Digitala Vetenskapliga Arkivet

Change search
Refine search result
123 1 - 50 of 106
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Abramoff, Rose Z.
    et al.
    Georgiou, Katerina
    Guenet, Bertrand
    Torn, Margaret S.
    Huang, Yuanyuan
    Zhang, Haicheng
    Feng, Wenting
    Jagadamma, Sindhu
    Kaiser, Klaus
    Kothawala, Dolly
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Mayes, Melanie A.
    Ciais, Philippe
    How much carbon can be added to soil by sorption?2021In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 152, no 2-3, p. 127-142Article in journal (Refereed)
    Abstract [en]

    Quantifying the upper limit of stable soil carbon storage is essential for guiding policies to increase soil carbon storage. One pool of carbon considered particularly stable across climate zones and soil types is formed when dissolved organic carbon sorbs to minerals. We quantified, for the first time, the potential of mineral soils to sorb additional dissolved organic carbon (DOC) for six soil orders. We compiled 402 laboratory sorption experiments to estimate the additional DOC sorption potential, that is the potential of excess DOC sorption in addition to the existing background level already sorbed in each soil sample. We estimated this potential using gridded climate and soil geochemical variables within a machine learning model. We find that mid- and low-latitude soils and subsoils have a greater capacity to store DOC by sorption compared to high-latitude soils and topsoils. The global additional DOC sorption potential for six soil orders is estimated to be 107 ± 13 Pg C to 1 m depth. If this potential was realized, it would represent a 7% increase in the existing total carbon stock.

    Download full text (pdf)
    fulltext
  • 2. Akselsson, Cecilia
    et al.
    Olsson, Jonas
    Belyazid, Salim
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Capell, René
    Can increased weathering rates due to future warming compensate for base cation losses following whole-tree harvesting in spruce forests?2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 128, no 1-2, p. 89-105Article in journal (Refereed)
    Abstract [en]

    Whole-tree harvesting, i.e. harvesting of stems, branches and tops, has become increasingly common during recent decades due to the increased demand for renewable energy. Whole-tree harvesting leads to an increase in base cation losses from the ecosystem, which can counteract recovery from acidification. An increase in weathering rates due to higher temperatures is sometimes suggested as a process that may counteract the acidifying effect of whole-tree harvesting. In this study the potential effect of increasing temperature on weathering rates was compared with the increase in base cation losses following whole-tree harvesting in spruce forests, along a temperature gradient in Sweden. The mechanistic model PROFILE was used to estimate weathering rates at National Forest Inventory sites at today's temperature and the temperature in 2050, as estimated by two different climate projections. The same dataset was used to calculate base cation losses following stem-only and whole-tree harvesting. The calculations showed that the increase in temperature until 2050 would result in an increase in the base cation weathering rate of 20-33 %, and that whole-tree harvesting would lead to an increase in base cation losses of 66 % on average, compared to stem-only harvesting. A sensitivity analysis showed that moisture changes are important for future weathering rates, but the effect of the temperature change was dominating even when the most extreme moisture changes were applied. It was concluded that an increase in weathering rates resulting from higher temperatures would not compensate for the increase in base cation losses following whole-tree harvesting, except in the northernmost part of Sweden.

  • 3. Akselsson, Cecilia
    et al.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Belyazid, Salim
    Capell, Réne
    SMHI, Research Department, Hydrology.
    Can increased weathering rates due to future warming compensate for base cation losses following whole-tree harvesting in spruce forests?2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 128, no 1-2, p. 89-105Article in journal (Refereed)
  • 4. Alfredsson, Hanna
    et al.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Clymans, Wim
    Stadmark, Johanna
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Conley, Daniel J.
    Amorphous silica pools in permafrost soils of the Central Canadian Arctic and the potential impact of climate change2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 124, no 1-3, p. 441-459Article in journal (Refereed)
    Abstract [en]

