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1.
  • Li, Qiang, et al. (författare)
  • Microbial Necromass, Lignin, and Glycoproteins for Determining and Optimizing Blue Carbon Formation
  • 2024
  • Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 58, s. 468-479
  • Tidskriftsartikel (refereegranskat)abstract
    • Coastal wetlands contribute to the mitigation of climate change through the sequestration of “blue carbon”. Microbial necromass, lignin, and glycoproteins (i.e., glomalin-related soil proteins (GRSP)), as important components of soil organic carbon (SOC), are sensitive to environmental change. However, their contributions to blue carbon formation and the underlying factors remain largely unresolved. To address this paucity of knowledge, we investigated their contributions to blue carbon formation along a salinity gradient in coastal marshes. Our results revealed decreasing contributions of microbial necromass and lignin to blue carbon as the salinity increased, while GRSP showed an opposite trend. Using random forest models, we showed that their contributions to SOC were dependent on microbial biomass and resource stoichiometry. In N-limited saline soils, contributions of microbial necromass to SOC decreased due to increased N-acquisition enzyme activity. Decreases in lignin contributions were linked to reduced mineral protection offered by short-range-ordered Fe (FeSRO). Partial least-squares path modeling (PLS-PM) further indicated that GRSP could increase microbial necromass and lignin formation by enhancing mineral protection. Our findings have implications for improving the accumulation of refractory and mineral-bound organic matter in coastal wetlands, considering the current scenario of heightened nutrient discharge and sea-level rise.
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2.
  • Liu, Linan, et al. (författare)
  • Silicon Effects on Biomass Carbon and Phytolith-Occluded Carbon in Grasslands Under High-Salinity Conditions
  • 2020
  • Ingår i: Frontiers in Plant Science. - : Frontiers Media S.A.. - 1664-462X. ; 11, s. 1-13
  • Tidskriftsartikel (refereegranskat)abstract
    • Changes in climate and land use are causing grasslands to suffer increasingly fromabiotic stresses, including soil salinization. Silicon (Si) amendment has been frequentlyproposed to improve plant resistance to multiple biotic and abiotic stresses and increaseecosystem productivity while controlling the biogeochemical carbon (C) cycle. However,the effects of Si on plant C distribution and accumulation in salt-suffering grasslandsare still unclear. In this study, we investigated how salt ions affected major elementalcomposition in plants and whether Si enhanced biomass C accumulation in grasslandspecies in situ. In samples from the margins of salt lakes, our results showed that thediffering distance away from the shore resulted in distinctive phytocoenosis, includinghalophytes and moderately salt-tolerant grasses, which are closely related to changingsoil properties. Different salinity (NaC/KC, ranging from 0.02 to 11.8) in plants causednegative effects on plant C content that decreased from 53.9 to 29.2% with theincrease in salinity. Plant Si storage [0.02–2.29 g Si m?2 dry weight (dw)] and plantSi content (0.53 to 2.58%) were positively correlated with bioavailable Si in soils(ranging from 94.4 to 192 mg kg?1). Although C contents in plants and phytoliths werenegatively correlated with plant Si content, biomass C accumulation (1.90–83.5 g Cm?2 dw) increased due to the increase of Si storage in plants. Plant phytolith-occludedcarbon (PhytOC) increased from 0.07 to 0.28h of dry mass with the increase of Sicontent in moderately salt-tolerant grasses. This study demonstrates the potential ofSi in mediating plant salinity and C assimilation, providing a reference for potentialmanipulation of long-term C sequestration via PhytOC production and biomass Caccumulation in Si-accumulator dominated grasslands.
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3.
  • Han, Guilin, et al. (författare)
  • Carbon-nitrogen isotope coupling of soil organic matter in a karst region under land use change, Southwest China
  • 2020
  • Ingår i: Agriculture, Ecosystems & Environment. - : Elsevier. - 0167-8809 .- 1873-2305. ; 301, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • The soil stable carbon (C) and nitrogen (N) isotopes are widely used to indicate C3/C4 vegetation history, N sources and transformation processes, respectively. However, land use change, particularly converting forest into farm land, alters soil organic matter (SOM) sources and processes in soils, resulting in a hard understanding of soil C and N fate. In the present study, soil organic carbon (SOC) and soil organic nitrogen (SON) contents, and their stable isotope compositions (δ13C and δ15N) were determined in the five soil profiles under land use change (i.e., conversion of native forest land into shrub land, grass land, maize field, and paddy land) in Lobo county, Guizhou province, Southwest China. A coupling of 13C and 15N isotope in SOM under land use change was verified whether it could provide more accurate indications of sources and transformation processes.The SOC and SON contents of native forest land at the 0∼20 cm depth were significantly larger than these under other transformed lands. The SOC and SON contents decreased exponentially with increasing soil depth under all land use types, and showed opposite trends with soil pH. The C/N ratios of SOM in the soils under undisturbed native forest decreased from 10 to 7 with increasing soil depth, while an irregular fluctuation along soil profile was shown in other transformed lands. Similarly to the most study in the soils under C3 forest, the δ13C and δ15N values of SOM in the soils under native forest at the 0∼50 cm depth increased with increasing soil depth, with the range of −27.7‰∼−25.7‰ and 6.5‰∼10.0‰, respectively. While decreasing trends of them in the soils below 50 cm depth were attributed to the mixing of 13C and 15N-depleted organic matters from bedrocks. However, the δ13C and δ15N values of SOM along the soil profiles under other transformed lands were intensively irregularly fluctuated between −29.1‰ and −19.0‰, 1.2‰ and 7.9‰, respectively. The single δ13C and δ15N signals in the soil profiles of transformed lands indeed revealed the alterations of historical C3/C4 composition and N transformation processes after land use change, but these indications were not specific. The result of the coupling of 13C and 15N isotope under native forest land reveals a positive relationship between them, which associated with full plant-absorption against 15N-depleted inorganic nitrogen derived from SOM mineralization. This study suggests that the coupling of CN isotope fractionation more likely occurs in the C3 forest ecosystem with high N utilization efficiency. However, the replacement of native forest by farm land or grass land will reduce soil N utilization efficiency.
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4.
  • Hao, Qian, et al. (författare)
  • Holocene carbon accumulation in lakes of the current east Asian monsoonal margin: Implications under a changing climate
  • 2020
  • Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 737, s. 1-13
  • Tidskriftsartikel (refereegranskat)abstract
    • Carbon (C) present in lake sediments is an important global sink for CO2; however, an in-depth understanding of the impact of climate variability and the associated changes in vegetation on sediment C dynamics is still lacking. A total of 13 lakes were studied to quantify the influence of climate and vegetation on the reconstructed Holocene C accumulation rate (CAR) in lake sediments of the modern East Asian monsoonal margin. The corresponding paleoclimate information was assessed, including the temperature (30–90°N in the Northern Hemisphere) and precipitation (indicated by the δ18O of the Sanbao, Dongge, and Hulu caves). The Holocene vegetation conditions were inferred by pollen records, including arboreal pollen/non-arboreal pollen and pollen percentages. The results showed that the peak CAR occurred during the mid-Holocene, coinciding with the strongest period of the East Asian summer monsoon and expansion of forests. Lakes in the temperate steppe (TS) regions had a mean CAR of 13.41 ± 0.88 g C m−2 yr−1, which was significantly greater than the CARs of temperate desert (TD) and highland meadow/steppe (HMS; 6.76 ± 0.29 and 7.39 ± 0.73 g C m−2 yr−1, respectively). The major influencing factor for the TS sub-region was vegetation dynamics, especially the proportion of arboreal vegetation, while temperature and vegetation coverage were more important for the HMS. These findings indicate that C accumulation in lake sediments is linked with climate and vegetation changes over long timescales; however, there was notable spatial heterogeneity in the CARs, such as opposing temporal changes and different major influencing factors among the three sub-regions during the mid-Holocene. Aridification and forest loss would decrease C storage. However, prediction of C accumulation remains difficult because of the spatial heterogeneity in CARs and the interaction between the CAR and various factors under future climate change conditions.
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5.
  • Hao, Qian, et al. (författare)
  • Organic blue carbon sequestration in vegetated coastal wetlands: Processes and influencing factors
  • 2024
  • Ingår i: Earth-Science Reviews. - 0012-8252 .- 1872-6828. ; 255, s. 104853-104853
  • Tidskriftsartikel (refereegranskat)abstract
    • Coastal wetlands play a vital role in carbon (C) sequestration, named ‘blue carbon’. The review aims to disentangle the processes and influencing factors, including elevated atmospheric CO2, global climate warming, sea level rise and anthropogenic activities. Firstly, we provided an overview of C processes, including input, output, and deposition, in coastal wetlands. We then summarized the impacts of different factors on C processes by modifying soil physicochemical properties, plant growth, vegetation type, and microbial community composition. Vegetation composition was a major contributor to C inputs, and C outputs was mainly controlled by microbial decomposition. Increased atmospheric CO2 concentration and associated climate warming often enhanced vegetation growth, while climate warming also promoted soil C decomposition. As a result, C storage could increase under mild warming conditions in the short-term, but decrease in the long-term as the severity of warming intensifies. Elevated salinity, caused by sea level rise, can be harmful to plant growth and inhibit organic C decomposition because of the reduced biomass and the weakened metabolic capacity of microorganisms. Most of human activities, such as reclamation, can lead to less C input and more C output, resulting in decreased C storage in coastal wetlands. Additionally, we also illustrate various coastal wetland restoration methods aimed at enhancing C sequestration, including legal frameworks, scientific theories, vegetation management, hydrological restoration, and other relevant constructions. Vegetation management could benefit plant growth and enhance C input effectively, and hydrological restoration can maintain the harmonious development of coastal wetland ecosystems. Other constructions, including breakwater, spillway, and dredged material, could protect coastal wetlands, especially facing sea level rise. This review offers valuable theoretical support and scientific references for the sustainable development and management of coastal wetlands in a changing climate.
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6.
