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  • 1.
    Abbott, Benjamin
    et al.
    Univ Rennes 1, OSUR, CNRS, ECOBIO,UMR 6553, Rennes, France.
    Baranov, Viktor
    Leibniz Inst Freshwater Ecol & Inland Fisheries, Berlin, Germany.
    Mendoza-Lera, Clara
    Ctr LyonVilleurbanne, UR MALY, Irstea, F-69616 Villeurbanne, France.
    Nikolakopoulou, Myrto
    Naturalea, Barcelona, Spain.
    Harjung, Astrid
    Univ Barcelona, E-08007 Barcelona, Spain.
    Kolbe, Tamara
    Univ Rennes 1, CNRS, OSURGeosci Rennes, UMR 6118, F-35014 Rennes, France.
    Balasubramanian, Mukundh
    BioSistemika Ltd, Ljubljana, Slovenia.
    Vaessen, Timothy N
    CEAB CSIC, Girona, Spain.
    Ciocca, Francesco
    Silixa, Elstree, England.
    Campeau, Audrey
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Romeijn, Paul
    Univ Birmingham, Sch Geog Earth & Environm Sci, Birmingham B15 2TT, W Midlands, England.
    Antonelli, Marta
    LIST, Esch Sur Alzette, Luxembourg.
    Goncalves, José
    Natl Inst Biol, Ljubljana, Slovenia.
    Datry, Thibault
    Ctr LyonVilleurbanne, UR MALY, Irstea, F-69616 Villeurbanne, France.
    Laverman, Anniet
    Univ Rennes 1, OSUR, CNRS, ECOBIO,UMR 6553, Rennes, France.
    de Dreuzý, Jean-Raynald
    Univ Rennes 1, CNRS, OSURGeosci Rennes, UMR 6118, F-35014 Rennes, France.
    David, Hannah M.
    Univ Birmingham, Sch Geog Earth & Environm Sci, Birmingham B15 2TT, W Midlands, England.
    Krause, Stefan
    Univ Birmingham, Sch Geog Earth & Environm Sci, Birmingham B15 2TT, W Midlands, England.
    Oldham, Carolyn
    Univ Western Australia, Civil Environm & Min Engn, Perth, WA, Australia.
    Pinay, Gilles
    Univ Rennes 1, OSUR, CNRS, ECOBIO,UMR 6553, Rennes, France.
    Using multi-tracer inference to move beyond single-catchment ecohydrology2016In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 160, p. 19-42Article in journal (Refereed)
    Abstract [en]

    Protecting or restoring aquatic ecosystems in the face of growing anthropogenic pressures requires an understanding of hydrological and biogeochemical functioning across multiple spatial and temporal scales. Recent technological and methodological advances have vastly increased the number and diversity of hydrological, biogeochemical, and ecological tracers available, providing potentially powerful tools to improve understanding of fundamental problems in ecohydrology, notably: 1. Identifying spatially explicit flowpaths, 2. Quantifying water residence time, and 3. Quantifying and localizing biogeochemical transformation. In this review, we synthesize the history of hydrological and biogeochemical theory, summarize modem tracer methods, and discuss how improved understanding of flowpath, residence time, and biogeochemical transformation can help ecohydrology move beyond description of site-specific heterogeneity. We focus on using multiple tracers with contrasting characteristics (crossing proxies) to infer ecosystem functioning across multiple scales. Specifically, we present how crossed proxies could test recent ecohydrological theory, combining the concepts of hotspots and hot moments with the Damkohler number in what we call the HotDam framework.

  • 2.
    Audet, Joachim
    et al.
    Swedish Univ Agr Sci, Dept Aquat Sci & Assessment, POB 7050, S-75007 Uppsala, Sweden.
    Wallin, Marcus B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Kyllmar, Katarina
    Swedish Univ Agr Sci, Dept Soil & Environm, POB 7014, S-75007 Uppsala, Sweden.
    Andersson, Stefan
    Swedish Univ Agr Sci, Dept Soil & Environm, POB 7014, S-75007 Uppsala, Sweden.
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Swedish Univ Agr Sci, Dept Aquat Sci & Assessment, POB 7050, S-75007 Uppsala, Sweden.
    Nitrous oxide emissions from streams in a Swedish agricultural catchment2017In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 236, p. 295-303Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Campeau, Audrey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bishop, Kevin
    Swedish Univ Agr Sci, Dept Aquat Sci & Assessment, Lennart Hjelms Vag 9, S-75651 Uppsala, Sweden.
    Amvrosiadi, Nino
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Billett, Mike
    Garnett, Mark
    Laudon, Hjalmar
    Öquist, Mats
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Current forest carbon fixation fuels stream CO2 emissions2019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 1876Article in journal (Refereed)
    Abstract [en]

    Stream CO2 emissions contribute significantly to atmospheric climate forcing. While there are strong indications that groundwater inputs sustain these emissions, the specific biogeochemical pathways and timescales involved in this lateral CO2 export are still obscure. Here, via an extensive radiocarbon (C-14) characterisation of CO2 and DOC in stream water and its groundwater sources in an old-growth boreal forest, we demonstrate that the C-14-CO2 is consistently in tune with the current atmospheric C-14-CO2 level and shows little association with the C-14-DOC in the same waters. Our findings thus indicate that stream CO2 emissions act as a shortcut that returns CO2 recently fixed by the forest vegetation to the atmosphere. Our results expose a positive feedback mechanism within the C budget of forested catchments, where stream CO2 emissions will be highly sensitive to changes in forest C allocation patterns associated with climate and land-use changes.

