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Diverse Regional Sensitivity of Summer Precipitation in East Asia to Ice Volume, CO2 and Astronomical Forcing
No full textThe relative influence of insolation, CO2, and ice sheets on the East Asian summer monsoon (EASM) is not well understood especially at regional scale. Here a Gaussian emulator based on simulations with HadCM3 is used to quantitatively assess how astronomical forcing, CO2, and northern hemisphere ice sheets affect the variation of the summer precipitation over the last 800 ky. Our results show that in the EASM domain north of 25 degrees N, the variation of the summer precipitation is dominated by precession, leading to strong 23-ky cycles, while the ice sheets only modulate the effect of insolation by influencing the land-sea pressure gradient. In the southern part, ice sheets play a more important role, generating 100-ky cycles, through influencing the latitude of the Intertropical Convergence Zone and the Hadley cell. Obliquity and CO2 have little effect on the summer precipitation as compared to precession and ice sheets
Heavy Metal Concentrations in Orchard Soils with Different Cultivation Durations and Their Potential Ecological Risks in Shaanxi Province, Northwest China
No full textThe heavy metal pollution of soils, resulting from long-term fertilizing activity, is becoming serious in many countries, endangering ecological safety and human health. This study employed inductively coupled plasma-mass spectrometry (ICP-MS) to investigate concentrations of eight heavy metal elements (Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn) in five apple orchard soil profiles after different cultivation durations, one modern intercropping farmland soil profile, and one natural soil profile from Baishui County, in Shaanxi Province, Northwest China. The potential risk associated with the presence of heavy metals in the soils was assessed by the single-factor pollution index (P-i), Nemerow comprehensive index (NCI), and potential ecological risk index (RI). Results showed that the average concentrations of Cr, Ni, As, Pb, and Hg in the farmland soil were higher than those in the apple orchard soils. The average concentrations of Ni, Cu, As, and Hg in the apple orchard soils reached the highest after 25 years of cultivation. The results imply that concentrations of heavy metals will increase with increasing cultivation time. The farmland soil had the highest NCIs, while the NCIs of the apple orchard soils also increased with cultivation time. Compared with the quality standards of pollution-free orchards and green food production areas, all P(i)s and NCIs were less than 1 and 0.7, respectively, indicating that the soils were in healthy condition. The RI results also suggest that the soils have a low ecological risk (RI < 150). Although the potential ecological risk is currently low, predicting and reducing heavy metal input should be considered
Climate change drivers alter root controls over litter decomposition in a semi-arid grassland
No full textPlant roots are the primary source of soil organic carbon (C) and critically support the growth and activities of microbes in the rhizosphere. Climate change factors may, however, modify root-microbial interactions and impact C dynamics in the rhizosphere. Yet, the direction and magnitude of interactive climate change effects, as well as the underlying mechanisms, remain unclear. Here we show evidence from a field experiment demonstrating that warming and precipitation changes strengthen root controls over litter decomposition in a semi-arid grassland. While warming and precipitation reduction suppressed microbial decomposition of root litter regardless of the root presence, precipitation increase stimulated litter decomposition only in the absence of roots, suggesting that plant competition for water constraints the activities of saprophytic microbes. Root presence increased microbial biomass but reduced microbial activities such as respiration, C cycling enzymes and litter decomposition, indicating that roots exert differential effects on microbes through altering C or water availability. In addition, nitrogen (N) input significantly reduced microbial biomass and microbial activities (respiration). Together, these results showed that alterations in soil moisture induced by climate change drivers critically modulate root controls over microbial decomposition in soil. Our findings suggest that warming-enhanced plant water utilization, combined with N-induced suppression of microbes, may provide a unique mechanism through which moderate increases in precipitation, warming and N input interactively suppress microbial decomposition, thereby facilitating short-term soil C sequestration in the arid and semi-arid grasslands
Seasonal variation and positive matrix factorization result reveal the sources of giant pandas' exposure to POPs
No full textPersistent organic pollutant (POPs) contamination was analyzed in samples collected from wild and captive giant pandas to characterize seasonal variation in concentrations of POPs and possible sources. POP concentrations in bamboo and fecal samples collected from captive pandas showed significant fluctuations compared with those collected from wild pandas in each season. The highest polychlorinated biphenyl (PCB) and organochlorine pesticide (OCP) concentrations were 1380 pg g-1 dw and 3140 pg g-1 dw, respectively, which were observed in captive bamboo samples in the summer. PCBs varied seasonally, whereas OCPs did not show apparent seasonal variation. Based on the seasonal variability, component analysis, and the positive matrix factorization results, we determined that the secondary volatilization of POPs during periods of high temperatures was the leading cause of the exposure of pandas to pollutants (45%), and atmospheric transport played a crucial role in the secondary distribution of pollutants in panda food. The other two sources of pollution were historical residues transmitted over long distances to protected areas (28%), as well as UP-POPs and new inputs from agricultural activities (27%). The concentrations of pollutants in bamboo shoots were significantly lower than those in bamboo. Therefore, bamboo shoots should be incorporated into the diet of captive pandas in the spring to reduce their exposure to pollutants. The absorption capacity of pollutants associated with the consumption of bamboo shoots was significantly lower than that associated with the consumption of bamboo. The diet of young captive pandas in the summer should also be managed with caution given their slightly stronger ability to absorb pollutants
