| 1. |
- Barnekow, Lena, et al.
(författare)
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Boreal forest dynamics in north-eastern Sweden during the last 10,000 years based on pollen analysis
- 2008
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 17:6, s. 687-700
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Tidskriftsartikel (refereegranskat)abstract
- A pollen record obtained from a 2.2-m sediment succession deposited in a small lake in the province of Vasterbotten, north-eastern Sweden, reveals the presence of continuous forest cover since 8,500 calendar years before present (cal B.P.). Forest with abundant Pinus (pine) and Betula (birch) initially colonized the area, followed by a dominance of deciduous trees, primarily Betula, from ca. 8,000 to ca. 3,200 cal B.P. Pollen accumulation rates of Quercus (oak), Ulmus (elm) and Tilia (linden) suggest the possible local presence of these thermophilous tree species during this period. The climate gradually became colder and moister around 3,500 cal B.P. and an increased abundance of Sphagnum spores indicates paludification. Picea (spruce) became established around 3,200 cal B.P. and less than 500 years later this was the dominant tree species around the lake. The fire frequency as inferred from charcoal particles exhibits a general increase from ca. 3,000 cal B.P. with subsequent charcoal accumulation maxima at around 2,800 cal B.P., 1,700 cal B.P. and in recent time. The human influence on vegetation was significant during the last 200-300 years. Soil erosion increased substantially and fern spores amount to ca. 55% of the total pollen assemblage in the uppermost samples. These results suggest an extensive anthropogenic impact on the local forest ecosystem, with abundant logging, burning and ditching in the vicinity of the lake. Independent evidence of sub-recent human-induced environmental change is provided by historical accounts. Complementary information on catchment soil development and aquatic nutrient status was provided by records of magnetic susceptibility and elemental carbon, and nitrogen contents obtained from the same sediment core.
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| 2. |
- Bragée, Petra
(författare)
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A palaeolimnological study of the anthropogenic impact on dissolved organic carbon in South Swedish lakes
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the past three decades, increases have been observed in dissolved organic carbon (DOC) concentrations and colour in the surface waters of lakes and rivers in parts of Europe and North America, raising concern about the effects on the quality of aquatic environments with consequences for biodiversity, resource availability and recreational use. Various hypotheses have been put forward to explain the recent increases in DOC concentration and numerous studies have been published linking them to declining anthropogenic atmospherically deposited sulphur. Others have argued that increases in DOC content are a consequence of changes in climate, land use or land management practices. The work presented in this thesis concentrates on identifying the major forcing mechanisms behind observed increases in DOC concentration in the upland area of southern Sweden during recent decades, by comparing variations in the total organic carbon (TOC) concentration in lake water inferred from lake sediments, in response to changes in land use, sulphur deposition and climate during the past eight centuries. Two small lakes with different catchment properties were selected for the study; one dominated by woodland with abundant peat deposits, and another located nearby with patches of agricultural land in an otherwise mainly forested terrain. A number of palaeolimnological methods were applied to the sediment sequences; decadal-scale variations in TOC concentration in the lakes were reconstructed based on visible-near infrared spectroscopy (VNIRS) of sediment successions, high-resolution (20-y) pollen-based reconstructions of local land use were quantified using the Landscape Reconstruction Algorithm (LRA) and the model Local Vegetation Estimates (LOVE), geochemical records provided further information on environmental changes in the lakes and their catchment areas, and changes in pH in the lakes were inferred from diatom analysis. Comparisons were made with population density data and climate records. The results obtained with the LRA and LOVE models revealed a dynamic land-use pattern, with agricultural expansion from AD 1500 to the end of the 1800s, when population growth and the related increase in the exploitation of the surrounding land had a major impact on catchment erosion and input of terrestrial inorganic and organic matter to the lakes. Evidence also exists of a period of agricultural expansion around AD 1200-1300, followed by partial abandonment of the landscape, which can probably be attributed to the Black Death pandemic. A transition from traditional to modern land use following the industrial revolution took place during the past century, and a concurrent shift in most of the proxy records at around AD 1900 suggests a marked change in external forcing mechanisms common to both lakes, related to a major decrease in population density and the introduction of modern land use. The results revealed generally high TOC concentrations in the lakes prior to AD 1900, with second-order variations associated mainly with changes in the intensity of agricultural land use. The TOC concentrations in the lakes started to decrease around AD 1900, and unusually low TOC concentrations were recorded in the period AD 1930-1990, followed by a recent increase. The variation in sulphur emissions, with an increase in the early 1900s to a peak around AD 1980 followed by a significant decrease, was probably the main driver of lake-water TOC dynamics during the past century. This demonstrates that declining atmospheric sulphur deposition is the most probable driver of the increase in TOC concentration during the past three decades and that these lakes may be recovering to their naturally high-TOC pre-depositional states. The results also demonstrate regional versus local forcing of environmental change and indicate broadly similar regional sensitivities to anthropogenic impact, although responses were site-specific due to the different properties of the catchment areas. Given the reduction in atmospheric sulphur emission during recent decades, it is likely that previously suppressed or masked effects of changes in land use, land management and climate during the past century will become progressively more important drivers of TOC concentrations in lake water in the future. Long-term records of environmental history on decadal to millennial time scales enabled the assessment of ecosystem variability and responses to past anthropogenic disturbance, and may be a useful tool for the development of future environmental management strategies.
