| 1. |
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| 2. |
- Albinsson, I., et al.
(författare)
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Ion association effects and ionic conduction in polyalkalene modified polydimethylsiloxanes
- 1992
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Ingår i: Solid State Ionics. - : Elsevier. - 0167-2738 .- 1872-7689. ; 53-56:Part 2, s. 1044-1053
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Tidskriftsartikel (refereegranskat)abstract
- Poly (ethylene oxide) and poly (propylene oxide) modified poly (dimethyl siloxane) (PDMS) have been complexed with LiCF3SO3, NaCF3SO3 and KCF3SO3. In order to study ion association in these systems, the nondegenerate symmetric stretch (A1, SO3) Raman modes have been studied as a function of temperature at several different salt concentrations. Ionic conductivity has also been measured. For the poly (ethylene oxide) modified PDMS (PEO-PDMS), ether oxygen to metal ratios ranged from 12500:1 to 9:1. Changing the cation from Li+ to Na+ to K+ increases the conductivity of the complex. Plots of the molar conductivity versus salt concentration show that the characteristic shape and the region of increase in the molar conductivity is influenced most by the fraction of “free” ions which increases with increasing salt concentration. Charged triplets and contact ion-pairs are also present at the higher salt concentrations; the number of triplets increases with concentration and temperature. Non-VTF behaviour is observed. For the poly (propylene oxide) modified PDMS (PPO-PDMS) (with excess PPO), phase separation is observed when these triflate salts are complexed in. These solutions above and below the boundary layer have been studied by Raman spectroscopy revealing that the upper region is siloxane rich. The formation of the boundary layer is attributed to an increasing difference in surface tension between the PPO/salt/PPO-PDMS complexes and the separate PPO, PPO-PDMS components. The boundary layer moves up with increase in salt concentration. There is evidence of “free” ions, contact-ion pairs, triplets and aggregates. Values of conductivity of 2.2×10−6 and 1.6×10−5 S/cm are quoted for 293 K and 8 mol% LiCF3SO3 in respectively PPO-PDMS/PPO and PEO-PDMS/PEO. Both are better conductors than the corresponding 8 mol% PPG4000/LiCF3SO3 complex.
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| 3. |
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| 4. |
- Cienciala, Emil, et al.
(författare)
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The effect of a north-facing forest edge on tree water use in a boreal Scots pine stand
- 2002
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Ingår i: Canadian Journal of Forest Research. - 0045-5067 .- 1208-6037. ; 32:4, s. 693-702
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Tidskriftsartikel (refereegranskat)abstract
- Tree water use and growth increment were studied in a north-facing forest edge of a 70 year old mono-specific stand of Scots pine (Pinus sylvestris) trees growing on poor sandy soils in the northern boreal zone of Sweden. The forest edge in this study bordered a clear-cut established two decades ago. There were differences in water use and growth increment during the growing season between trees growing at the forest edge and trees growing in the forest interior. These differences were likely related to soil conditions, such as access to soil moisture, soil temperature and soil frost conditions, whereas an effect of above ground microclimate was not found. The estimated tree water use and growth increment over one growing season tended to be larger for trees at the edge zone relative to those from the interior. The variability of the measured tree water fluxes was high, especially for the edge zone trees. There were also structural differences between the two groups of trees, most notably in the radial profile of conductive xylem, in tree height and in green crown length, but these differences were on the limits of statistical significance. The estimated seasonal transpiration was low, about 70 mm when estimated exclusively for trees from the forest interior and 107 mm when estimated exclusively for trees at the forest edge. This illustrates the likely magnitude of water use enhancement due to the conditions specific to forest edge.
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| 5. |
- Djodjic, Faruk, et al.
(författare)
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A Global Perspective on Phosphorus Management Decision Support in Agriculture: Lessons Learned and Future Directions
- 2019
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Ingår i: Journal of Environmental Quality. - : Wiley. - 0047-2425 .- 1537-2537. ; 48, s. 1218-1233
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of phosphorus (P) management decision support tools (DSTs) and systems (DSS), in support of food and environmental security has been most strongly affected in developed regions by national strategies (i) to optimize levels of plant available P in agricultural soils, and (ii) to mitigate P runoff to water bodies. In the United States, Western Europe, and New Zealand, combinations of regulatory and voluntary strategies, sometimes backed by economic incentives, have often been driven by reactive legislation to protect water bodies. Farmer-specific DSSs, either based on modeling of P transfer source and transport mechanisms, or when coupled with farm-specific information or local knowledge, have typically guided best practices, education, and implementation, yet applying DSSs in data poor catchments and/or where user adoption is poor hampers the effectiveness of these systems. Recent developments focused on integrated digital mapping of hydrologically sensitive areas and critical source areas, sometimes using real-time data and weather forecasting, have rapidly advanced runoff modeling and education. Advances in technology related to monitoring, imaging, sensors, remote sensing, and analytical instrumentation will facilitate the development of DSSs that can predict heterogeneity over wider geographical areas. However, significant challenges remain in developing DSSs that incorporate "big data" in a format that is acceptable to users, and that adequately accounts for catchment variability, farming systems, and farmer behavior. Future efforts will undoubtedly focus on improving efficiency and conserving phosphate rock reserves in the face of future scarcity or prohibitive cost. Most importantly, the principles reviewed here are critical for sustainable agriculture.
