| 1. |
- Jiang, Tao, et al.
(författare)
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Characteristics of dissolved organic matter (DOM) and relationship with dissolved mercury in Xiaoqing River-Laizhou Bay estuary, Bohai Sea, China
- 2017
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Ingår i: Environmental Pollution. - : Elsevier. - 0269-7491 .- 1873-6424. ; 223, s. 19-30
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Because of heterogeneous properties, dissolved organic matter (DOM) is known to control the environmental fate of a variety of organic pollutants and trace metals in aquatic systems. Here we report absorptive and fluorescence properties of DOM, in concurrence with concentrations of dissolved mercury (Hg), along the Xiaoqing River-Laizhou Bay estuary system located in the Bohai Sea of China. A mixing model consisting of the two end-members terrestrial and aquatic DOM demonstrated that terrestrial signatures decreased significantly from the river into the estuary. Quasi-conservative mixing behavior of DOM sources suggests that the variations in the average DOM composition were governed by physical processes (e.g., dilution) rather than by new production and/or degradation processes. In contrast to some previous studies of river-estuary systems, the Xiaoqing River-Laizhou Bay estuary system displayed a non-significant correlation between DOM and Hg quantities. Based on this and the variation of Hg concentration along the salinity gradient, we concluded that Hg showed a non-conservative mixing behavior of suggested end-member sources. Thus, rather than mixing, Hg concentration variations seemed to be controlled by biogeochemical processes.
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| 2. |
- Li, Chuxian
(författare)
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A peat core Hg stable isotope reconstruction of Holocene atmospheric Hg deposition at Amsterdam Island (37.8(o)S)
- 2023
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 0046-564X. ; 341, s. 62-74
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Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) stable isotopes have been broadly used to investigate the sources, transformation and deposition of atmospheric Hg during the industrial era thanks to the multiple isotope signatures deriving from mass-dependent (represented by delta Hg-202) and mass-independent fractionation (represented by AxxxHg) in the environment. Less is known about the impact of past climate change on atmospheric Hg deposition and cycling, and whether Hg isotopes covary with past climate. Here, we investigate Hg concentration and Hg isotope signatures in a 6600-year-old ombrotrophic peat record from Amsterdam Island (AMS, 37.8(o)S), and in modern AMS rainfall and gaseous elemental Hg (Hg-0) samples. Results show that Holocene atmospheric Hg deposition and plant Hg uptake covary with dust deposition, and are both lower under a high humidity regime associated with enhanced Southern Westerly Winds. Modern AMS gaseous Hg-0 and rainfall HgII isotope signatures are similar to those in the Northern Hemisphere (NH). Holocene peat delta Hg-199 and A200Hg are significantly correlated (R2 = 0.67, P < 0.001, n = 58), consistently oscillating between the modern Hg-0 and rainfall Hg-II end-members. Peat A200Hg and delta Hg-199 provide evidence of plant uptake of Hg-0 as the dominant pathway of Hg deposition to AMS peatland, with some exceptions during humid periods. In contrast to NH archives generally documenting a modern increase in delta Hg-199, recent peat layers (post-1900CE) from AMS show the lowest delta Hg-199 in the peat profile (-0.42 +/- 0.27 parts per thousand, 1cs, n = 8). This likely reflects a significant change in the post-depositional process on deposited anthropogenic Hg in 20th century (i.e. dark abiotic reduction), enabling more negative delta Hg-199 to be observed in AMS peat. We further find that the oscillations of Hg isotopes are consistent with established Holocene climate variability from dust proxies. We suggest peat Hg isotope records might be a valid rainfall indicator. (C) 2022 The Authors. Published by Elsevier Ltd.
