Institute of Earth Environment
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Integrated modelling for mapping spatial sources of dust in central Asia-An important dust source in the global atmospheric system
No full textSpatial mapping of dust sources in arid and semi-arid regions is necessary to mitigate on-site and off-site impacts. In this study, we apply a novel integrated modelling approach including leave one feature out (LOFO) - as a technique for feature selection -, deep learning (DL) models (gcForest and bidirectional long short-term memory (Bi-LSTM)), game theory (GT) and a Gaussian copula-based multivariate (GCBM) model for mapping dust sources in Central Asia (CA). Eight factors (precipitation, cation exchange capacity, bulk density, wind speed, slope, silt content, lithology and coarse fragment content) were selected by LOFO as effective for controlling dust emissions, and were used in the novel modelling process. Six statistical indicators were utilized to assess the performance of the two DL models and a hybrid copula-gcForest model, while a sensitivity analysis of the models was also carried out. The hybrid copula-gcForest model was identified as the most accurate, predicting that 16%, 7.1%, 9.5% and 67.4% of the study area is grouped at low, moderate, high and very high susceptibility classes for dust emissions, respectively. Based on permutation feature importance measure (PFIM) and Shapely Additive exPlanations (SHAP), bulk density, precipitation and coarse fragment content were evaluated as the three most important factors with the highest contributions to the predictive model output. The study area suffers from intense wind erosion and the generated spatial maps of dust sources may be helpful for mitigating and controlling dust phenomena in CA
Real-time prediction of river chloride concentration using ensemble learning
No full textReal-time river chloride prediction has received a lot of attention for its importance in chloride control and management. In this study, an artificial neural network model (i.e., multi-layer perceptron, MLP) and a statistical inference model (i.e., stepwise-cluster analysis, SCA) are developed for predicting chloride concentration in stream water. Then, an ensemble learning model based on MLP and SCA is proposed to further improve the modeling accuracy. A case study of hourly river chloride prediction in the Grand River, Canada is presented to demonstrate the model applicability. The results show that the proposed ensemble learning model, MLP-SCA, provides the best overall performance compared with its two ensemble members in terms of RMSE, MAPE, NSE, and R-2 with values of 11.58 mg/L, 27.55%, 0.90, and 0.90, respectively. Moreover, MLP-SCA is more competent for predicting extremely high chloride concentration. The prediction of observed concentrations above 150 mg/L has RMSE and MAPE values of 9.88 mg/L and 4.40%, respectively. The outstanding performance of the proposed MLP-SCA, particularly in extreme value prediction, indicates that it can provide reliable chloride prediction using commonly available data (i.e., conductivity, water temperature, river flow rate, and rainfall). The high-frequency prediction of chloride concentration in the Grand River can supplement the existing water quality monitoring programs, and further support the real-time control and management of chloride in the watershed. MLP-SCA is the first ensemble learning model for river chloride prediction and can be extended to other river systems for water quality prediction
Comparative observation of atmospheric nitrous acid (HONO) in Xi'an and Xianyang located in the GuanZhong basin of western China
No full textHONO is an important component of reactive nitrogen (N-r) and precursors of OH radical. However, the source and removal of HONO are not clear. Here, measurements of HONO (May 18-31, 2018) were conducted in Xi'an and Xianyang simultaneously for the first time. The relationship between HONO and other N-r (such as NO and NO2) in two cities was analyzed. The mixing ratio of HONO in Xi'an was 1.2 +/- 0.8 ppbv, and that in Xianyang was 1.2 +/- 1.1 ppbv. The nighttime HONO mixing ratio was higher in Xianyang, while the daytime HONO was higher in Xi'an. Compared with the contribution from heterogeneous process of NO2, direct emissions and homogeneous processes (NO + OH) were less important for nocturnal HONO formation in these two cities. The relative contribution of heterogeneous process in Xianyang was more important than that in Xi'an. The reaction of NO2 upon aerosols surface was identified as an important source of HONO for two sites. The conversion of NO2 on the other surfaces might attend the heterogeneous formation of HONO in Xianyang site. Daytime HONO budget analysis indicated that there was an additional unknown formation process of HONO at two sites. The net OH production rate from HONO (from 08:00 to 17:00) was 1.6 x 10(7) and 1.3 x 10(7) molecule/(cm(3) s) for Xian and Xianyang, 5.2 and 3.5 times higher than from O-3 photolysis. Besides, a dust storm appeared during this observation period, and the impact of local emission and transport processes was separately analyzed. The sources, characteristics, and effects of HONO identified in this study laid a foundation for further research on HONO and air pollution in the Guanzhong area
A 23.7-year long daily growth rate record of a modern giant clam shell from South China Sea and its potential in high-resolution paleoclimate reconstruction
