| 1. |
- Barão, Lúcia, et al.
(författare)
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Alkaline-extractable silicon from land to ocean: A challenge for biogenic silicon determination
- 2015
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Ingår i: Limnology and Oceanography. - : Wiley. - 1541-5856. ; , s. n/a-n/a
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Tidskriftsartikel (refereegranskat)abstract
- The biogeochemical cycling of silicon (Si) along the land-to-ocean continuum is studied by a variety of research fields and for a variety of scientific reasons. However, there is an increasing need to refine the methodology and the underlying assumptions used to determine biogenic silica (BSi) concentrations. Recent evidence suggests that contributions of nonbiogenic sources of Si dissolving during alkaline extractions, not corrected by standard silicate mineral dissolution correction protocols, can be substantial. The ratio between dissolved Si and aluminum (Al) monitored continuously during the alkaline extraction can be used to infer the origin of the Si fractions present. In this study, we applied both a continuous analysis method (0.5 M NaOH) and a traditional 0.1 M Na2CO3 extraction to a wide array of samples: (1) terrestrial vegetation, (2) soils from forest, cropland and pasture, (3) lake sediments, (4) suspended particulate matter and sediments from rivers, (5) sediments from estuaries and salt marshes and (6) ocean sediments. Our results indicate that the 0.1 M Na2CO3 extraction protocol can overestimate the BSi content, by simultaneously dissolving Si fractions of nonbiogenic origin that may represent up to 100% of the Si traditionally considered as biogenic, hampering interpretation especially in some deeper soil horizons, rivers and coastal oceanic sediments. Moreover, although the term amorphous Si was coined to reflect a growing awareness of nonbiogenic phases we show it is actually inappropriate in samples where silicate minerals may account for a large part of the extracted Si even after linear mineral correction.
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| 2. |
- Calogiuri, Tullia, et al.
(författare)
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Design and Construction of an Experimental Setup to Enhance Mineral Weathering through the Activity of Soil Organisms
- 2023
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Ingår i: Journal of Visualized Experiments. - : Journal of Visualized Experiments. - 1940-087X. ; :201
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Tidskriftsartikel (refereegranskat)abstract
- Enhanced weathering (EW) is an emerging carbon dioxide (CO2) removal technology that can contribute to climate change mitigation. This technology relies on accelerating the natural process of mineral weathering in soils by manipulating the abiotic variables that govern this process, in particular mineral grain size and exposure to acids dissolved in water. EW mainly aims at reducing atmospheric CO2 concentrations by enhancing inorganic carbon sequestration. Until now, knowledge of EW has been mainly gained through experiments that focused on the abiotic variables known for stimulating mineral weathering, thereby neglecting the potential influence of biotic components. While bacteria, fungi, and earthworms are known to increase mineral weathering rates, the use of soil organisms in the context of EW remains underexplored. This protocol describes the design and construction of an experimental setup developed to enhance mineral weathering rates through soil organisms while concurrently controlling abiotic conditions. The setup is designed to maximize weathering rates while maintaining soil organisms' activity. It consists of a large number of columns filled with rock powder and organic material, located in a climate chamber and with water applied via a downflow irrigation system. Columns are placed above a fridge containing jerrycans to collect the leachate. Representative results demonstrate that this setup is suitable to ensure the activity of soil organisms and quantify their effect on inorganic carbon sequestration. Challenges remain in minimizing leachate losses, ensuring homogeneous ventilation through the climate chamber, and avoiding flooding of the columns. With this setup, an innovative and promising approach is proposed to enhance mineral weathering rates through the activity of soil biota and disentangle the effect of biotic and abiotic factors as drivers of EW.
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| 3. |
- Clymans, Wim, et al.
