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Sökning: WFRF:(Kortelainen Pirkko)

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  • [1]2Nästa
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1.
  • Abbott, Benjamin W., et al. (författare)
  • Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire : an expert assessment
  • 2016
  • Ingår i: Environmental Research Letters. - : IOP Publishing: Open Access Journals / IOP Publishing. - 1748-9326 .- 1748-9326. ; 11:3
  • 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.
  • Algesten, Grete, et al. (författare)
  • Organic carbon budget for the Gulf of Bothnia
  • 2006
  • Ingår i: Journal of Marine Systems. - : Elsevier. - 0924-7963 .- 1879-1573. ; 63:3-4, s. 155-161
  • Tidskriftsartikel (refereegranskat)abstract
    • We calculated input of organic carbon to the unproductive, brackish water basin of the Gulf of Bothnia from rivers, point sources and the atmosphere. We also calculated the net exchange of organic carbon between the Gulf of Bothnia and the adjacent marine system, the Baltic Proper. We compared the input with sinks for organic carbon; permanent incorporation in sediments and mineralization and subsequent evasion of CO2 to the atmosphere. The major fluxes were riverine input (1500 Gg C year(-1)), exchange with the Baltic Proper (depending on which of several possible DOC concentration differences between the basins that was used in the calculation, the flux varied between an outflow of 466 and an input of 950 Gg C year(-1)), sediment burial (1100 Gg C year) and evasion to the atmosphere (3610 Gg C year(-1)). The largest single net flux was the emission of CO2 to the atmosphere, mainly caused by bacterial mineralization of organic carbon. Input and output did not match in our budget which we ascribe uncertainties in the calculation of the exchange of organic carbon between the Gulf of Bothnia and the Baltic Proper, and the fact that CO2 emission, which in our calculation represented 1 year (2002) may have been overestimated in comparison with long-term means. We conclude that net heterotrophy of the Gulf of Bothnia was due to input of organic carbon from both the catchment and from the Baltic Proper and that the future degree of net heterotrophy will be sensible to both catchment export of organic carbon and to the ongoing eutrophication of the Baltic Proper.
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3.
  • Algesten, Grete, 1974- (författare)
  • Regulation of carbon dioxide emission from Swedish boreal lakes and the Gulf of Bothnia
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The global carbon cycle is subject to intense research, where sources and sinks for greenhouse gases, carbon dioxide in particular, are estimated for various systems and biomes. Lakes have previously been neglected in carbon balance estimations, but have recently been recognized to be significant net sources of CO2. This thesis estimates emission of carbon dioxide (CO2) from boreal lakes and factors regulating the CO2 saturation from field measurements of CO2 concentration along with a number of chemical, biological and physical parameters. Concentration of dissolved organic carbon (DOC) was found to be the most important factor for CO2 saturation in lake water, whereas climatic parameters such as precipitation, temperature and global radiation were less influential. All lakes were supersaturated with and, thus, sources of CO2. Sediment incubation experiments indicated that in-lake mineralization processes during summer stratification mainly occurred in the pelagial. Approximately 10% of the CO2 emitted from the lake surface was produced in epilimnetic sediments. The mineralization of DOC and emission of CO2 from freshwaters was calculated on a catchment basis for almost 80,000 lakes and 21 major catchments in Sweden, together with rates of sedimentation in lakes and export of organic carbon to the sea. The total export of terrestrial organic carbon to freshwaters could thereby be estimated and consequently also the importance of lakes for the withdrawal of organic carbon export from terrestrial sources to the sea. Lakes removed 30-80% of imported terrestrial organic carbon, and mineralization and CO2 emission were much more important than sedimentation of carbon. The carbon loss was closely related to water retention time, where catchments with short residence times (<1 year) had low carbon retentions, whereas in catchments with long residence times (>3 years) a majority of the imported TOC was removed in the lake systems. The Gulf of Bothnia was also studied in this thesis and found to be a net heterotrophic system, emitting large amounts of CO2 to the atmosphere on an annual basis. The rate of CO2 emission was depending on the balance between primary production and bacterial respiration, and the system was oscillating between being a source and a sink of CO2.