No full textTridacna spp. usually have annual and even daily growth bands, and thus provide great potential to be the high-resolution recorders of past climate and environmental changes of the ocean. However, current studies mainly focus on the geochemical records of Tridacna shells, the environmental and climatic implications of long time sequenced daily growth increments are relatively unexplored. In this study, based on the confocal microscopic line-scanning imaging, a 23.7-year long (from 5 June 1989 to 21 February 2013) daily growth rate (DGR) record of Tridacna gigas shell MD3 from southern South China Sea was established and its climatic implication was investigated. On seasonal scale, significant positive correlation was found between the DGR and sea surface temperature (SST). The main growing season of T. gigas MD3 was from March to August, when sufficient sunlight and warmer SST prevailed. While high rainfall (low sunlight) from September to December and low SST from December to March hindered the growth of the shell in autumn and winter. On an inter-annual scale, the DGR of the shell varied periodically on timescales of 2-3 years and 4-5 years, which possibly represented the impacts of the Tropospheric Biennial Oscillation and El Nino-Southern Oscillation activities respectively. Our result suggested that the daily growth lines of T. gigas can establish an extraordinarily high-resolution chronology and have high potential to explore daily to inter-annual paleoenvironmental changes in tropical ocean. Compared with the paleoclimate reconstructions of geochemical approaches, this method has the advantages of low cost and short experimental time
Spatial and temporal variation in soil bulk density and saturated hydraulic conductivity and its influencing factors along a 500 km transect
No full textSoil bulk density (BD) and saturated hydraulic conductivity (Ks) are two critical soil physical parameters that affect soil water holding capacity, infiltration, carbon stocks, and many land and surface processes. Although variations in spatial and temporal BD and Ks are widely recognized and known to differ at different scales, little large-scale data is available. This study explores changes in spatial and temporal BD and Ks along a 500 km transect on the Chinese Loess Plateau (CLP). On seven different occasions, we took BD and Ks measurements in undisturbed soil samples within the surface (0-10 cm) and subsurface (10-20 cm) soil layers from August 2015 to October 2018 along this long transect. This transect covers two climate zones (subhumid and semiarid) and mainly includes five land-use types. BD and log10-transformed Ks (LogKs) exhibited weak and moderate spatial variations during different sampling periods along the long transect, respectively. The highest LogKs values of the two soil layers were observed in summer. Only BD (LogKs) in the surface soil layer of semiarid zone was significantly higher (lower). Grassland had slightly lower BD and higher Ks compared to the other land-use types. Climate had no significant effect on BD and Ks variability. Land-use type and season separately had a significant impact on BD and Ks variability, while sampling time significantly influenced both BD and Ks variability. Ks was negatively correlated with soil water content in spring, summer and autumn. In this long transect, spatial and temporal variations in BD and Ks are determined by land-use types, seasonal changes, sampling time and soil water condition. Understanding temporal BD and Ks variations and their dominant factors will help in the selection of soil physical parameters to optimize hydrological models more accurately at a regional scale
Speciated atmospheric mercury at the Waliguan Global Atmosphere Watch station in the northeastern Tibetan Plateau: implication of dust-related sources for particulate bound mercury
No full textTo understand the ambient levels and sources of atmospheric mercury (Hg) in the Tibetan Plateau, a full-year continuous measurement of speciated atmospheric mercury was conducted at the Waliguan (WLG) Baseline Observatory (3816ma.s.l.) from May 2012 to April 2013. Mean concentrations (+/- 1 SD) of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particulate bound mercury (PBM) during the whole study period were 1.90 +/- 0.80 ngm 3, 12.0 +/- 10.6 and 65.4 +/- 63.2 pg m(-3), respectively. Seasonal variations of GEM were very small, while those of PBM were quite large with mean values being 4 times higher in the cold (102.3 +/- 66.7 pg m(-3)) than warm (22.8 +/- 14.6 pg m(-3)) season. Anthropogenic emissions to the east of the Tibetan Plateau contributed significantly to GEM pollution at WLG, while dust particles originating from desert and Gobi regions in Xinjiang province and the Tibetan Plateau to the west of WLG were responsible for PBM pollution at WLG. This finding is also supported by the significant positive correlation between daily PBM concentration and daily cumulative absorbing aerosol index (AAI) in air masses transported during the preceding 2 d
Synthesis of Calcium Silicate Hydrate from Coal Gangue for Cr(VI) and Cu(II) Removal from Aqueous Solution
No full textBoth the accumulation of coal gangue and potentially toxic elements in aqueous solution have caused biological damage to the surrounding ecosystem of the Huainan coal mining field. In this study, coal gangue was used to synthesize calcium silicate hydrate (C-S-H) to remove Cr(VI) and Cu(II)from aqueous solutions and aqueous solution. The optimum parameters for C-S-H synthesis were 700 & DEG;C for 1 h and a Ca/Si molar ratio of 1.0. Quantitative sorption analysis was done at variable temperature, C-S-H dosages, solution pH, initial concentrations of metals, and reaction time. The solution pH was precisely controlled by a pH meter. The adsorption temperature was controlled by a thermostatic gas bath oscillator. The error of solution temperature was controlled at & PLUSMN; 0.3, compared with the adsorption temperature. For Cr(VI) and Cu(II), the optimum initial concentration, temperature, and reaction time were 200 mg/L, 40 & DEG;C and 90 min, pH 2 and 0.1 g C-S-H for Cr(VI), pH 6 and 0.07 g C-S-H for Cu(II), respectively. The maximum adsorption capacities of Cr(VI) and Cu(II) were 68.03 and 70.42 mg & BULL;g(-1), respectively. Furthermore, the concentrations of Cu(II) and Cr(VI) in aqueous solution could meet the surface water quality standards in China. The adsorption mechanism of Cu(II) and Cr(VI) onto C-S-H were reduction, electrostatic interaction, chelation interaction, and surface complexation. It was found that C-S-H is an environmentally friendly adsorbent for effective removal of metals from aqueous solution through different mechanisms.</p
