Institute of Earth Environment
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PM2.5 pollution in China's Guanzhong Basin and the USA's San Joaquin Valley mega-regions
No full textThe Guanzhong Basin (GZB) of northwest China is examined as a mega-region containing the mega-city of Xi'an. The concept of a "mega-region" is more accurate than that of a "mega-city" for air quality management as there is an interaction between urban and non-urban emissions. Parallels are drawn between the GZB and the San Joaquin Valley (SJV) mega-region of central California for excessive wintertime PM2.5 concentrations. Long-term chemical composition measurements show the usual high levels of organic and elemental carbon, minerals, sulfate, nitrate, and ammonium. Wintertime provides prolonged high pressure systems in both areas punctuated by unstable precipitation events. Sluggish nighttime winds allow pollutants such as ammonia from distant agricultural operations, to mix with urban pollutants, sometimes serving as a reactor to create secondary sulfates and nitrates, and possibly some secondary organic compounds. A shallow surface layer forms at night in the SJV and GZB that couples to an upper level inversion after sunrise, allowing pollutants accumulated aloft to mix to the surface. Although current air quality management strategies have focused on urban emissions, and PM2.5 levels are on a downward trend, future management efforts must consider reducing emissions from a variety of sources in the larger region of these basins. Agricultural emissions are important in the SJV, but are just being addressed in the GZB. Tactics developed for the SJV would probably be effective in other areas of the world with similar emissions, topography, and meteorology. Experiments related to agricultural NOx emissions, emission inventory enhancements, source apportionment, and estimates of precursor limitations for ammonium nitrate formation, have been conducted in the SJV that can be tested in the GZB
New chronology of the Chinese loess-paleosol sequence by leaf wax delta D records during the past 800 k.y.
No full textThe Chinese loess-paleosol sequences provide important archives for studying paleoenvironmental changes. However, the lack of independent and accurate time scales hinders the study between loess and other records. Asian stalagmite delta O-18 records indicate synchronous patterns of paleoprecipitation delta O-18 over large geographic regions. The record of hydrogen isotopic composition of plant wax (delta D-wax) in Chinese loess is also controlled by rainwater delta D. Both share a common origin. The linear relationship between rainfall delta O-18 and delta D variance provides the basis to tie together chronologies of the same climate event in different records. Here, we show a new loess chronology by correlating chronologies of marker boundaries of the prominent climate chronozones in stalagmite delta O-18 and summer insolation to the equivalent climate stratigraphy in the loess delta D-wax sequence. We first developed and tested this novel methodology with data since the last interglacial on a millennial scale, and then applied this approach to the loess delta D-wax sequence for the past 800 k.y. to improve the traditional chronology based on magnetic susceptibility and grain size. The new delta D-wax time series provides not only an improved chronology for studying paleoclimate changes during interglacial intervals, it also represents a unique database with which to better understand the links between the Asian monsoon changes in the Chinese loess and other global climate events, especially for the periods prior to 640 ka, for which stalagmite records are not available
Identification of nitrate sources in the Jing River using dual stable isotopes, Northwest China
No full textNitrate (NO3-) contamination has become a dominant international problem in the aquatic environment, so identifying the sources and transformations of NO3- is the basis for improving water quality. Since the Jing River is the largest tributary of the Wei River, to understand its water quality, this study collected surface water samples from the Shaanxi section of the Jing River during the dry season. The potential sources of NO3- were analyzed by hydrochemical and bi-isotopic methods, and the SIAR model was used to estimate the proportional contribution of each source. Results indicated that NO3--N was the main form of inorganic nitrogen in this area, and the average total nitrogen content was 10.23 mg center dot L-1, which showed that nitrogen pollution was highly serious; the transformation process of nitrogen in this study area was mainly nitrification; The results of Bayesian model showed that manure and sewage contributed to the most NO3- (64.39%) in the dry season, followed by soil nitrogen, which was 26.35%. These results help to adopt better nitrogen management measures to meet the national environmental quality standards for surface water