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| 6. |
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| 7. |
- Ferry, Anders, et al.
(författare)
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Spectroscopic studies of luminescent and ionically conducting Eu[N(CF3SO2)2]3-PPG4000 complexes
- 1998
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 109:7, s. 2921-2928
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Tidskriftsartikel (refereegranskat)abstract
- Alternating current impedance, Fourier transform Raman/infrared (IR), and luminescence excitation (continuous and time-resolved) measurements have been conducted on solutions of poly(propylene glycol) (MW 4000) complexed with Eu[N(CF3SO2)2]3 salt, EuTFSI3, along with differential scanning calorimetry (DSC) studies. From observed frequency shifts of characteristic internal anionic vibrational modes (Raman and IR), we conclude that the salt is solvated by the polymer host. The TFSI anions, however, interact extensively with Eu3+ cations at all concentrations investigated. Ion-polymer interactions are manifested as changes in characteristic vibrational modes of the polymer. Continuous and time-resolved site-selective luminescence data give, respectively, evidence for two different types of chemical environments for solvated Eu3+ cations. In particular, the strongly forbidden non-degenerate 5D0 - 7F0 transition exhibits a structured two-component profile in the spectra. DSC data show that the glass transition temperature, Tg, is only marginally affected by the introduction of a relatively high concentration of salt into the host matrix, whereas the resulting polymer-salt complex is of rubbery character, distinctly different from the pure host polymer, which is a viscous liquid at room temperature. The present findings are interpreted in terms of a phase-segregated microstructure. This conjecture is supported by previous studies on PPG4000-based electrolytes indicating microscopic phase anomalies.
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| 8. |
- Furlani, Maurizio, et al.
(författare)
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Time resolved luminescence and vibrational spectroscopic studies on complexes of poly(ethylene oxide) oligomers and EuTFSI3 salt
- 1998
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Ingår i: Solid State Ionics. - : Elsevier. - 0167-2738 .- 1872-7689. ; 113-115:1-2, s. 129-138
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Tidskriftsartikel (refereegranskat)abstract
- AC impedance, FT-Raman/IR, DSC, continuous and time resolved luminescence measurements have been conducted on solutions of poly(ethylene glycol) (PEG), MW 400, and poly(ethylene glycol)-dimethyl ether (DME), MW 425, complexed with Eu[N(CF3SO2)2]3 salt, EuTFSI3. Ion-polymer interactions are manifested as changes in characteristic vibrational modes of the polymer, including CH, and -OH stretching motions at ∼2700-3700 cm-1, and also in cation-induced polymer modes at ∼ 865-910 cm-1. Comparing the vibrational features of the TFSI anion (i.e., both Raman and IR), we find no modes that are substantially changing with increasing salt concentration, or upon change of cation (i.e., M = Li+, Na+ or Eu3+). This observation suggests that TFSI-salts are highly dissociated in PEO oligomer solvents even up to relatively high salt concentrations (i.e., O:M = 26: 1). Clear evidence of -OH end-group coordination in the PEG systems emerges from IR spectra and the strong dependence of T-g upon salt concentration, and also from the pronounced temperature dependence of the ionic conductivity. Despite of this, however, few distinct differences could be observed in the luminescence spectra between the PEG and the DME host materials. Luminescence spectra of Eu3+ show a relatively small distribution of energies (30 cm-1 FWHM in 5D0 - 7F0) in a low-symmetry site throughout the entire concentration range investigated for both PEG and DME solvents. The population decays of the 5D0 excited state, measured by exciting to the degenerate state 5D1 with a pulsed dye laser, are also very similar for the PEG and DME hosts (lifetimes = 0.35 ms).
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| 9. |
- Gebrehiwot, Solomon, et al.
