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- 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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- 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. |
- Ameli, Ali A., et al.
(författare)
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Where and When to Collect Tracer Data to Diagnose Hillslope Permeability Architecture
- 2021
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 57:8
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Tidskriftsartikel (refereegranskat)abstract
- The permeability architecture has a major influence on hillslope flow path and hydrogeochemistry. To constrain this architecture and overcome equifinality in the diagnosis of hillslope flow paths within hydrologic transport models, different types of complementary data (e.g., tracer) have been recommended. However, there is still little information on the extent to which such complementary data can unravel the permeability architecture, and where and when to measure such data to most efficiently constrain models. Here, we couple a Richards-based flow and transport model with extensive long-term field measurements to compare the relative value of different types of hydrometric and tracer data in discriminating between contrasting permeability (or saturated hydraulic conductivity ()) architectures, in the absence of macropore flow. Our results show that compared to streamflow and water table observations, stream tracer data have a stronger evaluative potential to constrain hillslope vertical pattern in , in particular during seasons when flow is on average low (e.g., winter or summer). Tracer data from within the hillslope are even more helpful to discriminate between different vertical patterns in Ks than stream tracer data. This suggests a higher evaluative potential for hillslope tracer observations. This evaluative potential of hillslope data depends on where and when the data are collected, and increases with depth from the soil surface, with distance from the stream and during seasons when flow is low. The findings also emphasize the importance of incorporating hillslope permeability architecture in hydrologic transport models in order to reduce the uncertainty in the predictions of stream water quality.
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- Bolou-Bi, Bolou Emile, et al.
(författare)
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Use of stable Mg isotope ratios in identifying the base cation sources of stream water in the boreal Krycklan catchment (Sweden)
- 2022
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 588
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Tidskriftsartikel (refereegranskat)abstract
- The knowledge of the sources of base cations in stream water is a prerequisite to assess potential effects of changing environmental conditions such as changing rainfall, weathering or groundwater flows on cation export with stream water. This study use stable Mg isotopes to identify potential sources in the well-studied catchment of Krycklan located on gneissic bedrock covered by quaternary sediments in Sweden. Samples were collected from open filed rain, throughfall, stream, soil, rock and litterfall. The delta Mg-26 values of these samples was determined and the contributions of different sources to Mg fluxes in the stream were determined from the variation of the Mg isotope and Sr / Mg ratios. The results show an overall variation of 1.10 parts per thousand between all samples. In addition, Magnesium isotope ratios varied little in the streamwater and in soil solution, except during snowmelt periods during which a large portion of the annual runoff occurs. Magnesium in the streamwater is explained as a mixture of three pools (open field rain, soil solution and groundwater) with the latter two influenced by catchment processes. Outside the snow-melt period, Mg in streamwater mainly derived from the groundwater, assumed to be mineral weathering signature in this catchment, with a contribution ranging from 12 to 63% to Mg fluxes. Open field rain dominates Mg fluxes in streamwater during spring flood (0 to 78%) and may contribute significantly during larger summer and autumn rainfall events. Soil solution input to streamwater range from 16 to 59% of Mg fluxes in streamwater. Our results demonstrate that delta Mg-26 values together with Mg concentrations and Sr/Mg ratios can be used to constrain the Mg sources of stream water and quantify weathering release rates.
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- Buffam, Ishi, et al.
(författare)
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Influence of the Landscape Template on Chemical and Physical Habitat for Brown Trout Within a Boreal Stream Network
- 2021
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Ingår i: Frontiers in Water. - : Frontiers Media SA. - 2624-9375. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- We used the distribution of stream-dwelling brown trout (Salmo trutta) in a 67 km(2) boreal catchment to explore the importance of environmental organizing factors at a range of spatial scales, including whole-catchment characteristics derived from map data, and stream reach chemical and physical characteristics. Brown trout were not observed at any sites characterized by pH < 5.0 during the spring snowmelt episode, matching published toxicity thresholds. Brown trout distributions were patchy even in less acidic regions of the stream network, positively associated with glaciofluvial substrate and negatively associated with fine sand/silty sediments. A multivariate model including only whole-catchment characteristics explained 43% of the variation in brown trout densities, while models with local site physical habitat characteristics or local stream chemistry explained 33 and 25%, respectively. At the stream reach scale, physical habitat apparently played a primary role in organizing brown trout distributions in this stream network, with acidity placing an additional restriction by excluding brown trout from acidic headwater streams. Much of the strength of the catchment characteristics-fish association could be explained by the correlation of catchment-scale landscape characteristics with local stream chemistry and site physical characteristics. These results, consistent with the concept of multiple hierarchical environmental filters regulating the distribution of this fish species, underline the importance of considering a range of spatial scales and both physical and chemical environments when attempting to manage or restore streams for brown trout.
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