Effects of Excessive Equatorial Cold Tongue Bias on the Projections of Tropical Pacific Climate Change. Part II: The Extreme El Nino Frequency in CMIP5 Multi-Model Ensemble
No full textUnder increased greenhouse gas (GHG) forcing, climate models tend to project a warmer sea surface temperature in the eastern equatorial Pacific than in the western equatorial Pacific. This El Nino-like warming pattern may induce an increase in the projected occurrence frequency of extreme El Nino events. The current models, however, commonly suffer from an excessive westward extension of the equatorial Pacific cold tongue accompanied by insufficient equatorial western Pacific precipitation. By comparing the Representative Concentration Pathway (RCP) 8.5 experiments with the historical simulations based on the Coupled Model Intercomparison Project phase 5 (CMIP5), a "present-future" relationship among climate models was identified: models with insufficient equatorial western Pacific precipitation error would have a weaker mean El Nino-like warming pattern as well as a lower increase in the frequency of extreme El Nino events under increased GHG forcing. Using this "present-future" relationship and the observed precipitation in the equatorial western Pacific, this study calibrated the climate projections in the tropical Pacific. The corrected projections showed a stronger El Nino-like pattern of mean changes in the future, consistent with our previous study. In particular, the projected increased occurrence of extreme El Nino events under RCP 8.5 forcing are underestimated by 30-35% in the CMIP5 multi-model ensemble before the corrections. This implies an increased risk of the El Nino-related weather and climate disasters in the future
Biodegradation performance and diversity of enriched bacterial consortia capable of degrading high-molecular-weight polycyclic aromatic hydrocarbons
No full textPolycyclic aromatic hydrocarbons (PAHs) are key organic pollutants in the environment that pose threats to the ecosystem and human health. The degradation of high molecular weight (HMW) PAHs by enriched bacterial consortia has been previously studied, while the involved metabolisms and microbial communities are still unclear and warrant further investigations. In this study, five bacterial consortia capable of utilizing different PAHs (naphthalene, anthracene, and pyrene) as the sole carbon and energy sources were enriched from PAH-contaminated soil samples. Among the five consortia, consortium TC exhibited the highest pyrene degradation efficiency (91%) after 19 d of incubation. The degradation efficiency was further enhanced up to 99% by supplementing yeast extract. Besides, consortium TC showed tolerances to high concentrations of pyrene (up to 1000 mg/L) and different heavy metal stresses (including Zn2+, Cd2+, and Pb2+). The dominant genus in consortium TC, GS, and PL showing relatively higher degradation efficiency for anthracene and pyrene was Pseudomonas, whereas consortium PG and GD were predominated by genus Achromobacter and class Enterobacteriaceae, respectively. Consortium TC, as a highly efficient HMW PAH-degrading consortium, could be applied for synergistic biodegradation of HMW PAHs and in situ bioremediation of the sites contaminated with both PAHs and heavy metals
Black carbon and dust in the Third Pole glaciers: Revaluated concentrations, mass absorption cross-sections and contributions to glacier ablation
No full textIn snow and ice, light-absorbing particles (LAN), such as black carbon (BC) and dust, accelerate the melting of Third Pole glaciers (TPGs). In this study, we revaluated LAP concentrations in the snow pits of TPGs (SP-TPGs), measured LAP mass absorption cross-sections (MACs), and simulated their effects on glacier darkening and melting based on the Spectral Albedo Model for Dirty Snow and a surface energy and mass balance model. The results indicated that because of their short distances to emission sources, the average BC concentrations measured in snow pits in the periphery of Third Pole were much higher than those measured in the inland Tibetan Plateau, and the average dust concentrations generally decreased from north to south. The average MACs of BC in the SP-TPCs varied from 3.1 to 7.7 m(2) g(-1) at 550 nm, most of the average spectral values were comparable in the visible and near-infrared bands to those calculated by Mie theory, except those in Urumqi Glacier No. 1 (UR), Syek Zapadniy Glacier (SZ), and Laohugou Glacier No.12 (LH), while the average