(författare)
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Amorphous Silica Preservation in an Anthropogenic Soil: An Explorative Study of "Plaggen" Soils
- 2013
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Ingår i: Progress in Silicones and Silicone-Modified Materials. - 0097-6156. ; 1154, s. 3-14
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Konferensbidrag (refereegranskat)abstract
- Amorphous Silica (ASi) is present in considerable amounts in most soils and serves as a (micro-)nutrient for many plants. However, our understanding of the response of this important nutrient pool to human or natural disturbances is still very limited. One of the reasons for this is the long time scales involved. This explorative study focuses on the effect of a historical agricultural system, called plaggen management, that was applied on sandy areas in Belgium, the Netherlands and Germany over a period of ca. 1000 yrs on ASi dynamics. The system was designed to maintain high nutrient levels (including C and Si) on arable fields through the addition of mixtures rich in animal manure and vegetation residues. The continuous addition of ASi over such a long time period allows to study if and to what extent ASi is preserved in such a soil system and how Si addition affects the build-up and availability of ASi pools. We quantified ASi pools (Na2CO3 extraction) in a soil profile with plaggen application, and a reference soil without plaggen application. Other measured soil properties were soil organic carbon (SOC) and grain size distribution. There was an important SOC (+20%) and ASi accumulation (+70%) and preservation at the plaggen site. Si losses from the soil column through leaching and crop harvest might thus be restricted by application of organic residue and Si fertilisation to maintain sustainable nutrient concentrations in the topsoil. Net C and Si accumulation rates were 45 kg C ha(-1) y(-1) and 77 kg SiO2 ha(-1) y(-1) respectively, not accounting for the removal of ASi through plant uptake nor for the mineralisation of part of the SOC. The vertical distribution of ASi within the profile, suggests that, contrary to SOC, most of the added ASi has remained stably stored in the soils and that only a smaller, labile pool was removed, most likely through dissolution rather than through plant uptake. Our results indicate that ASi addition leads to a build-up of Si pools in these sandy soils. While this results in increased Si availability, this effect is limited because most ASi remains stored for long time spans. To consolidate our preliminary research results, to answer unresolved questions and to validate proposed hypotheses, future research should: (I) collect additional profiles with higher vertical resolution; (2) include other Si fractions; (3) analyse the relationship between ASi and SOC to better understand the coupling of the ASi and C cycles; (4) develop a modelling approach that would allow one to investigate how ASi pools in soils may respond to future changes.
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| 4. |
- Clymans, Wim, et al.
(författare)
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Temporal dynamics of bio-available Si fluxes in a temperate forested catchment (Meerdaal forest, Belgium)
- 2013
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 1573-515X .- 0168-2563. ; 116:1-3, s. 275-291
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Tidskriftsartikel (refereegranskat)abstract
- Silicon (Si) is a key element in global biogeochemical cycling and recent research has shown that changes in the biological component of the Si cycle may lead to more rapid variations in the land-ocean Si transfer than previously thought. The objective of this paper is to better understand the controls on temporal Si dynamics in terrestrial ecosystems, by studying Si fluxes from a small forested catchment in central Belgium. An intensive monitoring program (2008-2010) of dissolved and amorphous silica (DSi and ASi) concentrations and load patterns show that DSi concentrations are significantly lower during winter-spring periods than during summer-autumn periods. In contrast to what was found in other studies, seasonal dynamics in Meerdaal forest are not controlled by variations in biological uptake or temperature, but mainly by the more important supply of pore-water to the groundwater table in winter-spring periods. Analysis of seasonal and event fluctuations in stream water DSi concentrations showed that final stream water is a mixture of old, DSi rich water pushed out of the soil, and new, DSi poor water delivered by quick flow. The mixing of old and new water finally resulted in streamwater DSi concentrations responding only moderately to variations in discharge (near-chemostatic behaviour). We estimated the total DSi export from the system to be ca. 65.1 x 10(3) mol km(-2) year(-1). Because Si delivery is biologically regulated through an important Si cycle in the vegetation-soil continuum, an anthropogenic (e.g. agricultural expansion) or climatic disturbance of terrestrial ecosystems may alter both water residence times through shifts in hydrological regimes and the DSi chemical equilibrium concentration in soils. In turn, these perturbations will potentially alter long-term DSi and ASi inputs to aquatic systems.
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| 5. |
- Corbett, Thomas, et al.