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4.
  • Creed, Irena F., et al. (författare)
  • Global change-driven effects on dissolved organic matter composition : Implications for food webs of northern lakes
  • Ingår i: Global Change Biology. - : Wiley-Blackwell. - 1354-1013 .- 1365-2486. ; 24:8, s. 3692-3714
  • Tidskriftsartikel (refereegranskat)abstract
    • Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.
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5.
  • de Wit, Heleen A., et al. (författare)
  • Current Browning of Surface Waters Will Be Further Promoted by Wetter Climate
  • 2016
  • Ingår i: ; 3:12, s. 430-435
  • Tidskriftsartikel (refereegranskat)abstract
    • Browning of surface waters because of increasing terrestrial dissolved organic carbon (OC) concentrations is a concern for drinking water providers and can impact land carbon storage. We show that positive trends in OC in 474 streams, lakes, and rivers in boreal and subarctic ecosystems in Norway, Sweden, and Finland between 1990 and 2013 are surprisingly constant across climatic gradients and catchment sizes (median, +1.4% year(-1); interquartile range, +0.8-2.0% year(-1)), implying that water bodies across the entire landscape are browning. The largest trends (median, +1.7% year(-1)) were found in regions impacted by strong reductions in sulfur deposition, while subarctic regions showed the least browning (median, +0.8% year(-1)). In dry regions, precipitation was a strong and positive driver of OC concentrations, declining in strength moving toward high rainfall sites. We estimate that a 10% increase in precipitation will increase mobilization of OC from soils to freshwaters by at least 30%, demonstrating the importance of climate wetting for the carbon cycle. We conclude that upon future increases in precipitation, current browning trends will continue across the entire aquatic continuum, requiring expensive adaptations in drinking water plants, increasing land to sea export of carbon, and impacting aquatic productivity and greenhouse gas emissions.
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6.
  • Denfeld, Blaize, et al. (författare)
  • Regional Variability and Drivers of Below Ice CO2 in Boreal and Subarctic Lakes
  • 2016
  • Ingår i: ; 19:3, s. 461-476
  • Tidskriftsartikel (refereegranskat)abstract
    • Northern lakes are ice-covered for considerable portions of the year, where carbon dioxide (CO2) can accumulate below ice, subsequently leading to high CO2 emissions at ice-melt. Current knowledge on the regional control and variability of below ice partial pressure of carbon dioxide (pCO(2)) is lacking, creating a gap in our understanding of how ice cover dynamics affect the CO2 accumulation below ice and therefore CO2 emissions from inland waters during the ice-melt period. To narrow this gap, we identified the drivers of below ice pCO(2) variation across 506 Swedish and Finnish lakes using water chemistry, lake morphometry, catchment characteristics, lake position, and climate variables. We found that lake depth and trophic status were the most important variables explaining variations in below ice pCO(2) across the 506 lakes(.) Together, lake morphometry and water chemistry explained 53% of the site-to-site variation in below ice pCO(2). Regional climate (including ice cover duration) and latitude only explained 7% of the variation in below ice pCO(2). Thus, our results suggest that on a regional scale a shortening of the ice cover period on lakes may not directly affect the accumulation of CO2 below ice but rather indirectly through increased mobility of nutrients and carbon loading to lakes. Thus, given that climate-induced changes are most evident in northern ecosystems, adequately predicting the consequences of a changing climate on future CO2 emission estimates from northern lakes involves monitoring changes not only to ice cover but also to changes in the trophic status of lakes.
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7.
