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Lake eutrophication in northeast China induced by the recession of the East Asian summer monsoon
No full textLakes are one of the most important freshwater resources on Earth and they provide a wide range of ecosystem services. However, due to rapid economic development and the intensification of human activities, many lakes have become eutrophic, which may threaten their status as water resources. Human activities have played a significant role in lake eutrophication, but whether this role is independent of, or coupled with, natural climate change requires further study. We selected Dali Lake, a large lake affected by human activity within the ancient warfare borders, to clarify the ecological response of a lake to climate change and human activity. We used analyses of sedimentary n-alkanes and AMS C-14 dating to reconstruct the paleolimnological evolution of Dali Lake since 15 cal kyr BP, and specifically to assess the timing and causes of eutrophication. The results show that the short-chain n-alkanes (C17-19-alkanes) in Dali Lake are mainly produced by bacteria and algae within the lake, and that the sedimentary absolute abundance of short-chain n-alkanes (A(17-19)-alkanes) can be used as a proxy for assessing the ecological status of the lake. The ecological status of Dali Lake was the most stable during the early to middle Holocene, when the East Asian summer monsoon was strong, but bacterial and algal outbreaks occurred during three episodes of a weakened summer monsoon-the Older Dryas, Younger Dryas, and the Common Era-when the lake experienced different degrees of eutrophication. During the recession of the East Asian summer monsoon, the weakening of precipitation recharge of the lake led to a reduction in lake area and an increase in nutrient concentrations in the lake water, while aeolian dust input was an additional nutrient source, leading to bacterial and algal outbreaks. During the Common Era, lake eutrophication occurred in the context of both summer monsoon recession and enhanced human activities, but their combined effects did not lead to more intense lake eutrophication than was caused by monsoon recession during the Younger Dryas. We conclude that, although human activities have enhanced the eutrophication of Dali Lake, the reduction in lake size due to monsoon recession and the resulting increase in the salinity and nutrient concentration of the lake water, combined with increased aeolian inputs, were a more important trigger of lake eutrophication. (C) 2022 Elsevier Ltd. All rights reserved
Phyto-mediated photocatalysis: a critical review of in-depth base to reactive radical generation for erythromycin degradation
No full textErythromycin (ERY), designated as a risk-prioritized macrolide antibiotic on the 2015 European Union watch list, is the third most commonly used antibiotic, most likely due to its ability to inhibit the protein. ERY has revealed record-high aquatic concentrations threatening the entire ecosystem and hence demands priority remedial measures. The inefficiency of various conventional ERY degradation methodologies opened up a gateway to advanced technologies. The conventional approach comprising of a chemically formulated, single photocatalyst has a major drawback of creating multiple environmental stresses. In this context, photocatalysis is grabbing tremendous attention as an efficient and cost-effective antibiotic treatment approach. Several studies have ascertained that ZnO, TiO2, Fe3O4, and rGO nanoparticles possess remarkable pollution minimizing operational capabilities. Additionally, composites are found much more effective in antibiotic removal than single nanoparticles. In this review, an attempt has been made to provide a comprehensive baseline for efficient reactive radical production by a phyto-mediated composite kept under a certain source of irradiation. Considerable efforts have been directed towards the in-depth investigation of rGO-embedded, phyto-mediated ZnO/TiO2/Fe3O4 photocatalyst fabrication for efficient ERY degradation, undergoing green photocatalysis. This detailed review provides photocatalytic nanocomposite individualities along with a hypothetical ERY degradation mechanism. It is assumed that derived information presented here will provoke innovative ideas for water purification incorporating green photocatalysis, initiating the construction of high-performance biogenic hierarchical nanocatalysts
OH-initiated atmospheric degradation of hydroxyalkyl hydroperoxides: mechanism, kinetics, and structure-activity relationship
