Institute of Earth Environment
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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
Sea surface temperature seasonality in the northern South China Sea during the middle Holocene derived from high resolution Sr/Ca ratios of Tridacna shells
No full textSeasonal climate variability is an important component of Earth's climate system, and has a significant impact on ecosystems and social systems. However, the temporal resolution of most proxy-based paleoclimate records is limiting to fully understand the past seasonal changes. Here, we used high-precision monthly resolution Sr/Ca records of three Tridacna squamosa specimens from the northern South China Sea (SCS) to reconstruct the sea surface temperature (SST) seasonality during three time periods from the middle Holocene. The results suggested that SST seasonality in the northern SCS during the middle Holocene (3.21 +/- 0.98 degrees C) was smaller than that for recent decades (AD 1994-2004, 4.32 +/- 0.59 degrees C). Analysis of modern instrumental data showed that the SST seasonality in the northern SCS was dominated by the winter SST, which was deeply influenced by the intensity of East Asian winter monsoon (EAWM). A strong EAWM usually resulted in cooler winter SST and a larger SST seasonality in the northern SCS. The reconstructed Holocene EAWM records showed that the EAWM strengthened from the middle to late Holocene, which was seen in our reconstruction of less SST seasonality changes during the middle Holocene in the northern SCS. This study highlighted that the Sr/Ca ratios from Tridacna shells can be used as a potential high-resolution indicator of past seasonal climate changes
The 173-kyr Obliquity Cycle Pacing the Asian Monsoon in the Eastern Chinese Loess Plateau From Late Miocene to Pliocene
No full textWe conduct magnetostratigraphy and cyclostratigraphy on an eolian red clay sequence spanning 7-3.1 Ma in the eastern Chinese Loess Plateau. We pay more attention to the unconventional 173-kyr obliquity modulated cycle which is associated with the secular frequency interference of orbital inclinations between Earth and Saturn. Similar to the 405-kyr eccentricity cycles, the 173-kyr obliquity band proved to be an important orbital driving component by the latest astronomical findings, and can serve as a chronometer of terrestrial air circulation reconstruction back to 7 Ma. Comparison with magneto-cyclo-bio-stratigraphic timescales of another noted eolian sequence from the adjacent area, the 173-kyr cycle is exceptionally presented as a robust recognition of the cyclical sedimentary patterns for the East Asia monsoon deposits
The 173-kyr Obliquity Cycle Pacing the Asian Monsoon in the Eastern Chinese Loess Plateau From Late Miocene to Pliocene
No full textWe conduct magnetostratigraphy and cyclostratigraphy on an eolian red clay sequence spanning 7-3.1 Ma in the eastern Chinese Loess Plateau. We pay more attention to the unconventional 173-kyr obliquity modulated cycle which is associated with the secular frequency interference of orbital inclinations between Earth and Saturn. Similar to the 405-kyr eccentricity cycles, the 173-kyr obliquity band proved to be an important orbital driving component by the latest astronomical findings, and can serve as a chronometer of terrestrial air circulation reconstruction back to 7 Ma. Comparison with magneto-cyclo-bio-stratigraphic timescales of another noted eolian sequence from the adjacent area, the 173-kyr cycle is exceptionally presented as a robust recognition of the cyclical sedimentary patterns for the East Asia monsoon deposits
Spatial distribution and potential sources of arsenic and water-soluble ions in the snow at Ili River Valley, China
No full textTrace elements and water-soluble ions in snow can be used as indicators to reveal natural and anthropogenic emissions. To understand the chemical composition, characteristics of snow and their potential sources in the Ili River Valley (IRV), snow samples were collected from 17 sites in the IRV from December 2018 to March 2019. Inverse distance weighting, enrichment factor (EF) analysis, and backward trajectory modelling were applied to evaluate the spatial distributions and sources of water-soluble ions and dissolved arsenic (As) in snow. The re-sults indicate that Ca2+ and SO42-were the dominant ions, and the concentrations of As ranged from 0.09 to 0.503 mu g L-1. High concentrations of As were distributed in the northwest and middle of the IRV, and the concentrations of the major ions were high in the west of the IRV. The strong correlation of As with F-, SO42-, and NO2- demonstrates that As mainly originated from coal-burning and agricultural activities. Principal component analysis showed that the ions originated from a combination of anthropogenic and crustal sources. The EFs showed that K+, SO42-, and Mg2+ were mainly influenced by human activities. Backward trajectory cluster analysis suggested that the chemical composition of snow was affected by soil dust transport from the western air mass, the unique terrain, and local anthropogenic activities. These results provide important sci-entific insights for atmospheric environmental management and agricultural production within the IRV
A method of the determination nitrate nitrogen (NO3--N) in high-salinity water samples
No full textThe determination of nitrate nitrogen (NO3--N) is a key step in the pretreatment of nitrogen isotope determination, but how to determine NO3--N in high-salinity water samples simply and efficiently is always a difficult problem. A spectrophotometric method for the determination of nitrate is presented and verified in this paper. Samples with different salinity were added to determine the known concentration gradient of NO3--N. The results show that the nitrate content can be determined between 0.2 similar to 2.8 mg/L by ultraviolet-visible spectrophotometer (hereafter as UVS), and the relative error is about 10%. A standard curve of the same salinity should be attempted for a water sample with known salinity. Precon-Isotope Mass Spectrometry (hereafter as Precon-MS) was used to verify the determination of sample concentration by UVS, and the relative error was less than 8%. This paper presents a simple and efficient method for the determination of NO3--N in high-salinity water samples, which has made great progress in the determination of nitrate nitrogen in samples and provides a theoretical basis for the determination of nitrogen isotopes in the pretreatment process of water samples
