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| 2. |
- Campeau, Audrey, et al.
(author)
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Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen : Implications for peat carbon stock stability
- 2017
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 23:12, s. 5523-5536
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Journal article (peer-reviewed)abstract
- The stability of northern peatland's carbon (C) store under changing climate is of major concern for the global C cycle. The aquatic export of C from boreal peatlands is recognized as both a critical pathway for the remobilization of peat C stocks as well as a major component of the net ecosystem C balance (NECB). Here, we present a full year characterization of radiocarbon content (14C) of dissolved organic carbon (DOC), carbon dioxide (CO2), and methane (CH4) exported from a boreal peatland catchment coupled with 14C characterization of the catchment's peat profile of the same C species. The age of aquatic C in runoff varied little throughout the year and appeared to be sustained by recently fixed C from the atmosphere (<60 years), despite stream DOC, CO2, and CH4 primarily being sourced from deep peat horizons (2–4 m) near the mire's outlet. In fact, the 14C content of DOC, CO2, and CH4 across the entire peat profile was considerably enriched with postbomb C compared with the solid peat material. Overall, our results demonstrate little to no mobilization of ancient C stocks from this boreal peatland and a relatively large resilience of the source of aquatic C export to forecasted hydroclimatic changes.
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| 3. |
- Campeau, Audrey, et al.
(author)
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Stable carbon isotopes reveal soil - stream DIC linkages in contrasting headwater catchments
- 2018
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In: Journal of Geophysical Research - Biogeosciences. - : American Geophysical Union (AGU). - 2169-8953 .- 2169-8961. ; 123:1, s. 149-167
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Journal article (peer-reviewed)abstract
- Large CO2 evasion to the atmosphere occurs as dissolved inorganic carbon (DIC) is transported from soils to streams. While this physical process has been the focus of multiple studies, less is known about the underlying biogeochemical transformations that accompany this transfer of C from soils to streams. Here we used patterns in stream water and groundwater C-13-DIC values within three headwater catchments with contrasting land cover to identify the sources and processes regulating DIC during its transport. We found that although considerable CO2 evasion occurs as DIC is transported from soils to streams, there were also other processes affecting the DIC pool. Methane production and mixing of C sources, associated with different types and spatial distribution of peat-rich areas within each catchment, had a significant influence on the C-13-DIC values in both soils and streams. These processes represent an additional control on C-13-DIC values and the catchment-scale cycling of DIC across different northern landscape types. The results from this study demonstrate that the transport of DIC from soils to streams results in more than just rapid CO2 evasion to the atmosphere but also represents a channel of C transformation, which questions some of our current conceptualizations of C cycling at the landscape scale. Plain Language Summary Large carbon dioxide emission to the atmosphere occurs as rainwater percolates through soils and into streams. This physical process is important for the global carbon cycle and has been the focus of multiple studies. However, less is known about the underlying processes that accompanies this transfer of carbon dioxide from soils to streams. Here we analyze the stable isotope composition of soil and stream carbon dioxide and demonstrate that methane production and mixing of carbon sources also occur in soils and streams. These processes were linked to different types and configurations of peat-rich areas, for example, bogs, fens, and riparian zones, found within each of the three studied catchments. Our results therefore demonstrate that the export of carbon dioxide from soils to streams not only results in emissions to the atmosphere but also represents a channel of transformation. This questions some of our current conceptualization of the catchment-scale cycling of carbon dioxide.