  • 4.
    Campeau, Audrey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bishop, Kevin
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Billett, Michael
    Biological and Environmental Sciences, Faculty of Natural Sciences, University of Stirling, Stirling, UK.
    Garnett, Mark
    NERC Radiocarbon Facility, Scottish Enterprise Technology Park, East Kilbride, Glasgow, UK.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Leach, Jason
    Department of Geography, Simon Fraser University, Burnaby, BC, Canada.
    Nilsson, Mats
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Öquist, Mats
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen: Implications for peat carbon stock stability2017In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 12, p. 5523-5536Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Campeau, Audrey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bishop, Kevin
    Nilsson, Mats
    Klemedtsson, Leif
    Laudon, Hjalmar
    Leith, Fraser
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Öquist, Mats
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Stable carbon isotopes reveal soil - stream DIC linkages in contrasting headwater catchments2018In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 123, no 1, p. 149-167Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Campeau, Audrey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Giesler, Reiner
    Climate Impacts Research Centre, Department of Ecology and Environmental Science, Umeå University, Abisko, Sweden.
    Löfgren, Stefan
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Mörth, Carl-Magnus
    Geology and Geochemistry, Stockholm University, Stockholm, Sweden.
    Schiff, Sherry
    Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada.
    Venkiteswaran, Jason
    Department of Geography and Environmental Studies, Wilfrid Laurier University, Waterloo, Ontario, Canada.
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Multiple sources and sinks of dissolved inorganic carbon across Swedish streams, refocusing the lens of stable C isotopes2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 9158Article in journal (Refereed)
    Abstract [en]

    It is well established that stream dissolved inorganic carbon (DIC) fluxes play a central role in the global C cycle, yet the sources of stream DIC remain to a large extent unresolved. Here, we explore large-scale patterns in delta C-13-DIC from streams across Sweden to separate and further quantify the sources and sinks of stream DIC. We found that stream DIC is governed by a variety of sources and sinks including biogenic and geogenic sources, CO2 evasion, as well as in-stream processes. Although soil respiration was the main source of DIC across all streams, a geogenic DIC influence was identified in the northernmost region. All streams were affected by various degrees of atmospheric CO2 evasion, but residual variance in delta C-13-DIC also indicated a significant influence of in-stream metabolism and anaerobic processes. Due to those multiple sources and sinks, we emphasize that simply quantifying aquatic DIC fluxes will not be sufficient to characterise their role in the global C cycle.

  • 7.
    Chmiel, Hannah Elisa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kokic, Jovana
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Denfeld, Blaize Amber
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Einarsdóttir, Karólina
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Köhler, Birgit
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Isidorova, Anastasija
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Bastviken, David
    Linköping University.
    Ferland, Marie-Ève
    Université du Québec à Montréal, Québec, Canada.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    The role of sediments in the carbon budget of a small boreal lake2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, no 5, p. 1814-1825Article in journal (Refereed)
    Abstract [en]

    We investigated the role of lake sediments as carbon (C) source and sink in the annual C budget of a small (0.07 km2), shallow (mean depth 3.4 m), and humic lake (mean DOC concentration 17 mg L-1) in boreal Sweden. Organic carbon (OC) burial and mineralization in sediments were quantified from 210Pb-dated sediment and laboratory sediment incubation experiments, respectively, and upscaled to the entire basin and to one whole year, by using sediment thickness derived sub-bottom profiling, basin morphometry, and water column monitoring data of temperature and oxygen concentration. Furthermore, catchment C import, open water metabolism, photochemical mineralization as well as carbon dioxide (CO2) and methane (CH4) emissions to the atmosphere, were quantified to relate sediment processes to other lake C fluxes. We found that on a whole-basin and annual scale, sediment OC mineralization was three times larger than OC burial, and contributed about 16% to the annual CO2 emission from the lake to the atmosphere. Remaining contributions to the CO2 emission were attributed to water column metabolism (31%), photochemical mineralization (6%), and catchment imports via inlet streams and inflow of shallow groundwater (47%). We conclude that on an annual and whole-basin scale 1) sediment OC mineralization dominated over OC burial, 2) water column OC mineralization contributed more than sediments to lake CO2 emission, and 3) catchment import of C to the lake was greater than lake-internal C cycling. 

  • 8.
    Denfeld, Blaize A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus B.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sahlée, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kokic, Jovana
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Chmiel, Hannah E.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Temporal and spatial carbon dioxide concentration patterns in a small boreal lake in relation to ice cover dynamics2015In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 20, no 6, p. 679-692Article in journal (Refereed)
    Abstract [en]

    Global carbon dioxide (CO2) emission estimates from inland waters commonly neglect the ice-cover season. To account for CO2 accumulation below ice and consequent emissions into the atmosphere at ice-melt we combined automatically-monitored and manually- sampled spatially-distributed CO2 concentration measurements from a small boreal ice-covered lake in Sweden. In early winter, CO2 accumulated continuously below ice, whereas, in late winter, CO2 concentrations remained rather constant. At ice-melt, two CO2 concentration peaks were recorded, the first one reflecting lateral CO2 transport within the upper water column, and the second one reflecting vertical CO2 transport from bottom waters. We estimated that 66%–85% of the total CO2 accumulated in the water below ice left the lake at ice-melt, while the remainder was stored in bottom waters. Our results imply that CO2 accumulation under ice and emissions at ice-melt are more dynamic than previously reported, and thus need to be more accurately integrated into annual CO2 emission estimates from inland waters.

  • 9.
    Dinsmore, Kerry
    et al.
    Centre for Ecology and Hydrology.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Johnson, Mark
    University of British Columbia.
    Billett, Michael
    Centre for Ecology and Hydrology.
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pumpanen, Jukka
    University of Helsinki.
    Ojala, Anne
    University of Helsinki.
    Contrasting CO2 concentration discharge dynamics in headwater streams: a multi-catchment comparison2013In: Journal of Geophysical Research-Biogeosciences, ISSN 2169-8953, Vol. 118, no 2, p. 445-461Article in journal (Refereed)
    Abstract [en]

    Aquatic CO2 concentrations are highly variable and strongly linked to discharge, but until recently, measurements have been largely restricted to low-frequency manual sampling. Using new in situ CO2 sensors, we present concurrent, high-frequency (<30 min resolution) CO2 concentration and discharge data collected from five catchments across Canada, UK, and Fennoscandinavia to explore concentration-discharge dynamics; we also consider the relative importance of high flows to lateral aquatic CO2 export. The catchments encompassed a wide range of mean CO2 concentrations (0.73–3.05 mg C L−1) and hydrological flow regimes from flashy peatland streams to muted outflows within a Finnish lake system. In three of the catchments, CO2 concentrations displayed clear bimodal distributions indicating distinct CO2 sources. Concentration-discharge relationships were not consistent across sites with three of the catchments displaying a negative relationship and two catchments displaying a positive relationship. When individual high flow events were considered, we found a strong correlation between both the average magnitude of the hydrological and CO2 response peaks, and the average response lag times. An analysis of lateral CO2 export showed that in three of the catchments, the top 30% of flow (i.e., flow that was exceeded only 30% of the time) had the greatest influence on total annual load. This indicates that an increase in precipitation extremes (greater high-flow contributions) may have a greater influence on the flushing of CO2 from soils to surface waters than a long-term increase in mean annual precipitation, assuming source limitation does not occur.