  • Hao, Qian, et al. (författare)
  • Silicon Affects Plant Stoichiometry and Accumulation of C, N, and P in Grasslands
  • 2020
  • Ingår i: Frontiers in Plant Science. - : Frontiers Media S.A.. - 1664-462X. ; 11, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon (Si) plays an important role in improving soil nutrient availability and plant carbon (C) accumulation and may therefore impact the biogeochemical cycles of C, nitrogen (N), and phosphorus (P) in terrestrial ecosystems profoundly. However, research on this process in grassland ecosystems is scarce, despite the fact that these ecosystems are one of the most significant accumulators of biogenic Si (BSi). In this study, we collected the aboveground parts of four widespread grasses and soil profile samples in northern China and assessed the correlations between Si concentrations and stoichiometry and accumulation of C, N, and P in grasses at the landscape scale. Our results showed that Si concentrations in plants were significantly negatively correlated (p< 0.01) with associated C concentrations. There was no significant correlation between Si and N concentrations. It is worth noting that since the Si concentration increased, the P concentration increased from less than 0.10% to more than 0.20% and therefore C:P and N:P ratios decreased concomitantly. Besides, the soil noncrystalline Si played more important role in C, N, and P accumulation than other environmental factors (e.g., MAT, MAP, and altitude). These findings indicate that Si may facilitate grasses in adjusting the utilization of nutrients (C, N, and P) and may particularly alleviate P deficiency in grasslands. We conclude that Si positively alters the concentrations and accumulation of C, N, and P likely resulting in the variation of ecological stoichiometry in both vegetation and litter decomposition in soils. This study further suggests that the physiological function of Si is an important but overlooked factor in influencing biogeochemical cycles of C and P in grassland ecosystems.
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7.
  • Hao, Qian, et al. (författare)
  • Soil silicon fractions along karst hillslopes of southwestern China
  • 2022
  • Ingår i: Journal of Soils and Sediments. - : Springer Nature. - 1439-0108 .- 1614-7480. ; 22, s. 1121-1134
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose The karst region in southwestern China is undergoing soil erosion and rocky desertification. The different silicon (Si) fractions along the hillslopes in this mountainous region could benefit plant growth and alleviate the ecological deterioration. However, extensive distribution of carbonate rocks may lead to limited plant available Si. The mountainous terrain in karst region also leads to more Si output, which seriously affects the biogeochemical cycle of Si in this area. Yet, the soil Si fractions in the karst region have not been fully evaluated. Methods Soil profiles and their corresponding plants were sampled from two typical karst mountains in Guizhou, China. The different fractions of non-crystalline Si in soil, accounting for the most important pool for Si availability to plants, were analyzed by the improved sequential chemical extraction and Si concentrations in plants grown in this region were also measured. Results The concentration and storage of non-crystalline Si were higher at lower slopes (storage was 2.44, 2.73, and 3.25 kg center dot m(-2) for upper, middle, and lower slopes, respectively) than other slope positions. Grasses dominated at lower slopes and contained significantly higher Si (mean +/- SD: 14.42 +/- 6.63 mg center dot g(-1)) than trees and shrubs (1.94 +/- 1.78 and 1.29 +/- 1.00 mg center dot g(-1), respectively), which were primarily distributed on upper slopes. However, Si concentrations of the same plant species in different slope positions had no significant correlation with soil acid Na acetate-Si, the Si regarded as directly available for plants. Conclusions This study suggests that plant species and soil properties have a significant impact on the soil Si distribution of hillslopes in karst region. Soil erosion may decrease non-crystalline Si concentrations in soils and impair Si uptake in grasses, which need to be considered in ecosystem management in this region.
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8.
  • Hao, Qian, et al. (författare)
  • Vegetation Determines Lake Sediment Carbon Accumulation during Holocene in the Forest-Steppe Ecotone in Northern China
  • 2021
  • Ingår i: Forests. - : MDPI. - 1999-4907. ; 12:6
  • Tidskriftsartikel (refereegranskat)abstract
    • To understand the past carbon accumulation of forest-steppe ecotone and to identify the main drivers of the long-term carbon dynamics, we selected Huangqihai Lake and analyzed the sediment records. We measured the organic carbon content (TOC; %) of sedimentary samples and quantified the carbon accumulation rate (CAR; g C m(-2) yr(-1)). Furthermore, the climate, soil erosion, and vegetation development of the past 6800 years were reconstructed using physicochemical parameters and pollen records. Human activities were also obtained from a 2200-year history record. Our results showed that the CAR was high during 5800 similar to 4100 cal yr BP (40 similar to 60 g C m(-2) yr(-1)), which is mainly attributed to the high sediment accumulation rate (SAR) during this period. Pearson's correlation, redundancy analysis and hierarchical variation partitioning analyses suggested that the CAR was influenced by the SAR and TOC, while vegetation dynamics (broadleaved tree percentage and vegetation coverage) and local soil erosion were the main drivers of the TOC and SAR. Especially when the vegetation was dominated by broadleaved forests, the CAR was significantly high due to the high gross primary productivity and carbon density of forest compared with steppe. Our study highlights the direct influence of local vegetation and soil erosion on the CAR, whereas climate might influence indirectly by changing local vegetation and soil conditions. Moreover, our results showed that human activities had positive influences on the carbon accumulation dynamics in this region since 2200 cal yr BP by influencing the SAR.
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9.
  • Ketzer, João Marcelo, et al. (författare)
  • Discovery of a major seafloor methane release site in Europe : The Landsort deep, Baltic Sea.
  • 2024
  • Ingår i: EGU General Assembly 2024. - : European Geosciences Union (EGU).
  • Konferensbidrag (refereegranskat)abstract
    • A recently acquired multidisciplinary dataset comprising acoustic surveys (high-resolution sub- bottom profiles, multi-beam bathymetry, and broad band mid-water echo sounder), geochemistry (gas chemical and isotopic composition, porewater chemistry), and sedimentology (core lithology and X-ray CT) in the area of the Landsort deep (450 m of depth), south of Stockholm Archipelago, revealed the existence of an extensive (20 km2) region of the seafloor where massive gas release is occurring in the form of multiple bubble streams. This new discovery represents a major seafloor methane release site in Europe and is comparable in area to other large sites worldwide such as the ones in Svalbard and in the South Atlantic Ocean associated with gas hydrate provinces. The gas is formed mostly by methane of microbial origin. Surprisingly, bubbles rise 100’s of meters above the seafloor and reach surface waters above the halocline/oxycline at around 80 m of depth. Some bubbles appear to reach the sea-air interface and their potential methane contribution to the atmosphere is under investigation. Another surprising observation is the absence of major seafloor features like pockmarks in the gas release area. The reasons for the seafloor methane release in the Landsort deep are still not entirely clear, but our preliminary acoustic and sedimentological data suggest that bottom currents may have acted to facilitate the accumulation of organic-rich sediments in a thick drift deposit during the Holocene and the modern warm period (latest 100 years). Our data further suggest that the high sedimentation rate in the drift deposit continuously supplies fresh organic matter that is quickly buried below a thin sulphate reduction zone, fueling vigorous methanogenesis and abundant methane formation. Similar methane release sites might be discovered in other known large drift deposits in the Baltic Sea. 
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10.
  • Nyman, Alexandra, et al. (författare)
  • A nationwide acid sulfate soil study : A rapid and cost-efficient approach for characterizing large-scale features
  • 2023
  • Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 869
  • Tidskriftsartikel (refereegranskat)abstract
    • Acid sulfate soils are sulfide-rich soils that pose a notable environmental risk as their strong acidity and low pH mobilizes metals from soil minerals leading to both acidification and metal contamination of the surrounding environment. In this study a rapid and cost-efficient approach was developed to resolve the main distribution patterns and geochemical features of acid sulfate soils throughout coastal plains stretching for some 2000 km in eastern, southern, and western Sweden. Of the investigated 126 field sites, 47 % had acid sulfate soils including 33 % active, 12 % potential, and 2 % pseudo acid sulfate soils. There were large regional variations in the extent of acid sulfate soils, with overall much higher proportions of these soils along the eastern coastal plains facing the Baltic Sea than the western coastal plains facing the Kattegatt/Skagerrak (Atlantic Ocean). The sulfur concentrations of the soil's parent material, consisting of reduced near-pH neutral sediments, were correlated inversely both with the minimum pH of the soils in situ (rS = −0.65) and the pH after incubation (oxidation) of the reduced sediments (rS = −0.77). This indicated the importance of sulfide levels in terms of both present and potential future acidification. Hence, the higher proportion of acid sulfate soils in the east was largely the result of higher sulfur concentrations in this part of the country. The study showed that the approach was successful in identifying large-scale spatial patterns and geochemical characteristics of importance for environmental assessments related to these environmentally unfriendly soils.
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11.
