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Vegetation dynamics and its response to climate change during the past 2000 years in the Altai Mountains, northwestern China
No full textOver the past 2000 years, a high-resolution pollen record from the Yushenkule Peat (46 degrees 45 '-46 degrees 57 ' N, 90 degrees 46 '-90 degrees 61 ' E, 2374 m a.s.l.) in the south-eastern Altai Mountains of northwestern China has been used to explore the changes in vegetation and climate. The regional vegetation has been dominated by alpine meadows revealed from pollen diagrams over the past 2000 years. The pollen-based climate was warm and wet during the Roman Warm Period (0-520 AD), cold and wet during the Dark Age Cold Period (520-900 AD), warm and wet during the Medieval Warm Period (900-1300 AD), and cold and dry during the Little Ice Age (1300-1850 AD). Combined with other pollen data from the Altai Mountains, we found that the percentage of arboreal pollen showed a reduced trend along the NW-SE gradient with decreasing moisture and increasing climatic continentality of the Altai Mountains over the past 2000 years; this is consistent with modern distributions of taiga forests. We also found that the taiga (Pinus forest) have spread slightly, while the steppe (Artemisia, Poaceae and Chenopodiaceae) have recovered significantly in the Altai Mountains over the past 2000 years. In addition, the relatively warm-wet climate may promote high grassland productivity and southward expansion of steppe, which favors the formation of Mongol political and military power
Abnormally warm-saline alkenone signature in Lake Tuosu in centennial cold-wet periods over the late Holocene: An exceptional case for alkenone application
No full textPaleoclimatic reconstructions on the arid/semi-arid northern Tibetan Plateau are important for understanding the complex interactions between the mid-latitude westerly and subtropical Asian monsoon circulations. The development of paleoclimatic reconstructions largely relies on the invention and application of proper quantitative/semi-quantitative temperature and salinity proxies. Over the last few decades, alkenones have shown great potential as indicators of the past temperatures and salinities of lakes on the northern Tibetan Plateau. Several alkenone-based temperature and salinity records have confirmed centennial warm-dry and cold-wet variations during the Holocene on the northern Tibetan Plateau. Herein, we present alkenone-based records from Lake Tuosu in the Qaidam Basin over the last similar to 1200 years. The alkenone signals show similar characteristics to published alkenone records in the nearby region during centennial warm periods (the Medieval Warm Period and Current Warm Period). However, the alkenones from Lake Tuosu demonstrate abnormally warm and saline signals during centennial cold periods (mainly during the Little Ice Age), in contrast to the widely recognized cold-wet conditions in the Qaidam Basin. Accordingly, the alkenone records from Lake Tuosu provide an exceptional case for the application of alkenones. The abnormally warm and saline alkenone signals from Lake Tuosu during centennial cold periods cannot be explained by either the presence of the C-37:3 alkenone isomer or seasonal bias in alkenone production. Changes in species composition might be an alternative reason for this, which requires a further investigation of the sources of alkenones in lakes in the future
Discussion of the paper "Loess genesis and worldwide distribution" by Yanrong Li, Wenhui Shi, Adnan Aydin, et al.