(författare)
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Hydrological change detection using modeling : Half a century of runoff from four rivers in the Blue Nile Basin
- 2013
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 49:6, s. 3842-3851
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Tidskriftsartikel (refereegranskat)abstract
- Land cover changes can have significant impacts on hydrological regime. The objective of this study was to detect possible hydrological changes of four watersheds in the Blue Nile Basin using a model-based method for hydrological change detection. The four watersheds, Birr, Upper-Didesa, Gilgel Abbay, and Koga range in size from 260 to 1800 km(2). The changes were assessed based on model parameters, model residuals, and in the overall function of the watersheds in transferring rainfall into runoff. The entire time series (1960-2004) was divided into three periods based on political and land management policy changes. A conceptual rainfall-runoff model, the HBV (Hydrologiska Byrans Vattenbalansavdelning) model, was used for the analysis, and suitable parameter sets for each period were found based on a Monte Carlo approach. The values of six out of nine parameters changed significantly between the periods. Model residuals also showed significant changes between the three periods in three of the four watersheds. On the other hand, the overall functioning of the watersheds in processing rainfall to runoff changed little. So even though the individual parameters and model residuals were changing, the integrated functioning of the watersheds showed minimal changes. This study demonstrated the value of using different approaches for detecting hydrological change and highlighted the sensitivity of the outcome to the applied modeling and statistical methods.
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| 10. |
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| 11. |
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| 12. |
- Jacobsson, Per, et al.
(författare)
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Ion association effects and phase separation in poly(propylene oxide) modified poly(dimethylsiloxane) complexed with triflate salts
- 1992
-
Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 33:13, s. 2778-2783
-
Tidskriftsartikel (refereegranskat)abstract
- Phase separation is observed in poly(propylene oxide) modified poly(dimethylsiloxane) (PPO-PDMS) with excess poly(propylene oxide) (PPO) when salts of MCF3SO3 (M = Li, Na) are added. The same behaviour is inferred for KCF3SO3. The solutions above and below the boundary layer have been studied by Raman spectroscopy and in particular by examining the non-degenerate, symmetric stretch (A1, SO3) Raman mode of the CF3SO3− anion. The upper part is siloxane rich; salt is present on both sides of the boundary layer with a much lower concentration in the upper part. The formation of the boundary layer is attributed to an increasing difference in surface tension between the PPO/salt/PPO-PDMS complexes and the separate PPO, PPO-PDMS components. The boundary layer moves up with increase in concentration. The number of ‘free’ ions decreases and ion association increases with increase in temperature. There is evidence of contact ion pairs, triplets and aggregates. Values of conductivity are quoted for 293 K.
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| 13. |
- Larsson, Carl Fredrik, 1980, et al.
(författare)
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Characteristics of lithium-ion batteries during fire tests
- 2014
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 271, s. 414-420
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Tidskriftsartikel (refereegranskat)abstract
- Commercial lithium-ion battery cells are exposed to a controlled propane fire in order to evaluate heat release rate (HRR), emission of toxic gases as well as cell temperature and voltage under this type of abuse. The study includes six abuse tests on cells having lithium-iron phosphate (LFP) cathodes and, as a comparison, one test on conventional laptop battery packs with cobalt based cathode. The influence of different state of charge (SOC) is investigated and a limited study of the effect of water mist application is also performed. The total heat release (THR) per battery energy capacity are determined to be 28-75 kJ Wh(-1) and the maximum HRR values to 110-490 W Wh(-1). Hydrogen fluoride (HF) is found in the released gases for all tests but no traceable amounts of phosphorous oxyfluoride (POF3) or phosphorus pentafluoride (PF5) are detected. An extrapolation of expected HF emissions for a typical automotive 10 kWh battery pack exposed to fire gives a release of 400-1200 g HF. If released in a confined environment such emissions of HF may results in unacceptable exposure levels.
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| 14. |
- Larsson, Carl Fredrik, 1980, et al.
(författare)
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Toxic fluoride gas emissions from lithium-ion battery fires
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 7:10018, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Lithium-ion battery fires generate intense heat and considerable amounts of gas and smoke. Although the emission of toxic gases can be a larger threat than the heat, the knowledge of such emissions is limited. This paper presents quantitative measurements of heat release and fluoride gas emissions during battery fires for seven different types of commercial lithium-ion batteries. The results have been validated using two independent measurement techniques and show that large amounts of hydrogen fluoride (HF) may be generated, ranging between 20 and 200 mg/Wh of nominal battery energy capacity. In addition, 15–22 mg/Wh of another potentially toxic gas, phosphoryl fluoride (POF3), was measured in some of the fire tests. Gas emissions when using water mist as extinguishing agent were also investigated. Fluoride gas emission can pose a serious toxic threat and the results are crucial findings for risk assessment and management, especially for large Li-ion battery packs.
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| 15. |
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| 16. |
- Mellander, Per-Erik, et al.