    We investigated the distribution, storage and landscape partitioning of soil amorphous silica (ASi) in a central Canadian region dominated by tundra and peatlands to provide a first estimate of the amount of ASi stored in Arctic permafrost ecosystems. We hypothesize that, similar to soil organic matter, Arctic soils store large amounts of ASi which may be affected by projected climate changes and associated changes in permafrost regimes. Average soil ASi storage (top 1 m) ranged between 9600 and 83,500 kg SiO2 ha(-1) among different land-cover types. Lichen tundra contained the lowest amounts of ASi while no significant differences were found in ASi storage among other land-cover types. Clear differences were observed between ASi storage allocated into the top organic versus the mineral horizon of soils. Bog peatlands, fen peatlands and wet shrub tundra stored between 7090 and 45,400 kg SiO2 ha(-1) in the top organic horizon, while the corresponding storage in lichen tundra, moist shrub- and dry shrub tundra only amounted to 1500-1760 kg SiO2 ha(-1). Diatoms and phytoliths are important components of ASi storage in the top organic horizon of peatlands and shrub tundra systems, while it appears to be a negligible component of ASi storage in the mineral horizon of shrub tundra classes. ASi concentrations decrease with depth in the soil profile for fen peatlands and all shrub tundra classes, suggesting recycling of ASi, whereas bog peatlands appeared to act as sinks retaining stored ASi on millennial time scales. Our results provide a conceptual framework to assess the potential effects of climate change impacts on terrestrial Si cycling in the Arctic. We believe that ASi stored in peatlands are particularly sensitive to climate change, because a larger fraction of the ASi pool is stored in perennially frozen ground compared to shrub tundra systems. A likely outcome of climate warming and permafrost thaw could be mobilization of previously frozen ASi, altered soil storage of biogenically derived ASi and an increased Si flux to the Arctic Ocean.

  • 5. Allain, Alienor
    et al.
    Alexis, Marie A.
    Bridoux, Maxime C.
    Humbert, Guillaume
    Agnan, Yannick
    Rouelle, Maryse
    Fingerprinting the elemental composition and chemodiversity of vegetation leachates: consequences for dissolved organic matter dynamics in Arctic environments2022In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515XArticle in journal (Refereed)
    Abstract [en]

    Dissolved organic matter is a key compartment for biogeochemical cycles in the Arctic and Subarctic terrestrial environments. With changing vegetation ecosystems, the chemical composition of organic matter is expected to shift and thus, the most labile part of it, namely the extractable fraction. To this date, few studies have focused on the fingerprinting of DOM fraction from different primary sources, and even less on its potential repercussions on the environment. In this study, we jointly characterized the chemical composition of bulk and water-extractable organic matter (WEOM) from different vegetation species typical of Subarctic ecosystems. Through a multi-analyses approach, including elementary analysis, solid state 13C nuclear magnetic resonance, UV and 3D fluorescence spectroscopy, and high-resolution mass spectrometry, our results highlighted that the quantity and composition of produced WEOM significantly differed between vegetation sources and specifically between plant functional types (PFT, e.g., lichens, graminoids, and trees and shrubs). The relevance of optical indices was questioned, and the use of several of them was discarded for unprocessed WEOM study. However, the DOM proxies (optical indices, molecular composition, and stoichiometry) enabled to conclude that the lichen WEOM was likely less degradable than vascular plants WEOM, and among the latter group, graminoids produced more degradable WEOM than trees and shrubs. This work reported specific organic fingerprints for the different PFT. Consequently, the ongoing changes of vegetation in Arctic and Subarctic regions may greatly affect the composition of DOM that enters the soil and the hydrosystems, as well as the biogeochemical processes it is involved in.

  • 6. Andersen, Jesper H.
    et al.
    Axe, Philip
    SMHI, Research Department, Oceanography.
    Backer, Hermanni
    Carstensen, Jacob
    Claussen, Ulrich
    Fleming-Lehtinen, Vivi
    Jarvinen, Marko
    Kaartokallio, Hermanni
    Knuuttila, Seppo
    Korpinen, Samuli
    Kubiliute, Aiste
    Laamanen, Maria
    Lysiak-Pastuszak, Elzbieta
    Martin, Georg
    Murray, Ciaran
    Mohlenberg, Flemming
    Nausch, Guenther
    Norkko, Alf
    Villnas, Anna
    Getting the measure of eutrophication in the Baltic Sea: towards improved assessment principles and methods2011In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 106, no 2, p. 137-156Article in journal (Refereed)
    Abstract [en]

    The eutrophication status of the entire Baltic Sea is classified using a multi-metric indicator-based assessment tool. A total of 189 areas are assessed using indicators where information on reference conditions (RefCon), and acceptable deviation (AcDev) from reference condition could be combined with national monitoring data from the period 2001-2006. Most areas (176) are classified as 'affected by eutrophication' and only two open water areas and 11 coastal areas are classified as 'unaffected by eutrophication'. The classification is made by application of the recently developed HELCOM Eutrophication Assessment Tool (HEAT), which is described in this paper. The use of harmonized assessment principles and the HEAT tool allows for direct comparisons between different parts of the Baltic Sea despite variations in monitoring activities. The impaired status of 176 areas is directly related to nutrient enrichment and elevated loads from upstream catchments. Baltic Sea States have implemented nutrient management strategies since years which have reduced nutrient inputs. However, eutrophication is still a major problem for large parts of the Baltic Sea. The 2007 Baltic Sea Action Plan is projected to further reduce nutrient inputs aiming for a Baltic Sea unaffected by eutrophication by 2021.