No full textSynthesis of Calcium Silicate Hydrate from Coal Gangue for Cr(VI) and Cu(II) Removal from Aqueous Solution
No full textBoth the accumulation of coal gangue and potentially toxic elements in aqueous solution have caused biological damage to the surrounding ecosystem of the Huainan coal mining field. In this study, coal gangue was used to synthesize calcium silicate hydrate (C-S-H) to remove Cr(VI) and Cu(II)from aqueous solutions and aqueous solution. The optimum parameters for C-S-H synthesis were 700 & DEG;C for 1 h and a Ca/Si molar ratio of 1.0. Quantitative sorption analysis was done at variable temperature, C-S-H dosages, solution pH, initial concentrations of metals, and reaction time. The solution pH was precisely controlled by a pH meter. The adsorption temperature was controlled by a thermostatic gas bath oscillator. The error of solution temperature was controlled at & PLUSMN; 0.3, compared with the adsorption temperature. For Cr(VI) and Cu(II), the optimum initial concentration, temperature, and reaction time were 200 mg/L, 40 & DEG;C and 90 min, pH 2 and 0.1 g C-S-H for Cr(VI), pH 6 and 0.07 g C-S-H for Cu(II), respectively. The maximum adsorption capacities of Cr(VI) and Cu(II) were 68.03 and 70.42 mg & BULL;g(-1), respectively. Furthermore, the concentrations of Cu(II) and Cr(VI) in aqueous solution could meet the surface water quality standards in China. The adsorption mechanism of Cu(II) and Cr(VI) onto C-S-H were reduction, electrostatic interaction, chelation interaction, and surface complexation. It was found that C-S-H is an environmentally friendly adsorbent for effective removal of metals from aqueous solution through different mechanisms.</p
Assessment of the emission mitigation effect on the wintertime air quality in the Guanzhong Basin, China from 2013 to 2017
No full textWith the completion of the Air Pollution Prevention and Control Action Plan (Action Plan) in the Guanzhong Basin (GZB), the wintertime fine particulate matters (PM2.5) concentration has decreased by 50.0 mu g m(-3) (33.4%) from 2013 to 2017. Considering the significant impacts of meteorological conditions on particulate pollution, the effectiveness of anthropogenic emissions abatement on the PM2.5 reduction in the GZB remain unclear. In this study, the WRF-Chem model was used to quantitatively evaluate the effectiveness of emissions mitigation on the particulate pollution in the GZB in December from 2013 to 2017. The model typically showed an affordable consistence with observations and simulation in meteorological parameters, atmospheric pollutants, and aerosol components. Sensitivity results revealed that emissions reduction decreases PM2.5 concentrations by around 17% in the GZB, about half of the observed PM2.5 decreased in December from 2013 to 2017, showing significant role of meteorological conditions in modulating particulate pollution. Emissions mitigation also decreased SO2, CO and O-3 concentrations by around 55%, 17%, and 7%, respectively, but increased NO2 concentrations by 27%. Additionally, the PM2.5 decrease in the GZB is mainly contributed by the reduction of sulfate and primary organic aerosols, caused by implementation of stringent SO2 mitigation measures and reduced coal use. However, the mitigation of elemental carbon, dust and nitrate aerosols are not significant, particularly with regarding to nitrate aerosols, which is influenced by increase of NO2 and decrease of sulfate. Specified emissions mitigation strategies need to be designed to further lower the PM PM2.5 level in the GZB
Estimates and determinants of soil organic carbon and total nitrogen stocks up to 5 m depth across a long transect on the Loess Plateau of China
No full textPurpose Carbon (C) and nitrogen (N) soil profiles are influenced by several environmental factors. However, the contents and distributions of these elements in deep soils and sediments are largely underestimated. We aimed to estimate the stocks, patterns, and driving factors of deep soil C and N on the Chinese Loess Plateau (CLP) after large-scale ecological restoration projects. Materials and methods Soil organic carbon (SOC) and total nitrogen (TN) contents in different soil layers were measured directly at 86 sites along a regional transect across the CLP. Results and discussion SOC and TN contents ranged from 1.97 to 6.83 g C kg(-1) and 0.24 to 0.72 g N kg(-1), respectively, as the soil depth varied from 0 to 5 m. The mean contents and degrees of variability of SOC and TN decreased with the increasing of soil depth. Based on SOC and TN content patterns, we divided the 0-5-m soil profile into layers of 0-0.1, 0.1-0.4, 0.4-1, and 1-5 m. In the 1-5-m soil layer, approximately 70% of the mean SOC stock (14.97 kg C m(-2)) and 71% of the mean TN stock (1.75 kg N m(-2)) were stored. A partial least square regression model showed satisfactory predictive performance, with R-2 and Q(2) > 0.5 for SOC and