  • Nyman, Alexandra, et al. (författare)
  • Multi-element features of active acid sulfate soils across the Swedish coastal plains
  • 2023
  • Ingår i: Applied Geochemistry. - : Elsevier. - 0883-2927 .- 1872-9134. ; 152
  • Tidskriftsartikel (refereegranskat)abstract
    • Acid sulfate soils are sulfide-rich soils with notable associated environmental risks. The low pH of these soils mobilizes metals from the soil minerals, which will lead to both acidification and metal contamination of the surrounding environment. This paper presents the results of a geochemical study of 66 profiles of acid sulfate soils collected from a total of 22 sites (three profiles for each site) on the Swedish coastal plains, which stretch for some 2000 km along the Baltic Sea and Kattegat. The reduced zone at the bottom of the profiles was characterized by pH frequently >6.0, the transition zone (above the reduced zone) by a steep pH gradient from near-neutral to weakly acidic, and the oxidized zone located above the transition zone by highly acidic conditions with a pH minimum <4.0. Each zone in each profile was sampled for geochemical analyses. The aqua regia extractable S concentrations ranged widely in the reduced zone (0.06–7.5%) and were strongly depleted in the oxidized zone (median decrease 69%) from extensive sulfide oxidation and associated severe acidification and sulfate leaching. In addition to S, there were significant losses from the oxidized zone of eight alkali and alkaline earth metals (Ba, Be, Ca, K, Li, Mg, Na, and Sr), four first row transition metals (Co, Mn, Ni, and Zn), three second row transition metals (Cd, Y, and Zr), the rare earth elements (Ce, La, and Yb), and Al, Th, and B. These elements would therefore be expected to be enriched in nearby surface waters, which was supported by hydrogeochemistry data from elsewhere in the boreal zone. Nineteen other chemical elements were not significantly lost from the oxidized zone relative to the reduced zone (Fe, Ti, W, Se, Sc, V, Cu, Cr, P, In, Te, Ag, Sb, Bi, Sn, Mo, U, As, and Pb) and therefore, would not be expected to occur in elevated concentrations in acid sulfate soil affected surface waters, as was supported by literature data from elsewhere in the boreal zone. A hypothesis of more extensive oxidation, acidification, and leaching of the soils in south Sweden (hemiboreal zone) than north Sweden (boreal zone) due to a warmer climate in the former region was rejected based upon pH and multi-element patterns from 9 field sites from the north and 12 field sites from the south. Consequently, the losses were likely primarily controlled by local factors, such as time since drainage and soil development. However, the oxidized zone was significantly thicker in the north (median: 75 cm) than south (median: 40 cm). This suggested that although the proportional losses (i.e., difference in elemental concentrations between the oxidized and reduced zones) were overall not different between the two regions, the total amount of elements lost from the soils will have been larger in the north. Of the elements with no significant losses, several were extracted with 1 M HCl to a larger extent in the oxidized than the reduced zone (Fe, As, Cr, Cu, Mo, Sc, Ti, U, and V). This indicated retention in the acidic environment following release from weathered and/or oxidized soil minerals. These elements, of which several are particularly toxic (As, Cr, and U), may thus be mobilized and leached if the soils geochemical conditions change either naturally or via human activities.
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12.
  • Qin, Zhilian, et al. (författare)
  • Vertical distributions of organic carbon fractions under paddy and forest soils derived from black shales : Implications for potential of long-term carbon storage
  • 2021
  • Ingår i: Catena (Cremlingen. Print). - : Elsevier. - 0341-8162 .- 1872-6887. ; 198, s. 1-8
  • Tidskriftsartikel (refereegranskat)abstract
    • Black shales are characterized by a high content of organic carbon (C). Few studies have focused on the influence of land use on soil organic C (SOC) fractions from soils derived from black shale (black shale soils). The objective of this study was to elucidate the influence of land use on SOC fractions in black shale soils combining chemical determination and stable C isotope analysis techniques. Herein, we determined labile organic C (LOC), semilabile organic C (Semi-LOC), and recalcitrant organic C (ROC) fractions in various depths of soils in paddy fields (0-70 cm) and forests (0-120 cm) from black shale distribution region in Hunan province, China, and then investigated delta C-13 values of these soils. Results showed that the contents of LOC, Semi-LOC, and ROC in paddy soils (1.63-7.35 g kg(-1), 0.35-1.21 g kg(-1), and 3.75-14.8 g kg(-1), respectively) and forest soils (0.73-4.94 g kg(-1), 0.12-0.89 g kg(-1), and 1.44-8.96 g kg(-1), respectively) are significantly decreased with increasing depth. The contribution made by LOC to SOC in paddy soils was significantly lower than that in forest soils, while the contribution made by ROC to SOC was significantly higher in paddy soils than that in forest soils. In these two land uses, the delta C-13 values were higher in SOC compared to the ROC fraction, while the delta C-13 values were close in the ROC fraction below 20 cm soil depth. Our study indicated that i) new C is mainly limited to the surface soil layer (0-10 cm) in forests, while it can be leached along the soil profiles in paddy fields; ii) the estimated ROC pool is similar to 900 Pg within the 0-100 cm soil layer in terrestrial ecosystems, which should better represent the ability of soil C sequestration.
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13.
  • Sandhi, Arifin, et al. (författare)
  • Arsenic in the water and agricultural crop production system : Bangladesh perspectives
  • 2022
  • Ingår i: Environmental Science and Pollution Research. - : Springer. - 0944-1344 .- 1614-7499. ; 29, s. 51354-51366
  • Forskningsöversikt (refereegranskat)abstract
    • The presence of high levels of carcinogenic metalloid arsenic (As) in the groundwater system of Bangladesh has been considered as one of the major environmental disasters in this region. Many parts of Bangladesh have extensively reported the presence of high levels of arsenic in the groundwater due to both geological and anthropogenic activities. In this paper, we reviewed the available literature and scientific information regarding arsenic pollution in Bangladesh, including arsenic chemistry and occurrences. Along with using As-rich groundwater as a drinking-water source, the agricultural activities and especially irrigation have greatly depended on the groundwater resources in this region due to high water demands for ensuring food security. A number of investigations in Bangladesh have shown that high arsenic content in both soil and groundwater may result in high levels of arsenic accumulation in different plants, including cereals and vegetables. This review provides information regarding arsenic accumulation in major rice varieties, soil-groundwater-rice arsenic interaction, and past arsenic policies and plans, as well as previously implemented arsenic mitigation options for both drinking and irrigation water systems in Bangladesh. In conclusion, this review highlights the importance and necessity for more in-depth studies as well as more effective arsenic mitigation action plans to reduce arsenic incorporation in the food chain of Bangladesh.
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14.
  • Shahabi-Ghahfarokhi, Sina, et al. (författare)
  • Extensive dispersion of metals from hemiboreal acid sulfate soil into adjacent drain and wetland
  • 2024
  • Ingår i: Applied Geochemistry. - : Elsevier Ltd.. - 0883-2927 .- 1872-9134. ; 136
  • Tidskriftsartikel (refereegranskat)abstract
    • Extensive red/brown precipitates of unknown origin and composition have caused ecological degradation of a wetland nature reserve (the Water Kingdom Biosphere Reserve) in the hemiboreal zone in south Sweden. Chemical analyses of samples containing the precipitates showed strong dominates of Fe and elevated levels of rare earth elements (REEs), Be, and U. In addition, synchrotron-based analyses indicated that the Fe in these precipitates was bound largely in akageneite and/or schwertmannite. Under nearby farmlands, acid sulfate soils, developing on sulfide-bearing sediments and notorious for abundant export of metals, were identified and found to be widespread, deep (down to the sampling depth of 180 cm or deeper), and very acidic (minimum pH range for soil profiles: 2.8–3.5). In-between the farmland and wetland was a central drain that can act as both a transporter and sink of elements leached from the acid sulfate soils. In the drain had accumulated sediments that had strongly elevated concentrations of Al (15%), ∑REE (2725 mg/kg), Be (15 mg/kg), and U (37 mg/kg). Based on these data and features, a conceptual model for the areas was proposed. The acid sulfate soil releases several major and trace elements, including Fe2+, which are transported in acidic waters via drainpipes to the central drain where pH increases, causing extensive precipitation of Al, REEs, Be, and U as well as Fe2+ oxidation and formation of Fe oxyhydroxides and oxyhydroxysulfates. A substantial part of the Fe2+ in the drain water, however, remains in solution, so when this water is ultimately pumped to the wetland, large amounts of Fe2+ together with significant amounts of Al, REEs, Be, and U and transported to the wetland where Fe2+ is finally oxidized, precipitated and retained. Yet several other metals, leached abundantly from the acid sulfate soils (Mn, Zn, Ni, Co, and Cd), were not found in elevated levels in any of the recipients and therefore most likely have been transported beyond our sampling sites and has thus reached further outin the ecologically sensitive wetland.
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15.
  • Shahabi-Ghahfarokhi, Sina, et al. (författare)
  • Removal and potential recovery of dissolved metals from acid sulfate soil drainage by spent coffee-grounds and dissolved organic carbon
  • 2022
  • Ingår i: Environmental Advances. - : Elsevier. - 2666-7657. ; 8
  • Tidskriftsartikel (refereegranskat)abstract
    • This study explores the reuse of spent coffee-grounds (SCGs) and the use of dissolved humic acid (DHA) to remediate acid sulfate (AS) soil drainage using adsorption and precipitation experiments, with changing pH,weight/volume, and concentrations (mg/L of dissolved organic carbon). In addition, this study aims to extend the usability of the SCGs, after being reacted with AS soil drainage, by identifying the potential recovery of incinerated SCGs from the ash of the SCGs produced incineration. As compared to DHA, the SCGs had greater efficiency in removing metals, such as Al (98%), Ca (96%), Co (94%), Fe (88%), Mn (100%), Ni (93%), and Zn (96%). However, the removal of Fe was significantly reduced when higher weight/volume of SCGs were introduced. In addition, SCGs could not bind sulfur, while DHA had removed up to 25% of S from the solution.This suggests the simultaneous use of SCGs and DHA could restrict the formation of problematic Fe(III) secondary compounds (e.g., schwertmannite/akaganeite) which are problematic in some AS soil settings. The results show that Co (69%), Ni (58%), Mn (60%), Fe (59%), Zn (55%), and Al (34%) had the highest recovery percentage by sequential chemical extraction, respectively. The recovery of metals, as well as the removal of dissolved metals from the drainage water, illustrates the effectiveness of the proposed approach for SCGs reuse.
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16.
