| 1. |
- Akselsson, Cecilia, et al.
(författare)
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Weathering rates in Swedish forest soils
- 2019
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 16:22, s. 4429-4450
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Forskningsöversikt (refereegranskat)abstract
- Soil and water acidification was internationally recognised as a severe environmental problem in the late 1960s. The interest in establishing “critical loads” led to a peak in weathering research in the 1980s and 1990s, since base cation weathering is the long-term counterbalance to acidification pressure. Assessments of weathering rates and associated uncertainties have recently become an area of renewed research interest, this time due to demand for forest residues to provide renewable bioenergy. Increased demand for forest fuels increases the risk of depleting the soils of base cations produced in situ by weathering. This is the background to the research programme Quantifying Weathering Rates for Sustainable Forestry (QWARTS), which ran from 2012 to 2019. The programme involved research groups working at different scales, from laboratory experiments to modelling. The aims of this study were to (1) investigate the variation in published weathering rates of base cations from different approaches in Sweden, with consideration of the key uncertainties for each method; (2) assess the robustness of the results in relation to sustainable forestry; and (3) discuss the results in relation to new insights from the QWARTS programme and propose ways to further reduce uncertainties. In the study we found that the variation in estimated weathering rates at single-site level was large, but still most sites could be placed reliably in broader classes of weathering rates. At the regional level, the results from the different approaches were in general agreement. Comparisons with base cation losses after stem-only and whole-tree harvesting showed sites where whole-tree harvesting was clearly not sustainable and other sites where variation in weathering rates from different approaches obscured the overall balance. Clear imbalances appeared mainly after whole-tree harvesting in spruce forests in southern and central Sweden. Based on the research findings in the QWARTS programme, it was concluded that the PROFILE/ForSAFE family of models provides the most important fundamental understanding of the contribution of weathering to long-term availability of base cations to support forest growth. However, these approaches should be continually assessed against other approaches. Uncertainties in the model approaches can be further reduced, mainly by finding ways to reduce uncertainties in input data on soil texture and associated hydrological parameters but also by developing the models, e.g. to better represent biological feedbacks under the influence of climate change.
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| 2. |
- Gustavsson, Johan, 1974, et al.
(författare)
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High-speed 850-nm VCSELs for 40 Gb/s transmission
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We have explored the possibility to extend the data transmission rate for standard 850-nm GaAs-based VCSELs beyond the 10 Gbit/s limit of today's commercially available directly-modulated devices. By sophisticated tailoring of the design for high-speed performance we demonstrate that 10 Gb/s is far from the upper limit. For example, the thermal conductivity of the bottom mirror is improved by the use of binary compounds, and the electrical parasitics are kept at a minimum by incorporating a large diameter double layered oxide aperture in the design. We also show that the intrinsic high speed performance is significantly improved by replacing the traditional GaAs QWs with strained InGaAs QWs in the active region. The best overall performance is achieved for a device with a 9 μm diameter oxide aperture, having in a threshold current of 0.6 mA, a maximum output power of 9 mW, a thermal resistance of 1.9 °C/mW, and a differential resistance of 80 Ω. The measured 3dB bandwidth exceeds 20 GHz, and we experimentally demonstrate that the device is capable of error-free transmission (BER
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| 3. |
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| 4. |
- Löfgren, Stefan, et al.