The critical mechanics of the initiation of loess flow failure and implications for landslides
No full textAn essential hypothesis is that the flow failure landslides occurring in the Chinese Loess Plateau may initiate in the high-moisture-content loess in the capillary zone rather than in the saturated zone within the slope. Two effective stress paths, namely, the monotonically increasing loading and wetting-based constant loading under undrained conditions, are performed on intact and mechanically compacted loess, aiming at specifying their hydromechanical trajectories when subjected to an increasing water content. The results indicate that static liquefaction is initiated when the soil moisture reaches a threshold during the wetting process after exhibiting a sharp increase in pore water pressure accompanied by strain-softening behavior. Accordingly, we define this state as the initiation of flow failure under the unsaturated framework to distinguish it from static liquefaction, and first propose its corresponding critical mechanics and criterion. Its validity and physical justification are mainly evidenced by the following observations: i) Significant difference in the pore characteristics of the test samples before and after flow failure initiation; ii) Approximate equivalence between the measured and predicted hydromechanical thresholds at the flow failure initiation state; iii) Existence of the strength envelope corresponding to the flow failure initiation state; and iv) The uniqueness of the modified critical state line in the full suction range. This paper provides a general approach to accurately identify the flow failure potential for unsaturated loess, especially in the capillarity zone within a slope, which is of vital importance to the early identification and risk mitigation of loess landslides with a fluidization pattern
Determination of iodine-129 in twenty soil and sediment reference materials
No full textIncreasing attention has been paid to I-129 in soils and sediments for the purpose of environmental radioactivity monitoring, and understanding historic nuclear activities and their impacts. Accurate measurement of I-129 is vital, which greatly increases the requirement of various certified reference materials (CRMs). However, only a few CRMs with low levels of I-129 are available for accurate determination of I-129 in samples remote from nuclear sites and facilities. Here, this work investigated the concentrations of I-129 and I-127, and I-129/I-127 atomic ratios in twenty Chinese soil and sediment CRMs commercially available, as well as one in-house soil standard material (XASTD), with high-temperature pyrolysis combustion coupled with ICP-MS and accelerator mass spectrometry (AMS) measurements. This study demonstrates that I-129 concentrations in the twenty CRMs and one laboratory soil standard range from 0.31 x 10(6) atoms per g to 34.7 x 10(6) atoms per g, which were 1-4 orders of magnitude lower than those of the reference materials in use. For accurate measurement of I-129, the effect of salinity content in the samples on the iodine current intensity of the AMS measurement is firstly discussed. Significant salinity effect occurred when a high-salinity sample is analysed, which is likely due to the formation of abundant strong oxidants during the pyrolysis process, resulting in the existence of iodine as iodate instead of iodide. And finally, an analytical procedure is recommended for the low- and high-salinity soil and sediment samples. In summary, the reported data of the CRMs and the laboratory in-house control soil standard would broaden the group of available reference materials, be useful for method development of low-level I-129 samples, interlaboratory comparison and short- and long-term quality control, as well as extend I-129 applications in geological, environmental and nuclear sciences
Environmental and health risks of VOCs in the longest inner-city tunnel in Xi & rsquo;an, Northwest China: Implication of impact from new energy vehicles
No full textTraffic source-dominated volatile organic compound (VOC) samples were collected during four time-intervals in a day (I: 7:30-10:30, II: 11:00-14:0 0, III: 16:30-19:30, and IV: 20:00-23:0 0) in a tunnel in summer, 2019, in Xi & rsquo;an, China. The total measured VOC (TVOC) in periods I and III (rush hours, 107.2 +/- 8.2 parts per billion by volume [ppbv]) was 1.8 times that in periods II and IV (non-rush hours, 58.6 +/- 13.8 ppbv), consistent with the variation in vehicle numbers in the tunnel. The considerably elevated ethane and ethylbenzene levels could have been attributed to emissions from compressed natural gas vehicles and the rapid development of methanol-fueled taxis in Xi & rsquo;an in 2019. The mixing ratios of benzene, toluene, ethylbenzene, and xylenes (BTEX) contributed 9.4%-12.7% to TVOCs, and the contributions were nearly 40% higher in periods I and III than in II and IV, indicating that BTEX levels were strongly affected by vehicle emissions. The indicators of motor vehicle emission, namely ethylene, propylene, toluene, m/p-xylenes, o-xylene, and propane, contributed to more than half of the ozone formation potential in this study. The noncarcinogenic risks of VOCs in this study were within the in-ternational safety standard, whereas the carcinogenic risks exceeded the standard by 2.3-4.6 times, suggesting that carcinogenic risks were more serious than noncarcinogenic risks. VOCs presented 2.2 and 1.4 times noncarcinogenic and carcinogenic risks during rush hours than during non-rush hours, respectively. Notably, the carcinogenic risk in period IV was comparable with that in period III; however, the vehicle numbers and VOC mixing ratios were the lowest at night, which may have attributed to the increasing number and proportion of methanol M100-fueled vehicles in the tunnel. Therefore, VOCs emitted by new energy vehicles should also be seriously considered while evaluating fossil fuel vehicle emissions.