  • 10. Dinsmore, Kerry
    et al.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Johnson, Mark
    Billett, Michael
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pumpanen, Jukka
    Ojala, Anne
    Research Spotlight  (E. Balcerak): Examining CO2 concentrations and flow dynamics in streams2013Other (Other (popular science, discussion, etc.))
  • 11.
    Einarsdóttir, Karólina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    High terrestrial carbon load via groundwater to a boreal lake dominated by surface water inflow2017In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122, no 1, p. 15-29Article in journal (Refereed)
    Abstract [en]

    The input of dissolved organic and inorganic carbon (DOC and DIC) via direct groundwater seepage to boreal lakes is often assumed to be small in noncarbonaceous areas. However, measurements are rare. We estimated the terrestrial load of DOC, DIC, and methane (CH4) to a small boreal lake for the open water period, on the basis of measured concentrations of carbon species in near-shore groundwater wells and inlet streams, and measured area-specific discharge. The subcatchment directly draining into the lake via groundwater seepage contributed 18% to the total water input during the open water season. Compared to stream and lake water, near-shore groundwater concentrations of DOC were slightly elevated, and groundwater DIC and CH4concentrations were highly elevated. Consequently, direct groundwater seepage contributed 27% to the total DOC load, 64% to the total DIC load, and 96% to the total CH4 load from the catchment to the lake. Groundwater DIC import corresponded only to 5–8% of lake carbon dioxide (CO2) emission. In incubation experiments, we observed higher photochemical DOC loss rates in stream and groundwater samples (18–55% DOC loss upon 72 h UV-A exposure) than in lake water (15% DOC loss) and detected significant DOC flocculation in groundwater samples in both light and dark incubations (2–24% DOC loss). We conclude that even in regions where lake hydrology is dominated by surface water inflow via inlet streams, direct groundwater seepage can represent an important carbon source to boreal lakes, and groundwater DOC may be susceptible to in-lake removal via degradation and flocculation.

  • 12.
    Guinea Barrientos, Héctor Estuardo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Swain, Ashok
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Uppsala Centre for Sustainable Development, CSD Uppsala.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Nyberg, Lars
    Disaster Management Cooperation in Central America: The Case of Rainfall-induced Natural Disasters2015In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 97, no 1, p. 85-96Article in journal (Refereed)
    Abstract [en]

    Rainfall-induced natural disasters rank first among all natural disasters in Central America. Due to the geographical conditions of the Central American region, it is common that two or more countries are struck by the same rainfall event, for example Hurricane Mitch in 1998 affected the entire Central American region, killing more than 18 000 people. As a consequence, Central American countries have started to promote regional policies and programs that aim for better preparation and response to these events, including disaster management cooperation. However, cooperation poses several challenges that may hinder its goals. In order to analyse these challenges, we present analysis in this paper of the current policy and legal institutions as well as the main challenges that may hinder international disaster management cooperation in Central America.

  • 13.
    Hawkes, Jeffrey A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Radoman, Nikola
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry. Stockholm Univ, Dept Environm Sci & Analyt Chem, Stockholm, Sweden.
    Bergquist, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Löfgren, Stefan
    Swedish Univ Agr Sci SLU, Dept Aquat Sci & Assessment, Sect Geochem & Hydrol, Uppsala, Sweden.
    Regional diversity of complex dissolved organic matter across forested hemiboreal headwater streams2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, no 1, article id 16060Article in journal (Refereed)
    Abstract [en]

    Dissolved organic matter (DOM) from soils enters the aquatic environment via headwater streams. Thereafter, it is gradually transformed, removed by sedimentation, and mineralised. Due to the proximity to the terrestrial source and short water residence time, the extent of transformation is minimal in headwaters. DOM has variable composition across inland waters, but the amount of variability in the terrestrial end member is unknown. This gap in knowledge is crucial considering the potential impact large variability would have on modelling DOM degradation. Here, we used a novel liquid chromatography –mass spectrometry method to characterise DOM in 74 randomly selected, forested headwater streams in an 87,000 km2 region of southeast Sweden. We found a large degree of sample similarity across this region, with Bray-Curtis dissimilarity values averaging 8.4 ± 3.0% (mean ± SD). The identified variability could be reduced to two principle coordinates, correlating to varying groundwater flow-paths and regional mean temperature. Our results indicate that despite reproducible effects of groundwater geochemistry and climate, the composition of DOM is remarkably similar across catchments already as it leaves the terrestrial environment, rather than becoming homogeneous as different headwaters and sub-catchments mix.

  • 14. Johnson, Mark S.
    et al.
    Billett, Michael F.
    Dinsmore, Kerry J.
    Wallin, Marcus
    Dyson, Kirstie E.
    Jassal, Rachhpal S.
    Direct and continuous measurements of dissolved carbon dioxide in freshwater aquatic systems: method and applications2010In: Ecohydrology, ISSN 1936-0584, E-ISSN 1936-0592, Vol. 3, no 1, p. 68-78Article in journal (Refereed)
    Abstract [en]

    Understanding of the processes that control CO2 concentrations in the aquatic environment has been hampered by the absence of a direct method to make continuous measurements over both short- and long-term time intervals. We describe an in situ method in which a non-dispersive infrared (NDIR) sensor is enclosed in a water impermeable, gas permeable polytetrafluoroethylene (PTFE) membrane and deployed in a freshwater environment. This allows measurements of CO2 concentration to be made directly at a specific depth in the water column without the need for pumps or reagents. We demonstrate the potential of the method using examples from different aquatic environments characterized by a range of CO2 concentrations (0·5–8·0 mg CO2-C l−1, equivalent to ca 40–650 µmol CO2 l−1). These comprise streams and ponds from tropical, temperate and boreal regions. Data derived from the sensor was compared with direct measurements of CO2 concentrations using headspace analysis. Sensor performance following long-term (>6 months) field deployment conformed to manufacturers' specifications, with no drift detected. We conclude that the sensor-based method is a robust, accurate and responsive method, with a wide range of potential applications, particularly when combined with other in situ sensor-based measurements of related variables.