  • Shahabi-Ghahfarokhi, Sina, et al. (författare)
  • The response of metal mobilization and redistribution to reoxygenation in Baltic Sea anoxic sediments
  • 2022
  • Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 837
  • Tidskriftsartikel (refereegranskat)abstract
    • To bring life back to anoxic coastal and sea basins, reoxygenation of anoxic/hypoxic zones has been proposed. This research focuses on the metals released during the oxidization of sediments from two locations in the anoxic Eastern Gotland Basin under a laboratory-scale study. Triplicate experimental cores and reference cores were collected from the North and South Eastern Gotland Basins. The oxygenation of the water column took place over a 96-hour experiment in a dark and 5 °C environment. In 12 and 24 hour intervals, the surface waters were exchanged and, over time, analyzed for pH, electroconductivity (EC), total organic carbon (TOC), soluble metal concentrations, and the top samples (0–10 cm) were analyzed with 3-step (E1: water-soluble, E2: exchangeable, and E3: organic-bound) sequential chemical extraction (SCE). Results show stable pH and decreasing EC in the column waters. The EC indicates that metals are released in the initial phases (12 h) of reoxygenation for both sites. Arsenic, Ba, Co, Mn, Rb, U, K, Sr, and Mo are released into the water column during the 96 hour experiment, and based on the calculations for the entire East Gotland Basin, would mean 8, 50, 0.55, 734, 53, 27, 347,178, 3468, and 156 μg L−1 are released, respectively. Elements Mn, Mo, U, and As are released in higher concentrations during the experiment than previously measured in the Eastern Gotland Basin, which provides vital information for future proposed remediation and natural geochemical processes with their known environmental impacts. The SCE results show that redox-sensitive metals (Mn, U, and Mo) are released in the highest concentrations into the solution. The relationship between the highest released metals (beside redox-sensitive) into solution over the oxygenation and their initial abundant phase is noticed, where the smallest released concentrations belong to K < Rb < Sr in E2, and As
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17.
  • Shilei, Yang, et al. (författare)
  • A review of carbon isotopes of phytoliths : implications for phytolith-occluded carbon sources
  • 2020
  • Ingår i: Journal of Soils and Sediments. - : Springer. - 1439-0108 .- 1614-7480. ; 20:4, s. 1811-1823
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose Phytolith-occluded carbon (PhytOC) is mainly derived from the products of photosynthesis, which can be preserved in soils and sediments for hundreds-to-thousands of years due to the resilient nature of the amorphous phytolith silica. Therefore, stable and radioactive carbon (C) isotopes of phytoliths can be effectively utilized in paleoecological and archeological research. However, there still exists debate about the applicability of C isotopes of phytoliths, as a “two-pool” hypothesis to characterize PhytOC sources has been proposed, whereby a component of the PhytOC is derived from soil organic matter (SOM) absorbed through plant roots. Therefore, it is necessary to review this topic to better understand the source of PhytOC. Materials and method We introduce the stable and radioactive C isotopic compositions of PhytOC, present the impacts of different extraction methods on the study of PhytOC, and discuss the implications of these factors for determining the sources of PhytOC. Results and discussion Based on this review, we suggest that organic matter synthesized by photosynthesis is the main source of PhytOC. However, it is important to make clear whether and how SOM-derived C present in phytoliths influence the controversial “too-old” skew and isotopic fractionation. Conclusions Though the two-pool hypothesis has been proved by many researches, the carbon isotopes of phytoliths still have potential in paleoecology and archeology, because the main source is photosynthesis and many previous studies put forward the availability of these parameters. This review also shows that phytolith C isotopes may vary with different organic C compounds within phytoliths, which needs further study at the molecular scale. Different phytolith extraction methods can influence 14C dating results.
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18.
  • Sjöberg, Susanne, et al. (författare)
  • Microbe-Mediated Mn Oxidation - A Proposed Model of Mineral Formation
  • 2021
  • Ingår i: Minerals. - : MDPI. - 2075-163X. ; 11:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Manganese oxides occur in a wide range of environmental settings either as coatings on rocks, sediment, and soil particles, or as discrete grains. Although the production of biologically mediated Mn oxides is well established, relatively little is known about microbial-specific strategies for utilizing Mn in the environment and how these affect the morphology, structure, and chemistry of associated mineralizations. Defining such strategies and characterizing the associated mineral properties would contribute to a better understanding of their impact on the local environment and possibly facilitate evaluation of biogenicity in recent and past Mn accumulations. Here, we supplement field data from a Mn rock wall deposit in the Ytterby mine, Sweden, with data retrieved from culturing Mn oxidizers isolated from this site. Microscopic and spectroscopic techniques are used to characterize field site products and Mn precipitates generated by four isolated bacteria (Hydrogenophaga sp., Pedobacter sp., Rhizobium sp., and Nevskia sp.) and one fungal-bacterial co-culture (Cladosporium sp.-Hydrogenophaga sp. Rhizobium sp.-Nevskia sp.). Two of the isolates (Pedobacter sp. and Nevskia sp.) are previously unknown Mn oxidizers. At the field site, the onset of Mn oxide mineralization typically occurs in areas associated with globular wad-like particles and microbial traces. The particles serve as building blocks in the majority of the microstructures, either forming the base for further growth into laminated dendrites-botryoids or added as components to an existing structure. The most common nanoscale structures are networks of Mn oxide sheets structurally related to birnessite. The sheets are typically constructed of very few layers and elongated along the octahedral chains. In places, the sheets bend and curl under to give a scroll-like appearance. Culturing experiments show that growth conditions (biofilm or planktonic) affect the ability to oxidize Mn and that taxonomic affiliation influences crystallite size, structure, and average oxidation state as well as the onset location of Mn precipitation.
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19.
  • Song, Zhaoliang, et al. (författare)
  • High potential of stable carbon sequestration in phytoliths of China's grasslands
  • 2022
  • Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 28:8, s. 2736-2750
  • Tidskriftsartikel (refereegranskat)abstract
    • Phytolith carbon (C) sequestration plays a key role in mitigating global climate change at a centennial to millennial time scale. However, previous estimates of phytolith-occluded carbon (PhytOC) storage and potential in China's grasslands have large uncertainties mainly due to multiple data sources. This contributes to the uncertainty in predicting long-term C sequestration in terrestrial ecosystems using Earth System Models. In this study, we carried out an intensive field investigation (79 sites, 237 soil profiles [0-100 cm], and 61 vegetation assessments) to quantify PhytOC storage in China's grasslands and to better explore the biogeographical patterns and influencing factors. Generally, PhytOC production flux and soil PhytOC density in both the Tibetan Plateau and the Inner Mongolian Plateau had a decreasing trend from the Northeast to the Southwest. The aboveground PhytOC production rate in China's grassland was 0.48 x 10(6) t CO2 a(-1), and the soil PhytOC storage was 383 x 10(6) t CO2. About 45% of soil PhytOC was stored in the deep soil layers (50-100 cm), highlighting the importance of deep soil layers for C stock assessments. Importantly, the Tibetan Plateau had the greatest contribution (more than 70%) to the PhytOC storage in China's grasslands. The results of multiple regression analysis indicated that altitude and soil texture significantly influenced the spatial distribution of soil PhytOC, explaining 78.1% of the total variation. Soil phytolith turnover time in China's grasslands was mainly controlled by climatic conditions, with the turnover time on the Tibetan Plateau being significantly longer than that on the Inner Mongolian Plateau. Our results offer more accurate estimates of the potential for phytolith C sequestration from ecological restoration projects in degraded grassland ecosystems. These estimates are essential to parameterizing and validating global C models.
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20.
  • Wu, Lele, et al. (författare)
  • Organic matter composition and stability in estuarine wetlands depending on soil salinity
  • 2024
  • Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 945
  • Tidskriftsartikel (refereegranskat)abstract
    • Coastal wetlands are key players in mitigating global climate change by sequestering soil organic matter. Soil organic matter consists of less stable particulate organic matter (POM) and more stable mineral-associated organic matter (MAOM). The distribution and drivers of MAOM and POM in coastal wetlands have received little attention, despite the processes and mechanisms differ from that in the upland soils. We explored the distribution of POM and MAOM, their contributions to SOM, and the controlling factors along a salinity gradient in an estuarine wetland. In the estuarine wetland, POM C and N were influenced by soil depth and vegetation type, whereas MAOM C and N were influenced only by vegetation type. In the estuarine wetland, SOM was predominantly in the form of MAOM (> 70 %) and increased with salinity (70 %–76 %), leading to long-term C sequestration. Both POM and MAOM increased with SOM, and the increase rate of POM was higher than that of MAOM. Aboveground plant biomass decreased with increasing salinity, resulted in a decrease in POM C (46 %–81 %) and N (52 %–82 %) pools. As the mineral amount and activity, and microbial biomass decreased, the MAOM C (2.5 %–64 %) and N pool (8.6 %–59 %) decreased with salinity. When evaluating POM, the most influential factors were microbial biomass carbon (MBC) and dissolved organic carbon (DOC). Key parameters, including MBC, DOC, soil salinity, soil water content, aboveground plant biomass, mineral content and activity, and bulk density, were identified as influencing factors for both MAOM abundance. Soil water content not only directly controlled MAOM, but together with salinity also indirectly regulated POM and MAOM by controlling microbial biomass and aboveground plant biomass. Our findings have important implications for improving the accumulation and increased stability of soil organic matter in coastal wetlands, considering the global sea level rise and increased frequency of inundation.
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21.
  • Wu, Yuntao, et al. (författare)
  • Climatic controls on stable carbon and nitrogen isotope compositions of temperate grasslands in northern China
  • 2023
  • Ingår i: Plant and Soil. - : Springer. - 0032-079X .- 1573-5036. ; 491, s. 133-144
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims The natural abundances of stable carbon (C) and nitrogen (N) isotopes (delta C-13 and delta N-15) are extensively used to indicate the C and N biogeochemical cycles at large spatial scales. However, the spatial patterns of delta C-13 and delta N-15 in plant-soil systems of grasslands in northern China and their main driving factors across regional climatic gradient are still not well understood. Methods We measured plant and soil delta C-13 and delta N-15 compositions as well as their associated environmental factors across 2000 km climatic gradient (-0.2 to 9 degrees C; 152 to 502 mm) in grasslands of northern China. Results The soil delta C-13 and delta N-15 values in surface were lower than those in bottom for temperate typical steppe but had no significant differences for temperate meadow steppe and temperate desert steppe. Soil delta C-13 values declined with increasing soil organic carbon (SOC) but increased as mean annual temperature (MAT). These changes were attributed to the microbial decomposition rate. The delta N-15 values in soil and plant were negatively correlated with MAT and mean annual precipitation (MAP), which were mainly related to the low soil organic matter mineralization rate and the shift of dominant species from C-4 to C-3. Conclusions Our results indicate the spatial patterns and different influencing factors on delta C-13 and delta N-15 values along the climatic gradient in grasslands of northern China. The findings will provide scientific references for future research on the C and N biogeochemical cycles of temperate grasslands.