(författare)
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A sub-field scale critical source area index for legacy phosphorus management using high resolution data
- 2016
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Ingår i: Agriculture, Ecosystems and Environment. - : Elsevier BV. - 0167-8809 .- 1873-2305. ; 233, s. 238-252
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Tidskriftsartikel (refereegranskat)abstract
- Diffuse phosphorus (P) mitigation in agricultural catchments should be targeted at critical source areas (CSAs) that consider source and transport factors. However, development of CSA identification needs to consider the mobilisation potential of legacy soil P sources at the field scale, and the control of (micro) topography on runoff generation and hydrological connectivity at the sub-field scale. To address these limitations, a 'next generation' sub-field scale CSA index is presented, which predicts the risk of dissolved P losses in runoff from legacy soil P. The GIS-based CSA Index integrates two factors; mobile soil P concentrations (water extractable P; WEP) and a hydrologically sensitive area (HSA) index. The HSA Index identifies runoff-generating-areas using high resolution LiDAR Digital Elevation Models (DEMs), a soil topographic index (STI) and information on flow sinks and effects on hydrological connectivity. The CSA Index was developed using four intensively monitored agricultural catchments (7.5-11 km(2)) in Ireland with contrasting agri-environmental conditions. Field scale soil WEP concentrations were estimated using catchment and land use specific relationships with Morgan P concentrations. In-stream total reactive P (TRP) concentrations and discharge were measured sub-hourly at catchment outlet bankside analysers and gauging stations during winter closed periods for fertiliser spreading in 2009-14, and hydrograph/loadograph separation methods were used to estimate TRP loads and proportions from quicicflow (surface runoff). A strong relationship between TRP concentrations in quicicflow and soil WEP concentrations (r(2) = 0.73) was used to predict dissolved P concentrations in runoff at the field scale, which were then multiplied by the HSA Index to generate sub-field scale CSA Index maps. Evaluation of the tool showed a very strong relationship between the total CSA Index value within the HSA and the total TRP load in quickflow (r(2) = 0.86). Using a CSA Index threshold value of >= 0.5, the CSA approach identified 1.1-5.6% of catchment areas at highest risk of legacy soil P transfers, compared with 4.0-26.5% of catchment areas based on an existing approach that uses above agronomic optimum soil P status. The tool could be used to aid cost-effective targeting of sub-field scale mitigation measures and best management practices at delivery points of CSA pathways to reduce dissolved P losses from legacy P stores and support sustainable agricultural production. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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| 17. |
- Mellander, Per-Erik, et al.
(författare)
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Challenges of Reducing Phosphorus Based Water Eutrophication in the Agricultural Landscapes of Northwest Europe
- 2018
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Ingår i: Frontiers in marine science. - : Frontiers Media SA. - 2296-7745. ; 5
-
Forskningsöversikt (refereegranskat)abstract
- In this paper, we outline several recent insights for the priorities and challenges for future research for reducing phosphorus (P) based water eutrophication in the agricultural landscapes of Northwest Europe. We highlight that new research efforts best be focused on headwater catchments as they are a key influence on the initial chemistry of the larger river catchments, and here many management interventions are most effectively made. We emphasize the lack of understanding on how climate change will impact on P losses from agricultural landscapes. Particularly, the capability to disentangle current and future trends in P fluxes, due to climate change itself, from climate driven changes in agricultural management practices and P inputs. Knowing that, future climatic change trajectories for Western Europe will accelerate the release of the most bioavailable soil P. We stress the ambiguities created by the large varieties of sources and storage/transfer processes involved in P emissions in landscapes and the need to develop specific data treatment methods or tracers able to circumvent them, thereby helping catchment managers to identify the ultimate P sources that most contribute to diffuse P emissions. We point out that soil and aqueous P exist not only in various chemical forms, but also in range of less considered physical forms e. g., dissolved, nanoparticulate, colloidal and other particulates, all affected differently by climate as well as other environmental factors, and require bespoke mitigation measures. We support increased high resolution monitoring of headwater catchments, to not only help verify the effectiveness of catchments mitigation strategies, but also add data to further develop new water quality models (e.g., those include Fe-P interactions) which can deal with climate and land use change effects within an uncertainty framework. We finally conclude that there is a crucial need for more integrative research efforts to deal with our incomplete understanding of the mechanisms and processes associated with the identification of critical source areas, P mobilization, delivery and biogeochemical processing, as otherwise even highintensity and high-resolution research efforts will only reveal an incomplete picture of the full global impact of the terrestrial derived P on downstream aquatic and marine ecosystems.
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| 18. |
- Mellander, Per-Erik, et al.
