| 1. |
- Nantke, Carla K.M., et al.
(författare)
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Human influence on the continental Si budget during the last 4300 years : δ30Sidiatom in varved lake sediments (Tiefer See, NE Germany)
- 2021
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 258
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Tidskriftsartikel (refereegranskat)abstract
- The continental silicon (Si) cycle, including terrestrial and freshwater ecosystems (lakes, rivers, estuaries), acts as a filter and modulates the amount of Si transported to the oceans. In order to link the variation in the terrestrial Si cycle to aquatic ecosystems, knowledge on changes in vegetation cover, soil disturbance and the impact of human activity are required. This study on varved lake sediments from Tiefer See near Klocksin (TSK) in northeastern Germany investigates Si isotope variations in diatom frustules (δ30Sidiatom) over the last ∼4300 years. δ30Sidiatom values vary between 0.37 and 1.63‰. The isotopic signal measured in centric (mostly planktonic) and pennate (mostly benthic) diatoms shows the same trend through most of the record. A decrease in δ30Sidiatom coinciding with early deforestation between 3900 and 750 a BP in the catchment area, points to an enhanced export of isotopically light dissolved silica (DSi) from adjacent soils to the lake. The burial flux of biogenic silica (BSi) observed in the lake sediments increases with cultivation due to enhanced nutrient supply (N, P and Si) from the watershed and nutrient redistribution caused by wind-driven increased water circulation. When the cultivation intensifies, we observe a shift to higher δ30Sidiatom values that we interpret to reflect a diminished Si soil pool and the preferential removal of the lighter 28Si by crop harvesting. Human activity influences the DSi supply from the catchment and appears to be the primary driver controlling the Si budget in TSK. Our data shows how land use triggers variations in continental Si cycling on centennial timescales and provides important information on the underlying processes.
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| 2. |
- Zahajská, Petra, et al.
(författare)
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The Holocene silicon biogeochemistry of Yellowstone Lake, USA
- 2023
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 322
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Tidskriftsartikel (refereegranskat)abstract
- Silicon (Si) is an essential macronutrient for diatoms, an important component of lacustrine primary productivity that represents a link between the carbon and silicon cycles. Reconstructions of lake silicon cycling thus provide an underexploited window onto lake and catchment biogeochemistry. Silicon isotope geochemistry has potential to provide these reconstructions, given the competing source and process controls can be deconvolved. The silica-rich volcanic and hydrothermal systems in Yellowstone National Park are a great source of dissolved silicon into Yellowstone Lake, a system with high silicon, and thus carbon, export rates and the formation of diatom–rich sediment. Yellowstone Lake sediments should be an archive of past silicon biogeochemistry, although the effect of sublacustrine hydrothermal activity or hydrothermal explosion events is unclear. Here, we analysed lake water, tributaries, and hydrothermal vent fluids from Yellowstone Lake for their dissolved Si concentrations, isotope composition (δ30Si) and Ge/Si ratios to evaluate the sources of variability in the lake's Si cycle. Bulk elemental composition and biogenic SiO2 (bSiO2) content, together with δ30Si and Ge/Si ratios from a single diatom species, Stephanodiscus yellowstonensis, were analysed in two sediment cores spanning the last 9880 cal. yr BP. We investigate these datasets to identify long term Holocene changes in hydrothermal activity and effects of large and short-term events i.e., hydrothermal and a volcanic eruption. Combinations of bSiO2, δ30Si and Ge/Si with XRF and lithology data revealed that Yellowstone Lake has a resilient biogeochemical system: hydrothermal explosions are visible in the lithology but have no identifiable impact on bSiO2 accumulation or on the δ30Si signature. Both cores show similarities that suggest a stable and homogeneous dSi source across the entire lake. A narrow range of δ30Si and Ge/Si values suggests that the productive layer of the lake was well mixed and biogeochemically stable, with consistently high hydrothermal inputs of Si throughout the Holocene to buffer against the disturbance events. Variation in bSiO2 concentration through time is weakly correlated with an increase towards younger sediment in the δ30Si fossil diatom record in both cores. This increase mirrors that seen in ocean records, and follows changes known in summer insolation, summer temperatures and lake water-column mixing since the deglaciation. This suggests that climate forcing, and soil formation ultimately govern the silicon isotope record, which we suggest is via a combination of changes in weathering stoichiometry, diatom production, and relative proportion of dSi sources.
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| 3. |
- Moldan, Filip, et al.