(författare)
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Organic carbon source controlled microbial olivine dissolution in small-scale flow-through bioreactors, for CO2 removal
- 2024
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Ingår i: NPJ MATERIALS DEGRADATION. - : Nature Publishing Group. - 2397-2106. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- The development of carbon dioxide removal methods, coupled with decreased CO2 emissions, is fundamental to achieving the targets outlined in the Paris Agreement limiting global warming to 1.5 degrees C. Here we are investigating the importance of the organic carbon feedstock to support silicate mineral weathering in small-scale flow through bioreactors and subsequent CO2 sequestration. Here, we combine two bacteria and two fungi, widely reported for their weathering potential, in simple flow through bioreactors (columns) consisting of forsterite and widely available, cheap organic carbon sources (wheat straw, bio-waste digestate of pig manure and biowaste, and manure compost), over six weeks. Compared to their corresponding abiotic controls, the inoculated straw and digestate columns release more total alkalinity (similar to 2 times more) and produce greater dissolved and solid inorganic carbon (29% for straw and 13% for digestate), suggesting an increase in CO2 sequestration because of bio-enhanced silicate weathering. Microbial biomass is higher in the straw columns compared to the digestate and manure compost columns, with a phospholipid fatty acid derived total microbial biomass 10 x greater than the other biotic columns. Scanning Electron Microscopy imaging shows the most extensive colonisation and biofilm formation on the mineral surfaces in the straw columns. The biotic straw and digestate columns sequester 50 and 14 mg C more than their abiotic controls respectively, while there is no difference in the manure columns. The selection of organic carbon sources to support microbial communities in the flow through bioreactors controlls the silicate weathering rates and CO2 sequestration.
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| 6. |
- Cox, T. J. S., et al.
(författare)
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A macro-tidal freshwater ecosystem recovering from hypereutrophication: the Schelde case study
- 2009
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Ingår i: Biogeosciences. - 1726-4189. ; 6:12, s. 2935-2948
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Tidskriftsartikel (refereegranskat)abstract
- We report a 40 year record of eutrophication and hypoxia on an estuarine ecosystem and its recovery from hypereutrophication. After decades of high inorganic nutrient concentrations and recurring anoxia and hypoxia, we observe a paradoxical increase in chlorophyll-a concentrations with decreasing nutrient inputs. We hypothesise that algal growth was inhibited due to hypereutrophication, either by elevated ammonium concentrations, severe hypoxia or the production of harmful substances in such a reduced environment. We study the dynamics of a simple but realistic mathematical model, incorporating the assumption of algal growth inhibition. It shows a high algal biomass, net oxygen production equilibrium with low ammonia inputs, and a low algal biomass, net oxygen consumption equilibrium with high ammonia inputs. At intermediate ammonia inputs it displays two alternative stable states. Although not intentional, the numerical output of this model corresponds to observations, giving extra support for assumption of algal growth inhibition. Due to potential algal growth inhibition, the recovery of hypereutrophied systems towards a classical eutrophied state, will need reduction of waste loads below certain thresholds and will be accompanied by large fluctuations in oxygen concentrations. We conclude that also flow-through systems, heavily influenced by external forcings which partly mask internal system dynamics, can display multiple stable states.
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| 7. |
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| 8. |
- Frings, Patrick J, 1986-, et al.
(författare)
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Tracing silicon cycling in the Okavango Delta, a sub-tropical flood-pulse wetland using silicon isotopes
- 2014
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Ingår i: Geochimica et Cosmochimica Acta. - 0016-7037 .- 1872-9533. ; 142:0, s. 132-148
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Tidskriftsartikel (refereegranskat)abstract
- Chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction, potentially confounding estimates of silicate weathering rates. Silicon isotopes (δ30Si) may be a useful tool to investigate these processes. Here, we present 82 δ30Si measurements from surface waters, pore waters, biogenic silica (BSi), clays, sand and vegetation from the Okavango Delta, Botswana, a freshwater sub-tropical, flood-pulse wetland. Hydrologically, the Okavango is dominated by evapotranspiration water losses to the atmosphere. It receives an annual pulse of water that inundates seasonal floodplains, while river baseflow is sufficient to maintain a permanent floodplain. δ30Si in dissolved silica (DSi) in surface waters along a 300 km transect at near-peak flood show a limited range (0.36–1.19‰), implying the Delta is well buffered by a balance of processes adding and removing DSi from the surface water. A key control on DSi concentrations is the uptake, production of BSi and recycling of Si by aquatic vegetation, although the net isotopic effect is necessarily small since all BSi re-dissolves on short timescales. In the sediments, BSi δ30Si (n = 30) ranges from −1.49‰ to +0.31‰ and during dissolution, residual BSi tends towards higher δ30Si. The data permit a field-based estimate of the fractionation associated with BSi dissolution, ε30BSi-DSi = −0.26‰, though it is unclear if this is an artefact of the process of dissolution. Clay δ30Si ranges from −0.97‰ to +0.10‰, (n = 15, mean = −0.31‰) and include the highest values yet published, which we speculate may be due to an equilibrium isotope effect during diagenetic transformation of BSi. Two key trends in surface water DSi δ30Si merit further examination: declining δ30Si in an area roughly corresponding to the permanent floodplains despite net DSi removal, and increasing δ30Si in the area corresponding to the seasonal floodplains. We infer that evaporative enrichment of surface waters creates two contrasting regimes. Chemical weathering of low δ30Si phases releases low δ30Si DSi in the relatively dilute waters of the permanent floodplains, whereas silicon removal via clay formation or vegetation uptake is the dominant process in the more enriched, seasonal floodplains.