No full textHydroxyalkyl hydroperoxides (HHPs), formed in the reactions of Criegee intermediates (CIs) with water vapor, play essential roles in the formation of secondary organic aerosol (SOA) under atmospheric conditions. However, the transformation mechanisms for the OH-initiated oxidation of HHPs remain incompletely understood. Herein, the quantum chemical and kinetics modeling methods are applied to explore the mechanisms of the OH-initiated oxidation of the distinct HHPs (HOCH2OOH, HOCH(CH3)OOH, and HOC(CH3)(2)OOH) formed from the reactions of CH2OO, anti-CH3CHOO, and (CH3)(2)COO with water vapor. The calculations show that the dominant pathway is H-abstraction from the -OOH group in the initiation reactions of the OH radical with HOCH2OOH and HOC(CH3)(2)OOH. H-abstraction from the -CH group is competitive with that from the -OOH group in the reaction of the OH radical with HOCH(CH3)OOH. The barrier of H-abstraction from the -OOH group slightly increases when the number of methyl groups increase. In pristine environments, the self-reaction of the RO2 radical initially produces a tetroxide intermediate via oxygen-to-oxygen coupling, and then it decomposes into propagation and termination products through asymmetric two-step O-O bond scission, in which the rate-limiting step is the first O-O bond cleavage. The barrier height of the reactions of distinct RO2 radicals with the HO2 radical is not affected by the number of methyl substitutions. In urban environments, the reaction with O-2 to form formic acid and the HO2 radical is the dominant removal pathway for the HOCH2O radical formed from the reaction of the HOCH2OO radical with NO. The beta-site C-C bond scission is the dominant pathway in the dissociation of the HOCH(CH3)O and HOC(CH3)(2)O radicals formed from the reactions of NO with HOCH(CH3)OO and HOC(CH3)(2)OO radicals. These new findings deepen our understanding of the photochemical oxidation of hydroperoxides under realistic atmospheric conditions
Exploring the photocatalytic conversion mechanism of gaseous formaldehyde degradation on TiO2-x-OV surface
No full textTo understand the conversion mechanism of photocatalytic gaseous formaldehyde (HCHO) degradation, strontium (Sr)-doped TiO2-x-OV catalysts was designed and synthesized in this study, with comparable HCHO removal performance. Our results proved that foreign-element doping reduced Ti4+ to the lower oxidation state Ti(4-x)+, and that the internal charge kinetics was largely facilitated by the unbalanced electron distribution. Oxygen vacancies (OVs) were developed spontaneously to realize an electron-localized phenomenon in TiO2-x-OV, thereby boosting O-2 adsorption and activation for the enhanced generation of reactive oxygen species (ROS). At the chemisorption stage, in-situ DRIFTS spectra and density functional theory calculation results revealed that surface adsorbed O-2 (O-ads) and lattice O (O-lat) engaged in the isomerisation of HCHO to dioxymethylene (DOM) on TiO2-x-OV and TiO2, respectively. Time-resolved DRIFTS spectra under light irradiation revealed that the DOM was then converted to formate and thoroughly oxidized to CO2 and H2O in TiO2-x-OV. While bicarbonate byproducts were detected from DOM hydroxylation or possible side conversion of CO2 in TiO2, owing to insufficient consumption of surface hydroxyl. Our study enhances the understanding on the photocatalytic oxidation of HCHO, thereby promoting the practical application in indoor air purification
Organic aerosol formation and aging processes in Beijing constrained by size-resolved measurements of radiocarbon and stable isotopic C-13
No full textThis study investigates the sources and atmospheric processes of size-resolved carbonaceous aerosols in winter 2018 in urban Beijing, based on analysis of dual-carbon isotopes (i.e., radiocarbon and the stable isotope C-13). We found a size dependence of fossil source contributions to elemental carbon (EC), but no clear size dependence for organic carbon (OC). Comparable fossil source contributions to water-insoluble OC (WIOC; 55 +/- 3%) and to water-soluble OC (WSOC; 54 +/- 4%) highlight the importance of secondary aerosol formation, considering that fossil sources emit only small amounts of primary WSOC. OC concentrations increased during high PM2.5 pollution events, with increased fossil and non-fossil WSOC concentrating at larger particles (0.44-2.5 mu m) than WIOC (0.25-2.5 mu m), highlighting the aqueous-phase chemistry as an important pathway for OC production. The ratio of C-13/C-12 (expressed as delta C-13) of total carbon (-27.0 parts per thousand to -23.3 parts per thousand) fell in the range of anthropogenic aerosol, reflecting small biogenic influence. delta C-13 of OC increased with desorption temperature steps (200 degrees C, 350 degrees C and 650 degrees C). The strongly enriched delta C-13(OC, 650) (-26.9 parts per thousand to -20.3 parts per thousand) and large mass fraction of OC650 degrees C in total desorbed OC, both increasing with the increase of particle sizes, were caused by photochemical aging, especially during low and moderate PM2.5 pollution events, when regional, aged aerosol played an important role. During low pollution events, higher delta C-13(OC, 650) and WSOC/OC ratios reflect a larger contribution and more extensive chemical processing of aged aerosol. In contrast, relatively low delta