(författare)
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Climate change impact on snow and soil temperature in boreal Scots pine stands
- 2007
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Ingår i: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 85:1/2, s. 179-193
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Tidskriftsartikel (refereegranskat)abstract
- Scenarios indicate that the air temperature will increase in high latitude regions in coming decades, causing the snow covered period to shorten, the growing season to lengthen and soil temperatures to change during the winter, spring and early summer. To evaluate how a warmer climate is likely to alter the snow cover and soil temperature in Scots pine stands of varying ages in northern Sweden, climate scenarios from the Swedish regional climate modelling programme SWECLIM were used to drive a Soil-Vegetation-Atmosphere Transfer (SVAT)-model (COUP). Using the two CO2 emission scenarios A and B in the Hadley centres global climate model, HadleyA and HadleyB, SWECLIM predicts that the annual mean air temperature and precipitation will increase at most 4.8 oC and 315 mm, respectively, within a century in the study region. The results of this analysis indicate that a warmer climate will shorten the period of persistent snow pack by 73 - 93 days, increase the average soil temperature by 0.9 � 1.5 oC at 10 cm depth, advance soil warming by 15 - 19 days in spring and cause more soil freeze-thaw cycles by 31 � 38 %. The results also predict that the large current variations in snow cover due to variations in tree interception and topography will be enhanced in the coming century, resulting in increased spatial variability in soil temperatures.
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| 19. |
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| 20. |
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| 21. |
- Mellander, Per-Erik
(författare)
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Kall mark kan ge träden vattenbrist
- 2001
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Ingår i: Miljötrender. - 1403-4743. ; 3-4, s. 8-9
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 22. |
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| 23. |
- Mellander, Per-Erik, et al.
(författare)
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Modelling the effect of low soil temperatures on transpiration by Scots pine
- 2006
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 20:9, s. 1929-1944
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Tidskriftsartikel (refereegranskat)abstract
- For ecosystem modelling of the Boreal forest it is important to include processes associated with low soil temperature during spring-early summer, as these affect the tree water uptake. The COUP model, a physically based SVAT model, was tested with 2 years of soil and snow physical measurements and sap flow measurements in a 70-year-old Scots pine stand in the boreal zone of northern Sweden. During the first year the extent and duration of soil frost was manipulated in the field. The model was successful in reproducing the timing of the soil warming after the snowmelt and frost thaw. A delayed soil warming, into the growing season, severely reduced the transpiration. We demonstrated the potential for considerable overestimation of transpiration by the model if the reduction of the trees' capacity to transpire due to low soil temperatures is not taken into account. We also demonstrated that the accumulated effect of aboveground conditions could be included when simulating the relationship between soil temperature and tree water uptake. This improved the estimated transpiration for the control plot and when soil warming was delayed into the growing season. The study illustrates the need of including antecedent conditions on root growth in the model in order to catch these effects on transpiration. The COUP model is a promising tool for predicting transpiration in high-latitude stands.
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| 24. |
- Mellander, Per Erik, et al.
(författare)
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Modelling variability of snow depths and soil temperatures in Scots pine stands.
- 2005
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Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923. ; 133:1/4, s. 109-118
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Tidskriftsartikel (refereegranskat)abstract
- Snow cover varies spatially and inter-annually in the boreal forest landscape due to the canopy influence on snow interception and snow surface energy balance. This is reflected in the soil temperature regime during winter and spring. Differences in the timing of soil warming have been shown to influence the trees� capacity to take up water and assimilate carbon. To understand the effects of forest management or a possible climate change on forest productivity, it is useful to have a tool for predicting the spatial and inter-annual variability of snow depths and soil warming during spring within different stands across the landscape. A SVAT-model (COUP) was used to simulate snow cover and soil temperature during a decade in eight Scots pine (Pinus sylvestris L) stands. The COUP-model proved to be a functional tool for simulating the intra-landscape variation in snow depth and soil temperature. The simulations revealed variability between the stands and between the years, as well as factors contributing to this variability. A more open stand together with low leaf area index resulted in deeper snow layers and, together with higher trees, also an earlier soil warming. The largest spatial variability in the timing of soil warming in spring between sites was found during years with little snow, which is a possible consequence of climate change-related warming in the boreal landscape of northern Sweden.
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| 25. |
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| 26. |
- Mellander, Per-Erik, et al.
(författare)
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Recovery of photosynthetic capacity in Scots pine : a model analysis of forest plots with manipulated winter/spring soil temperature regimes.
- 2008
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Ingår i: European Journal of Forest Research. - : Springer Science and Business Media LLC. - 1612-4669 .- 1612-4677. ; 127:1, s. 71-79
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Tidskriftsartikel (refereegranskat)abstract
- Both aboveground and belowground climate affects net primary production (NNP) and forest growth. Little is known about how above and belowground factors interact. The BIOMASS-model was tested to simulate photosynthetic recovery over a wide range of soil temperatures created by snow cover manipulations on tree-scale plots in a 20-year-old Scots pine stand in northern Sweden. The differences in timing of soil warming between the plots covered a span of two months. Carbon assimilation in needles, sap flow, needle water potential and climatic parameters were measured in the field. The simulations revealed that an early start of soil warming gave a relatively early photosynthetic recovery and a 7.5% increase of NPP. Late soil warming delayed the photosynthetic recovery and reduced the NPP by 13.7%. This indicated that soil temperature needed to be accounted for, as well as air temperature, when analysing photosynthetic recovery and NPP in boreal environment. The effects of differences in soil temperature were reflected in the simulated photosynthetic recovery. The model did not fully capture the delay of photosynthetic recovery caused by a late soil warming. It was possible to integrate the complexity of the soil climate effects into a threshold date for soil thaw, using sapflow measurements together with information about air temperature and a day degree sum, as long as water availability was not limiting water uptake by roots. Although a more realistic mechanism than that currently in BIOMASS is desirable as climate change shifts the typical patterns of interplay between air and soil temperature dynamics.
