| 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. |
- Buffam, Ishi, et al.
(författare)
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Environmental drivers of seasonal variation in green roof runoff water quality
- 2016
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Ingår i: Ecological Engineering. - : Elsevier. - 0925-8574 .- 1872-6992. ; 91, s. 506-514
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Tidskriftsartikel (refereegranskat)abstract
- Green (vegetated) roofs provide many beneficial environmental services but can also pose a disservice by leaching nutrients and metals, via storm water runoff, to downstream aquatic ecosystems. Current estimates of water quality impacts rely on limited samples (snapshots in time) and may not accurately reflect the true influence of green roof ecosystems, which likely vary temporally as do natural ecosystems. Using a 46 m(2) green roof in Cincinnati, OH, we analyzed runoff from >80 events over two years for pH, conductivity, and concentrations of dissolved nutrients, base cations, and metals. We related the variation in water chemistry to environmental variables including air temperature, storm event magnitude, and estimated antecedent moisture. We observed strong seasonal patterns in bioactive elements, with carbon, nitrogen, phosphorus, and base cation concentrations highest in the summer, and positively correlated with temperature. This suggests temperature-mediated processes such as microbial mineralization of organic matter, desorption or weathering, rather than plant uptake or hydrologic variation among storms, are the major controlling mechanisms for runoff water quality in this newly constructed green roof. The large temporal variation in green roof effluent water quality supports the need for long-term studies to characterize the complexity of these engineered ecosystems and their responsiveness to environmental variation. (C) 2016 Elsevier B.V. All rights reserved.
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| 3. |
- Karlsen, Reinert Huseby, et al.
(författare)
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Landscape controls on spatiotemporal discharge variability in a boreal catchment
- 2016
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 52:8, s. 6541-6556
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Tidskriftsartikel (refereegranskat)abstract
- Improving the understanding of how stream flow dynamics are influenced by landscape characteristics, such as soils, vegetation and terrain, is a central endeavor of catchment hydrology. Here we investigate how spatial variability in stream flow is related to landscape characteristics using specific discharge time series from 14 partly nested subcatchments in the Krycklan basin (0.12 - 68 km(2)). Multivariate principal component analyses combined with univariate analyses showed that while variability in landscape characteristics and specific discharge were strongly related, the spatial patterns varied with season and wetness conditions. During spring snowmelt and at the annual scale, specific discharge was positively related to the sum of wetland and lake area. During summer, when flows are lowest, specific discharge was negatively related to catchment tree volume, but positively related to deeper sediment deposits and catchment area. The results indicate how more densely forested areas on till soils become relatively drier during summer months, while wet areas and deeper sediment soils maintain a higher summer base flow. Annual and seasonal differences in specific discharge can therefore be explained to a large extent by expected variability in evapotranspiration fluxes and snow accumulation. These analyses provide an organizing principle for how specific discharge varies spatially across the boreal landscape, and how this variation is manifested for different wetness conditions, seasons and time scales.
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| 4. |
- Solomon, Christopher T., et al.
(författare)
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Ecosystem Consequences of Changing Inputs of Terrestrial Dissolved Organic Matter to Lakes : Current Knowledge and Future Challenges
- 2015
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 18:3, s. 376-389
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Tidskriftsartikel (refereegranskat)abstract
- Lake ecosystems and the services that they provide to people are profoundly influenced by dissolved organic matter derived from terrestrial plant tissues. These terrestrial dissolved organic matter (tDOM) inputs to lakes have changed substantially in recent decades, and will likely continue to change. In this paper, we first briefly review the substantial literature describing tDOM effects on lakes and ongoing changes in tDOM inputs. We then identify and provide examples of four major challenges which limit predictions about the implications of tDOM change for lakes, as follows: First, it is currently difficult to forecast future tDOM inputs for particular lakes or lake regions. Second, tDOM influences ecosystems via complex, interacting, physical-chemical-biological effects and our holistic understanding of those effects is still rudimentary. Third, non-linearities and thresholds in relationships between tDOM inputs and ecosystem processes have not been well described. Fourth, much understanding of tDOM effects is built on comparative studies across space that may not capture likely responses through time. We conclude by identifying research approaches that may be important for overcoming those challenges in order to provide policy- and management-relevant predictions about the implications of changing tDOM inputs for lakes.