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| 3. |
- 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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| 4. |
- Bragée, Petra, et al.
(författare)
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Lake ecosystem responses to catchment disturbance and airborne pollution: an 800-year perspective in southern Sweden
- 2013
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Ingår i: Journal of Paleolimnology. - : Springer Verlag (Germany). - 0921-2728 .- 1573-0417. ; 50:4, s. 545-560
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Tidskriftsartikel (refereegranskat)abstract
- Sediment sequences spanning the last 800 years from two small lakes in the south Swedish uplands were explored for assessment of effects of changing human population, local land-use practices and airborne pollution on lake-ecosystem functioning and resilience. Variations in nutrient cycling and deposition of lithogenic elements were studied, using a multi-proxy stratigraphic approach. Carbon and nitrogen elemental and isotopic analyses were applied in combination with records of hydrocarbons (n-alkanes) to investigate the sources and depositional conditions of sediment organic matter. Changes in fluvial and airborne delivery of inorganic matter were based on X-ray fluorescence measurements. The results reveal that population growth and related increases in land-use pressure had a major impact on catchment erosion and input of terrestrial organic matter to the lakes from the 1500s to the end of the 1800s. Evidence also exists of a brief period of catchment disturbance at ca. 1200-1300, followed by recovery, likely connected to the Black Death pandemic. At ca. 1900 synchronous shifts in most of the proxy records suggest a marked change in external forcing common to the two lakes related to a major decrease in population density and the introduction of modern forestry following the industrial revolution. Interestingly, the two sediment records exhibit generally coherent trends in C/N ratio, organic C content and delta C-13, both before and after 1900, indicating broadly similar sensitivities of the lake ecosystems to human impact. In contrast, deviating trends in total N content, delta N-15 and lithogenic element concentrations (K, Ti, Rb and Zr) reflect site-specific responses to local disturbances during the last century due to different nutrient conditions and catchment properties. Our companion sediment records highlight the importance of understanding long-term human impact on watersheds and demonstrate how regional versus local forcing of lake ecosystems, as well as site-specific responses related to catchment characteristics can be reconstructed.
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| 5. |
- Fredh, Daniel, et al.
(författare)
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The effect of local land-use changes on floristic diversity during the past 1000 years in southern Sweden
- 2017
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Ingår i: Holocene. - : SAGE Publications. - 0959-6836. ; 27:5, s. 694-711
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between land-use and floristic diversity in the landscape, for the last millennia, is analysed from two small lakes in southern Sweden. Pollen analysis and the Local Vegetation Estimates (LOVE) model are used to quantify land-cover at local scales with 100-year time windows. Floristic richness is estimated using palynological richness, and we introduce LOVE-based evenness as a proxy for floristic evenness on a local scale based on the LOVE output. The results reveal a dynamic land-use pattern, with agricultural expansion during the 13th century, a partly abandoned landscape around AD 1400, re-establishment during the 15th–17th centuries and a transition from traditional to modern land-use during the 20th century. We suggest that the more heterogeneous landscape and the more dynamic land-use during the 13th–19th centuries were of substantial importance for achieving the high floristic diversity that characterises the traditional landscape. Pollen-based studies of this type are helpful in identifying landscape characteristics and land-use practices that are important for floristic diversity and may therefore guide the development of ecosystem management strategies aiming at mitigating the on-going loss of species seen in the landscape of southern Sweden and many other regions worldwide.
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| 6. |
- Mazier, Florence, et al.
(författare)
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Two hundred years of land-use change in the South Swedish Uplands: comparison of historical map-based estimates with a pollen-based reconstruction using the landscape reconstruction algorithm
- 2015
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 24:5, s. 555-570
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Tidskriftsartikel (refereegranskat)abstract
- Long-term records of environmental history at decadal to millennial time-scales enable an assessment of ecosystem variability and responses to past anthropogenic disturbances and are fundamental for the development of environmental management strategies. This study examines the local variability of land-use history in the South Swedish Uplands over the last 200 years based on pollen records from three lake-sediment successions. Temporal changes in the proportional cover of 14 plant taxa were quantified as percentages using the landscape reconstruction algorithm (LRA). The LRA-based estimates of the extent of four land-use categories (cropland, meadows/grassland, wetland, outland/woodland) were compared to corresponding estimates based on historical maps and aerial photographs from ad 1769-1823, 1837-1895, 1946 and 2005. Although the LRA approach tends to overestimate grassland cover by 10-30 % for the two earliest time periods, the reconstructed vegetation composition is generally in good agreement with estimates based on the historical records. Subsequently, the LRA approach was used to reconstruct the 200-year history of local land-use dynamics at 20-year intervals around two small lakes. The qualitative assessment of difference approach, which requires fewer assumptions and parameters than LRA for objective evaluation of between-site differences in plant abundances, provides consistent results in general. Significant differences exist in the land-use history between the sites. Local catchment characteristics, such as soil conditions and wetland cover, appear important for the development of human impact on the landscape. Quantifications of past vegetation dynamics provide information on the amplitude, frequency and duration of the land-use changes and their effects on terrestrial and aquatic ecosystems, and should be taken into account when nature conservation strategies are developed.
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