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| 27. |
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| 28. |
- Mellander, Per-Erik
(författare)
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Sen vår ger kraftigt hämmad tillväxt
- 2004
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Att låga temperaturer i marken hämmar upptag av vatten och gasutbyte hos unga plantor är känt sedan tidigare. Nu visar sig detta gälla även för stora tallar. Tjälproblematiken bör därför uppmärksammas mer, även för bestånd som har lämnat plantstadiet. • För att träden ska kunna ta upp vatten på våren räcker det inte med att vattnet är ofruset. I rotzonens övre del måste vattnet ha en temperatur högre än 0°C för att rötterna ska kunna tillgodogöra sig det. • Tallarnas upptag av vatten från marken och kol från atmosfären minskar kraftigt när uppvärmningen av marken försenas in i växtperioden, och upptaget fortsätter att hämmas tills marktemperaturen är cirka +8°C. Vid högre temperaturer avgörs vatten- och kolupptaget främst av klimatet ovan mark.
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| 29. |
- Mellander, Per Erik, et al.
(författare)
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Snödjup och marktempertur i norrländska skogar idag och om 100 år
- 2005
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Ett framtida varmare klimat kan medföra att den snötäckta perioden i skogslandskapet förkortas, årsmedeltemperaturen i marken höjs, markuppvärmningen på våren sker tidigare, samt att fler cykler av frysning och upptining äger rum. • Tunnare snötäcke kan medföra en ökad rumslig variation i marktemperatur p.g.a. ett större relativt inflytande på snödjupet av topografin samt av trädens förmåga att fånga upp nederbörd och solstrålning. • Under vissa år kan ett varmare klimat på nordliga breddgrader medföra en försenad markuppvärmning och större mellanårsvariationer i täta bestånd.
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| 30. |
- Mellander, Per-Erik
(författare)
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Spring water stress in Scots pine: interaction of snow and soil temperature
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water use and net carbon assimilation during spring was examined on Scots pine trees exposed to different soil warming dynamics in the field. Sap flow, needle water potential and net carbon assimilation were measured on trees that were exposed to a wide range of soil temperature regimes caused by manipulating the snow cover on tree-scale soil plots. This made it possible to quantify the sensitivity of water uptake and recovery of gas exchange by Scots pine in the critical transition from winter dormancy to the growing season, which can be influenced by silvicultural practices. A part of the study was to find a tool for estimating the coupled effect of belowground and aboveground climate on transpiration, as well as to adapt this tool to the harsh climate of the boreal forest. Combining the results of field experiments on tree susceptibility to water stress with a physically based SVAT model as well as a model for estimating the recovery of photosynthesis helped to predict spatial and inter-annual variability of snow depths, soil warming, water uptake and net primary productivity during spring within different Scots pine stands across the landscape. This could provide a better basis for a more frostconscious forest management. The studies have confirmed the importance of low soil temperatures in combination with aboveground climate for root water uptake and net carbon assimilation during spring, when soil warming occurs after the start of the growing season. The studies have also confirmed that earlier, controlled laboratory studies on the inhibiting effects of low soil temperature on water relations and gas exchange for seedlings or saplings also hold true on mature trees in the field. The experimental data served well as the basis for model analyses of the interaction between belowground and aboveground conditions on water use and net photosynthesis. The results of the field studies and model analyses suggest that the effect of soil temperature on tree water uptake and net photosynthesis during spring, in conjunction with aboveground conditions, are factors that need to be considered in forest management in areas susceptible to soil frost and low soil temperatures.
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| 31. |
- Mellander, Per-Erik, et al.