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22.
  • Wu, Yuntao, et al. (författare)
  • Silicon promotes biomass accumulation in Phragmites australis under waterlogged conditions in coastal wetland
  • 2024
  • Ingår i: Plant and Soil. - : Springer Nature. - 0032-079X .- 1573-5036.
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims Previous studies have shown that silicon (Si) can affect plant growth and yield by regulating the availability of other nutrients. However, the mechanisms by which Si affects plant biomass accumulation in coastal wetlands are not well explored. Methods We conducted a sampling campaign across the whole growing season of Phragmites australis under waterlogging and drought conditions in coastal wetland, and quantified the effects of Si availability on biomass accumulation. Results Compared with drought condition, the waterlogged condition improved the utilization efficiency of nitrogen (N) and phosphorus (P) of P. australis regulated by higher Si contents. Meanwhile, the increased Si contents promoted the utilization of N and P in leaf, suggesting that the increase in Si contents optimizes the photosynthetic process. Lignin contents in P. australis decreased with the increasing Si contents, which confirmed that Si can replace structural carbon components. In addition, principal component analysis (PCA) showed aboveground biomass accumulation of P. australis was synchronized with Si accumulation, indicating that Si was a beneficial element to promote biomass accumulation. Conclusions Our study implies that increasing Si availability is conducive to biomass accumulation of P. australis in waterlogged wetlands, which will provide important scientific references for the management of coastal wetland ecosystem and the increase of global 'blue carbon' sequestration.
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23.
  • Xia, Shaopan, et al. (författare)
  • Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ13C-δ15N, and lignin biomarker
  • 2021
  • Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 27:2, s. 417-434
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite increasing recognition of the critical role of coastal wetlands in mitigating climate change, sea‐level rise, and salinity increase, soil organic carbon (SOC) sequestration mechanisms in estuarine wetlands remain poorly understood. Here, we present new results on the source, decomposition, and storage of SOC in estuarine wetlands with four vegetation types, including single Phragmites australis (P, habitat I), a mixture of P. australis and Suaeda salsa (P + S, habitat II), single S. salsa (S, habitat III), and tidal flat (TF, habitat IV) across a salinity gradient. Values of δ13C increased with depth in aerobic soil layers (0–40 cm) but slightly decreased in anaerobic soil layers (40–100 cm). The δ15N was significantly enriched in soil organic matter at all depths than in the living plant tissues, indicating a preferential decomposition of 14N‐enriched organic components. Thus, the kinetic isotope fractionation during microbial degradation and the preferential substrate utilization are the dominant mechanisms in regulating isotopic compositions in aerobic and anaerobic conditions, respectively. Stable isotopic (δ13C and δ15N), elemental (C and N), and lignin composition (inherited (Ad/Al)s and C/V) were not completely consistent in reflecting the differences in SOC decomposition or accumulation among four vegetation types, possibly due to differences in litter inputs, root distributions, substrate quality, water‐table level, salinity, and microbial community composition/activity. Organic C contents and storage decreased from upstream to downstream, likely due to primarily changes in autochthonous sources (e.g., decreased onsite plant biomass input) and allochthonous materials (e.g., decreased fluvially transported upland river inputs, and increased tidally induced marine algae and phytoplankton). Our results revealed that multiple indicators are essential to unravel the degree of SOC decomposition and accumulation, and a combination of C:N ratios, δ13C, δ15N, and lignin biomarker provides a robust approach to decipher the decomposition and source of sedimentary organic matter along the river‐estuary‐ocean continuum.
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24.
  • Xia, Shaopan, et al. (författare)
  • Silicon accumulation controls carbon cycle in wetlands through modifying nutrients stoichiometry and lignin synthesis of Phragmites australis
  • 2020
  • Ingår i: Environmental and Experimental Botany. - : Elsevier. - 0098-8472 .- 1873-7307. ; 175, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon (Si) is one of the most abundant elements in the Earth’s crust but its role in governing the biogeochemicalcycling of other elements remains poor understood. There is a paucity of information on the role of Si in wetlandplants, and how this may alter wetland C production and storage. Therefore, this study investigated Si distribution,nutrient stoichiometry and lignin abundance in Phragmites australis from a wetland system in China tobetter understand the biogeochemical cycling and C storage. Our data show that Si content (ranging between0.202% to 6.614%) of Phragmites australis is negatively correlated with C concentration (38.150%–47.220%).Furthermore, Si content was negatively antagonistically related to the concentration of lignin-derived phenols inthe stem (66.763–120.670 mg g-1 C) and sheath (65.400–114.118 mg g-1 C), but only a weak relationship wasobserved in the leaf tissue (36.439–55.905 mg g-1 C), which is relevant to the photosynthesis or stabilizationfunction of the plant tissues. These results support the notion that biogenic Si (BSi) can substitute lignin as astructural component, due to their similar eco-physiological functions, reduces costs associated with ligninbiosynthesis. The accumulation of BSi increased total biomass C storage and nutrient accumulation due togreater productivity of Phragmites australis. On the other hand, BSi regulated litter composition and quality (e.g.,nutrient stoichiometry and lignin) that provide a possibility for the factors affecting litter decomposition. Thuscompeting processes (i.e., biomass quantity vs quality) can be influenced by Si cycling in wetlands.
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25.
  • Xia, Shaopan, et al. (författare)
  • Storage, patterns and influencing factors for soil organic carbon in coastal wetlands of China
  • 2022
  • Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 28:20, s. 6065-6085
  • Tidskriftsartikel (refereegranskat)abstract
    • Soil organic carbon (SOC) in coastal wetlands, also known as "blue C," is an essential component of the global C cycles. To gain a detailed insight into blue C storage and controlling factors, we studied 142 sites across ca. 5000 km of coastal wetlands, covering temperate, subtropical, and tropical climates in China. The wetlands represented six vegetation types (Phragmites australis, mixed of P. australis and Suaeda, single Suaeda, Spartina alterniflora, mangrove [Kandelia obovata and Avicennia marina], tidal flat) and three vegetation types invaded by S. alterniflora (P. australis, K. obovata, A. marina). Our results revealed large spatial heterogeneity in SOC density of the top 1-m ranging 40-200 Mg C ha(-1), with higher values in mid-latitude regions (25-30 degrees N) compared with those in both low- (20 degrees N) and high-latitude (38-40 degrees N) regions. Vegetation type influenced SOC density, with P. australis and S. alterniflora having the largest SOC density, followed by mangrove, mixed P. australis and Suaeda, single Suaeda and tidal flat. SOC density increased by 6.25 Mg ha(-1) following S. alterniflora invasion into P. australis community but decreased by 28.56 and 8.17 Mg ha(-1) following invasion into K. obovata and A. marina communities. Based on field measurements and published literature, we calculated a total inventory of 57 x 10(6) Mg C in the top 1-m soil across China's coastal wetlands. Edaphic variables controlled SOC content, with soil chemical properties explaining the largest variance in SOC content. Climate did not control SOC content but had a strong interactive effect with edaphic variables. Plant biomass and quality traits were a minor contributor in regulating SOC content, highlighting the importance of quantity and quality of OC inputs and the balance between production and degradation within the coastal wetlands. These findings provide new insights into blue C stabilization mechanisms and sequestration capacity in coastal wetlands.
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26.
  • Xie, S., et al. (författare)
  • A re-assessment of metal pollution in the Dexing mining area in Jiangxi province, China : current status, hydro-geochemical controls, and effectiveness of remediation practices
  • 2022
  • Ingår i: International Journal of Environmental Science and Technology. - : Springer Nature. - 1735-1472 .- 1735-2630. ; 19, s. 10707-10722
  • Tidskriftsartikel (refereegranskat)abstract
    • This study re-assess the environmental impacts of the Dexing copper mine (the largest open-pit copper mine in Asia) on the Lean river and its two tributaries (the Dawu river and Jishui river) in the Jiangxi province, China, with particular focus on metal pollution as well as the effectiveness and side-effects of remediation activities. Results show that the Dawu river and its mixing zone with the Lean river were still heavily influenced by acid mine drainage (AMD) and loaded with elevated levels of metals, in particular Mn, Ni, and Al whose concentrations were frequently above the health-based guideline values. Manganese and Ni in the AMD-impacted waters were predicted to occur as free ions or sulfate and carbonate complexes, and thus highly-toxic to living organisms. Although Al in the AMD-impacted waters was predicted to exist largely as colloidal hydroxides with low bioavailability, abundant formation of such nano-sized particles could impair the respiratory and circulatory systems of aquatic macro-invertebrates. The integration and comparison of the results from the current and previous studies show that the concentrations of several metals (Cu, Zn, and Cd) in the Dawu river decreased significantly after 2011-2012, during which several remediation practices were implemented (e.g., AMD neutralization, excavation of contaminated sediments in impounded rivers, and rehabilitation of mine tailings and open-pit slopes). This provides evidence that these remediation practices have effectively limited the dispersion of metals from the mining area. However, AMD neutralization greatly enhanced the release of sulfate, making the mining area an even more important sulfate source.
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27.