  • 7.
    Berg, Björn
    et al.
    Dipartimento biologia strutturale e funzionale, Complesso universitario di Monte S. Angelo, Napoli, Italy; Department of forest ecology, University of Helsinki, Helsinki, Finland.
    Davey, M. P.
    Department of plant sciences, University of Cambridge, Cambridge, United Kingdom.
    De Marco, A.
    Dipartimento biologia strutturale e funzionale, Complesso universitario di Monte S. Angelo, Napoli, Italy.
    Emmett, B
    Centre for ecology and hydrology, Bangor.
    Faituri, M.
    Department of soils and water, Omar AlMukhtar university, Elbeida, Libyan Arab Jamahiriya.
    Hobbie, S. E.
    Department of ecology, evolution and behavior, University of Minnesota, St. Paul, USA.
    Johansson, Maj-Britt
    University of Gävle.
    Liu, C.
    Department of landscape science and engineering, College of agriculture and biology, Shanghai, ChinaShanghai Jiao Tong university,.
    McClaugherty, C.
    Department of biology, Mount Union college, Alliance, USA.
    Norell, L.
    Unit of applied statistics and mathematics, SLU, Uppsala, Sweden.
    Rutigliano, F. A.
    Dipartimento di scienze ambientali, Seconda Università degli studi di Napoli, Caserta, Italy.
    Vesterdal, L.
    Forest & landscape Denmark, University of Copenhagen, Hørsholm, Denmark.
    Virzo De Santo, A.
    Dipartimento biologia strutturale e funzionale, Complesso universitario de Monte S. Angelo, Napoli, Italy.
    Factors influencing limit values for pine needle litter decomposition: A synthesis for boreal and temperate pine forest systems2010In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 100, no 1, p. 57-73Article in journal (Refereed)
    Abstract [en]

    We synthesized available data for decomposition of pine (Pinus) needle litter in pine forests to determine the litter chemical characteristics and climate factors that explained variation in the limit value, i. e. the level of accumulated mass loss at which the decomposition process either continues at a very low rate or possibly stops. Our data base included 56 separate studies on decomposition of pine needle litter, spanning Scots pine, lodgepole pine, Aleppo pine, stone pine and white pine, mainly incubated at the site of collection. Studies had 5 to 19 samplings, on average 10, and the decomposition was followed to a mass loss ranging from 47 to 83%, on average 67%. The periods from 3.0 to 5.4 years, on average 3.9 years, were of sufficient duration to allow estimates of limit values of decomposition. We used a linear mixed model with regression effects to relate limit values to potential explanatory variables, namely the sites' long-term mean annual temperature (MAT) and mean annual precipitation (MAP) and to substrate-chemistry factors. Regarding the latter, we explored two models; one that included initial concentrations of water solubles, lignin, N, P, K, Ca, Mg, and Mn and one that included only lignin, N, Ca, and Mn to focus on those nutrients known to influence lignin degradation. Using backward elimination significant explanatory variables were determined. For litter decomposed in its site of origin we found the limit value to depend mainly on the initial concentration of Mn, with higher Mn concentrations resulting in higher accumulated mass loss. Thus, litter with higher Mn reached a higher limit value and left a smaller stable fraction. This is likely due to the fact that Mn is an essential component of ligninolytic enzymes important for degrading litter in the later stages of decomposition. Manganese has received little attention in decomposition studies to date. Given its significance in this synthesis, the role of Mn in influencing variation in the late stages of decomposition among ecosystems and among litters of other genera besides Pinus deserves further attention.

  • 8. Berggren Kleja, Dan
    et al.
    Svensson, M
    Majdi, Hooshang
    Langvall, O
    Jansson, P-E
    Lindroth, A
    Weslien, P
    Bergkvist, B
    Johansson, Maj-Britt
    Swedish University of Agricultural Sciences.
    Pools and fluxes of carbon in three Norway spruce ecosystems along a climatic gradient in Sweden2008In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 89, no 1, p. 7-25Article in journal (Refereed)
  • 9. Berggren Kleja, Dan
    et al.
    Svensson, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Majdi, Hooshang
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Langvall, Ola
    Bergkvist, Bo
    Johansson, Maj-Britt
    Weslien, Per
    Lindroth, Anders
    Pools and fluxes of carbon in three Norway spruce ecosystems along a climatic gradient in Sweden.2008In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 89, no 1, p. 7-25Article in journal (Refereed)
    Abstract [en]

