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Orbital-scale Asian summer monsoon variations: Paradox and exploration
No full textThe Asian summer monsoon (ASM) is a vast climate system, whose variability is critical to the livelihoods of billions of people across the Asian continent. During the past half-century, much progress has been made in understanding variations on a wide range of timescales, yet several significant issues remain unresolved. Of note are two long-standing problems concerning orbital-scale variations of the ASM. (1) Chinese loess magnetic susceptibility records show a persistent glacial-interglacial dominated similar to 100 kyr (thousand years) periodicity, while the cave oxygen-isotope (delta O-18) records reveal periodicity in an almost pure precession band (similar to 20 kyr periodicity)-the "Chinese 100 kyr problem". (2) ASM records from the Arabian Sea and other oceans surrounding the Asian continent show a significant lag of 8-10 kyr to Northern Hemisphere summer insolation (NHSI), whereas the Asian cave delta O-18 records follow NHSI without a significant lag-a discrepancy termed the "sea-land precession-phase paradox". How can we reconcile these differences? Recent and more refined model simulations now provide spatial patterns of rainfall and wind across the precession cycle, revealing distinct regional divergences in the ASM domain, which can well explain a large portion of the disparities between the loess, marine, and cave proxy records. Overall, we also find that the loess, marine, and cave records are indeed complementary rather than incompatible, with each record preferentially describing a certain aspect of ASM dynamics. Our study provides new insight into the understanding of different hydroclimatic proxies and largely reconciles the "Chinese 100 kyr problem" and "sea-land precession-phase paradox"
Heavy metals in different moss species in alpine ecosystems of Mountain Gongga, China: Geochemical characteristics and controlling factors
No full textTerrestrial mosses are promising tracers for research concerning metal atmospheric deposition and pollution. Concentrations of Cr, Co, Ni, Zn, Sr, Cd, Ba, and Pb in different moss species from Mountain Gongga, China were analyzed to investigate the effects of growth substrates, geographic elevation, and type of moss species on the accumulation characteristics of heavy metals, as well as to identify heavy metal sources. The ability of heavy metals to accumulate in moss varied significantly, with low concentrations of Cd and Co; medium concentrations of Cr, Ni, and Pb; and high concentrations of Zn, Sr, and Ba. Elevation significantly influenced the accumulation characteristics of heavy metals, with high concentrations found at lower elevations due to proximal pollution. Growth substrate and moss species were found to have certain influence on the bioconcentration capacities of heavy metals in moss in this study. Correlation analysis showed similar sources for Sr, Zn, and Ba, as well as for Ni, Co, and Cr. The positive matrix factorization (PMF) model was consistent with atmospheric deposition of Pb and Cd; substrate sources of Cr, Co, and Ni; and anthropogenic sources of Ba, Sr, and Zn. This research characterized the accumulation characteristics of heavy metals and their influence factors in different mosses found in alpine ecosystems and provides a reference for future studies in similar areas. (C) 2020 Elsevier Ltd. All rights reserved
How dusty was the last glacial maximum over Europe?
No full textOur study focuses on European loess sequences, particularly the eolian intervals in between the observed pedogenic units. The classical concept of soil formation from parent material is reformulated to estimate of the duration and the associated sedimentation rate (SR) and mass accumulation rate (MAR) of these paleodust intervals. We show that the Greenland Stadial (GS) duration in European loess deposits includes the thickness of the overlying pedogenic unit, which in fact developed downward into the upper part of the eolian unit. The lower stratigraphical limit of the eolian unit overlying the pedogenic unit corresponds to the restart of the dust sedimentation of the younger GS. We illustrate this interpretation first by computing both SRs and MARs first for the Nussloch key sequence, the most complete European series. The correlation between Nussloch and other European loess sequences, located along a 1800 km longitudinal transect, allows computation of SR and MAR for several identified GS events. Comparing GS from marine and ice core records, our study shows that the two last Bond cycles are preserved in every European eolian record.