  • Humborg, Christoph (författare)
  • Environmental Impacts - Freshwater Biogeochemistry
  • 2015
  • Ingår i: Second Assessment of Climate Change for the Baltic Sea Basin. - : Springer. - 9783319160054 - 9783319160061 ; , s. 307-336
  • Bokkapitel (refereegranskat)abstract
    • Climate change effects on freshwater biogeochemistry and riverine loads of biogenic elements to the Baltic Sea are not straight forward and are difficult to distinguish from other human drivers such as atmospheric deposition, forest and wetland management, eutrophication and hydrological alterations. Eutrophication is by far the most well-known factor affecting the biogeochemistry of the receiving waters in the various sub-basins of the Baltic Sea. However, the present literature review reveals that climate change is a compounding factor for all major drivers of freshwater biogeochemistry discussed here, although evidence is still often based on short-term and/or small-scale studies.
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8.
  • Humborg, Christoph, et al. (författare)
  • Environmental Impacts—Freshwater Biogeochemistry
  • 2015
  • Ingår i: Second Assessment of Climate Change for the Baltic Sea Basin. - Cham : Springer. - 9783319160054 - 9783319160061 ; , s. 307-336
  • Bokkapitel (övrigt vetenskapligt)
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9.
  • Jantze, Elin, 1983- (författare)
  • Waterborne Carbon in Northern Streams : Controls on dissolved carbon transport across sub-arctic Scandinavia
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Waterborne carbon (C) forms an active and significant part of the global C cycle, which is important in theArctic where greater temperature increases and variability are anticipated relative to the rest of the globe withpotential implications for the C cycle. Understanding and quantification of the current processes governing themovement of C by connecting terrestrial and marine systems is necessary to better estimate future changes ofwaterborne C. This thesis investigates how the sub-arctic landscape influences the waterborne carbon exportby combining data-driven and modeling methods across spatial and temporal scales. First, a study of the stateof total organic carbon monitoring in northern Scandinavia was carried out using national-scale monitoringdata and detailed data from scientific literature. This study, which highlights the consistency in land cover andhydroclimatic controls on waterborne C across northern Scandinavia, was combined with three more detailedstudies leveraging field measurements and modeling. These focused on the Abisko region to provide insightto processes and mechanisms across scales. The thesis highlights that the governing transport mechanismsof dissolved organic and inorganic carbon (DOC and DIC respectively) are fundamentally different due todifferences in release rates associated with the nature of their terrestrial sources (geogenic and organic matterrespectively). As such, the DIC mass flux exhibits a high flow-dependence whereas DOC is relatively flowindependent.Furthermore, these investigations identified significant relationships between waterborne C andbiogeophysical as well as hydroclimatic variables across large to small spatial scales. This thesis demonstratesthat both surface and sub-surface hydrological processes (such as flow pathway distributions) in combinationwith distributions of C sources and associated release rates are prerequisite for understanding waterborne Cdynamics in northern streams.
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10.
  • Raymond, Peter A., et al. (författare)
  • Global carbon dioxide emissions from inland waters
  • 2013
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 503:7476, s. 355-359
  • Tidskriftsartikel (refereegranskat)abstract
    • Carbon dioxide (CO2) transfer from inland waters to the atmosphere, known as CO2 evasion, is a component of the global carbon cycle. Global estimates of CO2 evasion have been hampered, however, by the lack of a framework for estimating the inland water surface area and gas transfer velocity and by the absence of a global CO2 database. Here we report regional variations in global inland water surface area, dissolved CO2 and gas transfer velocity. We obtain global CO2 evasion rates of 1.8(-0.25)(+0.25) petagrams of carbon (Pg C) per year from streams and rivers and 0.32(-0.26)(+0.52) Pg C yr(-1) from lakes and reservoirs, where the upper and lower limits are respectively the 5th and 95th confidence interval percentiles. The resulting global evasion rate of 2.1 Pg C yr(-1) is higher than previous estimates owing to a larger stream and river evasion rate. Our analysis predicts global hotspots in stream and river evasion, with about 70 per cent of the flux occurring over just 20 per cent of the land surface. The source of inland water CO2 is still not known with certainty and new studies are needed to research the mechanisms controlling CO2 evasion globally.
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