spectral MACs of dust in the SP-TPGs were considerably smaller in magnitude than most of the variations measured in other regions. Compared with the pure snow surfaces. BC and dust played comparable roles in reducing albedo in UR, SZ, LH, and Renlongba Glacier, whereas BC was the most prominent absorber in the other glaciers. The combined effect of BC and dust accelerated melting by 30.4-345.9 mm w.e. (19.7-453% of the total mass balance) through surface albedo darkening (0.06-0.17) and increased radiation absorption (25.8-65.7 W m(-2)) within one month of the ablation season. This study provides a new data set of LAP concentrations and MACs and helps to clarify the roles of these factors in the cryospheric environment of the Third Pole. (C) 2021 Elsevier B.V. All tights reserved
Pulsed carbon export from mountains by earthquake-triggered landslides explored in a reduced-complexity model
No full textIn mountain ranges, earthquakes can trigger widespread landsliding and mobilize large amounts of organic carbon by eroding soil and vegetation from hillslopes. Following a major earthquake, the landslide-mobilized organic carbon can be exported from river catchments by physical sediment transport processes or stored within the landscape where it may be degraded by heterotrophic respiration. The competition between these physical and biogeochemical processes governs a net transfer of carbon between the atmosphere and sedimentary organic matter, yet their relative importance following a large landslide-triggering earthquake remains poorly constrained. Here, we propose a model framework to quantify the post-seismic redistribution of soil-derived organic carbon. The approach combines predictions based on empirical observations of co-seismic sediment mobilization with a description of the physical and biogeochemical processes involved after an earthquake. Earthquake-triggered landslide populations are generated by randomly sampling a landslide area distribution, a proportion of which is initially connected to the fluvial network. Initially disconnected landslide deposits are transported downslope and connected to rivers at a constant velocity in the post-seismic period. Disconnected landslide deposits lose organic carbon by heterotrophic oxidation, while connected deposits lose organic carbon synchronously by both oxidation and river export. The modeling approach is numerically efficient and allows us to explore a large range of parameter values that exert a control on the fate of organic carbon in the upland erosional system. We explore the role of the climatic context (in terms of mean annual runoff and runoff variability) and rates of organic matter degradation using single pool and multi-pool models. Our results highlight the fact that the redistribution of organic carbon is strongly controlled by the annual runoff and the extent of landslide connection, but less so by the choice of organic matter degradation model. In the context of mountain ranges typical of the southwestern Pacific region, we find that model configurations allow more than 90 % of the landslide-mobilized carbon to be exported from mountain catchments. A simulation of earthquake cycles suggests efficient transfer of organic carbon out of a mountain range during the first decade of the post-seismic period. Pulsed erosion of organic matter by earthquake-triggered landslides is therefore an effective process to promote carbon sequestration in sedimentary deposits over thousands of years
East Asian monsoon during the past 10,000 years recorded by grain size of Yangtze River delta
No full textPaleoenvironmental research is critical for understanding delta evolution processes and managing delta sustainability, particularly for delta experiencing significant recent fluvial sediment discharge. Based on other previously reported optically stimulated luminescence (OSL) data, Holocene environmental changes of the Yangtze River delta in response to climate fluctuations and human activities were reviewed on the basis of grain-size analyses of core YZ07. The results of grain-size and end-member analysis (EMA) provide a detailed history of East Asian monsoon variability and environmental changes since similar to 10,000 cal year B.P. The lower median values (Md) and sand content reflect relatively cool and dry climate conditions between 10,000 and 9,570 cal year B.P. During the early Holocene (9,570-7,630 cal year B.P.), the highest Md values and sand contents and the lowest end member 2 (EM2) contents suggest the Holocene transgression. The increased Md values and sand contents indicate that the climate conditions were warm and wet during the mid-Holocene thermal optimum. From 4,690 to 4,150 cal year B.P., the climate was cool and