(författare)
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Impact of whole-tree harvest on soil and stream water acidity in southern Sweden based on HD-MINTEQ simulations and pH-sensitivity
- 2017
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 383, s. 49-60
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Tidskriftsartikel (refereegranskat)abstract
- The shift in major drivers of acidification from sulfur deposition to biological acidification has put the focus on the impact of biomass harvest for bioenergy on the acid base status of forests soils and surface waters. This paper presents a model-based assessment in which the impact of whole-tree harvest (WTH) is compared with that of no harvest at two different sulfur deposition levels by use of the HD-MINTEQ model. Additionally, the pH-sensitivity of 179 randomly selected boreal headwater streams was assessed. The results indicate that the exchangeable Ca2+ pool in humus and mineral soils (<= B-horizon) is most affected by harvest. Concerning the pH, the WTH impact is restricted to shallow soils and for a much shorter period of time. The impact of WTH on the soil solution was primarily restricted to the recharge area and much less pronounced in the discharge area. Due to high buffering capacity of riparian soils and low pH-sensitivity of many headwater streams, the pH effects of WTH on surface waters will most probably be small, at least over a rotation period of several decades. Over time perspectives of multiple rotations, the pH effects are more uncertain due to a possible slow successive protonation of organic matter in the riparian zone. Another important aspect is the currently restricted availability of mobile anion charge balancing the acidity produced by tree growth. Therefore, the acidity is to a large extent arrested in the soil. At the current low S deposition levels, southwestern Sweden seems to be the least vulnerable region to further acid input due to high buffer capacity at low pH. The streams in central and northern Sweden are much more pH-sensitive, but restricted availability of mobile strong acid anions and large buffer capacity in the soils make them less vulnerable to WTH. The partly diverging results between experimental and model studies indicate that one or more processes (hydrological, chemical or biological) are not fully understood or that available data are lacking for a proper parameterization. Thus, the results from long-term WTH experiments are very important for understanding the processes involved as well as for improving and validating model predictions. We therefore encourage societal support of maintaining monitoring and research coupled to such experiments. For the future and for improving our current understanding of biogeochemical dynamics in forest ecosystems subjected to active forestry as well as for policy and management purposes, a mixture of experiments and models ought to be used. (C) 2016 Elsevier B.V. All rights reserved.
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| 5. |
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| 6. |
- Tuyishime, J. R. Marius, et al.
(författare)
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Phosphorus abundance and speciation in acid forest Podzols - Effect of postglacial weathering
- 2022
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 406
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Tidskriftsartikel (refereegranskat)abstract
- The molecular speciation of phosphorus (P) in forest soils is of strategic importance for sustainable forest management. However, only limited information exists about soil P speciation in boreal forests. We combined P K-edge XANES spectroscopy, wet chemical P extractions, and X-ray diffraction analysis of soil minerals to investigate the vertical distribution of P species in seven podzolised forest soils differing in soil properties and climatic conditions. The results showed that the total P stock was on average, 4.0 g m(-2) in the Oe horizon, 9.5 g m(-2) in the A and E horizons, and substantially higher (117.5 g m(-2), and 109.3 g m(-2)) in the B and C horizons down to 80 cm depth, respectively. Although the Oe horizons contain a minor total P stock, 87% of it was stored as organic P. The composition of P species in the P-depleted A/E horizons was highly variable depending on the site. However, of the P stored in B and C horizons down to 80 cm, 58% was adsorbed P, mostly to Al, while apatite accounted for 25% of P, most of which was found in the C horizons. The apatite stocks in the A/E, B, and C horizons (down to 80 cm) accounted for 2.5%, 20%, and 77.2%, respectively, of the total apatite for all the mineral soils studied. These figures can be explained, first, by the dissolution of primary mineral apatite caused mainly by acidification. Second, P uptake by plants and microorganisms, and the associated formation of the Oe horizons, led to the formation of soil organic P. Further, the formation of organo-metal complexes and podzolization led to the translocation of P to the B horizons, where P accumulated mostly as P adsorbed to imogolite-type materials (e.g. allophane) and ferrihydrite, as shown by P K-edge XANES spectroscopy. In conclusion, this study shows that despite the young age of these soils (<15,000 years), most of the primary mineral apatite in the upper 30 cm has been transformed into organic P, and Fe-, Al-bound PO 4 . Moreover, the subsoil P, mainly consisting of adsorbed P to Al, and apatite, dominates the P inventory and probably serves as a long-term buffer of P.
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| 7. |
- Tuyishime, Marius, et al.