  • Yang, Xiaomin, et al. (författare)
  • Phytolith-rich straw application and groundwater table management over 36 years affect the soil-plant silicon cycle of a paddy field
  • 2020
  • Ingår i: Plant and Soil. - : Springer. - 0032-079X .- 1573-5036. ; 454, s. 343-358
  • Tidskriftsartikel (refereegranskat)abstract
    • Background and aims Silicon (Si) deficiency is a major constraint on rice production. The objective of this study was to evaluate the long-term influence of phytolith-rich straw return and groundwater table management on labile Si fractions in paddy soil and subsequent plant Si uptake. Methods A field experiment was conducted over 36 years in subtropical China with different application doses of phytolith-rich straw and a groundwater table of either 20 or 80 cm. An optimized sequential chemical extraction procedure allowed us to determine labile Si fractions, represented by CaCl2-Si, Acetic-Si, H2O2-Si, Oxalate-Si, and Na2CO3-Si. Additional analyses included the determination of amorphous silica particles in soil, phytoliths in supplied straw, Si in planted rice straw, and the dissolution rate of phytoliths extracted from supplied straw. Results Long-term application of phytolith-rich straw significantly increased the H2O2-Si and Na2CO3-Si contents. The CaCl2-Si (5.21-7.91 mg kg(- 1)), H2O2-Si (50.0-72.4 mg kg(- 1)) and Na2CO3-Si (3.33-4.60 g kg(- 1)) contents were positively correlated with soil organic carbon. The Si content (13.6-28.9 g kg(-& x200d;1)) in planted rice straw significantly (p < 0.05) increased with the application dose of phytolith-rich straw under both groundwater tables. This effect was significantly (p < 0.05) greater under 80 cm groundwater table than under 20 cm groundwater table for matching straw amendments. Conclusions This study indicates that long-term application of phytolith-rich straw and groundwater management significantly increase soil Si bioavailability by promoting accumulation of organic matter and phytoliths, and enhancing the soil-plant Si cycle.
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28.
  • Yang, Xiaomin, et al. (författare)
  • Quantification of different silicon fractions in broadleaf and conifer forests of northern China and consequent implications for biogeochemical Si cycling
  • 2020
  • Ingår i: Geoderma. - : Elsevier. - 0016-7061 .- 1872-6259. ; 361, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • The terrestrial biogeochemical silicon (Si) cycle significantly contributes to maintaining the functions and sustainability of terrestrial ecosystems. Over the short term, the biogeochemical Si cycle can be strongly influenced by dissolved Si, organic bound Si, Si adsorbed to pedogenic oxides/hydroxides, and biogenic and pedogenic amorphous Si. However, quantitative studies about these relatively soluble Si fractions are rare. In this study, we quantified different Si fractions in the 0–10 cm, 10–20 cm, 20–30 cm, 30–40 cm and 40–50 cm soil layers of broadleaf forests (Betula forest and Quercus forest) and conifer forests (Larix forest and Pinus forest) in northern China using a sequential chemical extraction scheme optimized for these Si fractions. The results showed that the total Si (Sit) in the soil layers consisted of 97.7–98.5% crystalline Si (Sicry) and 1.5–2.3% non-crystalline Si (Sinoncry) fractions. Within the Sinoncry fraction, the proportions of dissolved Si (Sidis), organic matter bound Si (Siorg), pedogenic oxides/hydroxides chemisorbed Si (Sisorb), and amorphous Si (Siamor) were 3.4–6.7%, 5.5–8.9%, 6.3–8.5%, and 77.7–84.8%, respectively. Although the Sidis fraction was the least abundant component, it is at the center of the interconversion processes among the different Sinoncry fractions. The Siamor fraction was the largest component of Sinoncry and was composed of 37.7–71.9% biogenic amorphous Si (Sibio-amor) and 28.1–62.3% pedogenic amorphous Si (Siped-amor). Our study indicated that i) Siped-amor fraction is more easily influenced by soil pH comparing to Sibio-amor fraction; ii) the Sibio-amor fraction contributes more to the biogeochemical Si cycle in broadleaf forests, whereas the Siped-amorfraction contributes more in conifer forests; and iii) soil pH, soil organic matter, and plant community differences can influence the vertical distribution of the different Sinoncry fractions and thus affect the multiple transformation processes among these Si fractions in studied forests.
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29.
  • Yang, Xiaoming, et al. (författare)
  • Spatial distribution of plant-available silicon and its controlling factors in paddy fields of China
  • 2021
  • Ingår i: Geoderma. - : Elsevier. - 0016-7061 .- 1872-6259. ; 401
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon (Si) is beneficial for rice health and production by alleviating various biotic and abiotic stresses. However, the continual export of grain off-farm may result in Si deficiency for rice plants. The current levels of plant available Si (PASi) in rice paddies in China remain unclear, as do the factors that control PASi content in these soils. We conducted a nationwide sampling campaign across the paddy fields of China between 2016 and 2019, and used calcium chloride extractable Si (Si-CaCl2) and buffered acetate extractable Si (Si-NaAc, pH = 4) to quantify PASi. We show that Si-CaCl2 pool was mainly influenced by mean annual temperature (MAT), soil salinity, soil organic carbon (SOC), mean annual precipitation (MAP), and soil pH, suggesting both pedological and biological control mechanisms. However, the Si-NaAc pool was influenced most by soil pH, MAT and MAP, implying pedological control. Compared to data from the 1990s, the Si-NaAc content decreased by 14.1% on a national scale with an annual decline rate of 0.54%. Based on our investigation, at least 65% of China’s paddy fields are deficient in PASi, which is an increase in area of ~15% over the last 20 years. The principal regions where PASi deficiency was recorded are mainly located in southern China, with the levels of Si deficiency lowering as the paddy fields are located further north. The continual off-site removal of PASi from rice grain and straw will need to be addressed through the use of Si-fertilizers, including organic amendments, to maintain a productive and sustainable rice industry in China.
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30.
  • Yu, Changxun, 1983-, et al. (författare)
  • A Combined X-ray Absorption and Mössbauer Spectroscopy Study on Fe Valence and Secondary Mineralogy in Granitoid Fracture Networks : Implications for Geological Disposal of Spent Nuclear Fuels
  • 2020
  • Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 54:5, s. 2832-2842
  • Tidskriftsartikel (refereegranskat)abstract
    • Underground repository in crystalline bedrock is a widely accepted solution for long-term disposal of spent nuclear fuels. During future deglaciations, meltwater will intrude via bedrock fractures to the depths of future repositories where O2 left in the meltwater could corrode metal canisters and enhance the migration of redox-sensitive radionuclides. Since glacial meltwater is poor in reduced phases, the quantity and (bio)accessibility of minerogenic Fe(II) in bedrock fractures determine to what extent O2 in future meltwater can be consumed. Here, we determined Fe valence and mineralogy in secondary mineral assemblages sampled throughout the upper kilometer of fractured crystalline bedrock at two sites on the Baltic Shield, using X-ray absorption and Mössbauer spectroscopic techniques that were found to deliver matching results. The data point to extensive O2-consuming capacity of the bedrock fractures, because Fe(II)-rich phyllosilicates were abundant and secondary pyrite was dispersed deep into the bedrock with no overall increase in Fe(II) concentrations and Fe(II)/Fe(III) proportions with depth. The results imply that repeated Pleistocene deglaciations did not cause a measurable decrease in the Fe(II) pool. In surficial fractures, largely opened during glacial unloading, ferrihydrite and illite have formed abundantly via oxidative transformation of Fe(II)-rich phyllosilicates and recently exposed primary biotite/hornblende.
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31.
  • Yu, Changxun, 1983-, et al. (författare)
  • Biogeochemical cycling of iron (hydr-)oxides and its impact on organic carbon turnover in coastal wetlands : A global synthesis and perspective
  • 2021
  • Ingår i: Earth-Science Reviews. - : Elsevier. - 0012-8252 .- 1872-6828. ; 218
  • Forskningsöversikt (refereegranskat)abstract
    • Coastal wetlands host large and dynamic reservoirs of organic carbon (C) and are also biogeochemical hotspots for a wide range of Fe (hydr-)oxides with different chemical reactivities, properties, and functions. The cycling of these iron (hydr-)oxides is closely coupled to that of organic C, which in turn strongly influences the magnitude and dynamics of organic C turnover in these ecosystems. This review synthesizes and summarizes current knowledge of distribution, turnover, and controls of Fe (hydr-)oxides, as well as their ecological roles and impacts on organic C turnover in coastal wetland ecosystems globally. Regional hydro-geochemical processes and anthropogenic activities in the uplands as well as soil texture exert a first-order control on the abundance and distribution of Fe (hydr-)oxides in coastal wetland soils, while the activities of plant roots and macro-organisms act as important biological drivers for the formation, transformation, and turnover of Fe (hydr-)oxides as well as associated organic C in both rhizosphere/burrows and bulk soils. The reported rates of dissimilatory Fe reduction (DFeR) are correlated with incubation temperature and the sizes of reactive Fe(III) phases. However, the contributions of DFeR to total anaerobic carbon oxidation were found to be correlated only with the size of reactive Fe(III) pools, meaning that all the identified processes contributing to the accumulation and formation of Fe hydroxides could increase the importance of the DFeR-dominated respiratory pathway and suppress sulfate reduction and methanogenesis. Additionally, Fe plaques dominated by amorphous Fe hydroxides are formed and cycled in close interaction with the activities of wetland plant roots, and likely provide several important ecological functions and contribute to maintaining high levels of plant productivity in coastal wetlands under different environmental stresses. The features and findings presented in this review not only contribute to an improved understanding of the biogeochemical cycle and ecological roles of Fe (hydr-)oxides in coastal wetlands, but also provide a basis for future studies on some highlighted key research areas. Such future studies will further increase our ability to understand and predict how the size, stability, and turnover of Fe (hydr-)oxides and organic C in coastal wetlands will respond to and affect global climate change.
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32.