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| 5. |
- Temnerud, Johan, et al.
(författare)
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Map-based prediction of organic carbon in headwater streams improved by downstream observations from the river outlet
- 2016
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 13:2, s. 399-413
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Tidskriftsartikel (refereegranskat)abstract
- In spite of the great abundance and ecological importance of headwater streams, managers are usually limited by a lack of information about water chemistry in these headwaters. In this study we test whether river outlet chemistry can be used as an additional source of information to improve the prediction of the chemistry of upstream headwaters (size < 2 km(2)), relative to models based on map information alone. We use the concentration of total organic carbon (TOC), an important stream ecosystem parameter, as the target for our study. Between 2000 and 2008, we carried out 17 synoptic surveys in 9 mesoscale catchments (size 32-235 km(2)). Over 900 water samples were collected in total, primarily from headwater streams but also including each catchment's river outlet during every survey. First we used partial least square regression (PLS) to model the distribution (median, interquartile range (IQR)) of headwater stream TOC for a given catchment, based on a large number of candidate variables including sub-catchment characteristics from GIS, and measured river chemistry at the catchment outlet. The best candidate variables from the PLS models were then used in hierarchical linear mixed models (MM) to model TOC in individual headwater streams. Three predictor variables were consistently selected for the MM calibration sets: (1) proportion of forested wetlands in the sub-catchment (positively correlated with headwater stream TOC), (2) proportion of lake surface cover in the sub-catchment (negatively correlated with headwater stream TOC), and (3) river outlet TOC (positively correlated with headwater stream TOC). Including river outlet TOC improved predictions, with 5-15% lower prediction errors than when using map information alone. Thus, data on water chemistry measured at river outlets offer information which can complement GIS-based modelling of headwater stream chemistry.
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| 6. |
- Tiwari, Tejshree, et al.
(författare)
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Inferring scale-dependent processes influencing stream water biogeochemistry from headwater to sea
- 2017
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 62, s. S58-S70
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Tidskriftsartikel (refereegranskat)abstract
- Understanding how scale-dependent processes regulate patterns of water chemistry remains a challenge in aquatic biogeochemistry. This study evaluated how chemical properties of streams and rivers vary with drainage size and explored mechanisms that may underlie nonlinear changes with increasing scale. To do this, we contrasted concentrations of total organic carbon (TOC) with pH and cations (Ca and Mg) from 69 catchments in northern Sweden, spanning a size gradient from headwaters (<0.01 km(2)) to major rivers and estuaries (>100,000 km(2)). Across this gradient, we evaluated (1) changes in average concentrations and temporal variation, (2) scale breaks in catchment area-concentration relationships, and (3) the potential importance of groundwater inputs and instream processes as drivers of change. Results indicated that spatial and temporal signals converge at approximate to 2-10 km(2) as streams draining distinct headwater catchments coalesce and mix. Beyond 10 km(2), streams tended to lose headwater signatures, reflecting a transition from shallow to deep groundwater influence. This was accompanied by a second break at approximate to 70-500 km(2) corresponding to reduced spatial variability and a convergence of the response to snowmelt, as the dominance of deep groundwater influence increased with catchment scale. Larger catchments showed greater effect of instream processing on TOC, as concentrations predicted from the conservative mixing of upstream signals and dilution with deep groundwater were lower than measured. This study improves the understanding of scaling biogeochemical patterns and processes in stream networks, highlighting thresholds that imply shifts in the factors that shape variation in chemistry from headwaters to the sea.
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