Bulk SR and MAR are estimated and compared for these two Bond cycles, showing the highest SRs and MARs in western Europe. These indices also indicate that the last stadials, embedding an Henrich event, were not the dustiest in every Bond cycle. Our estimated MAR also differ from previously published computations, which did not take into account the various pedogenic units present in the studied loess sequences. The bulk SR and MAR estimates computed for the two last Bond Cycles from Chinese sequences from the Loess Plateau indicate lower atmospheric dust than in Europe during the Last Glacial Maximum. SR and MAR estimates computed from the fine-grained material for European records fit with Earth System model reconstructions. (C) 2020 Elsevier Ltd. All rights reserved
Mutation test and multiple-wavelet coherence of PM2.5 concentration in Guiyang, China
No full textThe negative effects of PM2.5 concentration in urban development are becoming more and more prominent. Bernaola-Galvan Segmentation Algorithm (BGSA) and wavelet analysis are powerful tools for processing non-linear and non-stationary signals. First, we use BGSA that reveals there are 41 mutation points in the PM2.5 concentration in Guiyang. Then, we reveal the multi-scale evolution of PM2.5 concentration in Guiyang by wavelet analysis. In the first part, we performed one-dimensional continuous wavelet transform (CWT) on the eight monitoring points in the study area, and the results showed that they have obviously similar multi-scale evolution characteristics, with a high-energy and significant oscillation period of 190-512 days. Next, the wavelet transform coherence (WTC) reveals the mutual relationship between the PM2.5 concentration and the atmospheric pollutants and meteorological factors. PM2.5 concentration variation is closely linked to that of PM10 concentration. But, it is not to be ignored that the increase in the SO2 and NO2 concentrations will cause the PM2.5 concentration to rise on different scales. Lastly, the variation of the PM2.5 concentration can be better explained by the combination of multiple factors (2-4) using the multiple-wavelet coherence (MWC). Under the combination of the two factors, the average temperature (Avgtem) and relative humidity (ReH) have the highest AWC and PASC. In the case of the combination of four factors, CO-Avgtem-Wind-ReH plays the largest role in determining PM2.5 concentration
Decreasing concentrations of carbonaceous aerosols in China from 2003 to 2013
No full textCarbonaceous aerosols were characterized in 19 Chinese cities during winter and summer of 2013. Measurements of organic carbon (OC) and elemental carbon (EC) levels were compared with those from 14 corresponding cities sampled in 2003 to evaluate effects of emission changes over a decade. Average winter and summer OC and EC decreased by 32% and 17%, respectively, from 2003 to 2013, corresponding to nationwide emission control policies implemented since 2006. The extent of carbon reduction varied by season and by location. Larger reductions were found for secondary organic carbon (SOC, 49%) than primary organic carbon (POC, 25%). PM2.5 mass and total carbon concentrations were three to four times higher during winter than summer especially in the northern cities that use coal combustion for heating
Stable-isotope tracing of vadose-zone water transport in Achnatherum splendens grassland of the Qinghai Lake Basin, NE Qinghai-Tibet Plateau, China
No full textThe vadose zone serves as a connection and transformation link between the atmosphere, plants, soil, surface water and groundwater. It is considered to be an important component of the geosphere and has sensitive interactions with the hydrosphere, biosphere, and atmosphere, which greatly impacts the environment and human health. This study was conducted in the Achnatherum splendens grassland of the Qinghai Lake Basin, NE Qinghai-Tibet Plateau, China, and can provide references and guidance for research on the mechanisms governing the circulation and evolution of vadose-zone water in cold arid regions. Precipitation, dustfall, and vadose zone samples were collected to investigate transport in the vadose zone water using stable isotopes of hydrogen (delta H-2) and oxygen (delta O-18) as well as chloride as environmental tracers. The results showed that precipitation was the main source of chloride in the research area, accounting for 86.5% of total chloride deposition. The soil water in the vadose zone was mainly recharged by local precipitation. Strong evaporation occurred before the precipitation infiltrated and