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| 3. |
- Li, Chuxian
(författare)
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Inorganic versus organic fertilizers: How do they lead to methylmercury accumulation in rice grains
- 2022
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 314
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Tidskriftsartikel (refereegranskat)abstract
- Both inorganic and organic fertilizers are widely used to increase rice yield. However, these fertilizers are also found to aggravate mercury methylation and methylmercury (MeHg) accumulation in paddy fields. The aim of this study was to reveal the mechanisms of inorganic and organic fertilizers on MeHg accumulation in rice grains, which are not yet well understood. Potting cultures were conducted in which different fertilizers were applied to a paddy soil. The results showed that both inorganic and organic fertilizers increased MeHg concentrations rather than biological accumulation factors (BAFs) of MeHg in mature rice grains. Inorganic fertilizers, especially ni-trogen fertilizer, enhanced the bioavailability of mercury and the relative amount Hg-methylating microbes and therefore intensified mercury methylation in paddy soil and MeHg accumulation in rice grains. Unlike inorganic fertilizers, organic matter (OM) in organic fertilizers was the main reason for the increase of MeHg concentra-tions in rice grains, and it also could immobilize Hg in soil when it was deeply degraded. The enhancement of MeHg concentrations in rice grains induced by inorganic fertilizers (5.18-41.69%) was significantly (p < 0.05) lower than that induced by organic fertilizers (80.49-106.86%). Inorganic fertilizers led to a larger increase (50.39-99.28%) in thousand-kernel weight than MeHg concentrations (5.18-41.69%), resulting in a dilution of MeHg concentrations in mature rice grains. Given the improvement of soil properties by organic fertilizer, increasing the proportion of inorganic fertilizer application may be a better option to alleviate MeHg accumu-lation in rice grains and guarantee the rice yield in the agricultural production.
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| 4. |
- Li, Chuxian, et al.
(författare)
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Mercury deposition and redox transformation processes in peatland constrained by mercury stable isotopes
- 2023
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Peatland vegetation takes up mercury (Hg) from the atmosphere, typically contributing to net production and export of neurotoxic methyl-Hg to downstream ecosystems. Chemical reduction processes can slow down methyl-Hg production by releasing Hg from peat back to the atmosphere. The extent of these processes remains, however, unclear. Here we present results from a comprehensive study covering concentrations and isotopic signatures of Hg in an open boreal peatland system to identify post-depositional Hg redox transformation processes. Isotope mass balances suggest photoreduction of HgII is the predominant process by which 30% of annually deposited Hg is emitted back to the atmosphere. Isotopic analyses indicate that above the water table, dark abiotic oxidation decreases peat soil gaseous Hg0 concentrations. Below the water table, supersaturation of gaseous Hg is likely created more by direct photoreduction of rainfall rather than by reduction and release of Hg from the peat soil. Identification and quantification of these light-driven and dark redox processes advance our understanding of the fate of Hg in peatlands, including the potential for mobilization and methylation of HgII.
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| 5. |
- Li, Chuxian, et al.
(författare)
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Recent 210Pb, 137Cs and 241Am accumulation in an ombrotrophic peatland from Amsterdam Island (Southern Indian Ocean)
- 2017
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Ingår i: Journal of Environmental Radioactivity. - : Elsevier BV. - 0265-931X. ; 175-176, s. 164-169
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Tidskriftsartikel (refereegranskat)abstract
- Over the past 50 years, 210Pb, 137Cs and 241Am have been abundantly used in reconstructing recent sediment and peat chronologies. The study of global aerosol-climate interaction is also partially depending on our understanding of 222Rn-210Pb cycling, as radionuclides are useful aerosol tracers. However, in comparison with the Northern Hemisphere, few data are available for these radionuclides in the Southern Hemisphere, especially in the South Indian Ocean. A peat core was collected in an ombrotrophic peatland from the remote Amsterdam Island (AMS) and was analyzed for 210Pb, 137Cs and 241Am radionuclides using an underground ultra-low background gamma spectrometer. The 210Pb Constant Rate of Supply (CRS) model of peat accumulations is validated by peaks of artificial radionuclides (137Cs and 241Am) that are related to nuclear weapon tests. We compared the AMS 210Pb data with an updated 210Pb deposition database. The 210Pb flux of 98 ± 6 Bq·m−2·y−1 derived from the AMS core agrees with data from Madagascar and South Africa. The elevated flux observed at such a remote location may result from the enhanced 222Rn activity and frequent rainfall in AMS. This enhanced 222Rn activity itself may be explained by continental air masses passing over southern Africa and/or Madagascar. The 210Pb flux at AMS is higher than those derived from cores collected in coastal areas in Argentina and Chile, which are areas dominated by marine westerly winds with low 222Rn activities. We report a 137Cs inventory at AMS of 144 ± 13 Bq·m−2 (corrected to 1969). Our data thus contribute to the under-represented data coverage in the mid-latitudes of the Southern Hemisphere.
