when the saturation vapor pressure deficit is enhanced, leading to prolonged periods where the atmosphere is replenished to necessary saturation levels for local precipitation. Relative to cold warm-rain seasons, hot warm-rain seasons with higher SAT witness cold-dry air advection in the upper level, lower convective available potential energy, and stronger vapor divergence over EMC, which tends to suppress precipitation occurrence. With future warming, the increasing frequency and duration of dry spells in the warm-rain season is likely to be conducive to the occurrence of severe droughts and heatwaves in EMC, with negative impacts on socio-economic development in China
Refined Source Apportionment of Atmospheric PM2.5 in a Typical City in Northwest China
No full textThe Xixian New District (XXND), established in 2014, is the seventh national-level new district in China, but research on air pollution there has been limited. This study focused on the characteristics and sources of PM2.5 in XXND from 2017 to 2018. The average annual PM2.5 mass was 67 mu g m(-3); loadings were high in winter and low in summer. Organic carbon (18.2%), nitrate (17.0%), and sulfate (13.1%) were the main chemical components of PM2.s. A refined statistical assessment of sources was conducted using the CAS-HERM receptor model, and it showed that primary sources accounted for similar to 58.5% of the PM2.5 annual mass, of which dust accounted for 23.3% (road, construction, and soil dust accounted for 11.4%, 8.0% and 3.9%, respectively) while motor vehicles contributed 10.1% (diesels 8.7% and gasoline vehicles 1.4%). Secondary sources for sulfates, nitrates, and organic aerosols accounted for similar to 41.5% of the PM2.5 mass. A complementary analysis using the WRF-CHEM model showed that regional transport accounted for 60.8% of the PM2.5 during the winter high-pollution period, which also implies the importance of secondary aerosols
The first detection of the Madden-Julian Oscillation signal in daily to hourly resolution proxy records derived from a natural archive of Giant Clam Shell (Tridacna spp.)
No full textThe Madden-Julian Oscillation (MJO) is the most prominent mode of intraseasonal variability in the tropics which is responsible for much of the observed intraseasonal climate variance not only there but also in higher latitudes. The short time-span of modern instrumental data limits our understanding of the MJO and obtaining MJO information from natural archives could extend this greatly. Here a Giant Clam shell (Tridacna spp.) with a life span about two years (from January 29, 2012 to December 9, 2013) was collected from the northern South China Sea, in the western Pacific. Several daily to hourly resolution biological and geochemical proxy records, including the daily growth rate, hourly Fe/Ca, Sr/Ca and fluorescence intensity, were developed to compare these with local weather/climate records. Spectral analyses suggested that these ultra-high resolution proxy records can clearly record MJO variability in the tropics. The substantial connection between the proxy records and MJO possibly linking through the local effective solar radiation, SST, precipitation and wind speeds. This is the first record of the MJO signal in a natural paleoclimate archive. Our findings provide new insights to study the MJO beyond the instrumental records, and since fossil Tridacna shells from different geological times can be used to investigate the MJO under various climate conditions. (C) 2020 Elsevier B.V. All rights reserved
Chemical etching fabrication of uniform mesoporous Bi@Bi2O3 nanospheres with enhanced visible light-induced photocatalytic oxidation performance for NOx
No full textBulk materials with a microporous structure are adverse to light adsorption, photoelectron and reactant transport in a photocatalytic reaction. Mesoporous photocatalysts have shown many marked advantages in photo catalytic fields. Herein, uniform mesoporous Bi@Bi2O3 nanospheres were fabricated by HCl-ethanol chemical etching at low temperature (60 degrees C). The obtained mesoporous photocatalysis increased the NO removal efficiency (16%) and inhibited toxic NO2 generation (3%) under visible light irradiation. Further oxidation of Bi and calcination at high temperatures were avoided during template removal. Moreover, the as-prepared sample possessed a remarkably narrower pore size distribution (3.2-3.9 nm) and stronger light and NO adsorption ability than the bulk microporous Bi@Bi2O3. Work function and the electron spin resonance test results also indicated that the position of the entire energy bands on Bi2O3 was lowered. The amount of reactive oxygen species generated over the uniform mesoporous structure was higher than that over bulk Bi@Bi2O3. However, photoelectrochemical measurements indicated that the separation efficiencies of the photo-generated carriers were not improved over the uniform mesoporous Bi@Bi2O3. Comprehensive studies have shown that the oxi-dation ability rather than the enhanced separation efficiency of charge carriers accounted for the enhanced photocatalytic activity. This work elucidates the roles of a uniform mesoporous structure in NOx photocatalytic oxidation and provides an efficient strategy for structural engineering in preparing highly reactive and practical photocatalysts