  • 15.
    Kokic, Jovana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sahlée, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Vachon, Dominic
    Umeå Univ, Dept Ecol & Environm Sci, Umeå, Sweden.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    High spatial variability of gas transfer velocity in streams revealed by turbulence measurements2018In: INLAND WATERS, ISSN 2044-2041, E-ISSN 2044-205X, Vol. 8, no 4, p. 461-473Article in journal (Refereed)
    Abstract [en]

    Streams are major sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere, but current large-scale estimates are associated with high uncertainties because knowledge concerning the spatiotemporal control on stream emissions is limited. One of the largest uncertainties derives from the choice of gas transfer velocity (k600), which describes the physical efficiency of gas exchange across the water–atmosphere interface. This study therefore explored the variability in k600 and subsequent CO2 and CH4 emission rates within and across streams of different stream order (SO). We conducted, for the first time in streams, direct turbulence measurements using an acoustic Doppler velocimeter (ADV) to determine the spatial variability in k600 across a variety of scales with a consistent methodology. The results show high spatial variability in k600 and corresponding CO2 and CH4 emissions at small spatial scales, both within stream reaches and across SO, especially during high discharge. The k600 was positively related to current velocity and Reynolds number. By contrast, no clear relationship was found between k600 and specific stream characteristics such as width and depth, which are parameters often used in empirical models of k600. Improved understanding of the small-scale variability in the physical properties along streams, especially during high discharge, is therefore an important step to reduce the uncertainty in existing gas transfer models and emissions for stream systems. The ADV method was a useful tool for revealing spatial variability in this work, but it needs further development. We recommend that future studies conduct measurements over shorter time periods (e.g., 10–15 min instead of 40 min) and at more sites across the reach of interest, and thereby derive more reliable mean-reach k600 as well as more information about controls on the spatial variability in k600

  • 16.
    Kokic, Jovana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Chmiel, Hannah
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Denfeld, Blaize
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Carbon dioxide evasion from headwater systems strongly contributes to the total export of carbon from a small boreal lake catchment2015In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 1, p. 13-28Article in journal (Refereed)
    Abstract [en]

    Inland waters are hotspots for carbon (C) cycling and therefore important for landscape C budgets. Small streams and lakes are particularly important; however, quantifying C fluxes is difficult and has rarely been done for the entire aquatic continuum, composed of connected streams and lakes within the same catchment. We investigated carbon dioxide (CO2) evasion and fluvial fluxes of dissolved inorganic carbon and dissolved organic carbon (DIC and DOC) in stream and lake systems within the 2.3km(2) catchment of a small boreal lake. Our results show pronounced spatial and temporal variability in C fluxes even at a small spatial scale. C loss from the catchment through CO2 evasion from headwaters for the total open water-sampling period was 9.7g C m(-2) catchment, dominating the total catchment C loss (including CO2 evasion, DIC, and DOC export from the lake, which were 2.7, 0.2, and 5.2g C m(-2) catchment, respectively). Aquatic CO2 evasion was dominated by headwater streams that occupy similar to 0.1% of the catchment but contributed 65% to the total aquatic CO2 evasion from the catchment. The importance of streams was mainly an effect of the higher gas transfer velocities than compared to lakes (median, 67 and 2.2cmh(-1), respectively). Accurately estimating the contribution of C fluxes from headwater streams, particularly the temporal and spatial dynamics in their gas transfer velocity, is key to landscape-scale C budgets. This study demonstrates that CO2 evasion from headwaters can be the major pathway of C loss from boreal catchments, even at a small spatial scale.

  • 17.
    Leach, Jason
    et al.
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, Umea, Sweden.
    Larsson, Anna
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, Umea, Sweden.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Nilsson, Mats
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, Umea, Sweden.
    Laudon, Hjalmar
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, Umea, Sweden.
    Twelve-year interannual and seasonal variability of stream carbon export from a boreal peatland catchment2016In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 7, p. 1851-1866Article in journal (Refereed)
    Abstract [en]

    Understanding stream carbon export dynamics is needed to accurately predict how the carbon balance of peatland catchments will respond to climatic and environmental change. We used a 12year record (2003-2014) of continuous streamflow and manual spot measurements of total organic carbon (TOC), dissolved inorganic carbon (DIC), methane (CH4), and organic carbon quality (carbon-specific ultraviolet absorbance at 254nm per dissolved organic carbon) to assess interannual and seasonal variability in stream carbon export for a peatland catchment (70% mire and 30% forest cover) in northern Sweden. Mean annual total carbon export for the 12year period was 12.2 gCm(-2) yr(-1), but individual years ranged between 6 and 18 gCm(-2) yr(-1). TOC, which was primarily composed of dissolved organic carbon (>99%), was the dominant form of carbon being exported, comprising 63% to 79% of total annual exports, and DIC contributed between 19% and 33%. CH4 made up less than 5% of total export. When compared to previously published annual net ecosystem exchange (NEE) for the studied peatland system, stream carbon export typically accounted for 12 to 50% of NEE for most years. However, in 2006 stream carbon export accounted for 63 to 90% (estimated uncertainty range) of NEE due to a dry summer which suppressed NEE, followed by a wet autumn that resulted in considerable stream export. Runoff exerted a primary control on stream carbon export from this catchment; however, our findings suggest that seasonal variations in biologic and hydrologic processes responsible for production and transport of carbon within the peatland were secondary influences on stream carbon export. Consideration of these seasonal dynamics is needed when predicting stream carbon export response to environmental change.

  • 18.
    Leith, Fraser Leith
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Dinsmore, Kerry
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Billett, Michael
    Heal, Kate
    Laudon, Hjalmar
    Öquist, Mats
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Carbon dioxide transport across the hillslope–riparian–stream continuum in a boreal headwater catchment2015In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, p. 1881-1892Article in journal (Refereed)
  • 19.
    Natchimuthu, Sivakiruthika
    et al.
    Linkoping Univ, Dept Themat Studies Environm Change, S-58183 Linkoping, Sweden.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Klemedtsson, Leif
    Univ Gothenburg, Dept Earth Sci, S-40530 Gothenburg, Sweden.
    Bastviken, David
    Linkoping Univ, Dept Themat Studies Environm Change, S-58183 Linkoping, Sweden.
    Spatio-temporal patterns of stream methane and carbon dioxide emissions in a hemiboreal catchment in Southwest Sweden2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 39729Article in journal (Refereed)
    Abstract [en]

    Global stream and river greenhouse gas emissions seem to be as large as the oceanic C uptake. However, stream and river emissions are uncertain until both spatial and temporal variability have been quantified. Here we investigated in detail the stream CH4 and CO2emissions within a hemiboreal catchment in Southwest Sweden primarily covered by coniferous forest. Gas transfer velocities (k600), CH4 and CO2 concentrations were measured with multiple methods. Our data supported modelling approaches accounting for various stream slopes, water velocities and discharge. The results revealed large but partially predictable spatio-temporal variabilities in k600, dissolved gas concentrations, and emissions. The variability in CO2 emission was best explained by the variability in k, while dissolved CH4concentrations explained most of the variability in CH4 emission, having implications for future measurements. There were disproportionately large emissions from high slope stream reaches including waterfalls, and from high discharge events. In the catchment, stream reaches with low slope and time periods of moderate discharge dominated (90% of area and 69% of time). Measurements in these stream areas and time periods only accounted for <36% of the total estimated emissions. Hence, not accounting for local or episodic high emissions can lead to substantially underestimated emissions.