    This paper presents an integrated analysis of organic carbon (C) pools in soils and vegetation, within-ecosystem fluxes and net ecosystem exchange (NEE) in three 40-year old Norway spruce stands along a north-south climatic gradient in Sweden, measured 2001-2004. A process-orientated ecosystem model (CoupModel), previously parameterised on a regional dataset, was used for the analysis. Pools of soil organic carbon (SOC) and tree growth rates were highest at the southernmost site (1.6 and 2.0-fold, respectively). Tree litter production (litterfall and root litter) was also highest in the south, with about half coming from fine roots (< 1 mm) at all sites. However, when the litter input from the forest floor vegetation was included, the difference in total litter input rate between the sites almost disappeared (190-233 g C m(-2) year(-1)). We propose that a higher N deposition and N availability in the south result in a slower turnover of soil organic matter than in the north. This effect seems to overshadow the effect of temperature. At the southern site, 19% of the total litter input to the O horizon was leached to the mineral soil as dissolved organic carbon, while at the two northern sites the corresponding figure was approx. 9%. The CoupModel accurately described general C cycling behaviour in these ecosystems, reproducing the differences between north and south. The simulated changes in SOC pools during the measurement period were small, ranging from -8 g C m(-2) year(-1) in the north to +9 g C m(-2) year(-1) in the south. In contrast, NEE and tree growth measurements at the northernmost site suggest that the soil lost about 90 g C m(-2) year(-1).

  • 10.
    Bonaglia, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Bartoli, Marco
    Marchant, Hannah K.
    Bruchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Seasonal oxygen, nitrogen and phosphorus benthic cycling along an impacted Baltic Sea estuary: regulation and spatial patterns2014In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 119, no 1-3, p. 139-160Article in journal (Refereed)
    Abstract [en]

    The regulatory roles of temperature, eutrophication and oxygen availability on benthic nitrogen (N) cycling and the stoichiometry of regenerated nitrogen and phosphorus (P) were explored along a Baltic Sea estuary affected by treated sewage discharge. Rates of sediment denitrification, anammox, dissimilatory nitrate reduction to ammonium (DNRA), nutrient exchange, oxygen (O2) uptake and penetration were measured seasonally. Sediments not affected by the nutrient plume released by the sewage treatment plant (STP) showed a strong seasonality in rates of O2 uptake and coupled nitrification-denitrification, with anammox never accounting for more than 20% of the total dinitrogen (N2) production. N cycling in sediments close to the STP was highly dependent on oxygen availability, which masked temperature-related effects. These sediments switched from low N loss and high ammonium (NH4+) efflux under hypoxic conditions in the fall, to a major N loss system in the winter when the sediment surface was oxidized. In the fall DNRA outcompeted denitrification as the main nitrate (NO3-) reduction pathway, resulting in N recycling and potential spreading of eutrophication. A comparison with historical records of nutrient discharge and denitrification indicated that the total N loss in the estuary has been tightly coupled to the total amount of nutrient discharge from the STP. Changes in dissolved inorganic nitrogen (DIN) released from the STP agreed well with variations in sedimentary N2 removal. This indicates that denitrification and anammox efficiently counterbalance N loading in the estuary across the range of historical and present-day anthropogenic nutrient discharge. Overall low N/P ratios of the regenerated nutrient fluxes impose strong N limitation for the pelagic system and generate a high potential for nuisance cyanobacterial blooms.

  • 11.
    Burrows, E.H.
    et al.
    Univ New Hampshire.
    Bubier, J.L.
    Mount Holyoke College.
    Mosedale, A.
    Univ New Hampshire.
    Cobb, G.W.
    Mount Holyoke College.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Net Ecosystem Exchange of Carbon Dioxide in a Temperate Poor Fen: A Comparison of Automated and Manual Chamber Techniques,2005In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 76, no 1, p. 21-45Article in journal (Refereed)
    Abstract [en]