Identification of areas vulnerable to soil erosion and risk assessment of phosphorus transport in a typical watershed in the Loess Plateau
No full textSoil erosion is an increasingly serious eco-environmental problem and an important driver of phosphorus loss, which not only reduces soil productivity but also decreases water availability. The integration of the universal soil loss equation (USLE) and the geographic information system (GIS) technique is globally popular for erosion prediction and assessment. The Fen River basin is located in the east of the Loess Plateau and has eco-environmental problems of soil erosion and eutrophication because of excess phosphorus content. This study attempted to use the USLE model to evaluate soil erosion and the transport of the resulting particulate phosphorus in the Fen River basin under a GIS framework. The results showed that soil erosion in 15.8% of the study area exceeded 8000 t/(km(2).a) and was mainly distributed in the upper Fen River basin. Soil erosion was greatest in the bareland area, with an average of approximately 1.22 x 10(4) t/(km(2).a), followed by that in grassland. Soil erosion in the study area is most sensitive to the rainfall erodibility (R), followed by the soil erodibility (K), topographic factors including slope steepness (S) and slope length (L), the soil and water conservation factor (P), and the vegetation cover and management factor (C). Similar to soil erosion, the high-risk areas of particulate phosphorus transport were mainly concentrated in the upper reaches of the basin. The study also pointed out that the combined use of available data sources with the USLEmodel and GIS technique is a viable option to calculate soil erosion and assess the risk of particulate phosphorus transport, which could provide a scientific basis for reducing soil erosion and controlling phosphorus migration. (C) 2020 Elsevier B.V. All rights reserved
Comparing interglacials in eastern Australia: A multi-proxy investigation of a new sedimentary record
No full textThe widespread formation of organic rich sediments in south-east Australia during the Holocene (Marine Isotope Stage [MIS] 1) reflects the return of wetter and warmer climates following the Last Glacial Maximum (LGM). Yet, little is known about whether a similar event occurred in the region during the previous interglacial (MIS 5e). A 6.8 m sediment core (#LC2) from the now ephemeral Lake Couridjah, Greater Blue Mountains World Heritage Area, Australia, provides insight into this question. Organic rich sediments associated with both MIS 1 and 5e are identified using C-14 and optically stimulated luminescence (OSL) dating techniques. Also apparent are less organic sedimentary units representing MIS 6, 5d and 2 and a large depositional hiatus. Sediment delta C-13 values (-34 to -26 parts per thousand) suggests that C-3 vegetation dominates the organic matter source through the entire sequence. The pollen record highlights the prevalence of sclerophyll trees and shrubs, with local hydrological changes driving variations in the abundance of aquatic and lake-margin species. The upper Holocene sediment (0-1.7 m) is rich in organic matter, including high concentrations of total organic carbon (TOC; 20-40%), fine charcoal and macrophyte remains. These sediments are also characterised by a large proportion of epiphytic diatoms and a substantial biogenic component (chironomids and midges). These attributes, combined with low delta C-13 and delta N-15 values, and C:N ratios of approximately 20, indicate a stable peat system in a swamp like setting, under the modern/Holocene climate. In comparison, the lower organic rich unit (MIS 5e-d) has less TOC (5-10%), is relatively higher in delta C-13 and delta N-15, and is devoid of macrophyte remains and biogenic material. Characterisation of the organic matter pool using C-13-NMR spectroscopy identified a strong decomposition signal in the MIS 5e organic sediments relative to MIS 1. Thus the observed shifts in delta C-13, delta N-15 and C:N data between the two periods reflects changes in the organic matter pool, driven by decompositional processes, rather than environmental conditions. Despite this, high proportions of aquatic pollen taxa and planktonic diatoms in the MIS 5e-d deposits, and their absence in the Holocene indicates that last interglacial Lake Couridjah was deeper and, or, had more permanent water, than the current one. (C) 2020 Elsevier Ltd. All rights reserved