recharged soil water. The soil water, chloride content, and isotope values in the soil profile varied across different depths. The annual potential recharge from precipitation to the vadose zone soil water was 9.20 mm/yr, accounting for 2.17% of the local precipitation. The actual recharge from precipitation to groundwater was 26.29 mm/yr, accounting for 6.19% of the local precipitation. The infiltration recharge from preferential and piston flow accounted for 66.40% and 33.60% of the total infiltration recharge to groundwater, respectively, indicating that preferential flow was the main source of groundwater recharge in the studied grassland. The results of this study were compared with those of other relevant studies. The recharge mechanisms of the vadose zone soil water and groundwater varied between different regions and were controlled mainly by the spatiotemporal distribution of precipitation, topographic characteristics, and soil structure. These findings provide a reference and guidance for research on the circulation and evolution of vadose-zone water in the Qinghai Lake Basin and Qinghai-Tibet Plateau
Stable isotopes and chloride ion of precipitation events in the northeastern Tibetan Plateau, China
No full textStable isotopes and chloride ion of precipitation are ideal environmental tracers to explain and reveal the formation and evolution mechanisms of water bodies. It is crucial to investigate the stable isotopes and chloride in precipitation events in the northeastern part of the Tibetan Plateau (NETP) due to the limitation of available data. This study sampled each event of precipitation during the period from July 2018 to June 2019 and the monthly dustfall in the NETP to investigate the temporal changes of stable isotopes and chloride in precipitation, and to reveal the moisture source of precipitation over the NETP using a back trajectory model. Results showed that the delta H-2 values of precipitation ranged from -183.51 parts per thousand to 17.75 parts per thousand, and the delta O-18 values ranged from -25.18 parts per thousand to 0.48 parts per thousand. The slope of the Local Meteoric Water Line was slightly lower than 8 due to the effect of below-cloud secondary evaporation on the precipitation process. Most d-excess values were higher than 10 parts per thousand because moisture recycled from the continent and Qinghai Lake surface mixed with precipitation. The chloride in precipitation accounted for 86.5% of the annual total deposition mass of chloride (1329.64 mg/m(2)), indicating that precipitation was the main source of chloride in the NETP. The temperature and amount effects of stable isotope in the precipitation were obvious in the NETP. The precipitation was predominantly derived from the Westerly Circulation from September through May and the East Asian Monsoon from June to August, with precipitation amounts of 246.5 mm and 178.0 mm, respectively, indicating that the precipitation over the NETP brought by the Westerly Circulation was more than that brought by the East Asian Monsoon. The air mass over the NETP transited in late May and early September, and a slight change in transition period would mainly be related to the intensity of the East Asian Monsoon, which is strongly influenced by El Nino-Southern Oscillation. These results provide not only baseline data for hydrological and climatological studies of the NETP but also valuable insights into the hydrological process in the inland arid area of Asia
Removal mechanism and quantitative control of trichloroethylene in a post-plasma-catalytic system over Mn-Ce/HZSM-5 catalysts
No full textIt is urgent to control trichloroethylene (TCE) due to its harmful effect on the environment and humans. Here, a post-plasma-catalytic (PPC) system combining Mn-Ce/HZSM-5 catalysts and a corona discharge reactor was developed for TCE degradation. Among the tested catalysts, MnCe1/HZSM-5 (Ce/Mn molar ratio = 1) showed the best catalytic performance due to its better reducibility and higher content of adsorbed oxygen. The PPC configuration markedly lowered the activation temperature of the catalyst. Then, the optimization of the TCE degradation process in the PPC system was performed using response surface methodology. The results showed that the discharge power was the dominant factor affecting the TCE degradation process, followed by the gas flow rate and relative humidity (RH). The optimum TCE removal efficiency of 99.9%, CO2 yield of 52.84% and CO yield of 22.74% were obtained under the following operating conditions: discharge power 1.13 W, gas flow rate 0.5 L min(-1) and RH 18.77%. The stability of the PPC system over the MnCe1/HZSM-5 catalyst was successfully evaluated by a long-time test. Finally, the TCE degradation pathway in the PPC system was also proposed. This study strengthens the understanding of the TCE decomposition mechanism and paves a way for quantitative control of TCE in the PPC system