  • 20.
    Nilsson, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bergström, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Rutgersson, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Podgrajsek, Eva
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Wallin, Marcus B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bergström, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Dellwik, Ebba
    Landwehr, Sebastian
    Ward, Brian
    Evaluating humidity and sea salt disturbances on CO2 flux measurements2018In: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 35, p. 859-875Article in journal (Refereed)
    Abstract [en]

    Global oceans are an important sink of atmospheric carbon dioxide (CO2). Therefore, understanding the air-sea flux of CO2 is a vital part in describing the global carbon balance. Eddy covariance (EC) measurements are often used to study CO2 fluxes from both land and ocean. CO2 are usually measured with infrared absorption sensors, which at the same time measure water vapor. Studies have shown that presence of water vapor fluctuations in the sampling air potentially result in erroneous CO2 flux measurements due to cross-sensitivity of the sensor. Here we compare measured CO2 fluxes from both enclosed path Li-Cor 7200 sensors and open-path Li-Cor 7500 instruments from an inland measurement site and a marine site. We also introduce new quality control criteria based upon a Relative Signal Strength Indicator (RSSI). The sampling gas in one of the Li-Cor 7200 instruments was dried by means of a multi-tube diffusion dryer so that the water vapor fluxes were close to zero. With this setup we investigated the effect that cross-sensitivity of the CO2 signal to water vapor can have on the CO2 fluxes. The dryer had no significant effect on the CO2 fluxes. We tested the hypothesis that the cross-sensitivity effect is caused by hygroscopic particles such as sea salt by spraying a saline solution on the windows of the Li-Cor 7200 instruments during the inland field test. Our results confirm earlier findings that sea salt contamination can affect CO2 fluxes significantly and confirm earlier findings, that drying the sampling air for the gas analyzer is an effective method to reduce this signal contamination.

  • 21.
    Nydahl, Anna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    No long-term trends in pCO2 despite increasing organic carbon concentrations in boreal lakes, streams and rivers2017In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 31, no 6, p. 985-995Article in journal (Refereed)
    Abstract [en]

    Concentrations of dissolved organic carbon (DOC) from terrestrial sources have been increasing in freshwaters across large parts of the boreal region. According to results from large-scale field and detailed laboratory studies, such a DOC increase could potentially stimulate carbon dioxide (CO2) production, subsequently increasing the partial pressure of CO2 (pCO2) in freshwaters. However, the response of pCO2 to the presently observed long-term increase in DOC in freshwaters is still unknown. Here we tested whether the commonly found spatial DOC-pCO2 relationship is also valid on a temporal scale. Analyzing time series of water chemical data from 71 lakes, 30 streams, and 4 river mouths distributed across all of Sweden over a 17 year period, we observed significant DOC concentration increases in 39 lakes, 15 streams, and 4 river mouths. Significant pCO2 increases were, however, only observed in six of these 58 waters, indicating that long-term DOC increases in Swedish waters are disconnected from temporal pCO2 trends. We suggest that the uncoupling of trends in DOC concentration and pCO2 are a result of increased surface water runoff. When surface water runoff increases, there is likely less CO2 relative to DOC imported from soils into waters due to a changed balance between surface and groundwater flow. Additionally, increased surface water runoff causes faster water flushing through the landscape giving less time for in situ CO2 production in freshwaters. We conclude that pCO2 is presently not following DOC concentration trends, which has important implications for modeling future CO2 emissions from boreal waters.

  • 22.
    Nydahl, Anna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Laudon, Hjalmar
    Institutionen för skogens ekologi och skötsel, SLU, Umeå.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Groundwater carbon within a boreal catchment – spatiotemporal variability of a hidden aquatic carbon poolIn: Article in journal (Other academic)
  • 23.
    Nydahl, Anna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Hiller, Carolin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Attermeyer, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Garrison, Julie A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Chaguaceda, Fernando
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Scharnweber, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Colored organic matter increases CO2 in meso-eutrophic lake water through altered light climate and acidity2019In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 64, no 2, p. 744-756Article in journal (Refereed)
    Abstract [en]

    Many surface waters across the boreal region are browning due to increased concentrations of colored allochthonous dissolved organic carbon (DOC). Browning may stimulate heterotrophic metabolism, may have a shading effect constraining primary production, and may acidify the water leading to decreased pH with a subsequent shift in the carbonate system. All these effects are expected to result in increased lake water carbon dioxide (CO2) concentrations. We tested here these expectations by assessing the effects of both altered allochthonous DOC input and light conditions through shading on lake water CO2 concentrations. We used two mesocosm experiments with water from the meso‐eutrophic Lake Erken, Sweden, to determine the relative importance of bacterial activities, primary production, and shifts in the carbonate system on CO2 concentrations. We found that DOC addition and shading resulted in a significant increase in partial pressure of CO2 (pCO2) in all mesocosms. Surprisingly, there was no relationship between bacterial activities and pCO2. Instead the experimental reduction of light by DOC and/or shading decreased the photosynthesis to respiration ratio leading to increased pCO2. Another driving force behind the observed pCO2 increase was a significant decrease in pH, caused by a decline in photosynthesis and the input of acidic DOC. Considering that colored allochthonous DOC may increase in a warmer and wetter climate, our results could also apply for whole lake ecosystems and pCO2 may increase in many lakes through a reduction in the rate of photosynthesis and decreased pH.