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| 4. |
- Meier, Hannes, 1983-
(author)
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Superfluid Phase Transitions in Disordered Systems
- 2011
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Licentiate thesis (other academic/artistic)abstract
- This thesis presents results from large scale Monte Carlo simulations of systems subject to a superfluid phase transition in the presence of disorder. The simulations are performed by state-of-the-art, collective Monte Carlo algorithms treating phase degrees of freedom in effective models with amplitude fluctuations integrated out.In Paper I a model system for the possible solid to supersolid transition in 4He is presented.The Wolff cluster algorithm is used to study how the presence of linearly correlated random defects is able to alter the universality class of the 3-dimensional XY-model. In the pure case the superfluid density and heat capacity have singular onsets, which are not seen in the supersolid experiments where instead a smooth onset is obtained. Using finite size scaling of Monte Carlo data, we find a similar smooth onset in our simulations, governed by exponents ν=1 for the superfluid density and α=-1 for the heat capacity. These results are in qualitative agreement with experiments for the observed transition in solid 4He.In Paper II a systematic investigation of the scaling result z=d for the dynamic critical exponentat the Bose glass to superfluid quantum phase transition is performed. The result z=d has been believed to be exact for about 20 years, but although it has been questioned lately no accurate estimate of z has been available. An effective link current model of quantum bosons at T=0 with disorder in 2D is simulated using highly effective worm Monte Carlo simulations.The data analysis is based on a finite size scaling approach todetermine the quantum correlation time from simulationdata for boson world lines without any a priori assumption on the critical parameters. The resulting critical exponents are z=1.8 \pm 0.05, ν=1.15 \pm 0.03, and η=-0.3 \pm 0.1. This suggests that z=d is not satisfied.
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| 6. |
- Wallin, Kjell, et al.
(author)
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Skattning av antalet kornknarrar på Öland 2008
- 2008
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Reports (other academic/artistic)abstract
- Rapporten redovisar resultatet av en inventering vars syfte var att beräkna det totala antalet spelande kornknarrar på Öland och att beskriva de spelande hanarnas uppehållsmiljö. Inventeringen genomfördes med stratifierad stickprovtagning av 300 provpunkter jämnt fördelade över hela Öland under perioden maj – juli 2008, där varje punkt besöktes minst två gånger. Bandspelare som spelade upp kornknarrens läte användes för att öka chansen att upptäcka kornknarr. Metoden innebar dock ingen större förbättring. Som metod för att beräkna antalet spelande hanar har avståndsinventering använts från utvalda punkter. Bestämning av kornknarrarnas position har gjorts genom ”triangulering”. Skattningen av det maximala antalet spelande kornknarrar är 206 stycken. Genom skillnaden i uppträdande och antal, mellan första och andra inventeringstillfället, med 147 respektive 61 hanar, antyds att denna siffra kan vara en överskattning. En vidare diskussion av detta görs i rapporten. Geografiskt har kornknarren sin tyngdpunkt på mellersta och östra Öland. Uppehållsmiljön utgjordes till större delen av vall, betesmark och träda, vilket överensstämmer med tidigare gjorda studier på Öland. En jämförelse mellan rapporteringssystemet Svalan och skattning genom stickprovstagning visar på relativt stora skillnader i antal spelande kornknarrar, både tidsmässigt och geografiskt. Antalet kornknarrar som rapporteras till Svalan avtar från mitten av juni medan inventeringen visar att spelandet fortsätter med bibehållen intensitet in i juli. Observationerna från Svalan är koncentrerade till Ölands sydöstra delar medan observationerna från inventeringen är mer jämnt fördelade över ön, även om det finns en viss östlig förtätning.
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| 7. |
- Wallin, Mats, et al.