(författare)
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Summer Rains and Dry Seasons in the Upper Blue Nile Basin : The Predictability of Half a Century of Past and Future Spatiotemporal Patterns
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:7, s. e68461-
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Tidskriftsartikel (refereegranskat)abstract
- During the last 100 years the Ethiopian upper Blue Nile Basin (BNB) has undergone major changes in land use, and is now potentially facing changes in climate. Rainfall over BNB supplies over two-thirds of the water to the Nile and supports a large local population living mainly on subsistence agriculture. Regional food security is sensitive to both the amount and timing of rain and is already an important political challenge that will be further complicated if scenarios of climate change are realized. In this study a simple spatial model of the timing and duration of summer rains (Kiremt) and dry season (Bega), and annual rain over the upper BNB was established from observed data between 1952 and 2004. The model was used to explore potential impacts of climate change on these rains, using a down-scaled ECHAM5/MP1-OM scenario between 2050 and 2100. Over the observed period the amount, onset and duration of Kiremt rains and rain-free Bega days have exhibited a consistent spatial pattern. The spatially averaged annual rainfall was 1490 mm of which 93% was Kiremt rain. The average Kiremt rain and number of rainy days was higher in the southwest (322 days) and decreased towards the north (136 days). Under the 2050-2100 scenario, the annual mean rainfall is predicted to increase by 6% and maintain the same spatial pattern as in the past. A larger change in annual rainfall is expected in the southwest (ca. +130 mm) with a gradually smaller change towards the north (ca. +70 mm). Results highlight the need to account for the characteristic spatiotemporal zonation when planning water management and climate adaptation within the upper BNB. The presented simple spatial resolved models of the presence of Kiremt and annual total rainfall could be used as a baseline for such long-term planning.
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| 32. |
- Mellander, Per-Erik, et al.
(författare)
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The bog as an element in the boreal forest biome
- 1996
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Ingår i: Nordic hydrological conference 1996 : Akureyri, Iceland, 13-15 August 1996 / Nordic Association for Hydrologi. - Reykjavík : Icelandic Hydrological Committee. ; , s. 798-, s. 389-398
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 33. |
- Mellander, Per-Erik, et al.
(författare)
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The influence of soil temperature on transpiration: : a plot scale manipulation in a young Scots pine stand
- 2004
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127. ; 195:1-2, s. 15-28
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Tidskriftsartikel (refereegranskat)abstract
- Classic studies have stressed the importance of forest management for soil frost and the dynamics of soil warming during spring. But, we know very little about the potential loss of forest production due to cold soils. Liquid soil water may not be available to trees due to cold soil conditions, thus reducing transpiration and photosynthesis. We believe that these effects need to be quantified in order to keep silvicultural practices from inadvertently reducing forest growth through effects on soil temperature. In order to test this hypothesis it is important to know more about water uptake in the field by trees in cold environments. The snow cover was manipulated on plots in a young stand of Pinus sylvestris L. to create plots with different timings of soil warming. Soil profile temperature and liquid water content, as well as snow and frost depths, were measured together with tree physiological parameters such as sap flow, stomatal conductance and needle water potential. The study has confirmed the importance of the soil temperature for tree water uptake when soil warming was delayed beyond the start of growing season as defined by air temperature. The absence of frost (and hence the presence of liquid water) was not sufficient to enable water uptake. It was rather elevation of soil temperature above zero in the upper soil layers that was required for substantial water uptake, in combination with other site factors. Below ca. +8 °C, soil temperature was a factor in the restriction of transpiration, explained by a lower stomatal conductance and likely decreased root permeability. The effect of a certain soil temperature was not the same at different times due to its interaction with aboveground factors such as air temperature and day-length. The effect of low soil temperature increased with the persistence of low temperatures after the start of the growing season. The timings of soil warming induced by our study were within the spatial and inter-annual variation of soil warming in this region. Thus, we conclude that influences of forest management on soil temperature can affect the transpiration deficit during spring, with potential implications for forest productivity
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| 34. |
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| 35. |
- Nordgren, A, et al.
(författare)
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Tree root and soil heterotrophic respiration as revealed by girdling of boreal Scots pine forest: : extending observations beyond the first year
- 2003
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Ingår i: Plant, Cell and Environment. - : Wiley. - 0140-7791. ; 26:8, s. 1287-1296
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Tidskriftsartikel (refereegranskat)abstract
- Limitations in available techniques to separate autotrophic (root) and soil heterotrophic respiration have hampered the understanding of forest C cycling. The former is here defined as respiration by roots, their associated mycorrhizal fungi and other micro-organisms in the rhizosphere directly dependent on labile C compounds leaked from roots. In order to separate the autotrophic and heterotrophic components of soil respiration, all Scots pine trees in 900 m2 plots were girdled to instantaneously terminate the supply of current photosynthates from the tree canopy to roots. Högberg et al. (Nature 411, 789-792, 2001) reported that autotrophic activity contributed up to 56% of total soil respiration during the first summer of this experiment. They also found that mobilization of stored starch (and likely also sugars) in roots after girdling caused an increased apparent heterotrophic respiration on girdled plots. Herein a transient increase in the δ13C of soil CO2 efflux after girdling, thought to be due to decomposition of 13C-enriched ectomycorrhizal mycelium and root starch and sugar reserves, is reported. In the second year after girdling, when starch reserves of girdled tree roots were exhausted, calculated root respiration increased up to 65% of total soil CO2 efflux. It is suggested that this estimate of its contribution to soil respiration is more precise than the previous based on one year of observation. Heterotrophic respiration declined in response to a 20-day-long 6 °C decline in soil temperature during the second summer, whereas root respiration did not decline. This did not support the idea that root respiration should be more sensitive to variations in soil temperature. It is suggested that above-ground photosynthetic activity and allocation patterns of recent photosynthates to roots should be considered in models of responses of forest C balances to global climate change
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| 36. |
- Nyberg, Lars, et al.
