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Intra-leaf heterogeneities of hydrogen isotope compositions in leaf water and leaf wax of monocots and dicots
No full textSeveral recent studies showed that leaf wax n-alkane delta H-2 values (delta H-2(wax)) within a leaf were heterogeneous in a small number of species. It still remains unclear whether the heterogeneity of intra-leaf delta H-2(wax) values is general for various species, how delta H-2(wax) values vary spatially and temporally, and whether there is a common explanation for the intra-leaf delta H-2(wax) heterogeneity in higher plants. Here we compared the hydrogen isotope compositions of leaf wax and corresponding leaf water (delta H-2(lw)) across leaf sections among a variety of monocot and dicot plant species. There is significant and consistent heterogeneity for both delta H-2(wax) and delta H-2(lw), i.e., base-to-tip 2H-enrichment for monocots (except Hemerocallis citrina, and Dactylis glomerata) whereas base-to-tip and center-to-edge increases in delta H-2(wax) and delta H-2(lw) for dicots. The consistent occurrence of variations of delta H-2(lw) and delta H-2(wax) values within a leaf imply that delta H-2(wax) values probably inherit point-to-pint from in-situ delta H-2(lw) values, and thus the intra-leaf delta H-2(wax) heterogeneity mainly results from the spatial pattern of intra-leaf delta H-2(lw) values associated with veinal structures between dicots and monocots. The general heterogeneity of intra-leaf delta H-2(wax) values further intensifies that it is necessarily needed for in-depth understanding leaf wax biomarker. (C) 2021 Elsevier B.V. All rights reserved
Holocene Environmental Archaeology of the Yangtze River Valley in China: A Review
No full textThe Yangtze River Valley is an important economic region and one of the cradles of human civilization. It is also the site of frequent floods, droughts, and other natural disasters. Conducting Holocene environmental archaeology research in this region is of great importance when studying the evolution of the relationship between humans and the environment and the interactive effects humans had on the environment from 10.0 to 3.0 ka BP, for which no written records exist. This review provides a comprehensive summary of materials that have been published over the past several decades concerning Holocene environmental archaeology in the Yangtze River Valley, to further understand large-scale regional Holocene environmental and cultural interaction within this area. The results show that: (1) in recent years, Holocene envi-ronmental archaeology research in the Yangtze River Valley has primarily taken paleoflood and sea-level change stratigraphical events to be the foundational threads for study. This began with research on the spatiotemporal distribution of archaeological sites, typical archaeological site stratigraphy, and research on background features concerning environmental evolution recorded by the regional natural sedimentary strata. (2) Significant progress has been made at the upper, middle, and lower reaches of the Yangtze River, indicating that Holocene environmental ar-chaeology research along the Yangtze River Valley is deepening and broadening. (3) Dramatic changes to Neolithic cultures that occurred approximately 4.0 ka BP were influenced by climate change and associated consequences, although the impacts differed on the various Neolithic cultures in the Yangtze River Valley. Local topography, regional climate, and varying survival strategies may have contributed to these differences. (4) Newly-published research pays particular attention to the sedimentary records of the past with resolutions as high as one year to several months, the degree to which humans altered the quality of their natural environment, and human adjustments to settlement and subsistence practices during periods of Holocene climate change. The application of technologies such as remote sensing, geographic information systems (GIS), and molecular biological analysis are also gradually being extended into the research field of Holocene environmental archaeology in the Yangtze River Valley
Characteristics of Chemical Speciation in PM1 in Six Representative Regions in China
No full textA better knowledge of aerosol properties is of great significance for elucidating the complex mechanisms behind frequently occurring haze pollution events. In this study, we examine the temporal and spatial variations in both PM1 and its major chemical constituents using three-year field measurements that were collected in six representative regions in China between 2012 and 2014. Our results show that both PM1 and its chemical compositions varied significantly in space and time, with high PM1 loadings mainly observed in the winter. By comparing chemical constituents between clean and polluted episodes, we find that the elevated PM1 mass concentration during pollution events should be largely attributable to significant increases in organic matter (OM) and inorganic aerosols like sulfate, nitrate, and ammonium (SNA), indicative of the critical role of primary emissions and secondary aerosols in elevating PM1 pollution levels. The ratios of PM1/PM2.5 are found to be generally high in Shanghai and Guangzhou, while relatively low ratios are seen in Xi'an and Chengdu, indicating anthropogenic emissions were more likely to accumulate in forms of finer particles. With respect to the relative importance of chemical components and meteorological factors quantified via statistical modeling practices, we find that primary emissions and secondary aerosols were the two leading factors contributing to PM1 variations, though meteorological factors also played important roles in regulating the dispersion of atmospheric PM