Chromophoric dissolved organic carbon cycle and its molecular compositions and optical properties in precipitation in the Guanzhong basin, China
No full textThe investigation of water-soluble organic carbon (WSOC), which is important in the biogeochemical cycle of precipitation, can provide a comprehensive view of chromophores within the atmospheric boundary layer. In this work, the optical properties and molecular characteristics of WSOC in precipitation over the Guanzhong Basin (GB) of North China were investigated using ultraviolet-visible (UV-vis) absorption and excitation-emission matrix (EEM) fluorescence spectra, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with electrospray ionization (ESI). Furthermore, sources and wet deposition of WSOC were estimated using in-situ measurements and modeling. The light-absorption by WSOC at 250-300 nm (UV region) and 400-550 nm (visible region) was 64.17% and 15.36% relative to the estimated total light-absorption, respectively. Parallel factor (PARAFAC) analysis revealed three types of fluorophores in WSOC at Xi'an (XN), including two humic-like substances (HULIS) and one protein-like substance (PRLIS), with HULIS accounting for 79% of total fluorescence intensity. FT-ICR MS analysis revealed that CHO and CHON were the most abundant components of WSOC at XN, each containing a variety of lignins, protein/amino sugars, and lipids. Moreover, the positive matrix factorization (PMF) model identified the contributions from three main sources (secondary precursors and aerosols, and coal combustion) of WSOC in precipitation at XN. The annual wet deposition flux of WSOC in precipitation at XN was estimated as about 0.63 g C m(-2) yr(-1), lower than that at other polluted cities. These findings add to our understanding of chromophoric dissolved organic carbon budgets, which is critical for accurately assessing the global carbon cycle
Comparison of analytical sensitivity and efficiency for SARS-CoV-2 primer sets by TaqMan-based and SYBR Green-based RT-qPCR
No full textThe pandemic of coronavirus disease 2019 (COVID-19) continues to threaten public health. For developing countries where vaccines are still in shortage, cheaper alternative molecular methods for SARS-CoV-2 identification can be crucial to prevent the next wave. Therefore, 14 primer sets recommended by the World Health Organization (WHO) was evaluated on testing both clinical patient and environmental samples with the gold standard diagnosis method, TaqMan-based RT-qPCR, and a cheaper alternative method, SYBR Green-based RT-qPCR. Using suitable primer sets, such as ORF1ab, 2019_nCoV_N1 and 2019_nCoV_N3, the performance of the SYBR Green approach was comparable or better than the TaqMan approach, even when considering the newly dominating or emerging variants, including Delta, Eta, Kappa, Lambda, Mu, and Omicron. ORF1ab and 2019_nCoV_N3 were the best combination for sensitive and reliable SARS-CoV-2 molecular diagnostics due to their high sensitivity, specificity, and broad accessibility
Asynchronous variations of East Asian summer monsoon, vegetation and soil formation at Yulin (North China) in the Holocene
No full textIn the East Asian monsoon region, Chinese speleothem delta O-18 records exhibit a maximum monsoon strength during the early Holocene. However, other proxy data from lakes or loess, interpreted as monsoon rainfall, show a mid-Holocene monsoon optimum. This discrepancy may come from specific climate interpretation of different proxies. Here we report multiproxy records from a single loess-palaeosol sequence at Yulin in the monsoon marginal northern China, based on an independent and high-precision chronology. Our long-chain n-alkane delta D values, together with related biomarker proxies including the average chain length and concentration of long-chain n-alkanes, reveal a weakening trend in monsoon strength and less woody vegetation since similar to 6 ka. However, other soil formation-related proxies, such as magnetic susceptibility, grain-size distribution and total organic carbon, show a decreasing trend since 4-3 ka. We find that monsoon and vegetation are controlled by insolation variation, while soil formation is more related to temperature and humidity changes. Our multiple proxy comparison reveals different controlling mechanisms leading to different interpretations in monsoon, vegetation and soil formation reconstructions. This finding suggests that previous debates on Holocene monsoon changes in East Asia probably stem from the specific proxy interpretation. (C) 2022 John Wiley & Sons, Ltd
Lipid biomarkers in Lake Wudalianchi record abrupt environmental changes from the volcanic eruption in 1776
No full textVolcanic eruptions can cause abrupt changes in surrounding environments, but detailed sediment records of such changes are rare. The very high sediment accumulation rate in Lake Wudalianchi, a volcanic-dammed freshwater lake in northeastern China, provides an excellent opportunity for reconstructing volcanic-induced environmental change. Here we use multiple lipid biomarkers to reconstruct changes in aquatic ecosystems, hydrology, and methane cycling before and after a regional explosive volcanic eruption in 1776. Our results indicate that the Wudalianchi catchment was a shallow organic-rich marsh environment with abundant aquatic emergent macrophytes and an intense microbial methane cycle before the volcanic eruption. Following the volcanic eruption, the marsh was rapidly transformed into an oligohaline lake environment due to river channel damming by lava. Associated with the abrupt environmental change, we observe corresponding changes of cyclisation ratios of branched glycerol dialkyl glycerol tetraethers or brGDGTs (CBT and CBT ' indices), and the inferred pH displays an abrupt increase of -1.3. Group 1 alkenones emerge abruptly after the eruption when the inferred pH exceeds 8. Our results provide the first high-resolution reconstruction of environmental change induced by volcanic eruption and demonstrate the high efficacy of the lipid biomarkers in recording aquatic and terrestrial changes