(författare)
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Phosphorus speciation in the organic layer of two Swedish forest soils 13-24 years after wood ash and nitrogen application
- 2022
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 521
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Tidskriftsartikel (refereegranskat)abstract
- Application of wood ash to forests can restore pools of phosphorus (P) and other nutrients, which are removed following whole tree harvesting. Yet, the mechanisms that affect the fate of ash-P in the organic layer are less well known. Previous research into the extent to which ash application leads to increased P solubility in the soil is contradictory. We combined synchrotron P K-edge XANES spectroscopy, mu-XRF microscopy, and chemical ex-tractions to examine the speciation and solubility of P. We studied organic horizons of two long-term field ex-periments, Riddarhyttan (central Sweden), which had received 3, 6, and 9 Mg ash ha -1, and Ro center dot dalund (northern Sweden), where 3 Mg ash ha- 1 had been applied alone or combined with N every-three years since 2003. At the latter site, we also determined P in aboveground tree biomass. Overall, the ash application increased P in the organic layer by between 6 and 28 kg P ha -1, equivalent to 17-39 % of the initial P content in the applied ash. At Ro center dot dalund, there was 4.6 kg Ca-bound P ha- 1 (9.5 %) in the ash treatment compared to 1.6 kg ha- 1 in the ash + N treatment and < 0.4 kg ha- 1 in the N treatment and the control. At Riddarhyttan, only the treatment with the highest ash dose had residual Ca-bound P (3.8 kg ha -1). In contrast, the ash application increased Al-bound P (p < 0.001) with up to 15.6 kg P ha -1. Moreover, the ash increased Olsen-P by up to two times. There was a strong relationship between the concentrations of Olsen-P and Al-bound P (R2 = 0.83, p < 0.001) as well as Fe-bound P (R2 = 0.74, p = 0.003), suggesting that the ash application resulted in an increased amount of relatively soluble P associated with hydroxy-Al and hydroxy-Fe compounds. Further, there was an 18 % increase in P uptake by trees in the ash treatment. By contrast, repeated N fertilization, with or without ash, reduced Olsen-P. The lower P extractability was concomitant with a 39 % increase in plant P uptake in the N treatment, which indicates elevated P uptake in response to higher N availability. Hence, the application of wood ash increased Al-bound P, easily available P, and P uptake. N fertilization, while also increasing tree P uptake, instead decreased easily available P and did not cause a shift in soil P speciation.
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| 8. |
- Zandén, Olle, 1956-
(författare)
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Samtal om samspel. Kvalitetsuppfattningar i musiklärares dialoger om ensemblespel på gymnasiet
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this thesis is to analyse music teachers’ collegiate discourses on ensemble playing with regard to dialogically expressed criteria and conceptions of quality, and to relate these criteria and conceptions to the national governing documents for upper secondary ensemble education. The study has two theoretical perspectives, that is, a didactical perspective and a dialogical perspective. The research setting as well as the research questions are clearly didactical, whilst dialogical theory is used both as a foundation for the research method and as an ontology against which the findings are interpreted. Topic analysis, which is based on a dialogical theory of sense-making according to which meaning is constituted in a double dialogical process between interactants, situation and socio-cultural traditions is the method used. Four groups of music teachers have discussed video excerpts of popular music ensembles from ensemble classes, and these discussions have been analysed with respect to topics displaying conceptions of musical and didactical quality. Topics are created through communicative projects, in which two or more people display a mutual understanding of what they are talking about. Thus, all conceptions of quality elicited from the participant groups of ensemble teachers are the result of intersubjective sense-making. The results show that the ideal of informal music-making is so strong that the groups describe teacher intervention as detrimental to musical progress. Very little is said about the sounding music, whereas physical expressivity, autonomy and joy of playing are prominent topics. The apparent lack of music-specific, “contextual” criteria and the low valuation of the teachers’ work are discussed as possible threats to the existence of music as a subject in the national curriculum.
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