Groundwater hydrochemistry, source identification and pollution assessment in intensive industrial areas, eastern Chinese loess plateau
No full textGroundwater is essential for regional ecological-economic system and is an important resource of drinking water, especially in the Chinese Loess Plateau (CLP), where is a typical water-limited ecosystem. Groundwater quality deterioration will affect water security and exacerbate the water shortages. Groundwater hydrochemistry, pollution source apportionment, quality and health risks were evaluated based on analysis of major ions and selected trace elements in seasonal samples of the Fen River Basin (FRB) in the eastern CLP. Groundwaters in the FRB were mainly HCO3--Ca-2(+)-Na+ water type with low dissolved solutes in upstream samples, high values in midstream samples and medium values in downstream samples. Solutes in upstream samples were mainly derived from carbonate weathering, while those in midstream and downstream samples came from silicate weathering, evaporites dissolution and anthropogenic sources. Self-organizing map (SOM) showed the hydrochemistry remained unchanged from dry to wet season for most sampling points. The seasonal variations of Ag, Cd, Ni, Pb, and Tl were significant due to anthropogenic input. High NO3- in upstream and downstream samples resulted primarily from sewage discharge, and high SO42- in midstream and downstream samples was from gypsum- and coal-related industries. In addition, anthropogenic input related to coal industries significantly aggravates pollution of As, Ni, Ag, Fe, and Mn. Influenced by evaporites and anthropogenic input, midstream samples had high salinity, total hardness and water quality indices (WQIs) and were unsuitable for irrigation or drinking purposes. Seasonal variation of WQI in the FRB was unsignificant except Jiaokou River sub-basin, where groundwater quality was worse in the wet season than the dry season due to coal mining. Great attention should be paid to the high non-carcinogenic risks of exposure to F, V, Mn, and Cr via dermal absorption, particularly for children. Overall, groundwater quality in the FRB was best in upstream, medium in midstream and worst in midstream based on different index. Groundwater quality is deteriorated by anthropogenic input and the sewage discharge in the FRB should be strictly controlled. Our report provides a reference for groundwater pollution evaluation and source identification in similar areas. (c) 2021 Elsevier Ltd. All rights reserved
Geochemical fractionation and spectroscopic fingerprinting for evaluation of the environmental transformation of potentially toxic metal(oid)s in surface-subsurface soils
No full textThe contamination of soil by toxic metal(oid)s has emerged as a major concern worldwide, particularly in developing countries. A metals behavior in the soil environment is influenced by organic matter, mineral phases, and oxidation states in which a particular metal exists. However, the spectroscopic evidence of metal(oid)s interactions in soil with organic matter and mineral phases can induce an extensive understanding. The surface and sub-surface soils (0-50 cm) from four sites of upper Indus basin, Pakistan, were collected and analyzed by using FTIR (Fourier-transform infrared spectroscopy), XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy) in addition to ICP-MS (inductively coupled plasma mass spectrometry) and geochemical fractionation. Geochemical fractionation of metal(oid)s indicated that As, Cu, Ni, Pb, and Zn were mostly found in the potentially bioavailable fractions. However, an increase in the residual fraction was observed from top to bottom. The absorption bands of FTIR spectra were divided into three spectral regions 700-400, 1700-800, and 3700-2800 cm(-1). The soil was found rich in organic matter and capable of retaining metals as abundant peaks were observed in the mid-infrared region. The mineralogical analysis of soil samples testified silicon oxides and zeolite as major mineral phases. The XPS spectra showed broad peaks of As(III), As2O3, As4S4, PbO2, and PbCo3. The study concludes that the source identification of metal(oid)s in the upper Indus is crucial to find out the particular source of contamination in the soil