C-13(OC, 200) (-27.2 parts per thousand to -25.7 parts per thousand) suggests the influence of secondary OC formation on the more volatile OC desorbed at 200 degrees C. delta(13)C(OC, 20)0 was similar for all particle sizes and for different pollution events, pointing to an internal mixture of local and aged regional OC. Our results show that the organic aerosol in Beijing arises from a mixture of various sources and complex formation processes, spanning local to regional scales. Particle sizes < 250 nm show strong contribution from local secondary OC formation, whereas refractory OC in particles around 1 mu m shows strong evidence for regional aging processes. In summary, primary emission, secondary and aqueous-phase formation, and (photo-) chemical aging all need to be considered to understand organic aerosol in this region and their importance varies with particle size
Sediment Soot Radiocarbon Indicates that Recent Pollution Controls Slowed Fossil Fuel Emissions in Southeastern China
No full textFossil fuel (FF) combustion emissions account for a large, but uncertain, amount of the soot in the atmosphere, play an important role in climate change, and adversely affect human health. However, historical estimates of FF contributions to air pollution are limited by uncertainties in fuel usage and emission factors. Here, we constrained FF soot emissions from southeastern China over the past 110 years, based on a novel radiocarbon method applied to sedimentary soot. The reconstructed soot accumulations reflect the integrated effects of increased FF use caused by economic development and reductions in emissions due to pollution controls. A sharp increase in FF soot started in 1950 as southeastern China industrialized and developed economically, but decreased FF soot fluxes in recent years suggest that pollution controls reduced soot emissions. We compare FF soot history to changes in CO2 emissions, industrial and economic activities, and pollution controls and show that FF soot fluxes are more readily controlled than atmospheric CO2. Our independent FF soot record provides insights into the effects of economic development and controls on air pollution and the environmental impacts from the changes in soot emissions
Water Resource Management Implications for a Desert Oasis From Tree-Ring delta O-18 Variations in Populus Euphratica in Northwest China
No full textPaleoclimatic data has often been applied to demonstrate the influence of anthropogenic activities on runoff to desert rivers, and such features as reservoirs are clearly known to influence available water in downstream riparian settings. The impact of human activities on the hydrology of a downstream desert oasis is, however, an open question. High-resolution hydroclimate paleo-reconstructions for desert oases are lacking, partly because paleoclimate proxies in extremely dry deserts are insensitive to extremely low precipitation. Here, we first attempt to reconstruct regional precipitation (r = -0.743, p < 0.001, n = 49) for the interval 1886-2009 from the stable oxygen isotope ratio (delta O-18) of five Populus euphratica trees growing in the Ejina Oasis, on the lower reaches of the Heihe River in extremely arid Northwest China. The delta O-18 series for P. euphratica in the oasis (similar to 900 m a.s.l) abruptly increases relative to an delta O-18 series of Qinghai spruce (Picea crassifolia) growing in upper limit of forest (similar to 3,000 m a.s.l) in Longshou Mountain (middle reaches of the Heihe River) after about 2000, when the Ecological Water Diversion Project on the Heihe River was implemented. This finding implies that the Ejina Oasis suffered from serious drought during the last decade, or at least that the Oasis is stressed more than expected by current climate conditions. Other evidence also indicates that human activities contributed to a decrease in air moisture in the Ejina Oasis after 2000. To mitigate water stress on the oasis, we recommend some practical measures to ensure the rational development of the desert oasis
Water Flow Characteristics Controlled by Slope Morphology under Different Rainfall Capacities and Its Implications for Slope Failure Patterns
No full textThe high sensitivity of loess slopes to water has been emphasized in many studies. However, it is still limited in terms of the understanding of slope morphological differentiation on the overall and local failure patterns in slopes, as well as on the acquisition method of hydrological dynamics. In this study, rainfall characteristics and slope surface morphological differences were introduced. Geoelectric and environmental factors were monitored. On this basis, apparent resistivity corrected by seasonal temperature and its relationship with soil water content was calibrated. The water migration characteristics and potential failure patterns of three slope morphologies were evaluated. The results are: (i) the improved resistivity method can better reflect the water flow movement within