    We used five analytical approaches to compare net ecosystem exchange (NEE) of carbon dioxide (CO2) from automated and manual static chambers in a peatland, and found the methods comparable. Once per week we sampled manually from 10 collars with a closed chamber system using a LiCor 6200 portable photosynthesis system, and simulated four photosynthetically active radiation (PAR) levels using shrouds. Ten automated chambers sampled CO2 flux every 3 h with a LiCor 6252 infrared gas analyzer. Results of the five comparisons showed (1) NEE measurements made from May to August, 2001 by the manual and automated chambers had similar ranges: -10.8 to 12.7 μmol CO 2 m-2 s-1 and -17.2 to 13.1 μmol CO 2 m-2 s-1, respectively. (2) When sorted into four PAR regimes and adjusted for temperature (respiration was measured under different temperature regimes), mean NEE did not differ significantly between the chambers (p < 0.05). (3) Chambers were not significantly different in regression of ln( - respiration) on temperature. (4) But differences were found in the PAR vs. NEE relationship with manual chambers providing higher maximum gross photosynthesis estimates (GPmax), and slower uptake of CO 2 at low PAR (α) even after temperature adjustment. (5) Due to the high variability in chamber characteristics, we developed an equation that includes foliar biomass, water table, temperature, and PAR, to more directly compare automated and manual NEE. Comparing fitted parameters did not identify new differences between the chambers. These complementary chamber techniques offer a unique opportunity to assess the variability and uncertainty in CO 2 flux measurements.

  • 12.
    Casas-Ruiz, Joan P.
    et al.
    Catalan Inst Water Res ICRA, Emili Grahit 101, Girona 17003, Spain..
    Tittel, Joerg
    UFZ Helmholtz Ctr Environm Res, Dept Lake Res, Bruckstr 3a, D-39114 Magdeburg, Germany..
    von Schiller, Daniel
    Univ Basque Country, Fac Sci & Technol, Dept Plant Biol & Ecol, Apdo 644, Bilbao 48080, Spain..
    Catalan, Nuria
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Obrador, Biel
    Univ Barcelona, Dept Ecol, Av Diagonal 643, E-08028 Barcelona, Spain..
    Gomez-Gener, Lluis
    Univ Barcelona, Dept Ecol, Av Diagonal 643, E-08028 Barcelona, Spain..
    Zwirnmann, Elke
    Leibniz Inst Freshwater Ecol & Inland Fisheries, Muggelseedamm 301, D-12587 Berlin, Germany..
    Sabater, Sergi
    Catalan Inst Water Res ICRA, Emili Grahit 101, Girona 17003, Spain.;Univ Girona, Inst Aquat Ecol, Girona 17071, Spain..
    Marce, Rafael
    Catalan Inst Water Res ICRA, Emili Grahit 101, Girona 17003, Spain..
    Drought-induced discontinuities in the source and degradation of dissolved organic matter in a Mediterranean river2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 127, no 1, p. 125-139Article in journal (Refereed)
    Abstract [en]

    The composition of dissolved organic matter (DOM) in rivers results from the different sources and in-stream transformations along the land to ocean aquatic continuum. Riverine DOM sources are highly dependent on the hydrological connection between the river channel and the surrounding terrestrial ecosystems, but how the lack of this connectivity (e.g., during drought episodes) affects the sources and biodegradation of DOM in rivers remains unclear. Here we identified the DOM sources as well as the different DOM pools that are respired along a Mediterranean river during drought by combining absorbance-fluorescence spectroscopy, size-exclusion chromatography, biodegradation assays, and stable and radiocarbon isotopes. DOM composition was highly heterogeneous along the river in response to different sources and in-stream processes in each distinct aquatic environment (i.e., isolated water pools, running waters, and impounded waters in weirs). The reduced hydrological connectivity with terrestrial ecosystems promoted the influence of autochthonous DOM sources. Still, tree leaves from overhanging canopies stood out as an important terrestrial DOM source, especially in sites where water residence time was high such as isolated pools and weirs. Degradation of leaf leachates was a relevant process in these sites, whereas autochthonous DOM and groundwater millennial DOM (> 1300 year B.P.) seemed to be degraded in running waters. Overall, our results highlight that the drought-induced hydrological disconnection entails a great spatial heterogeneity in the sources of DOM, which at the same time determines the different DOM pools that are respired in each environment along the river.

  • 13. Catalán, Núria
    et al.
    Obrador, Biel
    Alomar, Carmen
    Pretus, Joan Lluis
    Seasonality and landscape factors drive dissolved organic matter properties in Mediterranean ephemeral washes2013In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 112, p. 261-274Article in journal (Refereed)
  • 14.
    Chi Fru, Ernest
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Cardiff University, UK.
    Callac, Nolwenn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Posth, Nicole R.
    Argyraki, Ariadne
    Ling, Yu-Chen
    Ivarsson, Magnus
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kilias, Stephanos P.
    Arsenic and high affinity phosphate uptake gene distribution in shallow submarine hydrothermal sediments2018In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 141, no 1, p. 41-62Article in journal (Refereed)
    Abstract [en]