TN stocks in the 0.1-0.4-m soil layer. Climatic factors, soil water content (SWC), and field capacity strongly affected SOC and TN stocks in all soil layers. The significance of clay content, SWC, and normalized difference vegetation index varied with soil depth and became the strongest in the 1-5-m soil layer. The highest proportion of SOC and TN stocks for this soil layer were found in grassland and in 450-550 mm rainfall zone. Conclusion Considerable amounts of SOC and TN stocks were stored in the 1-5-m-deep soils. Land-use types and rainfall zones can significantly affect the SOC and TN stocks. This information is helpful for identifying local land uses associated with high SOC and TN stocks and is essential for accurately estimating and predicting regional C and N stocks and cycles in terrestrial ecosystems
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
The formation and evolution of secondary organic aerosol during summer in Xi'an: Aqueous phase processing in fog-rain days
No full textSecondary organic aerosol (SOA) is an important contributor to organic aerosol (OA), however, the model simulations of SOA concentrations and oxidation states remain significant uncertainties because of inadequate cognition of its formation and aging chemistry. In this study, SOA formation and evolution processes during summer in XIan were investigated, based on high-resolution online measurements of non-refractory PM2.5 (NR-PM2.5) species and OA source apportionment using positive matrix factorization. The results showed that the total SOA, including less oxidized-oxygenated OA (LO-OOA), more oxidized-oxygenated OA (MO-OOA), and aqueous-phase-processed oxygenated OA (aq-OOA), on average constituted 69% of OA, and 43% of NR-PM2.5, suggesting the high atmospheric oxidation capacity and the dominance of SOA during summer in Xi'an. Photochemical oxidation processes dominated the summertime SOA formation both during non-fog-rain days and fog-rain days, which were responsible for the formation of both LO-OOA and MO-OOA. Consistently, LO-OOA and MO-OOA in total contributed 59% to OA during non-fog-rain days and 56% to OA during fog-rain days, respectively. On the contrary, aq-OOA was mainly observed during fog-rain days, which increased dramatically from 2% of OA during non-fog-rain days to 19% of OA during fog-rain days with the mass concentration increasing accordingly from 0.3 mu g m(-3) to 2.5 mu g m(-3). Episodic analyses further highlighted the persistently high RH high aerosol liquid water content (ALWC) was the driving factor of aq-OOA formation, and high O-x condition could further enhance its formation. Meanwhile, air masses from east and southeast were much favorable for the formation of long-time fog-rain days, which facilitated aq-OOA production during summer in Xi'an. (C) 2020 Elsevier B.V. All rights reserved
Spectral absorption properties of organic carbon aerosol during a polluted winter in Beijing, China
No full textA fraction of organic carbon (OC) is found to exhibit the capability to absorb solar radiation. However, the absorption properties of OC remain poorly characterized partly due to uncertainties in determination methods. In this study, the absorption coefficient (b(ap)) of OC (b(ap,OC)) in Beijing during a polluted winter was estimated on the basis of the combined measurements of black carbon (BC) size distribution and total aerosol b(ap) (b(ap,meas)). The bare BC b(ap) (b(ap,bareBC)) calculated using Mie theory on the basis of measured size distribution exhibited weak wavelength dependence, with a mean absorption Angstrom exponent (AAE) of 0.56 +/- 0.04 within the 470-660 nm wavelength range, which was lower than the value of 1 commonly used for freshly emitted BC. The calculated b(ap,bareBC) was compared with b(ap,meas) at 950 nm to derive the coating thickness of BC, from which the calculation of coated BC b(ap) (b(ap,coatBC)) within 370-660 nm was based using the core-shell Mie model. Given the thick coatings, the AAE of coated BC, with a mean of 0.53 +/- 0.12, was slightly lower than that of bare BC. Subsequently, b(ap,OC) was obtained by subtracting b(ap,coatBC) from bap,meas, accounting for 59.57 +/- 4.82% of bap,meas at 370 nm on average. The average mass absorption efficiency of OC was estimated to be 1.48 +/- 0.36 m(2) g(-1) at 370 nm. b(ap,OC) significantly decreased as wavelength increased, deriving an AAE of OC with a mean of 2.72 +/- 0.32 within the 370-660 nm range. The level of b(ap,OC) estimated on the basis of a widely used attribution method assuming a constant BC AAE of 1 was similar to 60% lower than the currently presented value, probably underestimating OC radiative effect by a factor of >3. More accurate estimations of b(ap,OC) based on more advanced measurements and suitable theory calculations are recommended to provide more reliable assessments of OC radiative effects. (C) 2020 Elsevier B.V. All rights reserved