| 1. |
- Abbott, Benjamin W., et al.
(författare)
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Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire : an expert assessment
- 2016
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 11:3
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Tidskriftsartikel (refereegranskat)abstract
- As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%-85% of permafrost carbon release can still be avoided if human emissions are actively reduced.
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| 2. |
- 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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| 3. |
- Ameli, A. A., et al.
(författare)
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Hillslope permeability architecture controls on subsurface transit time distribution and flow paths
- 2016
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Ingår i: Journal of Hydrology. - : Elsevier B.V.. - 0022-1694 .- 1879-2707. ; 543, s. 17-30
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Tidskriftsartikel (refereegranskat)abstract
- Defining the catchment transit time distribution remains a challenge. Here, we used a new semi-analytical physically-based integrated subsurface flow and advective–dispersive particle movement model to assess the subsurface controls on subsurface water flow paths and transit time distributions. First, we tested the efficacy of the new model for simulation of the observed groundwater dynamics at the well-studied S-transect hillslope (Västrabäcken sub-catchment, Sweden). This system, like many others, is characterized by exponential decline in saturated hydraulic conductivity and porosity with soil depth. The model performed well relative to a tracer-based estimate of transit time distribution as well as observed groundwater depth–discharge relationship within 30 m of the stream. Second, we used the model to assess the effect of changes in the subsurface permeability architecture on flow pathlines and transit time distribution in a set of virtual experiments. Vertical patterns of saturated hydraulic conductivity and porosity with soil depth significantly influenced hillslope transit time distribution. Increasing infiltration rates significantly decreased mean groundwater age, but not the distribution of transit times relative to mean groundwater age. The location of hillslope hydrologic boundaries, including the groundwater divide and no-flow boundary underlying the hillslope, changed the transit time distribution less markedly. These results can guide future decisions on the degree of complexity that is warranted in a physically-based rainfall–runoff model to efficiently and explicitly estimate time invariant subsurface pathlines and transit time distribution.
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| 4. |
- Audet, Joachim, et al.
(författare)
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Nitrous oxide emissions from streams in a Swedish agricultural catchment
- 2017
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Ingår i: Agriculture, Ecosystems & Environment. - : Elsevier BV. - 0167-8809 .- 1873-2305. ; 236, s. 295-303
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Tidskriftsartikel (refereegranskat)abstract
- Excess nitrogen fertiliser in agricultural soils might be leached to streams and converted to the greenhouse gas nitrous oxide (N2O). To assess the importance of N2O emissions from agricultural streams, concentration dynamics and emissions N2O emissions in streams were investigated in a 32 km2 lowland agricultural catchment located in Sweden. Dissolved N2O concentration was measured at nine occasions between December 2014 and August 2015 at nine stream stations. The stream stations represented sub-catchments with different land use characteristics with agricultural land use ranging from 0 to 63% of the area. Stream N2O percentage saturation ranged 40-2701% and showed large spatial and temporal variations. Statistical analysis using mixed models revealed that N2O concentration was significantly linked to nitrate concentration in the stream water, to the percentage arable land in the sub catchments as well as to the stream water discharge. Using two empirical equations to estimate the N2O emissions showed that streams were generally a source of N2O to the atmosphere (mean 108 and 175 mu g N m(-2) h(-1) with first and second equation). The catchment scale estimate of N2O stream emissions was compared to the estimate obtained using IPCC guidelines linking N fertilisation inputs and leaching to N2O emissions. The comparison suggested that N2O stream emission calculated using the IPCC methodology might be underestimated. A coarse estimate suggests that N2O stream emissions represent about 4% of the total N2O emissions from N-fertiliser at the catchment scale. Hence while streams covered only 0.1% of the catchment area they were of disproportionate importance as a source of N2O to the atmosphere.
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| 5. |
- Bergman, Inger, et al.
(författare)
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The influence of sulphate deposition on the seasonal variation of peat pore water methyl Hg in a boreal mire
- 2012
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:9, s. e45547-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we investigate the hypothesis that long-term sulphate (SO42-) deposition has made peatlands a larger source of methyl mercury (MeHg) to remote boreal lakes. This was done on experimental plots at a boreal, low sedge mire where the effect of long-term addition of SO42- on peat pore water MeHg concentrations was observed weekly throughout the snow-free portion of 1999. The additions of SO42- started in 1995. The seasonal mean of the pore water MeHg concentrations on the plots with 17 kg ha(-1) yr(-1) of sulphur (S) addition (1.3 +/- 0.08 ng L-1, SE; n=44) was significantly (p<0.0001) higher than the mean MeHg concentration on the plots with 3 kg ha(-1) yr(-1) of ambient S deposition (0.6 +/- 0.02 ng L-1, SE; n=44). The temporal variation in pore water MeHg concentrations during the snow free season was larger in the S-addition plots, with an amplitude of >2 ng L-1 compared to +/-0.5 ng L-1 in the ambient S deposition plots. The concentrations of pore water MeHg in the S-addition plots were positively correlated (r(2)=0.21; p=0.001) to the groundwater level, with the lowest concentrations of MeHg during the period with the lowest groundwater levels. The pore water MeHg concentrations were not correlated to total Hg, DOC concentration or pH. The results from this study indicate that the persistently higher pore water concentrations of MeHg in the S-addition plots are caused by the long-term additions of SO42- to the mire surface. Since these waters are an important source of runoff, the results support the hypothesis that SO42- deposition has increased the contribution of peatlands to MeHg in downstream aquatic systems. This would mean that the increased deposition of SO42- in acid rain has contributed to the modern increase in the MeHg burdens of remote lakes hydrologically connected to peatlands.