  • 24.
    Nydahl, Anna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Highly variable explanations of long-term pCO2 increases in boreal lakes and streamsIn: Article in journal (Other academic)
  • 25. Peacock, Mike
    et al.
    Audet, Joachim
    Jordan, Sabine
    Smeds, Jacob
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Wallin, Marcus B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Greenhouse gas emissions from urban ponds are driven by nutrient status and hydrology2019In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 10, no 3, article id e02643Article in journal (Refereed)
    Abstract [en]

    Inland waters emit significant quantities of greenhouse gases (GHGs) such as methane (CH4) and carbon dioxide (CO2) to the atmosphere. On a global scale, these emissions are large enough that their contribution to climate change is now recognized by the Intergovernmental Panel on Climate Change. Much of the past focus on GHG emissions from inland waters has focused on lakes, reservoirs, and rivers, and the role of small, artificial waterbodies such as ponds has been overlooked. To investigate the spatial variation in GHG fluxes from artificial ponds, we conducted a synoptic survey of forty urban ponds in a Swedish city. We measured dissolved concentrations of CH4 and CO2, and made complementary measurements of water chemistry. We found that CH4 concentrations were greatest in high‐nutrient ponds (measured as total phosphorus and total organic carbon). For CO2, higher concentrations were associated with silicon and calcium, suggesting that groundwater inputs lead to elevated CO2. When converted to diffusive GHG fluxes, mean emissions were 30.3 mg CH4·m−2·d−1 and 752 mg CO2·m−2·d−1. Although these fluxes are moderately high on an areal basis, upscaling them to all Swedish urban ponds gives an emission of 8336 t CO2eq/yr (±1689) equivalent to 0.1% of Swedish agricultural GHG emissions. Artificial ponds could be important GHG sources in countries with larger proportions of urban land.

  • 26.
    Venkiteswaran, Jason J.
    et al.
    University of Waterloo.
    Schiff, Sherry L.
    University of Waterloo.
    Wallin, Marcus B.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Large carbon dioxide fluxes from headwater boreal and sub-boreal streams2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 7, p. e101756-Article in journal (Refereed)
    Abstract [en]

    Half of the world's forest is in boreal and sub-boreal ecozones, containing large carbon stores and fluxes. Carbon lost from headwater streams in these forests is underestimated. We apply a simple stable carbon isotope idea for quantifying the CO2 loss from these small streams; it is based only on in-stream samples and integrates over a significant distance upstream. We demonstrate that conventional methods of determining CO2 loss from streams necessarily underestimate the CO2 loss with results from two catchments. Dissolved carbon export from headwater catchments is similar to CO2 loss from stream surfaces. Most of the CO2 originating in high CO2 groundwaters has been lost before typical in-stream sampling occurs. In the Harp Lake catchment in Canada, headwater streams account for 10% of catchment net CO2 uptake. In the Krycklan catchment in Sweden, this more than doubles the CO2 loss from the catchment. Thus, even when corrected for aquatic CO2 loss measured by conventional methods, boreal and sub-boreal forest carbon budgets currently overestimate carbon sequestration on the landscape.

  • 27.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    ADV.k600.CO2.CH42018Data set
  • 28.
    Wallin, Marcus
    Swedish University of Agricultural Sciences.
    Evasion of CO2 from streams: Quantifying a carbon component of the aquatic conduit in the boreal landscape2011Doctoral thesis, comprehensive summary (Other academic)
  • 29.
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Stream.CO2.CH4.concentrations.Sweden2017Data set
  • 30.
    Wallin, Marcus B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Löfgren, Stefan
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala.
    Erlandsson, Martin
    Department of Geography and Environmental Science, University of Reading, Reading, United Kingdom.
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Uppsala Centre for Sustainable Development, CSD Uppsala.
    Representative regional sampling of carbon dioxide and methane concentrations in hemiboreal headwater streams reveal underestimates in less systematic approaches2014In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 28, no 4, p. 465-479Article in journal (Refereed)
    Abstract [en]

    Boreal headwater streams have been identified as hotspots for water-air exchange of greenhouse gases (GHG´s). Despite these findings GHG concentrations and fluxes in headwaters are to a great extent unexplored at large (regional/national) scales. This study was the first to systematically determine the concentrations of CO2 and CH4 in hemiboreal (southern boreal and boreonemoral) headwater streams. The use of a headspace sampling method focusing on GHG´s in combination with a statistically representative selection of more than 200 streams across two regions in Sweden was the basis for defining the base flow supersaturation level of CO2 and CH4. All streams were supersaturated relative to the atmosphere in CO2 (median concentration, 1.9 (±1.1) mg C L-1) and the majority in CH4 (median concentration, 7.1 (±54.0) µg C L-1 for the 82% of streams in which CH4 was detected). The spatial variability in both CO2 and CH4 was high but positively related to total organic carbon, mean annual temperature and proportion of peatland in the catchment. There were however regional differences in the spatial controls, which is something that predictive models need to consider. The large and representative data set allowed for comparison between a headspace and an alkalinity-based method for determining CO2 in these headwaters. More than 50% of the streams contained no alkalinity which made the alkalinity based determination of CO2 impossible. In addition, half of the streams with alkalinity alkalinities low enough (<0.07 mEq L-1) to make the CO2 determination very uncertain. The streams with low pH and no alkalinity contained median CO2 concentrations that were 45% higher than the streams containing alkalinity. Therefore large scale generalizations about the supersaturation of CO2 from such headwaters will be significantly underestimated if (1) headwaters are underrepresented, and (2) the headwaters are sampled but CO2 is calculated from their alkalinity.

  • 31.
    Wallin, Marcus B.
    et al.
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Öquist, Mats G.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umea, Sweden.
    Buffam, Ishi
    Department of Biological Sciences and Department of Geography, University of Cincinnati, Cincinnati, Ohio, USA.
    Billett, Michael F.
    Centre for Ecology and Hydrology, Edinburgh Research Station, Bush Estate, Penicuik, UK.
    Nisell, Jakob
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Bishop, Kevin H.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Spatiotemporal variability of the gas transfer coefficient (KCO2) in boreal streams: Implications for large scale estimates of CO2 evasion2011In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 25, no 3, p. GB3025-Article in journal (Refereed)
    Abstract [en]

    Boreal streams represent potentially important conduits for the exchange of carbon dioxide (CO(2)) between terrestrial ecosystems and the atmosphere. The gas transfer coefficient of CO(2) (K(CO2)) is a key variable in estimating this source strength, but the scarcity of measured values in lotic systems creates a risk of incorrect flux estimates even when stream gas concentrations are well known. This study used 114 independent measurements of K(CO2) from 14 stream reaches in a boreal headwater system to determine and predict spatiotemporal variability in K(CO2). The K(CO2) values ranged from 0.001 to 0.207 min(-1) across the 14 sites. Median K(CO2) for a specific site was positively correlated with the slope of the stream reach, with higher gas transfer coefficients occurring in steeper stream sections. Combining slope with a width/depth index of the stream reach explained 83% of the spatial variability in K(CO2). Temporal variability was more difficult to predict and was strongly site specific. Variation in K(CO2), rather than pCO(2), was the main determinant of stream CO(2) evasion. Applying published generalized gas transfer velocities produced an error of up to 100% in median instantaneous evasion rates compared to the use of actual measured K(CO2) values from our field study. Using the significant relationship to local slope, the median K(CO2) was predicted for 300,000 km of watercourses (ranging in stream order 1-4) in the forested landscape of boreal/nemoral Sweden. The range in modeled stream order specific median K(CO2) was 0.017-0.028 min(-1) and there was a clear gradient of increasing K(CO2) with lower stream order. We conclude that accurate regional scale estimates of CO(2) evasion fluxes from running waters are possible, but require a good understanding of gas exchange at the water surface.