  • Yu, Changxun, 1983-, et al. (författare)
  • Iron‑sulfur geochemistry and acidity retention in hydrologically active macropores of boreal acid sulfate soils : Effects of mitigation suspensions of fine-grained calcite and peat
  • 2023
  • Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 856:Part 2
  • Tidskriftsartikel (refereegranskat)abstract
    • Acid sulfate soils discharge large amounts of sulfuric acid along with toxic metals, deteriorating water quality and ecosystem health of recipient waterbodies. There is thus an urgent need to develop cost-effective and sustainable measures to mitigate the negative effects of these soils. In this study, we flushed aseptically-prepared MQ water (reference) or mitigation suspensions containing calcite, peat or a combination of both through 15-cm-thick soil cores from an acid sulfate soil field in western Finland, and investigated the geochemistry of Fe and S on the surfaces of macropores and in the solid columnar blocks (interiors) of the soil columns. The macropore surfaces of all soil columns were strongly enriched in total and HCl-extractable Fe and S relative to the interiors, owing to the existence of abundant Fe oxyhydroxysulfates (schwertmannite and partly jarosite) as yellow-to-brownish surface-coatings. The dissolution/hydrolysis of Fe oxyhydroxysulfates (predominantly jarosite) on the macropore surfaces of the reference columns, although being constantly flushed, effectively buffered the permeates at pH close to 4. These results suggest that Fe oxyhydroxysulfates accumulated on the macropore surfaces of boreal acid sulfate soils can act as long-lasting acidification sources. The treatments with mitigation suspensions led to a (near-)complete conversion of jarosite to Fe hydroxides, causing a substantial loss of S. In contrast, we did not observe any recognizable evidence indicating transformation of schwertmannite. However, sulfate sorbed by this mineral might be partially lost through anion-exchange processes during the treatments with calcite. No Fe sulfides were found in the peat-treated columns. Since Fe sulfides can support renewed acidification events, the moderate mineralogical changes induced by peat are desirable. In addition, peat materials can act as toxic-metal scavengers. Thus, the peat materials used here, which is relatively cheap in the boreal zone, is ideal for remediating boreal acid sulfate soils and other similar jarosite-bearing soils.
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33.
  • Yu, Changxun, 1983-, et al. (författare)
  • Manganese cycling and transport in boreal estuaries impacted by acidic Mn-rich drainage
  • 2024
  • Ingår i: GEOCHIMICA ET COSMOCHIMICA ACTA. - : Elsevier. - 0016-7037 .- 1872-9533 .- 0046-564X. ; 365, s. 136-157
  • Tidskriftsartikel (refereegranskat)abstract
    • As critical transition zones between the land and the sea, estuaries are not only hotspots of hydrogeochemical and microbial processes/reactions, but also play a vital role in processing and transferring terrestrial fluxes of metals and nutrients to the sea. This study focused on three estuaries in the Gulf of Bothnia. All of them expe-rience frequent inputs of acidic and Mn/metal-rich creek waters due to flushing of acid sulfate soils that are widespread in the creeks catchments. Analyzing existing long-term water chemistry data revealed a strong sea-sonal variation of Mn loads, with the highest values in spring (after snow melt) and autumn (after heavy rains). We sampled surface waters, suspended particulate matter (SPM), and sediments from the estuarine mixing zones and determined the loads and solid-phase speciation of Mn as well as the composition and metabolic potentials of microbial communities. The results showed that the removal, cycling, and lateral transport of Mn were governed by similar phases and processes in the three estuaries. Manganese X-ray absorption spectroscopy data of the SPM suggested that the removal of Mn was regulated by silicates (e.g., biotite), organically complexed Mn(II), and MnOx (dominated by groutite and phyllomanganates). While the fractional amounts of silicate-bound Mn(II) were overall low and constant throughout the estuaries, MnOx was strongly correlated with the Mn loadings of the SPM and thus the main vector for the removal of Mn in the central and outer parts of the estuaries, along with organically complexed Mn(II). Down estuary, both the fractional amounts and average Mn oxidation state of the MnOx phases increased with (i) the total Mn loads on the SPM samples and (ii) the relative abundances of several potential Mn-oxidizing bacteria (Flavobacterium, Caulobacter, Mycobacterium, and Pedobacter) in the surface waters. These features collectively suggested that the oxidation of Mn, probably mediated by the potential Mn-oxidizing microorganisms, became more extensive and complete towards the central and outer parts of the es-tuaries. At two sites in the central parts of one estuary, abundant phyllomanganates occurred in the surface sediments, but were converted to surface-sorbed Mn(II) phases at deeper layers (>3-4 cm). The occurrence of phyllomanganates may have suppressed the reduction of sulfate in the surface sediments, pushing down the methane sulfate transition zone that is typically shallow in estuarine sediments. At the outermost site in the estuary, deposited MnOx were reduced immediately at the water-sediment interface and converted most likely to Mn carbonate. The mobile Mn species produced by the Mn reduction processes (e.g., aqueous Mn(II) and ligand complexed Mn(III)) could partly diffuse into the overlying waters and, together with the estuarine Mn loads carried by the surface waters, transfer large amounts of reactive Mn into open coastal areas and subsequently contribute to Mn shuttling and inter-linked biogeochemical processes over the seafloor. Given the widespread occurrence of acid sulfate soils and other sulfidic geological materials on many coastal plains worldwide, the identified Mn attenuation and transport mechanisms are relevant for many estuaries globally.
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34.
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35.
  • Yu, Changxun, 1983-, et al. (författare)
  • Storage and Distribution of Organic Carbon and Nutrients in Acidic Soils Developed on Sulfidic Sediments : The Roles of Reactive Iron and Macropores
  • 2024
  • Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 58:21, s. 9200-9212
  • Tidskriftsartikel (refereegranskat)abstract
    • In a boreal acidic sulfate-rich subsoil (pH 3–4) developing on sulfidic and organic-rich sediments over the past 70 years, extensive brownish-to-yellowish layers have formed on macropores. Our data reveal that these layers (“macropore surfaces”) are strongly enriched in 1 M HCl-extractable reactive iron (2–7% dry weight), largely bound to schwertmannite and 2-line ferrihydrite. These reactive iron phases trap large pools of labile organic matter (OM) and HCl-extractable phosphorus, possibly derived from the cultivated layer. Within soil aggregates, the OM is of a different nature from that on the macropore surfaces but similar to that in the underlying sulfidic sediments (C-horizon). This provides evidence that the sedimentary OM in the bulk subsoil has been largely preserved without significant decomposition and/or fractionation, likely due to physiochemical stabilization by the reactive iron phases that also existed abundantly within the aggregates. These findings not only highlight the important yet underappreciated roles of iron oxyhydroxysulfates in OM/nutrient storage and distribution in acidic sulfate-rich and other similar environments but also suggest that boreal acidic sulfate-rich subsoils and other similar soil systems (existing widely on coastal plains worldwide and being increasingly formed in thawing permafrost) may act as global sinks for OM and nutrients in the short run.
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36.
  • Zhang, Xiaodong, et al. (författare)
  • Storage of soil phytoliths and phytolith-occluded carbon along aprecipitation gradient in grasslands of northern China
  • 2020
  • Ingår i: Geoderma. - : Elsevier. - 0016-7061 .- 1872-6259. ; 364, s. 1-9
  • Tidskriftsartikel (refereegranskat)abstract
    • Climatic factors including mean annual precipitation (MAP) significantly influence the carbon (C) cycle interrestrial ecosystems and Earth overall. Phytolith-occluded carbon (PhytOC) is an important C sequestrationmechanism and as such plays a vital role in global long-term C sequestration. Understanding the spatialvariability in the storage of soil phytoliths and PhytOC and its relationship with climate is critical for evaluatingthe impact of global climate change on terrestrial ecosystem functions. However, little is known about theresponses of soil phytoliths and PhytOC to MAP in grassland ecosystems. This study sampled soil from 24natural, semi-arid steppe sites along a 2,500 km transect with a precipitation gradient of 243–481 mm yr−1 innorthern China. We investigated the influence of precipitation on the spatial distributions of soil phytoliths andPhytOC storage. Storage of soil phytoliths in bulk soil (0–100 cm depth) ranged from 21.3 ± 0.4 to88.4 ± 20.3 t ha−1 along the precipitation gradient. Amounts of soil phytoliths and PhytOC storage weresignificantly and positively correlated with MAP. Multiple regression analysis revealed that phytolith storage inbulk soil was best predicted by MAP (R = 0.5) and soil organic carbon (SOC, R = 0.4), with these two variablesaccounting for about 58% of the total variation observed. Considering the forecasted increase in MAP in theInner Mongolian steppe due to climate change, and the strong influence of MAP on the annual net primaryproductivity (ANPP) and related soil PhytOC input from litter decomposition in this region, we expect thatecosystem primary productivity will increase from deserts to meadow steppe and thereby promote soil PhytOCstorage. These findings have important implications for understanding the dynamics of soil phytoliths, andpredicting the impacts of global climate change on ecosystem functions and management practices in the EastAsian steppe ecosystems.
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37.
  • Zheng, Xiaodi, et al. (författare)
  • Biogeochemical cycle and isotope fractionation of copper in plant-soil systems : a review
  • 2024
  • Ingår i: Reviews in Environmental Science and Biotechnology. - : Springer. - 1569-1705 .- 1572-9826. ; 23, s. 21-41
  • Tidskriftsartikel (refereegranskat)abstract
    • Copper (Cu) is a bio-essential element and a potentially toxic pollutant in the plant-soil systems. Analysis of stable Cu isotopes can be a powerful tool for tracing the biogeochemical cycling of Cu in plant-soil systems. In this review, we examined the analysis method of stable Cu isotope ratios in plants and soils, and discussed the biogeochemical processes, including redox reactions, mineral dissolution, abiotic and biotic sorption, which fractionate Cu isotopes in plant-soil systems. We also reviewed the variability of the isotopic signature in different plants and plant tissues, as well as different soil types and profiles to discuss the relationship between the biogeochemical transformation of Cu and its isotope fractionation in plant-soil systems. The collected data show that delta 65Cu values range from - 2.59 to + 1.73 parts per thousand in plant-soil systems, and increment 65Cu values range from - 1.00 to - 0.11 parts per thousand between the plant and soil. The variation in the increment 65Cu value between the plant and soil is mainly in response to the different uptake strategies during the acquisition of Cu from soils. Cu isotope analyses are proved to be a suitable technique during the biogeochemical transformation of Cu in plant-soil systems, especially during redox reactions. Ultimately, research challenges and future directions for Cu isotope techniques as a proxy for Cu biogeochemical cycles are also proposed. This review is beneficial for soil safety, food safety, and the sustainable development of agriculture and human health.