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| 6. |
- Li, Chuxian
(författare)
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Use smaller size of straw to alleviate mercury methylation and accumulation induced by straw incorporation in paddy field
- 2022
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Ingår i: Journal of Hazardous Materials. - : Elsevier BV. - 0304-3894 .- 1873-3336. ; 423
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Tidskriftsartikel (refereegranskat)abstract
- Straw sizes were found to affect the methylmercury (MeHg) accumulation in rice grains induced by straw incorporation. The mechanism behind, however, still remains unclear. Here, we incorporated rice straw in different sizes (powder, 2 cm and 5 cm) into a Hg-contaminated paddy soil. Our results showed that straw sizes regulated the release of different fractions of organic matter (OM) in straw residues and further Hg methylation in paddy soil. The easily degradable OM (EDOM) was a key driving factor that facilitated net Hg methylation, though it only occupied a small fraction (1.12-3.12%) of the soil OM. Powdered straw reduced the duration of net Hg methylation by 74.39% compared to 5 cm straw, resulting in a strong and rapid net Hg methylation in paddy soil before the rice flowering. After the release of EDOM, the humified OM dominated in paddy soil and bound to MeHg, leading to less MeHg being transported to rice grains during the grain filling. Powdered straw decreased MeHg accumulation by 25.32% in the mature rice grains compared with 5 cm straw. Our study suggests that straw powdering before incorporation provides a feasible pathway for reducing MeHg accumulation in rice grains induced by straw incorporation.
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| 7. |
- Peng, Haijun, et al.
(författare)
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Climatic controls on the dynamic lateral expansion of northern peatlands and its potential implication for the 'anomalous' atmospheric CH4 rise since the mid-Holocene
- 2024
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 908
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the dynamic changes in peatland area during the Holocene is essential for unraveling the connections between northern peatland development and global carbon budgets. However, studies investigating the centennial to millennial -scale process of peatland expansion and its climate and environmental drivers are still limited. In this study, we present a reconstruction of the peatland area and lateral peatland expansion rate of a peatland complex in northern Sweden since the mid -Holocene, based on Ground Penetrating Radar measurements of peat thickness supported by radiocarbon (14C) dates from four peat cores. Based on this analysis, lateral expansion of the peatland followed a northwest -southeast directionality, constrained by the undulating post-glacial topography. The areal extent of peat has increased non -linearly since the mid -Holocene, and the peatland lateral expansion rate has generally been on the rise, with intensified expansion occurring after around 3500 cal yr BP. Abrupt declines in lateral expansion rates were synchronized with the decreases in total solar irradiance superimposed on the millennial ice -rafted debris events in the northern high latitudes. Supported by the temporal evolution of peatland extent in four other Fennoscandian peatlands, it appears that the northern peatland areal extent during the early to middle Holocene was much smaller compared to previous empirical model reconstructions based on basal age compilations. Interestingly, our reconstruction shows the increments of peat area since the mid -Holocene coincide with the rise in atmospheric CH4 concentration, and that abrupt variations in atmospheric CH4 on decadal to centennial timescales could be synchronized with peatland lateral expansion rates. Based on our analysis we put forward the hypothesis that lateral expansion of northern peatlands is a significant driver of dynamics in the late Holocene atmospheric CH4 budget. We strongly urge for more empirical data to quantify lateral expansion rates and test such hypotheses.
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