Temperature Variations and Possible Forcing Mechanisms over the Past 300 Years Recorded at Lake Chaonaqiu in the Western Loess Plateau
No full textUnderstanding the synchronicity of and discrepancy among temperature variations on the western Loess Plateau (WLP), China, is critical for establishing the drivers of regional temperature variability. Here we present an authigenic carbonate-content timeseries spanning the last 300 years from sediments collected from Lake Chaonaqiu in the Liupan Mountains, WLP, as a decadal-scale record of temperature. Our results reveal six periods of relatively low temperature, during the intervals AD 1743-1750, 1770-1780, 1792-1803, 1834-1898, 1930-1946, and 1970-1995, and three periods of relatively high temperature during 1813-1822, 1910-1928, and since 2000. These findings are consistent with tree-ring datasets from the WLP and correlate well with extreme cold and warm events documented in historical literature. Our temperature reconstruction is also potentially representative of large-scale climate patterns over northern China and more broadly over the Northern Hemisphere. The Pacific Decadal Oscillation (PDO) might be the dominant factor affecting temperature variations over the WLP on decadal timescales.</p
Persistent orbital influence on millennial climate variability through the Pleistocene
No full textAbundant evidence from marine, ice-core and terrestrial records demonstrates that Earth's climate has experienced co-evolution of orbital- and millennial-scale variability through the Pleistocene. The varying magnitude of millennial climate variability (MCV) was linked to orbitally paced glacial cycles over the past 800 kyr. Before this interval, global glaciations were less pronounced but more frequent, yet scarcity of a long-term integration of high-resolution continental and marine records hampers our understanding of the evolution and dynamics of MCV before the mid-Pleistocene transition. Here we present a synthesis of four centennial-resolved elemental time series, which we interpret as proxies for MCV, from North Atlantic, Iberian margin, Balkan Peninsula (Lake Ohrid) and Chinese Loess Plateau. The proxy records reveal that MCV was pervasive and persistent over the mid-latitude Northern Hemisphere during the past 1.5 Myr. Our results suggest that the magnitude of MCV is not only strongly modulated by glacial boundary conditions on Earth after the mid-Pleistocene transition, but also persistently influenced by variations in precession and obliquity through the Pleistocene. The combination of these four proxies into a new MCV stack offers a credible reference for further assessing the dynamical interactions between orbital and millennial climate variability.
Orbital forcing consistently influenced the magnitude of millennial-scale climate variability through the Pleistocene, according to an analysis of four high-resolution Northern Hemisphere proxy records covering the past 1.5 Myr
Interdecadal change in the influence of El Nino in the developing stage on the central China summer precipitation
No full textThe central China summer precipitation (CCSP) is of great importance to the people's livelihood of this densely populated region, including the agriculture, ecosystems, water resources, economies, and health. Based on the observed precipitation, sea surface temperature (SST), and atmospheric reanalysis datasets, the present study investigates the effects of El Nino in the developing stage on the CCSP during 1960-2014. The results show that the CCSP anomalies exhibit significant negative correlations with the El Nino-related SST anomalies in both the simultaneous summer and the following winter, implying that the developing El Nino is important for modulating the CCSP. However, this climatic teleconnection of El Nino is unstable, with an obvious interdecadal change around the late 1980s. Specifically, the negative correlation is not statistically significant in the previous epoch before the late 1980s (1960-1988), but dramatically strengthens since the late 1980s (the post epoch for 1989-2014). Such an interdecadal change is closely associated with the change of the El Nino-related SST anomaly pattern. Compared to the previous epoch, the central Pacific El Nino occurs more frequently in the post epoch, leading to an interdecadal shift of the maximum warm SST anomalies from the eastern Pacific to the central Pacific. The resultant westward extension of the atmospheric circulation responses induces an anomalous low-level cyclone covering South China in the post epoch. It would prevent the southwest monsoon from delivering the moisture to the north and hence reduce the CCSP. While, in the previous epoch, the anomalous cyclone locates east of South China, exerting insignificant influence on the CCSP. This work highlights a strengthening effect of El Nino on the CCSP since the late 1980s, with great implications for the regional seasonal climate prediction