  • 32.
    Wallin, Marcus
    et al.
    Swedish Univ Agr Sci, Dept Aquat Sci & Assessment, SE-75007 Uppsala, Sweden.
    Buffam, Ishi
    Univ Wisconsin, Dept Zool, Madison, WI 53706 USA ; Swedish Univ Agr Sci, Dept Forest Ecol & Management, SE-90183 Umea, Sweden .
    Oquist, Mats
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, SE-90183 Umea, Sweden .
    Laudon, Hjalmar
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, SE-90183 Umea, Sweden .
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Temporal and spatial variability of dissolved inorganic carbon in a boreal stream network: Concentrations and downstream fluxes2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, p. G02014-Article in journal (Refereed)
    Abstract [en]

    Carbon dioxide (CO2) and dissolved inorganic carbon (DIC) concentrations and export were analyzed throughout a 67 km(2) boreal stream network in northern Sweden. 700 DIC and CO2 samples from 14 subcatchments were collected in 2006 and 2007. All sites were consistently supersaturated in CO2 with respect to the atmosphere. Temporal variability of DIC and CO2 concentration was best correlated with discharge, with concentrations generally diluting at high discharge. However, the variability in CO2 concentration was also dependent on the specific pH range of the stream, as variability was greatest in acidic headwater streams and lowest in larger circumneutral streams. In the larger ones the increase in the CO2 proportion of DIC at increased discharge counteracts the dilution of CO2. The shift toward proportionally more CO2 of the DIC at higher discharge is caused by decline in pH. Spatial patterns showed that DIC and CO2 concentrations were best correlated with peatland coverage of the subcatchment. The highest concentrations were found in headwater streams draining peatlands. The downstream export of DIC from the catchment outlet constitutes 19% of the total downstream export of carbon (DIC + DOC), or 0.7 (+/-0.09) g C m(-2) yr(-1). This study demonstrates the importance of including fluvial fluxes of inorganic carbon in landscape carbon budgets via runoff, and also highlights the need to account for stream evasion of CO2 to the atmosphere in such estimates since it can be larger than the downstream DIC export.

  • 33.
    Wallin, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Campeau, Audrey
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Audet, Joachim
    Swedish Univ Agr Sci, Dept Aquat Sci & Assessment, Uppsala, Sweden.
    Bastviken, David
    Linköping Univ, Dept Themat Studies Environm Change, Linköping, Sweden.
    Bishop, Kevin
    Swedish Univ Agr Sci, Dept Aquat Sci & Assessment, Uppsala, Sweden.
    Kokic, Jovana
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Laudon, Hjalmar
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, Umeå, Sweden.
    Lundin, Erik
    Umeå Univ, Dept Ecol & Environm Sci, Climate Impacts Res Ctr, Umeå, Sweden.
    Löfgren, Stefan
    Swedish Univ Agr Sci, Dept Aquat Sci & Assessment, Uppsala, Sweden.
    Natchimuthu, Sivakiruthika
    Linköping Univ, Dept Themat Studies Environm Change, Linköping, Sweden.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Teutschbein, Claudia
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Grabs, Thomas J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Carbon dioxide and methane emissions of Swedish low-order streams: a national estimate and lessons learnt from more than a decade of observations2018In: Limnology and Oceanography: Letters, ISSN 2378-2242, Vol. 3, no 3, p. 156-167Article in journal (Refereed)
    Abstract [en]

    Low‐order streams are suggested to dominate the atmospheric CO2 source of all inland waters. Yet, many large‐scale stream estimates suffer from methods not designed for gas emission determination and rarely include other greenhouse gases such as CH4. Here, we present a compilation of directly measured CO2 and CH4 concentration data from Swedish low‐order streams (> 1600 observations across > 500 streams) covering large climatological and land‐use gradients. These data were combined with an empirically derived gas transfer model and the characteristics of a ca. 400,000 km stream network covering the entire country. The total stream CO2 and CH4 emission corresponded to 2.7 Tg C yr−1 (95% confidence interval: 2.0–3.7) of which the CH4 accounted for 0.7% (0.02 Tg C yr−1). The study highlights the importance of low‐order streams, as well as the critical need to better represent variability in emissions and stream areal extent to constrain future stream C emission estimates.

  • 34.
    Wallin, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Grabs, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Buffam, Ishi
    Department of Biological Sciences and Department of Geography, University of Cincinnati, Cincinnati, USA.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Ågren, Anneli
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Öquist, Mats
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Evasion of CO2 from streams: The dominant component of the carbon export through the aquatic conduit in a boreal landscape2013In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, no 3, p. 785-797Article in journal (Refereed)
    Abstract [en]

    Evasion of gaseous carbon (C) from streams is often poorly quantified in landscape C budgets. Even though the potential importance of the capillary network of streams as C conduits across the land-water-atmosphere interfaces is sometimes mentioned, low-order streams are often left out of budget estimates due to being poorly characterized in terms of gas exchange and even areal surface coverage. We show that evasion of C is greater than all the total dissolved C (both organic and inorganic) exported downstream in the waters of a boreal landscape. In this study evasion of carbon dioxide (CO2) from running waters within a 67 km2 boreal catchment was studied. During a four year period (2006-2009) 13 streams were sampled on 104 different occasions for dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). From a locally determined model of gas exchange properties, we estimated the daily CO2 evasion with a high-resolution (5×5 m) grid based stream evasion model comprising the entire ~100 km stream network. Despite the low areal coverage of stream surface the evasion of CO2 from the stream network constituted 53% (5.0 (±1.8) g C m−2 yr−1) of the entire stream C flux (9.6 (±2.4) g C m−2 yr−1) (lateral as DIC, DOC and vertical as CO2). In addition, 72% of the total CO2 loss took place already in the 1st and 2nd order streams. This study demonstrates the importance of including CO2 evasion from low-order boreal streams into landscape C budgets since it more than doubled the magnitude of the aquatic conduit for C from this landscape. Neglecting this term will consequently result in an overestimation of the terrestrial C sink strength in the boreal landscape.

