| 1. |
- Bragée, Petra, et al.
(författare)
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Historical TOC concentration minima during peak sulfur deposition in two Swedish lakes
- 2015
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 12:2, s. 307-322
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Tidskriftsartikel (refereegranskat)abstract
- Decadal-scale variations in total organic carbon (TOC) concentration in lake water since AD1200 in two small lakes in southern Sweden were reconstructed based on visible-near-infrared spectroscopy (VNIRS) of their recent sediment successions. In order to assess the impacts of local land-use changes, regional variations in sulfur, and nitrogen deposition and climate variations on the inferred changes in TOC concentration, the same sediment records were subjected to multi-proxy palaeolimnological analyses. Changes in lake-water pH were inferred from diatom analysis, whereas pollen-based land-use reconstructions (Landscape Reconstruction Algorithm) together with geochemical records provided information on catchment-scale environmental changes, and comparisons were made with available records of climate and population density. Our long-term reconstructions reveal that inferred lake-water TOC concentrations were generally high prior to AD1900, with additional variability coupled mainly to changes in forest cover and agricultural land-use intensity. The last century showed significant changes, and unusually low TOC concentrations were inferred at AD1930-1990, followed by a recent increase, largely consistent with monitoring data. Variations in sulfur emissions, with an increase in the early 1900s to a peak around AD1980 and a subsequent decrease, were identified as an important driver of these dynamics at both sites, while processes related to the introduction of modern forestry and recent increases in precipitation and temperature may have contributed, but the effects differed between the sites. The increase in lake-water TOC concentration from around AD1980 may therefore reflect a recovery process. Given that the effects of sulfur deposition now subside and that the recovery of lake-water TOC concentrations has reached pre-industrial levels, other forcing mechanisms related to land management and climate change may become the main drivers of TOC concentration changes in boreal lake waters in the future.
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| 2. |
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| 3. |
- Yang, Bingjie, et al.
(författare)
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Impacts of long-term land use on terrestrial organic matter input to lakes based on lignin phenols in sediment records from a Swedish forest lake
- 2021
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 774
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Tidskriftsartikel (refereegranskat)abstract
- Organic carbon burial in lake sediments plays an important role in the global carbon cycle, and is heavily affected by the terrestrial organic matter input. However, few studies have focused on long-term changes in terrestrial organic matter input to lakes in response to land-use changes. The aim of this study was to assess variations in sedimentary terrestrial organic matter over the last 1000 years based on lignin biomarker records from two sediment cores from Lake Skottenesjön, southwestern Sweden. In combination with pollen-based quantitative land cover reconstruction, we investigated the impacts of centennial-scale land-use changes on terrestrial organic matter input to lake sediments. The results show that human activities in the catchment had significant impacts on terrestrial organic export by modifying the vegetation cover. Intensified use of the forest in the 18th and 19th centuries led to enhanced soil erosion, and increased terrestrial organic matter input to the lake. Although farmland expanded between the 12th and the middle of 14th century, no significant change in terrestrial organic matter input was observed at that time. Much higher export of terrestrial organic and minerogenic matter to the lake was observed during the period of modern forestry in the 20th century as compared to previous periods of minor forest disturbance, such as 11th century. The changes in the vegetation cover in the catchment considerably modified the composition of terrestrial organic matter deposited in the lake sediments, which is reflected by the composition of lignin phenols. This study demonstrates that the combination of lignin phenols analysis and pollen-based quantitative land cover reconstruction is a useful approach for investigating long-term changes in terrestrial organic matter delivery to lake ecosystems. © 2021 The Authors
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| 4. |
- Yang, Bingjie, et al.