dry, corresponding to the cool event, as indicated by the finer grain size. Subsequently, between 4,150 and 2,850 cal year B.P., the grain size derived from the Md value and sand content increased, which reflect a wet and warm episode. The climate, which shifted from warm and wet to cool and dry between 2,850 and 1,020 cal year B.P., may have caused a reduction in the sand contents and Md values. After 1,020 cal year B.P., the lowest values of Md and Standard deviation (Sd) and the highest contents of EM2 and clay suggest that the Yangtze River delta has been severely affected by anthropogenic activity. The variability of the East Asian monsoon intensity in the Yangtze River delta strongly correlates with other East Asian monsoon paleoclimate records in China. These results are important for investigations into the interactions between regional systems and global change in monsoonal climatic regions and can provide an example of the evolution of a large scale geomorphic feature resulting from river-sea interaction
How much has the Sun influenced Northern Hemisphere temperature trends? An ongoing debate
No full textIn order to evaluate how much Total Solar Irradiance (TSI) has influenced Northern Hemisphere surface air temperature trends, it is important to have reliable estimates of both quantities. Sixteen different estimates of the changes in TSI since at least the 19(th) century were compiled from the literature. Half of these estimates are "low variability" and half are "high variability". Meanwhile, five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using: 1) only rural weather stations; 2) all available stations whether urban or rural (the standard approach); 3) only sea surface temperatures; 4) tree-ring widths as temperature proxies; 5) glacier length records as temperature proxies. The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates, suggesting that urbanization bias might still be a problem in current global temperature datasets - despite the conclusions of some earlier studies. Nonetheless, all five estimates confirm that it is currently warmer than the late 19(th) century, i.e., there has been some "global warming" since the 19(th) century. For each of the five estimates of Northern Hemisphere temperatures, the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting. The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC's recommended "anthropogenic forcings" time series. For all five Northern Hemisphere temperature series, different TSI estimates suggest everything from no role for the Sun in recent decades (implying that recent global warming is mostly human-caused) to most of the recent global warming being due to changes in solar activity (that is, that recent global warming is mostly natural). It appears that previous studies (including the most recent IPCC reports) which had prematurely concluded the former, had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates. Therefore, several recommendations on how the scientific community can more satisfactorily resolve these issues are provided
Indian summer monsoon variability over last 2000 years inferred from sediment magnetic characteristics in Lugu Lake, southwest China
No full textKnowledge of climatic change during the past 2000 years in southwestern China is important for understanding the evolution of the Indian summer monsoon (ISM). For this study, we conducted systematic analysis of magnetic minerals in sediments from Lugu Lake in northwestern Yunnan Province. Magnetic measurements suggest that magnetite dominated the studied magnetic mineral assemblages. Both natural origins and anthropogenic activities are considered to be the sources of the magnetic minerals based on the correlations of chi vs. chi(fd)% and chi(ARM)/chi. The magnetic minerals of natural origins can be attributed to terrestrial detrital input rather than biogenic sources. Combined with diatom and geochemical records, magnetic parameters including chi, chi(fd)%, and Sratio can be used as sensitive indicators of ISM change, and suggest that two significant dry periods occurred in the Medieval Warm Period (MWP, 800-1300 CE) and Roman Warm Period (RWP, 0-400 CE) and two relatively wet intervals in the Dark Ages Cold Period (DACP, 400-800 CE) and Little Ice Age (LIA, 1300-1850 CE). Significant shifts of magnetic parameters in Lugu Lake samples revealed sensitivity to precipitation-controlled catchment erosion. The climatic patterns shown by the magnetic characteristics were generally similar to those in extensive areas dominated by the ISM. We speculate that rainfall caused by the ISM during the last 2000 years may be related to the variations of El Nino/Southern Oscillation (ENSO) and the mean position migration of the ITCZ