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| 9. |
- Frings, Patrick, et al.
(författare)
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Tracing silicon cycling in the Okavango Delta, a sub-tropical flood-pulse wetland using silicon isotopes
- 2014
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 142, s. 132-148
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Tidskriftsartikel (refereegranskat)abstract
- Chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction, potentially confounding estimates of silicate weathering rates. Silicon isotopes (d30Si) may be a useful tool to investigate these processes. Here, we present 82 d30Si measurements from surface waters, pore waters, biogenic silica (BSi), clays, sand and vegetation from the Okavango Delta, Botswana, a freshwater sub-tropical, flood-pulse wetland. Hydrologically, the Okavango is dominated by evapotranspiration water losses to the atmosphere. It receives an annual pulse of water that inundates seasonal floodplains, while river baseflow is sufficient to maintain a permanent floodplain. d30Si in dissolved silica (DSi) in surface waters along a 300 km transect at near-peak flood show a limited range (0.36–1.19&), imply- ing the Delta is well buffered by a balance of processes adding and removing DSi from the surface water. A key control on DSi concentrations is the uptake, production of BSi and recycling of Si by aquatic vegetation, although the net isotopic effect is necessarily small since all BSi re-dissolves on short timescales. In the sediments, BSi d30Si (n = 30) ranges from
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| 10. |
- Jacobs, S., et al.
(författare)
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Restoration of tidal freshwater vegetation using controlled reduced tide (CRT) along the Schelde Estuary (Belgium)
- 2009
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 1096-0015 .- 0272-7714. ; 85:3, s. 368-376
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Tidskriftsartikel (refereegranskat)abstract
- Throughout the world, tidal marshes are being restored to obtain natural protection against recurring storm surges and sea level rise and to preserve the resources these habitats provide. Managed realignment, or breaching of the seaward dikes, is a restoration technique increasingly used; yet unsuitable site elevation has been a major constraint to habitat development. Controlled reduced tide (CRT), a new technique to implement tidal regime on low elevated sites, could offer solutions for several problems associated with reconstruction or mitigation of tidal marshes. We followed vegetation development at 3-month intervals during two years after implementation of the first pilot CRT treatment, which aimed to restore tidal freshwater marsh habitat in an agricultural site where elevation relative to the estuarine marshes has lowered. The development of the plant community and its driving forces (flooding, remnant vegetation) were studied. Arrival and establishment of typical tidal freshwater marsh vegetation was rapid, and a clear elevation gradient developed by eradication of terrestrial species and colonisation by estuarine species. Remnant vegetation substantially reduced the number of new established species. General development trajectory as well as the changing effect of driving forces and their interaction point to a swift ecosystem shift during the first two surveys, and a gradual species saturation during the seven following surveys. Vegetation communities seem to deviate from the nearby tidal freshwater marshes, but show similarities with tidal freshwater marshes described for the beginning of the 20th century. The CRT-technique provides strong potential for durable, adaptive restoration of tidal marshes on sites with low elevation. Wider implementation of the CRT technique could increase the total surface of tidal freshwater marshes with fully developed vegetation gradients. (C) 2009 Elsevier Ltd. All rights reserved.
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