  • 35.
    Wallin, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Weyhenmeyer, Gesa
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Bastviken, David
    Chmiel, Hannah E.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Peter, Simone
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Klemedtsson, Leif
    Temporal control on concentration, character and export of dissolved organic carbon in two hemiboreal headwater streams draining contrasting catchments2015In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 5, p. 832-846Article in journal (Refereed)
    Abstract [en]

    Although lateral carbon (C) export from terrestrial to aquatic systems is known to be an important component in landscape C balances, most existing global studies are lacking empirical data on the soil C export. In this study, the concentration, character, and export of dissolved organic carbon (DOC) were studied during 2 years in two hemiboreal headwater streams draining catchments with different soil characteristics (mineral versus peat soils). The streams exposed surprisingly similar strong air temperature controls on the temporal variability in DOC concentration in spite of draining such different catchments. The temporal variability in DOC character (determined by absorbance metrics, specific ultraviolet absorbance 254 (SUVA254) as a proxy for aromaticity and a254/a365 ratio as a proxy for mean molecular weight) was more complex but related to stream discharge. While the two streams showed similar ranges and patterns in SUVA254, we found a significant difference in median a254/a354, suggesting differences in the DOC character. Both streams responded similarly to hydrological changes with higher a254/a365 at higher discharge, although with rather small differences in a254/a365 between base flow and high flow (<0.3). The DOC exports (9.6–25.2 g C m−2 yr−1) were among the highest reported so far for Scandinavia and displayed large interannual and intraannual variability mainly driven by irregular precipitation/discharge patterns. Our results show that air temperature and discharge affect the temporal variability in DOC quantity and character in different ways. This will have implications for the design of representative sampling programs, which in turn will affect the reliability of future estimates of landscape C budgets.

  • 36.
    Weyhenmeyer, Gesa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kosten, Sarian
    Wallin, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tranvik, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Jeppesen, Erik
    Roland, Fabio
    Significant fraction of CO2 emissions from boreal lakes derived from hydrologic inorganic carbon inputs2015In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 8, no 12, p. 933-936Article in journal (Refereed)
    Abstract [en]

    Annual CO2 emissions from lakes and other inland waters into the atmosphere are estimated to almost entirely compensate the total annual carbon uptake by oceans. CO2 supersaturation in lakes, which results in CO2 emissions, is frequently attributed to CO2 produced within the lake. However, lateral inorganic carbon flux through watersheds can also be sizeable. Here we calculated lake surface water CO2 concentrations and emissions using lake pH, alkalinity and temperature from a compilation of data from 5,118 boreal lakes. Autumn surface water CO2 concentrations and CO2 emissions from the 5,118 lakes co-varied with lake internal autumn CO2 production. However, using a mass balance approach we found that CO2 emission in the majority of lakes was sustained by inorganic carbon loading from the catchment rather than by internal CO2 production. Small lakes with high dissolved organic carbon and phosphorus concentrations, shorter retention times and longer ice-free seasons had the highest CO2 concentrations. CO2 emissions from these small lakes was twice that of comparable lakes in colder regions, and similar to emissions from subtropical and tropical lakes. We conclude that changes in land use and climate that increase dissolved inorganic carbon may cause emission levels from boreal lakes to approach those of lakes in warmer regions.

  • 37.
    Åberg, Jan
    et al.
    Department of Ecology and Environmental Science, Umeå University.
    Wallin, Marcus B.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Evaluating a fast headspace method for measuring DIC and subsequent calculation of pCO2 in freshwater systems2014In: Inland Waters, ISSN 2044-2041, EISSN 2044-205X, Vol. 4, no 2, p. 157-166Article in journal (Refereed)
    Abstract [en]

    A variety of different sampling and analysis methods are found in the literature for determining carbon dioxide (CO2) in freshwaters, methods that rarely have been evaluated or compared. Here we present an evaluation of an acidified headspace method (AHS) in which the dissolved inorganic carbon (DIC) is measured from an acidified sample and the partial pressure (pCO2) is calculated from DIC using pH and water temperature. We include information on practical sampling, accuracy, and precision of the DIC/pCO2 determination and a storage test of samples. The pCO2 determined from the AHS method is compared to that obtained from the more widely used direct headspace method (DHS) in which CO2 is equilibrated between the water and gas phases at ambient pH. The method was tested under both controlled laboratory conditions as well as wintertime field sampling. The accuracy of the DIC detection was on average 99% based on prepared standard solutions. The pCO2 determination in lab, using the DHS method as a reference, showed no significant difference, although the discrepancy between the methods was larger in samples with <1000 µatm. The precision of the pCO2 determination was on average ±4.3%, which was slightly better than the DHS method (±6.7%). In the field, the AHS method determined on average 10% higher pCO2 than the DHS method, which was explained by the extreme winter conditions (below −20 °C) at sampling that affected the sampling procedure of the DHS method. Although samples were acidified to pH 2, respiration processes were still occurring (at a low rate), and we recommend that analyses are conducted within 3 days from sampling. The AHS method was found to be a robust method to determine DIC and pCO2 in acidic to pH-neutral freshwater systems. The simple and quick sampling procedure makes the method suitable for time-limited sampling campaigns and sampling in cold climate.

  • 38.
    Öquist, Mats G.
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU).
    Bishop, Kevin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Uppsala Centre for Sustainable Development, CSD Uppsala.
    Grelle, Achim
    Department of Ecology, Swedish University of Agricultural Sciences (SLU).
    Klemedtsson, Leif
    Department of Earth Sciences, Gothenburg University.
    Köhler, Stephan J.
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences (SLU).
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU).
    Lindroth, Anders
    Department of Physical Geography and Ecosystem Analysis, Lund University.
    Ottosson Löfvenius, Mikaell
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU).
    Wallin, Marcus B.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Nilsson, Mats B.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU).
    The full annual carbon balance of boreal forestsis highly sensitive to precipitation2014In: Environmental Science and Technology Letters, ISSN 2328-8930, Vol. 1, no 7, p. 315-319Article in journal (Refereed)
    Abstract [en]

    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.

  • 39. Öquist, Mats G.
    et al.
    Wallin, Marcus
    Seibert, Jan
    Bishop, Kevin
    Laudon, Hjalmar
    Dissolved inorganic carbon export across the soil/stream interface and its fate in a boreal headwater stream2009In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 43, p. 7364-7369Article in journal (Refereed)
1 - 39 of 39
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