(author)
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Fågelfaunan på Ölands sjömarker - inventeringar 1988-2008
- 2009
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Reports (other academic/artistic)abstract
- Fåglarna på Ölands sjömarker har varit föremål för tre heltäckande inventeringar under de senaste 20 åren. Dessutom har delar av Öland inventerats årligen sedan 2003. För ändamålet är Ölands sjömarker indelade i 96 delområden. De artgrupper som inventerats är ”Vadare”, ”Änder, svanar och gäss” samt ”Tärnor och måsfågel”. Vid inventeringarna har antalet häckande par bedömts genom parräkning, boräkning och revirkartering. Vid sidan av fågelinventeringen har även hävden på sjömarkerna bedömts av inventerarna. Resultaten från inventeringarna har analyserats med syfte att beskriva enskilda fågelarters populationsutveckling på Öland som helhet och i respektive delområde. Dataunderlaget för hela perioden, 1988–2008, är ojämnt då fler inventeringar gjorts efter 2000. Därför har utvärderingen av arternas trender i första hand baserats på perioden 1998–2008. Utvecklingen är positiv för 14 arter medan sju arter visar en negativ utveckling. Skillnaden mellan artgrupperna är påtaglig. Änder, svanar och gäss ökar medan vadare i huvudsak uppvisar en negativ utveckling. Arter som ökar är silvertärna, skrattmås, sothöna, storskrake, vigg, grågås, gravand, knölsvan, skedand, snatterand, kricka, gräsand, större strandpipare och tofsvipa. Arter som minskar är ejder, kanadagås, strandskata, rödspov, ljungpipare, brushane och sydlig kärrsnäppa. Sett över hela perioden, 1988–2008, är förändringarna så stora att de med säkerhet kan utläsas för ytterligare några arter. Det är för havstrut och vitkindad gås som ökat medan silltrut, svärta, stjärtand, storspov och roskarl minskat. Arter som svärta, strandskata, sydlig kärrsnäppa, brushane, ljungpipare och rödspov ser ut att vara på väg att försvinna. Hävden på Ölands sjömarker har ökat under de senaste 20 åren. Relationen mellan hävden och antalet häckande vadare är svagt positiv och en stark hävd behöver inte betyda många vadare. Hävden är nödvändig i förvaltningen av av sjömarkerna men andra faktorer har förmodligen ett starkare inflytande på vadarnas populationsutveckling.
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| 8. |
- Öquist, Mats, et al.
(author)
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The full annual carbon balance of boreal forestsis highly sensitive to precipitation
- 2014
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In: Environmental Science and Technology Letters. - : American Chemical Society (ACS). - 2328-8930. ; 1:7, s. 315-319
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Journal article (peer-reviewed)abstract
- The boreal forest carbon balance is predicted to be particularly sensitive to climate change. Carbon balance estimates of these biomes stem mainly from eddy-covariance measurements of net ecosystem exchange (NEE). However, a full net ecosystem carbon balance (NECB) must include the lateral carbon export (LCE) through discharge. We show that annual LCE at a boreal forest site ranged from 4 to 28%, averaging 11% (standard deviation of 8%), of annual NEE over 13 years. Annual LCE and NEE are strongly anticorrelated; years with weak NEE coincide with high LCE. The decreased NEE in response to increased precipitation is caused by a reduction in the amount of incoming radiation caused by clouds. If our finding is also valid for other sites, it implies that increased precipitation at high latitudes may shift forest NECB in large areas of the boreal biome. Our results call for future analysis of this dual effect of precipitation on NEE and LCE.
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| 9. |
- Acosta, Cecilia M., et al.
(author)
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Effect of an Individualized Lung Protective Ventilation on Lung Strain and Stress in Children Undergoing Laparoscopy : An Observational Cohort Study
- 2024
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In: Anesthesiology. - : American Society of Anesthesiologists. - 0003-3022 .- 1528-1175. ; 140:3, s. 430-441
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Journal article (peer-reviewed)abstract