(författare)
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Millennial-scale land-use changes and their effect on a small lake in southern Sweden based on pollen and lignin phenols
- 2019
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Konferensbidrag (refereegranskat)abstract
- In this study, a sediment sequence from Lake Skottenesjön, southern Sweden was investigated to reconstruct the effect of forestry and land-use on erosion rates and delivery of organic and minerogenic matter to the lake. Catchment-scale vegetation changes during the last 1000 years were reconstructed quantitatively using pollen analysis and the Landscape Reconstruction Algorithm (LRA). Organic matter in the lake sediments was analyzed using lignin phenols and bulk carbon stable isotopes. Changes in the delivery of minerogenic matter were analyzed using X-ray fluorescence scanning. Variations in pollen assemblages, lignin phenol concentration and other geochemical proxies show that deforestation, agricultural activities and other human impacts on the lake catchment modified the organic and inorganic matter deposition in the lake. Between ca. AD 1000 and ca. AD 1350, the local land-use was characterized by small-scale agricultural activities associated with the medieval expansion. During this period, the woodland cover was dominated by deciduous trees, as revealed by both pollen composition and high values in the ratio between syringyl and vanillyl phenols (S/V). Increased deposition of terrestrial organic matter was indicated by the high concentration of lignin phenols. Around AD 1350, much of the farmland was abandoned and coniferous woodland cover increased as revealed by the pollen composition. A progressive decline in the lignin phenol concentration after ca. AD 1350 reflects a reduction of terrestrial organic matter input to the lake, probably as a direct effect of increased forestation of the catchment. After ca. AD 1650, both cultivated crops and pasture & meadows expanded in the catchment as seen in pollen assemblages. The increased land-use indicated by the pollen data is in agreement with the population increase documented in the study area between ca. AD 1700 and ca. AD 1850, but locally the human impact remained high for some time after the regional peak in population. Substantial increases in lithogenic elements (K, Ti, Rb) together with lower TOC content and higher C/N ratios indicate enhanced soil erosion from ca. AD 1650 to ca. AD 1950. Elevated δ13C values during this period reflect an increase in lake productivity that can be attributed to higher nutrient input associated with intensive soil erosion. S/V ratios increased in concert with an increase in deciduous trees and a distinct drop in coniferous woodland cover due to timber exploitation. Cinnamyl to vanillyl phenol ratios (C/V) increased together with an increase in grassland cover. The flux of lignin phenols increased drastically reflecting a substantial elevation of terrestrial organic matter input as a consequence of intensive human activities. This study illustrates that the combination of pollen and lignin phenols is useful for investigating past changes in the delivery of organic matter in response to the anthropogenic impact on lake catchments.
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| 5. |
- Yang, Bingjie, et al.
(författare)
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Quantitative landscape reconstruction and erosion history during the past 1,100 years in the Skogaryd Research Catchment, southern Sweden
- 2020
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 29:6, s. 657-70
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Tidskriftsartikel (refereegranskat)abstract
- A sediment sequence from a small forest lake in southwestern Sweden was investigated to explore the effects of forestry and land-use on catchment erosion and delivery of organic and minerogenic matter to the lake. Catchment-scale vegetation changes during the last 1,100 years were reconstructed quantitatively at 50-year resolution using pollen analysis and the Landscape reconstruction algorithm (LRA). Variations in terrestrial organic matter input to lake sediments were assessed by total organic carbon (TOC) content and carbon to nitrogen (C/N) ratios. Changes in minerogenic matter were analysed using X-ray fluorescence (XRF) scanning. The results show that Skogaryd was not intensively used for agriculture throughout the past 1,100 years, but its land-use changes were very sensitive to societal changes. Between ca. ad 950 and 1350, local land-use was characterized by small-scale agricultural activities associated with the Medieval expansion, and enhanced soil erosion was recorded by increased K, Ti and Rb deposition. Around ad 1350 much of the farmland was abandoned, most likely in response to outbreaks of plague. The abandonment of farmland caused increased coniferous woodland cover and lower soil erosion. From the 16th century land-use expanded and gradually intensified, concurrent with a population increase documented in the study area between ca. ad 1600 and 1850. Intensive exploitation of the forest led to soil erosion and increased terrestrial organic and minerogenic matter export to the lake. These processes peaked with the artificial drainage of a nearby wetland for agricultural purposes. During the 20th century, modern forestry management started with the plantation of conifers, and soil erosion declined.
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