Identification of the featured-element in fine road dust of cities with coal contamination by geochemical investigation and isotopic monitoring
No full textThe exploitation of coal releases large amounts of contaminants into the environment. However, the featured pollutants of coal utilization as well as the scope and degree of their impact remain to be revealed. To identify the featured-element of coal contamination in a complex environment, a typical coal resource city was selected, and the major elements, 18 trace elements, as well as ?13C, ?15N, and ?34S in the fine road dust and certain source materials were analyzed. Through multiple analysis methods, the featured-element was determined step-by-step: firstly, elements with enrichment coefficients greater than two in road dust were focused: Zn, Hg, Pb, Cu, Cd, and Cr; secondly, difference analysis showed a significant difference (p < 0.05) of Hg and Cu concentration at different distance from the coal-fired power plant, making Hg and Cu the only candidates for the featuredelement; finally, through coal-related source materials determination, Cu was not qualified as a featuredelement. Therefore, Hg was the only left element to be considered as the featured-element. To be more convincing, more analyses were performed to support Hg as the featured-element: cluster analysis and isotope monitoring indicated Hg in road dust could originate from coal combustion; X-ray photoelectron spectroscopy was also conducted, where the forms of Hg in road dust with possible source materials were compared, and the presence of HgO and Hg only in the road dust near the power plant indicated the impact of the power plant on the surrounding dust. Through the health risk assessment, it was found that Hg in the road dust had no health risk, though the study area still had Pb, Cr, and As risks, which were not closely related to the pollutants released by coal-related sources
Post-fire co-stimulation of gross primary production and ecosystem respiration in a meadow grassland on the Tibetan Plateau
No full textPredicting post-fire ecosystem CO2 exchange requires an explicit understanding of the sensitivity of gross primary production (GPP), ecosystem respiration (ER) and net ecosystem exchange (NEE) to post-fire conditions. However, the simultaneous effects of fire on GPP, ER and NEE are rarely evaluated. We established a three-year manipulative fire experiment in a meadow grassland on the Tibetan Plateau to investigate the responses of GPP, ER and NEE to prescribed fire. We found that fire on average increased GPP by 13% and ER by 9%, leading to an increase in NEE by 20% across the three years. There was no clear relationship between post-fire changes in soil temperature and ecosystem CO2 exchange, yet reductions in soil volumetric moisture were positively related to changes in GPP, ER and NEE. These results suggest that post-fire stimulation of GPP, ER and NEE cannot be fully explained by changes in soil temperature and soil moisture. Besides, changes in GPP, ER and NEE were positively related to fire-induced increases in graminoid biomass, legume biomass and soil inorganic nitrogen. Taken together, our results suggest the interwoven control of biotic and abiotic factors on post-fire GPP, ER and NEE, yet also that shifts in plant functional type biomass may outweigh the negative effects of reduced soil moisture on ecosystem CO2 exchange. These results underscore how simultaneous documentation of GPP, ER and NEE dynamics can advance a mechanistic understanding of CO2 exchange under fire disturbance
Time series of atmospheric Delta(CO2)-C-14 recorded in tree rings from Northwest China (1957-2015)
No full textRadiocarbon (C-14) is a unique and important tool for understanding carbon cycle in the nature, and its use can be significantly enhanced where reliable historical atmospheric Delta(CO2)-C-14 records can be established. In China, continuous atmospheric Delta(CO2)-C-14 records since the 1950s are scarce, a period when dramatic variations of Delta(CO2)-C-14 occurred caused by intensive human activities. In this research, Delta C-14 of Qinghai spruce tree rings collected from Huangzhong (HZ) (36.27 degrees N, 101.67 degrees E, 2982 m amsl) were measured by Accelerator Mass Spectrometry, and a Delta(CO2)-C-14 time series from 1957 to 2015 was reconstructed. The results show that HZ Delta C-14 was generally higher than the contemporaneous average level in the mid-high latitudes of the Northern Hemisphere. The