(c) 2021 Elsevier Ltd. All rights reserved
The influence of ice sheet and solar insolation on Holocene moisture evolution in northern Central Asia
No full textThe arid region of Central Asia is one of the world's major sources of dust and exerts a significant influence on marine ecosystems, atmospheric carbon dioxide concentrations, the global radiation budget, and thus global climate change. Recent global warming has considerably reduced mid-latitude net precipitation by decreasing the latitudinal temperature gradient between the Equator and the Arctic; however, the influence of ice sheet and solar insolation on moisture evolution in Central Asia during the Holocene remains uncertain. Here we show that the relative wet conditions during the early Holocene in northern Central Asia (NCA) were controlled principally by the southern position of the mid-latitude Westerlies under the negative phase of the North Atlantic Oscillation (NAO), a pattern that was influenced by the substantial remnants of the Laurentide and Fennoscandian ice sheets. Subsequent northward migration of the mid-latitude Westerlies under a positive NAO phase resulted in persistent drought conditions during the middle Holocene thermal maximum, due to the combined effects of relatively higher summer insolation and Arctic amplification as well as sea ice loss. In contrast, southward migration of the mid-latitude Westerlies since approximately 3.6 cal kyr BP, driven by declining summer insolation and coincident with the negative NAO phase, increased regional precipitation towards to persistent relatively wet conditions in Central Asia. This reconstructed pattern of Holocene moisture availability contrasts markedly with the increase in precipitation over Central Asia under the current anthropogenically forced warming, thereby justifying further investigation into the multiple forcing mechanisms driving natural and anthropogenic climate change
Salinity-controlled isomerization of lacustrine brGDGTs impacts the associated MBT5ME terrestrial temperature index
No full textBranched glycerol dialkyl glycerol tetraethers (brGDGTs) are microbial molecular fossils ubiquitous in natural environments. The correlation between the Methylation Index of brGDGTs (the MBT5ME paleothermometer) and temperature offers an important tool for reconstructing past terrestrial temperatures. However, factors other than temperature could also affect the distribution of brGDGTs in lacustrine systems, hampering the quantitative application of this paleothermometer. Here we investigated brGDGT distributions in contemporary sediments collected from 52 lakes in mid-latitude Asia. Combined with published brGDGT data from other lakes across the globe, we have found a strong salinity control on the relative abundance of 5-methyl brGDGTs versus their late-eluting isomers (including 6-methyl, 7-methyl, and unknown isomers). This allows the development of novel indices based on the isomerization of brGDGTs for tracing past lake water salinity. We also demonstrate , that salinity-controlled isomerization of pentamethylated and hexamethylated brGDGTs can significantly impact the MBT5ME paleothermometer, , potentially leading to an overestimation of past temperature, but the temperature signal can be extracted out of the MBT5ME index after correcting the salinity effect. As demonstrated in application to a Lake Qinghai (China) sediment core spanning the last 18 kyr, our finding could facilitate the simultaneous retrieval of reliable temperature and salinity records using brGDGTs in lacustrine settings, in particular for lakes that have experienced large salinity changes during the geological past. (C) 2021 Elsevier Ltd. All rights reserved
Process optimization of plasma-catalytic formaldehyde removal using MnOx-Fe2O3 catalysts by response surface methodology
No full textTo remove the toxic formaldehyde efficiently, a non-thermal plasma (NTP) system incorporated with MnOx-Fe2O3 catalyst has been developed herein. A response surface methodology (RSM) was utilized to explore the effects of a variety of experimental parameters (gas flow rate, molar ratio of Fe/Mn, and discharge power) on formaldehyde degradation systematically. The results demonstrated that the discharge power has the greatest impact on the formaldehyde degradation process, while the molar ratio of Fe/Mn has the least influence. Moreover, the amount of adsorbed oxygen species, reducibility, and average specific surface area of the tested catalyst are estimated as the dominant factors influencing the catalytic performance. Importantly, the optimal formaldehyde removal efficiency (95.01%) and CO2 selectivity (86.20%) were acquired at 5 W discharge power, 0.5 L min(-1) gas flow rate, and 0.71 Fe/Mn molar ratio. This study can thus provide an efficient strategy for formaldehyde removal