(författare)
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Soil frost effects on soil water and runoff dynamics along a boreal forest transect: 1. Field investigations
- 2001
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087. ; 15:6, s. 909-926
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Tidskriftsartikel (refereegranskat)abstract
- To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic-rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995–96) had abnormally low snow precipitation, which gave a deep frost down to 40–80 cm, whereas the two following winters had frost depths of 5–20 cm. During winter 1995–96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amount of frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5–7 vol.% in the mineral soil and 10–15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated during snowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage.
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| 37. |
- Satolli, D, et al.
(författare)
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Macro- and microscopic properties of nonaqueous proton conducting membranes based on PAN.
- 2003
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 150:3, s. A267-A273
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report the electrochemical and physical characterization of proton-conducting gels prepared by means of a swelling procedure proved successful for the synthesis of membranes of interest for lithium battery technology. Basically, this new approach considers the formation of a precursor membrane by the gelification of a selected polymer matrix, e.g., a poly (acrylonitrile), matrix using a suitable solvent. This membrane is then embedded in an acidic solution: by a phase inversion process, the gelling solvent leaves the polymer matrix to be replaced by the acid solution, to finally obtain a self-standing, proton-conducting membrane. Impedance spectroscopy analysis demonstrated the good conductivity of the materials, and infrared, Raman, and fuel-cell studies confirm that this conductivity is due to protonic transport.
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| 38. |
- Stahli, M., et al.
(författare)
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Soil frost effects on soil water and runoff dynamics along a boreal transect : 2. Simulations
- 2001
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 15:6, s. 927-941
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Tidskriftsartikel (refereegranskat)abstract
- A physically based SVAT-model was rested with soil and snow physical measurements, as well as runoff data fr om an 8600 m(2) catchment in northern Sweden in order to quantify the influence of soil frost on spring snowmelt runoff in a moderately sloped, boreal forest. The model was run as an array of connected profiles cascading to the brook. For three winter seasons (1995-98) it was able to predict the onset and total accumulation of the runoff with satisfactory accuracy. Surface runoff was identified as only a minor fraction of the total runoff occurring during short periods in connection with ice blocking of the water-conducting pores. Little surface runoff, though, does not mean that soil frost is unimportant for spring runoff. Simulations without frost routines systematically underestimated the total accumulated runoff. The possibility of major frost effects appearing in response to specific combinations of weather conditions were also tested. Different scenarios of critical initial conditions for the winter, e.g, high water saturation and delayed snow accumulation leading to an increased frost penetration, were tested. These showed that under special circumstances there is potential for increased spring runoff due to soil frost.
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| 39. |
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| 40. |
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| 41. |
- Vestin, Jenny L. K., et al.
(författare)
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Soil solution and stream water chemistry in a forested catchment I: Dynamics
- 2008
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 144:1/2, s. 256-270
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Tidskriftsartikel (refereegranskat)abstract
- Soil solution and stream water chemistry were studied during two years in a catchment in Bispgården in central Sweden (63°07′N, 16°70′E). Soil samples and soil solution were collected in a slope at two distances (10 and 80 m) from a stream. The aims were to examine interactions between recharge (podzol) and discharge (arenosol) areas and to investigate the relations between soil solution and stream water chemistry. The parent material was similar within the catchment, but the content of C and N were higher in the discharge area most likely due to the difference in hydrological conditions compared to the recharge area. Exchangeable cations and base saturation were higher in the discharge area than in the recharge area, which may be due to the higher content of C. The concentrations in soil solution of H, DOC, NO3, SO4, Al, Si, Ca and K charge area compared to the recharge area which was probably caused by transportation of elements in soil and retention due to the increased content of C. During snow melt, the concentrations in soil solution of DOC, SO4, Al, Si, Ca and K were low due to dilution and low biological activity. The concentrations were then increasing during the seasons as an effect of biological activity and mineral weathering. NO3 concentration in soil solution was found in higher concentrations during snow melting and was then diminishing during summer likely as a result of biological uptake. After a dry period followed by an intensive rain in August 2003, the stream water chemistry was markedly altered for a few days. The concentrations of H, DOC SO4, Al and Ca were increased and the concentration of Si was decreased in the stream water. It therefore appeared that the stream water mirrored the upper soil horizons in the discharge area during high flows, while reflecting the lower soil horizons and ground water during low flows.
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