the slope, and it performs well after being corrected by temperature; (ii) the characteristics of surface runoff and water infiltration are directly affected by the cumulative rainfall value, and especially when the cumulative rainfall is >70 mm threshold, the surface runoff quickly infiltrates into the deep of the slope along the preferential paths; (iii) the interception ability of loess slope morphology to the surface runoff is concave slope > convex slope > linear slope; (iv) with the continuous rainfall, the convex surface of a slope is prone to be damaged by saturated mud flow. When the cumulative rainfall threshold is 70 mm, the preferential flow is easily excited on the concave surface of the slope, resulting in local collapse at the slope toe and mid-deep landslides
Differential health and economic impacts from the COVID-19 lockdown between the developed and developing countries: Perspective on air pollution
No full textIt is enlightening to determine the discrepancies and potential reasons for the degree of impact from the COVID-19 control measures on air quality as well as the associated health and economic impacts. Analysis of air quality, socio-economic factors, and meteorological data from 447 cities in 46 countries indicated that the COVID-19 control measures had significant impacts on the PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 mu m) concentrations in 20 (reduced PM2.5 concentrations of -7.4-29.1 mu g m(-3)) of the selected 46 countries. In these 20 countries, the robustly distinguished changes in the PM2.5 concentrations caused by the control measures differed between the developed (95% confidence interval (CI): -2.7-5.5 mu g m(-3)) and developing countries (95% CI: 8.3-23.2 mu g m(-3)). As a result, the COVID-19 lockdown reduced death and hospital admissions change from the decreased PM2.5 concentrations by 7909 and 82,025 cases in the 12 developing countries, and by 78 and 1214 cases in the eight developed countries. The COVID-19 lockdown reduced the economic cost from the PM2.5 related health burden by 54.0 million dollars in the 12 developing countries and by 8.3 million dollars in the eight developed countries. The disparity was related to the different chemical compositions of PM2.5. In particular, the concentrations of primary PM2.5 (e.g., BC) in cities of developing countries were 3-45 times higher than those in developed countries, so the mass concentration of PM2.5 was more sensitive to the reduced local emissions in developing countries during the COVID-19 control period. The mass fractions of secondary PM2.5 in developed countries were generally higher than those in developing countries. As a result, these countries were more sensitive to the secondary atmospheric processing that may have been enhanced due to reduced local emissions
Factors controlling the spatial variability of soil aggregates and associated organic carbon across a semi-humid watershed
No full textY Soil aggregates (SA) play crucial roles in soil organic carbon (SOC) sequestration. Different SA fractions contribute differently to the sequestration of SOC. However, few studies have examined the factors controlling SA fractions and associated SOC contents across a watershed. Soil samples were collected at 0-10 cm (surface layer) and 10-20 cm (subsurface layer) from 88 sites across a semi-humid watershed (1.1 km(2)) on the Loess Plateau, China. These samples were separated into macroaggregates (MA), microaggregates (MI), and silt + clay fractions (SC) by wet-sieving, and SOC content of each fraction was determined. The objectives were to: 1) investigate the spatial variability of SA fractions and associated SOC contents as well as their main controls across an entire watershed, and 2) explore the linkages between soil aggregation and SOC sequestration. The bulk and aggregate SOC contents of all SA fractions showed moderate variability, with coefficient of variations of 23.3-31.9%. Geostatistical analysis indicated that the spatial patterns of SA fractions and SOC content varied with aggregate size. From combined Spearman's correlation analysis and structural equation modelling, we found that soil texture was an important control on the spatial variability of all SA fractions and associated SOC contents. Vegetation dynamics and management practices associated with land use were also important controls on MA and MI and their associated SOC contents, especially in the surface layer. However, SC and its associated SOC content were more sensitive to ecohydrological processes related to topography. Among the land uses, grassland had the greatest SOC sequestration potential. The fine roots of herbs can wrap MI in MA and increase SOC content within MA, which is the primary mechanism responsible for SOC sequestration in grasslands. These results indicate that using vegetation with fine root systems for restoration is a good strategy to increase SOC sequestration in this region. (C) 2021 Elsevier B.V. All rights reserved