    The toxicity of arsenic (As) towards life on Earth is apparent in the dense distribution of genes associated with As detoxification across the tree of life. The ability to defend against As is particularly vital for survival in As-rich shallow submarine hydrothermal ecosystems along the Hellenic Volcanic Arc (HVA), where life is exposed to hydrothermal fluids containing up to 3000 times more As than present in seawater. We propose that the removal of dissolved As and phosphorus (P) by sulfide and Fe(III)(oxyhydr)oxide minerals during sediment-seawater interaction, produces nutrient-deficient porewaters containing<2.0ppb P. The porewater arsenite-As(III) to arsenate-As(V) ratios, combined with sulfide concentration in the sediment and/or porewater, suggest a hydrothermally-induced seafloor redox gradient. This gradient overlaps with changing high affinity phosphate uptake gene abundance. High affinity phosphate uptake and As cycling genes are depleted in the sulfide-rich settings, relative to the more oxidizing habitats where mainly Fe(III)(oxyhydr)oxides are precipitated. In addition, a habitat-wide low As-respiring and As-oxidizing gene content relative to As resistance gene richness, suggests that As detoxification is prioritized over metabolic As cycling in the sediments. Collectively, the data point to redox control on Fe and S mineralization as a decisive factor in the regulation of high affinity phosphate uptake and As cycling gene content in shallow submarine hydrothermal ecosystems along the HVA.

  • 15. Christensen, T R
    et al.
    Panikov, N
    Mastepanov, M
    Joabsson, A
    Stewart, A
    Oquist, M
    Sommerkorn, M
    Reynaud, S
    Svensson, B
    Biotic controls on CO2 and CH4 exchange in wetlands - a closed environment study2003In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 64, no 3, p. 337-354Article in journal (Refereed)
    Abstract [en]

    Wetlands are significant sources of the important greenhouse gas CH4. Here we explore the use of an experimental system developed for the determination of continuous fluxes of CO2 and CH4 in closed ecosystem monoliths including the capture of (CO2)-C-14 and (CH4)-C-14 following pulse labelling with (CO2)-C-14. We show that, in the ecosystem studied, ebullition (bubble emission) may account for 18 to 50% of the total CH4 emission, representing fluxes that have been difficult to estimate accurately in the past. Furthermore, using plant removal and C-14 labelling techniques, we use the system to detail the direct influence of vascular plants on CH4 emission. This influence is observed to be dependent on the amount of vascular plants present. The results that may be produced using the presented experimental set-up have implications for an improved understanding of wetland ecosystem/atmosphere interactions, including possible feedback effects on climate change. In recent years much attention has been devoted to ascertaining and subsequently using the relationship between net ecosystem productivity and CH4 emission as a basis for extrapolation of fluxes across large areas. The experimental system presented may be used to study the complex relationship between vascular plants and CH4 emission and here we show examples of how this may vary considerably in nature between and even within ecosystems.

  • 16. Christensen, TR
    et al.
    Panikov, N
    Mastepanov, M
    Joabsson, A
    Stewart, A
    Oquist, M
    Sommerkorn, M
    Reynaud, S
    Svensson, Bo
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Biotic controls on CO2 and CH4 exchange in wetlands - a closed environment study2003In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 64, no 3, p. 337-354Article in journal (Refereed)
    Abstract [en]

    Wetlands are significant sources of the important greenhouse gas CH4. Here we explore the use of an experimental system developed for the determination of continuous fluxes of CO2 and CH4 in closed ecosystem monoliths including the capture of (CO2)-C-14 and (CH4)-C-14 following pulse labelling with (CO2)-C-14. We show that, in the ecosystem studied, ebullition (bubble emission) may account for 18 to 50% of the total CH4 emission, representing fluxes that have been difficult to estimate accurately in the past. Furthermore, using plant removal and C-14 labelling techniques, we use the system to detail the direct influence of vascular plants on CH4 emission. This influence is observed to be dependent on the amount of vascular plants present. The results that may be produced using the presented experimental set-up have implications for an improved understanding of wetland ecosystem/atmosphere interactions, including possible feedback effects on climate change. In recent years much attention has been devoted to ascertaining and subsequently using the relationship between net ecosystem productivity and CH4 emission as a basis for extrapolation of fluxes across large areas. The experimental system presented may be used to study the complex relationship between vascular plants and CH4 emission and here we show examples of how this may vary considerably in nature between and even within ecosystems.