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38.
  • Zheng, Xiaodi, et al. (författare)
  • Extreme Copper Isotope Fractionation Driven by Redox Oscillation During Gleysols Weathering in Mun River Basin, Northeast Thailand
  • 2023
  • Ingår i: Journal of Geophysical Research - Earth Surface. - : John Wiley & Sons. - 2169-9003 .- 2169-9011. ; 128:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The fractionation of copper (Cu) isotope is a process related to the redox fluctuation during soil Cu biogeochemical cycling. For Cu isotope composition in weathered gleysols of tropical zones, the increased rates of redox fluctuations are assumed to occur during gleysol evolution due to the seasonal exchange of groundwater and river water. However, the impact of the frequency of redox fluctuations on soil Cu isotope signatures is rarely documented. Here, we analyzed the variations of Cu content and isotope fractionation in two low-humic gleysol profiles with different pedogenetic processes during weathering in the same basin (Mun River Basin), and found that the frequency of redox fluctuations could determine the magnitude of Cu isotope fractionation. We record an increased light Cu isotopes and identify the stable Cu(I) species retained in the residual soils with the increased frequency of redox fluctuation. Several processes contribute to Cu isotope fractionation at different soil horizons, but most isotope fractionation is related to the re-adsorption or re-precipitation by iron and manganese oxyhydroxide (i.e., ferrihydrite and pyrolusite), especially at the iron or manganese-rich zone. Cu isotope fractionation is sensitive to increased redox fluctuations in the terrestrial ecosystem, and may have significant implications for assessing soil ecological vulnerability under future climate change scenarios.
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39.
  • Åström, Mats E., 1963-, et al. (författare)
  • Extensive accumulation of rare earth elements in estuarine sediments affected by leaching of acid sulfate soils
  • 2020
  • Ingår i: Boreal Environment Research. - : Finnish Environmental Inst. - 1239-6095 .- 1797-2469. ; 25, s. 105-120
  • Tidskriftsartikel (refereegranskat)abstract
    • The concentrations, loads and speciation of rare earth elements (REEs) were studied in a 3.5 m thick mud depositional succession from an estuary in the Gulf of Bothnia. The uppermost 182.5 cm of the mud, estimated to have deposited from the early 1970s to 2011 (sampling year), had very high REE concentrations (596-1456 ppm) and accumulation rates (5.2-28 g m(-2) year(-1)). This was explained by large REE export from acid sulfate soils after they became efficiently drained with modern drainage techniques. Geochemical and synchrotron-based spectroscopic (XANES) analyses showed that the REEs in the mud are relatively firmly bound in non-clastic phases, likely adsorbed by clay minerals and also to some extent by iron oxyhydroxides. Below 182.5 cm, the REE concentrations successively decreased down to background values at the base at 3.5 m, reflecting less efficient drainage and leaching of the acid sulfate soils in previous decades and centuries.
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40.
  • Åström, Mats, et al. (författare)
  • Sura sulfatjordar i Sverige : Ny kunskap och underlag för åtgärder
  • 2024
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Målsättningen med projektet har varit att öka kunskapen om sura sulfatjordars utbredning och karaktär i Sverige. De viktigaste resultaten är: Sura sulfatjordar har en betydligt större förekomst och är framförallt betydligt surare och svavelrikare i sydöstra och södra Sverige än vad som tidigare varit känt, medan däremot förekomsten kring Vänern är liten. Norröver (Västerbotten, Norrbotten) är förekomsten hög, vilket varit känt sedan tidigare.  Den nationella karteringen som gjordes i studien baserades på gles provtagning, vilket var vad projektets omfattning tillät. Detta innebär emellertid att för mellan-och sydsverige finns ännu ingen detaljkarta över förekomst av sura sulfatjordar. För att kunna genomföra en sådan kartering så effektivt och fort som möjligt, vilket det finns behov av, testades en ny karteringsteknik i ett valt område (väster om sjön Hjälmaren). Tekniken, som gav positiva resultat, genomfördes med maskininlärning och baserades på helikopterburna resistivitetsmätningar, höjddata (Lantmäteriet), nationella marktäckedata (Naturvårdsverket) och SGU:s jordartskarta. Den testades via fältundersökningar och har potential att genom­föras på större områden. Med avseende på pH, aciditet samt totalhalter, syralösliga (1M HCl-lakning) halter och vattenlösliga halter av grundämnen är de sura sulfatjordarna relativt likadana runtom i landet med tanke på de rätt stora regionala variationer som förekommer i temperatur, paleosedimentationsmiljöer och markanvändningen. Denna förhållandevis homogena geokemiska karaktär underlättar förståelsen av hur de sura sulfatjordarna fungerar i termer av bland annat historiska, nutida och framtida effekter (försurning och metallbelastning) på miljön. Den förenklar också planering av åtgärder för att minska syra och metalläckage från dessa jordar, och bedömning av vad som är att förvänta vid återskapande av våtmarker på dessa jordar. På lokal nivå kan skillnaderna emellertid vara stora, t.ex. kan i den reducerade zonen där svavelhalten normalt är kring 1 % vara så hög som 5–7 % med avsevärd potentiellt ökad risk för miljön.  En betydande övergripande regional fysikalisk-kemisk skillnad finns däremot på så vis att i norr har de sura sulfatjordarna ett betydligt tjockare surt skikt (median 75 cm) än de i söder (median 40 cm). En av konsekvenserna är att de sydliga sura sulfatjordarna sannolikt är mer känsliga för framtida sänkningar i grundvattennivån, d.v.s. det finns större potential för ytterligare omfattande syrabildning och metallfrisättning till följ av grundvattensänkningar förorsakade av långa torrperioder eller effektiverad dränering. Även de mikrobiella samhällena i den sura sulfatjorden är delvis annorlunda i norr än i söder. Till exempel, det finns en högre relativ förekomst av Ktedonobacteraceae i de norra delarna och Gallionellaceae i södra delarna av landet. Dessa skillnader är med största sannolikhet kopplade till temperaturskillnaderna mellan norr och söder, inklusive djup och tidsmässig längd av frost i marken. Kunskap om mer exakt vilka skillnaderna är mellan den mikrobiella aktiviteten i söder och norr kommer att belysas av en pågående mer ingående ”omics” studie där fokus är på de kemiska reaktioner som mikroberna bidrar till att ske eller påskynda.Återvätning av sura sulfatjordar kan åstadkomma positiva miljöeffekter. Detta gäller särskilt när den sekundära järnmineralogin (bildad efter att den sura sulfat­jorden uppstått) domineras av schwertmannit och ferrihydrit, vilka mikrober under reducerande förhållanden relativt enkelt förmår bryta ner (reducera) vilket leder till en förhöjning av pH. Det, i sin tur, leder till att ett flertal metaller som blir toxiska redan vid relativt låga halter, såsom kadmium, nickel, mangan och beryllium, kommer att fastläggs istället för att läcka till närmiljön. Återvätning av sura sulfatjordar kan också skapa negativa miljöeffekter. Detta kan ske i form av ökad mobilisering och läckage av spårämnen som arsenik, krom och uran, men i första hand av ökad frisättning och rörlighet av tvåvärt järn. Den sura sulfatjorden har ett exceptionellt stort förråd av järn som kan bidra till detta, bundet i de sekundära mineralen schwertmannit, jarosit och ferrihydrit. I nästan 20 % av de undersökta sura sulfatjordarna motsvarar detta förråd > 2,0 % av hela den sura oxiderade zonens torrvikt, vilket är anmärknings­värt högt. Det finns därför anledning till oro över vad de stora mängder järn som potentiellt kan frigöras skulle ha på våtmarken i sig på och vattensystem nedströms restaureringen. Sura sulfatjordar förekommer främst i låglänta områden som återfinns under den högsta kustlinjen. Det finns därför risk att metaller som läcker från dessa jordar hamnar i våtmarker, som likaledes förekommer i dessa områden. Detta har skett på ett omfattande sätt på en plats som undersökts i södra Sverige där framförallt järn fällts ut och påverkat både floran och faunan i våtmarken. Detta är ett fenomen att vara uppmärksam på i områden med sur sulfatjord, utöver den mer välkända påverkan i form av försurning och metallkontaminering av vattendrag. Det finns ett antal metoder som utvecklats, framförallt i Finland, för att minska läckage av syra och metaller från sura sulfatjordar under åkermark. På basen av genomgången litteratur och diskussioner med relevanta aktörer, bedöms den bästa metoden vara en kombination av teknikerna reglerbar dränering, underbevattning och injicering av kalkstenssuspension via täckdikningssystem. Denna teknikkombination förväntas leda till: (i) minskad oxidation och högre pH i jordarna, (ii) minskat läckage av syra och metaller till närmiljön, och (iii) positiva effekter på skörden på åkrarna (bör dock undersökas mer systematiskt) och kan därför ge en vinn-vinn situation. Ytterligare rekommenderas undersökning av möjligheter med och effekter av kalkfilterdiken. Att förhindra en sänkning av grundvattenytan i sura sulfatjordar är den viktigaste preventiva åtgärden både på kort och lång sikt. Detta är i sig ingen ny slutsats, men projektet har tagit fram data som mer exakt visar vad som kommer att ske i termer av bildning av aciditet och frisättning av metaller när grundvattennivån når djupare ner i den sura sulfatjordens underliggande reducerade och pH-neutrala grundvattenzon. Redan en sänkning ner i övergångszonen, d.v.s. den zon som ligger strax under det sura skiktet och där pH stiger snabbt, kommer frigöra avsevärda mängder aciditet och metaller med känd giftighet.
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