peak value of HZ Delta C-14 occurred in 1964 (as bomb peak) was higher than that of other tree ring records in East Asia at a similar latitude, likely due to the impact of the atmosphere nuclear tests at Semipalatinsk (Kazakhstan). The record shows no obvious disturbance of Lop Nor nuclear weapons tests (in Northwest China) during 1964-1980, except for 1971. A local Suess effect began to appear since 2001, and the estimated atmospheric fossil fuel-derived CO2 (CO2ff) concentration increased from 3.5 ppm to 8.8 ppm from 2006 to 2015. This is associated with the implementation of the "Western Development" strategy in China. HZ Delta C-14 records document background Delta C-14 data, useful for regional carbon cycle research and atmospheric CO2ff quantification in the region. These data also provide baseline values for assessment environmental safety connected with nuclear power plants in China. (C) 2021 Elsevier Ltd. All rights reserved
Impacts of primary emissions and secondary aerosol formation on air pollution in an urban area of China during the COVID-19 lockdown
No full textRestrictions on human activities were implemented in China to cope with the outbreak of the Coronavirus Disease 2019 (COVID-19), providing an opportunity to investigate the impacts of anthropogenic emissions on air quality. Intensive real-time measurements were made to compare primary emissions and secondary aerosol formation in Xi?an, China before and during the COVID-19 lockdown. Decreases in mass concentrations of particulate matter (PM) and its components were observed during the lockdown with reductions of 32-51%. The dominant contributor of PM was organic aerosol (OA), and results of a hybrid environmental receptor model indicated OA was composed of four primary OA (POA) factors (hydrocarbon-like OA (HOA), cooking OA (COA), biomass burning OA (BBOA), and coal combustion OA (CCOA)) and two oxygenated OA (OOA) factors (less oxidized OOA (LO-OOA) and more-oxidized OOA (MO-OOA)). The mass concentrations of OA factors decreased from before to during the lockdown over a range of 17% to 58%, and they were affected by control measures and secondary processes. Correlations of secondary aerosols/Delta CO with Ox (NO2 + O-3) and aerosol liquid water content indicated that photochemical oxidation had a greater effect on the formation of nitrate and two OOAs than sulfate; however, aqueous-phase reaction presented a more complex effect on secondary aerosols formation at different relative humidity condition. The formation efficiencies of secondary aerosols were enhanced during the lockdown as the increase of atmospheric oxidation capacity. Analyses of pollution episodes highlighted the importance of OA, especially the LO-OOA, for air pollution during the lockdown
Spatio-temporal distribution of Quaternary loess across Central Asia
No full textCentral Asia (CA) is one of the main loess regions in the world and provides important information for the understanding of paleoclimate and paleoenvironmental changes. However, the spatio-temporal variability of the loess distribution is still not fully understood. Combining previous studies with our recent field investigations, we focus on the spatial distribution and ages of loess sediments in CA. Loess sediments are mainly distributed on the windward piedmonts of Central Asian high mountains, e.g. the Tianshan Mountains, Kunlun Mountains, and river terraces, with distinct pedogenic characteristics. The distribution of loess sediments is not only related to atmospheric circulations and regional climate but also closely related to landforms. Based on field observations and the pedogenic environment, we recommend that the loess distribution should be divided into three subregions (Western CA, Northern CA, and Eastern CA), which are approximately coincident with the 60% and 30% winter-half year's precipitation percentage contours, and also correspond to three loess depocenters with thicknesses over 200 m. Paleomagnetic, luminescence dating and AMS C-14 geochronology indicated that most of the loess outcrops have developed since the last interglacial-glacial period; although CA loess sediments can span the entire Quaternary period and even extend into the Pliocene. AMS C-14 can provide reliable ages for the last 25-30 kyr. Quartz OSL and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating techniques, based on well-bleached natural environmental materials, can provide reliable ages younger than 80 ka. The luminescence ages of older samples may be underestimated due to signal saturation problems. Dating of deposits at some elevated locations in CA shows rapid and discontinuous deposition, implying that caution is required in the interpretation of proxies and paleoenvironment. Spatial-temporal distributions of Central Asian loess luminescence ages indicate different clusters in different loess subregions, but generally the periods of strong dust activity occurred during cold glacial periods or stadials. New dating techniques should be developed to enable high-resolution paleoclimate reconstruction
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