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| 6. |
- Bishop, Kevin, et al.
(författare)
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Boundary-Crossing Field Research Marks the Way to Evidence-Based Management of Mercury in Forest Landscapes
- 2022
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Ingår i: Journal of Geophysical Research: Biogeosciences. - 2169-8953 .- 2169-8961. ; 127
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Tidskriftsartikel (refereegranskat)abstract
- The atmospheric deposition of long-range atmospheric mercury pollution presents forest managers with a "wicked" problem-forestry operations run the risk of mobilizing this pollution legacy. Management of that risk would benefit from a process-based understanding of how forest management influences the mercury cycle. This commentary highlights the value for building such an understanding of a comprehensive Before-After-Control-Impact study reported by McCarter et al. (2022), on the Marcel Experimental Forest in the north-central continental US. That study looked at how different types of forest harvest influenced the movement of mercury through the landscape. The results of this study place it at the minimal end of the range of impacts on Hg mobilization resulting from forest harvest. What makes this paper, together with the companion papers resulting from this study, particularly valuable for improving the understanding of forestry influences on mercury is the number of system boundaries that the study crossed: between land and atmosphere, from a forested hillslope down into a wetland, and finally up into the biota on that wetland.Plain Language Summary Forest harvest can mobilize toxic mercury from forest soils and move it into living organisms. This mercury originated in air pollution created far away from the forest, but forest managers still need to deal with the risks of this "pollution legacy" to people, fish and wildlife. A recent study in the north-central US took a detailed look at how two different types of forest harvest mobilized mercury in the soil. This study showed a relatively small impact of the forest harvest on mercury relative to some other studies. Since previous studies have found a wide range of mercury responses to forest harvest, this carefully designed and executed study has value in adding to the evidence base about forest management impacts on mercury in the environment. What is particularly valuable about this study is its comprehensiveness, since it crosses a number of environmental system boundaries: between the forest and the atmosphere, from upslope mineral soils into a downslope peatland, and from the wetland environment into the biota.
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| 7. |
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| 8. |
- Bishop, Kevin
(författare)
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Forest water-use efficiency: Effects of climate change and management on the coupling of carbon and water processes
- 2023
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 534
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Forskningsöversikt (refereegranskat)abstract
- Forests are essential in regulating global carbon and water cycles and are critical in mitigating climate change. Water-use efficiency, defined by the ratio of plant productivity per unit water use, is widely used to quantify the interactions between forest carbon and water cycles and could be potentially used to manage the carbon and water tradeoffs of forests under different environmental conditions. This paper reviews the literature on how biophysical variables and management practices affect forest water-use efficiency. We found that water-use ef-ficiency varies greatly with forest type, species, age, environmental conditions, and forest management practices. Climatic stresses (e.g., drought and heatwave) often pose negative effects on forest instantaneous water-use ef-ficiency (WUEins), particularly over a short term. Unexpectedly, plantations and natural forests have no statistical differences in WUEins. In addition, WUEins can be effectively improved by forest thinning. These results have important implications for managing the tradeoffs between carbon sequestration and water yield of forests. Finally, four important knowledge gaps, including species-specific water-use efficiency, long-term forest water -use efficiency dynamics, water-use efficiency responses to forest management, and the integrated effects of human and natural disturbances on plantation water-use efficiency are identified and discussed.
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| 9. |
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| 10. |
- Bishop, Kevin
(författare)
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Managing Forests and Water for People under a Changing Environment
- 2020
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Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- The Earth has entered the Anthropocene epoch and forest managers are facing unprecedented challenges to meet multiple ecosystem service demands from forests. Understanding the complex forest-water relations under a changing environment must add a human dimension, and this is essential in the move towards sustainable forest management in the 21st century. This Special Issue contains 10 papers presented at a joint international forest and water conference in Chile in 2018. These studies provide global examples on new advancements in sciences in forest ecohydrology, watershed management, and ecosystem service assessment under various geographical and socioeconomic settings.
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