  • 17. Clair, T.A.,
    et al.
    Dennis, I.F.
    Vet, R.
    Laudon, Hjalmar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Long-term trends in catchment organic carbon and nitrogen exports from three acidified catchments in Nova Scotia, Canada2008In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Biogeochemistry, Vol. 87, no 1, p. 83-97Article in journal (Refereed)
    Abstract [en]

    We sampled two streams in southwestern Nova Scotia from 1983 to 2004 and one stream from 1992 to 2004 for total organic carbon (TOC) and nitrogen (TN) in order to investigate if changes in catchment exports could be determined over the sampling periods, and if so what were the controlling factors. We first show that early TOC measurements underestimated concentrations due to analytical shortcomings and then produce a correction to adjust values to more accurate levels. Our trend results showed that TOC concentrations decreased in the two streams with the longest record, from 1980 to 1992 when acid deposition to the area decreased most rapidly, and have remained constant since then. TOC exports only decreased at one site over the total sampling period. As expected, we also measured seasonal changes in exports, with the autumn period showing TOC and TN exports as high as during spring snowmelt. We found that only 24% of deposition N is exported from the larger catchments, most of it in organic form, while the smallest catchment exported 16%. We also show a constant increase in TN from 1994 to the present at all three sites sampled. Our results do not support the hypothesis that reductions in sulfur acidification lead to increases in catchment organic carbon mobilization to streams.

    Download full text (pdf)
    fulltext
  • 18.
    Comstedt, Daniel
    et al.
    Örebro University, School of Science and Technology.
    Boström, Björn
    Örebro University, School of Science and Technology.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    Autotrophic and heterotrophic soil respiration in a Norway spruce forest: estimating the root decomposition and soil moisture effects in a trenching experiment2011In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 104, no 1-3, p. 121-132Article in journal (Refereed)
    Abstract [en]

    The two components of soil respiration, autotrophic respiration (from roots, mycorrhizal hyphae and associated microbes) and heterotrophic respiration (from decomposers), was separated in a root trenching experiment in a Norway spruce forest. In June 2003, cylinders (29.7 cm diameter) were inserted to 50 cm soil depth and respiration was measured both outside (control) and inside the trenched areas. The potential problems associated with the trenching treatment, increased decomposition of roots and ectomycorrhizal mycelia and changed soil moisture conditions, were handled by empirical modelling. The model was calibrated with respiration, moisture and temperature data of 2004 from the trenched plots as a training set. We estimate that over the first 5 months after the trenching, 45% of respiration from the trenched plots was an artefact of the treatment. Of this, 29% was a water difference effect and 16% resulted from root and mycelia decomposition. Autotrophic and heterotrophic respiration contributed to about 50% each of total soil respiration in the control plots averaged over the two growing seasons. We show that the potential problems with the trenching, decomposing roots and mycelia and soil moisture effects, can be handled by a modelling approach, which is an alternative to the sequential root harvesting technique.

  • 19.
    Dahlgren Strååt, Kim
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sobek, Anna
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Smedberg, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Undeman, Emma
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Modeling total particulate organic carbon (POC) flows in the Baltic Sea catchment2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 128, no 1-2, p. 51-65Article in journal (Refereed)
    Abstract [en]

    The largest input source of carbon to the Baltic Sea catchment is river discharge. A tool for modeling riverine particulate organic carbon (POC) loads on a catchment scale is currently lacking. The present study describes a novel dynamic model for simulating flows of POC in all major rivers draining the Baltic Sea catchment. The processes governing POC input and transport in rivers described in the model are soil erosion, in-stream primary production and litter input. The Baltic Sea drainage basin is divided into 82 sub-basins, each comprising several land classes (e.g. forest, cultivated land, urban areas) and parameterized using GIS data on soil characteristics and topography. Driving forces are temperature, precipitation, and total phosphorous concentrations. The model evaluation shows that the model can predict annual average POC concentrations within a factor of about 2, but generally fails to capture the timing of monthly peak loads. The total annual POC load to the Baltic Sea is estimated to be 0.34 Tg POC, which constitutes circa 7-10 % of the annual total organic carbon (TOC) load. The current lack of field measurements of POC in rivers hampers more accurate predictions of seasonality in POC loads to the Baltic Sea. This study, however, identifies important knowledge gaps and provides a starting point for further explorations of large scale POC mass flows.

  • 20. De Brabandere, Loreto
    et al.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kononets, Mikhail Y.
    Viktorsson, Lena
    Stigebrandt, Anders
    Thamdrup, Bo
    Hall, Per O. J.
    Oxygenation of an anoxic fjord basin strongly stimulates benthic denitrification and DNRA2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 126, no 1-2, p. 131-152Article in journal (Refereed)
    Abstract [en]