(författare)
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MAGIC library – A tool to assess surface water acidification
- 2020
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Ingår i: Ecological Indicators. - : Elsevier BV. - 1470-160X .- 1872-7034. ; 112
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a tool, the MAGIC library, which provides an acidification assessment for any given lake or stream in Sweden based on ten parameters describing lake geographical position, surface area, annual discharge and observed lake water chemistry. The MAGIC library consists of two key components: a library of the existing MAGIC model simulations for 2438 lakes and an analogue matching routine that selects the library lake which is most similar to the evaluation lake described by the ten parameters. The acidification assessment modelled by MAGIC for the library lake is then assumed valid for the evaluation lake. For more than 90% of the library lakes tested, the MAGIC library provided the same acidification assessment as the site-specific MAGIC model simulation. Labour and data requirements for assessment by the MAGIC library are very modest relative to the needs of site-specific MAGIC (or other similar) model simulations. The relative ease of use is essential for a country like Sweden, with a population of 100 000 lakes. The MAGIC library has a web interface (http://magicbiblioteket.ivl. se) to provide single assessments interactively or multiple assessments by uploading the ten required parameters for multiple sites. Conceptually the library has built-in flexibility and could be adapted for other types of ecosystems or assessments. In this paper we describe the MAGIC library concept and evaluate the performance of the MAGIC library in comparison to site-specific MAGIC modelling.
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| 4. |
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| 5. |
- Stadmark, Johanna, et al.
(författare)
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Success in grant applications for women and men
- 2020
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Ingår i: Advances in Geosciences. - : Copernicus GmbH. - 1680-7340 .- 1680-7359. ; 53, s. 107-115
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Tidskriftsartikel (refereegranskat)abstract
- Sex-disaggregated data on the success rates of applications to the individual grants at the European Research Council and selected national funding agencies show similar outcomes for women and men. There are large differences in success rates between countries and in all countries with applicants to the European Research Council men are applying disproportionally more (and women less) compared to the demography of the researchers in the higher education sectors in the respective countries. Therefore, the proportion of women funded is even lower than their representation in the fields of Natural Science and Engineering and Technology. Some contributing factors are discussed and the question on how the current and future success rates could be interpreted is raised.
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| 6. |
- Zahajská, Petra, et al.
(författare)
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Modern silicon dynamics of a small high-latitude subarctic lake
- 2021
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Ingår i: Biogeosciences. - : European Geosciences Union (EGU). - 1726-4170 .- 1726-4189. ; 18:7, s. 2325-2345
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Tidskriftsartikel (refereegranskat)abstract
- High biogenic silica (BSi) concentrations occur sporadically in lake sediments throughout the world; however, the processes leading to high BSi concentrations vary. We explored the factors responsible for the high BSi concentration in sediments of a small, high-latitude subarctic lake (Lake 850). The Si budget of this lake had not been fully characterized before to establish the drivers of BSi accumulation in this environment. To do this, we combined measurements of variations in stream discharge, dissolved silica (DSi) concentrations, and stable Si isotopes in both lake and stream water with measurements of BSi content in lake sediments. Water, radon, and Si mass balances revealed the importance of groundwater discharge as a main source of DSi to the lake, with groundwater-derived DSi inputs 3 times higher than those from ephemeral stream inlets. After including all external DSi sources (i.e., inlets and groundwater discharge) and estimating the total BSi accumulation in the sediment, we show that diatom production consumes up to 79 % of total DSi input. Additionally, low sediment accumulation rates were observed based on the dated gravity core. Our findings thus demonstrate that groundwater discharge and low mass accumulation rate can account for the high BSi accumulation during the last 150 cal yr BP. Globally, lakes have been estimated to retain one-fifth of the annual DSi terrestrial weathering flux that would otherwise be delivered to the ocean. Well-constrained lake mass balances, such as presented here, bring clarity to those estimates of the terrestrial Si cycle sinks.
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| 7. |
- Zahajská, Petra, et al.
(författare)
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What is diatomite?
- 2020
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Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; , s. 48-52
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Forskningsöversikt (refereegranskat)abstract
- Different types of biogenic remains, ranging from siliceous algae to carbonate precipitates, accumulate in the sediments of lakes and other aquatic ecosystems. Unicellular algae called diatoms, which form a siliceous test or frustule, are an ecologically and biogeochemically important group of organisms in aquatic environments and are often preserved in lake or marine sediments. When diatoms accumulate in large numbers in sediments, the fossilized remains can form diatomite. In sedimentological literature, "diatomite"is defined as a friable, light-coloured, sedimentary rock with a diatom content of at least 50%, however, in the Quaternary science literature diatomite is commonly used as a description of a sediment type that contains a "large"quantity of diatom frustules without a precise description of diatom abundance. Here we pose the question: What is diatomite? What quantity of diatoms define a sediment as diatomite? Is it an uncompacted sediment or a compacted sediment? We provide a short overview of prior practices and suggest that sediment with more than 50% of sediment weight comprised of diatom SiO2 and having high (>70%) porosity is diatomaceous ooze if unconsolidated and diatomite if consolidated. Greater burial depth and higher temperatures result in porosity loss and recrystallization into porcelanite, chert, and pure quartz.
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