- Background: Exaggerated lung strain and stress could damage lungs in anesthetized children. The authors hypothesized that the association of capnoperitoneum and lung collapse in anesthetized children increases lung strain-stress. Their primary aim was to describe the impact of capnoperitoneum on lung strain-stress and the effects of an individualized protective ventilation during laparoscopic surgery in children.Methods: The authors performed an observational cohort study in healthy children aged 3 to 7 yr scheduled for laparoscopic surgery in a community hospital. All received standard protective ventilation with 5 cm H2O of positive end-expiratory pressure (PEEP). Children were evaluated before capnoperitoneum, during capnoperitoneum before and after lung recruitment and optimized PEEP (PEEP adjusted to get end-expiratory transpulmonary pressure of 0), and after capnoperitoneum with optimized PEEP. The presence of lung collapse was evaluated by lung ultrasound, positive Air-Test (oxygen saturation measured by pulse oximetry 96% or less breathing 21% O2 for 5 min), and negative end-expiratory transpulmonary pressure. Lung strain was calculated as tidal volume/end-expiratory lung volume measured by capnodynamics, and lung stress as the end-inspiratory transpulmonary pressure.Results: The authors studied 20 children. Before capnoperitoneum, mean lung strain was 0.20 ± 0.07 (95% CI, 0.17 to 0.23), and stress was 5.68 ± 2.83 (95% CI, 4.44 to 6.92) cm H2O. During capnoperitoneum, 18 patients presented lung collapse and strain (0.29 ± 0.13; 95% CI, 0.23 to 0.35; P < 0.001) and stress (5.92 ± 3.18; 95% CI, 4.53 to 7.31 cm H2O; P = 0.374) increased compared to before capnoperitoneum. During capnoperitoneum and optimized PEEP, children presenting lung collapse were recruited and optimized PEEP was 8.3 ± 2.2 (95% CI, 7.3 to 9.3) cm H2O. Strain returned to values before capnoperitoneum (0.20 ± 0.07; 95% CI, 0.17 to 0.22; P = 0.318), but lung stress increased (7.29 ± 2.67; 95% CI, 6.12 to 8.46 cm H2O; P = 0.020). After capnoperitoneum, strain decreased (0.18 ± 0.04; 95% CI, 0.16 to 0.20; P = 0.090), but stress remained higher (7.25 ± 3.01; 95% CI, 5.92 to 8.57 cm H2O; P = 0.024) compared to before capnoperitoneum.Conclusions: Capnoperitoneum increased lung strain in healthy children undergoing laparoscopy. Lung recruitment and optimized PEEP during capnoperitoneum decreased lung strain but slightly increased lung stress. This little rise in pulmonary stress was maintained within safe, lung-protective, and clinically acceptable limits.
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| 10. |
- Agerskov, Simon, et al.
(author)
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Absence of Disproportionately Enlarged Subarachnoid Space Hydrocephalus, a Sharp Callosal Angle, or Other Morphologic MRI Markers Should Not Be Used to Exclude Patients with Idiopathic Normal Pressure Hydrocephalus from Shunt Surgery
- 2019
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In: American Journal of Neuroradiology. - 0195-6108. ; 40:1, s. 74-79
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Journal article (peer-reviewed)abstract
- BACKGROUND AND PURPOSE: Several studies have evaluated the use of MR imaging markers for the prediction of outcome after shunt surgery in idiopathic normal pressure hydrocephalus with conflicting results. Our aim was to investigate the predictive value of a number of earlier proposed morphologic MR imaging markers in a large group of patients with idiopathic normal pressure hydrocephalus. MATERIALS AND METHODS: One hundred sixty-eight patients (mean age, 70 +/- 9.3 years) with idiopathic normal pressure hydrocephalus, subjected to standardized quantification of clinical symptoms before and after shunt surgery, were included in the study. Outcome was calculated using a composite score. Preoperative T1, FLAIR, and flow-sensitive images were analyzed regarding the presence of 13 different morphologic MR imaging markers. RESULTS: The median Evans index was 0.41 (interquartile range, 0.37-0.44). All patients had an aqueductal flow void sign present and white matter hyperintensities. The median callosal angle was 68.8 degrees (interquartile range, 57.7 degrees-80.8 degrees). Dilated Sylvian fissures were found in 69%; focally dilated sulci, in 25%; and widening of the interhemispheric fissure, in 55%. Obliteration of the sulci at the convexity was found in 36%, and 36% of patients were characterized as having disproportionately enlarged subarachnoid space hydrocephalus. Sixty-eight percent of patients improved after surgery. None of the investigated MR imaging markers were significant predictors of improvement after shunt surgery. CONCLUSIONS: Disproportionately enlarged subarachnoid space hydrocephalus, a small callosal angle, and the other MR imaging markers evaluated in this study should not be used to exclude patients from shunt surgery. These markers, though they may be indicative of idiopathic normal pressure hydrocephalus, do not seem to be a part of the mechanisms connected to the reversibility of the syndrome.
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