    Hypoxia hampers eutrophication reduction efforts by enabling high nutrient fluxes from sediment to bottom waters. Oxygenation of hypoxic water bodies is often proposed to reduce benthic ammonium and phosphate release. This study investigates the functional response of benthic nitrate-reducing processes to a long-term engineered oxygenation effort in a density-stratified fjord with euxinic bottom waters. Oxygenation was achieved by mixing surface water with deep, euxinic water, which increased oxygen and nitrate concentrations in the deep water column. The presence of nitrate instigated benthic nitrate reduction in the newly oxidized sediments by equally stimulating denitrification and dissimilatory nitrate reduction to ammonium (DNRA). DNRA and total nitrate reduction rates, as well as the contribution of DNRA to total nitrate reduction, decreased with increasing exposure time of the sediments to oxygen. The relative importance of DNRA as a nitrate sink was correlated to nitrate concentrations, with more nitrate being reduced to ammonium at higher bottom water nitrate concentrations. Overall, engineered oxygenation decreased the net efflux of dissolved inorganic nitrogen from the sediments by stimulating net nitrate removal through denitrification.

  • 21.
    Destouni, Georgia
    et al.
    KTH, Superseded Departments (pre-2005), Land and Water Resources Engineering.
    Prieto, Carmen
    KTH, Superseded Departments (pre-2005), Land and Water Resources Engineering.
    On the possibility for generic modeling of submarine groundwater discharge2003In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 66, no 1-2, p. 171-186Article in journal (Refereed)
    Abstract [en]

    We simulate large-scale dynamics of submarine groundwater discharge (SGD) in three different coastal aquifers on the Mediterranean Sea. We subject these aquifers to a wide range of different groundwater management conditions, leading to widely different net groundwater drainage from land to sea. The resulting SGD at steady-state is quantifiable and predictable by simple linearity in the net land-determined groundwater drainage, defined as total fresh water drainage minus groundwater extraction in the coastal aquifer system. This linearity appears to be general and independent of site-specific, variable and complex details of hydrogeology, aquifer hydraulics, streamlines and salinity transition zones in different coastal systems. Also independently of site-specifics, low SGD implies high seawater content due to seawater intruding into the aquifer and mixing with fresh groundwater within a wide salinity transition zone in the aquifer. Increasing SGD implies decreasing seawater content, decreased mixing between seawater and fresh groundwater and narrowing of the salinity transition zone of brackish groundwater in the aquifer.

  • 22.
    Duc, Nguyen Thanh
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick, M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, David
    Implications of temperature and sediment characteristics on methane formation and oxidation in lake sediments2010In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 100, no 1-3, p. 185-196Article in journal (Refereed)
    Abstract [en]

    Methane emissions from aquatic environments depend on methane formation (MF) and methane oxidation (MO) rates. One important question is to what extent increased temperatures will affect the balance between MF and MO. We measured potential MF and MO rates simultaneously at 4, 10, 20 and 30A degrees C in sediment from eight different lakes representing typical boreal and northern temperate lake types. Potential MF rates ranged between 0.002 and 3.99 mu mol CH4 g(d.w.) (-1) day(-1), potential MO rates ranged from 0.01 to 0.39 CH4 g(d.w.) (-1) day(-1). The potential MF rates were sensitive to temperature and increased 10 to 100 fold over the temperature interval studied. MF also differed between lakes and was correlated to sediment water content, percent of organic material and C:N ratio. Potential MO did not depend on temperature or sediment characteristics but was instead well explained by MF rates at the in situ temperature. It implies that elevated temperatures will enhance MF rates which may cause increased methane release from sediments until MO increases as well, as a response to higher methane levels.

  • 23.
    Eriksson Hägg, Hanna
    et al.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Humborg, Christoph
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Swaney, D. P.
    Mörth, Carl-Magnus
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Riverine nitrogen export in Swedish catchments dominated by atmospheric inputs2012In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 111, no 1-3, p. 203-217Article in journal (Refereed)
    Abstract [en]

    We present the first estimates of net anthropogenic nitrogen input (NANI) in European boreal catchments. In Swedish catchments, nitrogen (N) deposition is a major N input (31-94%). Hence, we used two different N deposition inputs to calculate NANI for 36 major Swedish catchments. The relationship between riverine N export and NANI was strongest when using only oxidized deposition (NOy) as atmospheric input (r(2) = 0.70) rather than total deposition (i.e., both oxidized and reduced nitrogen, NOy + NHx deposition, r(2) = 0.62). The y-intercept (NANI = 0) for the NANI calculated with NOy is significantly different from zero (p = 0.0042*) and indicates a background flux from the catchment of some 100 kg N km(-2) year(-1) in addition to anthropogenic inputs. This agrees with similar results from North American boreal catchments. The slope of the linear regressions was 0.25 for both N deposition inputs (NOy and NOy + NHx), suggesting that on average, 25% of the anthropogenic N inputs is exported by rivers to the Baltic Sea. Agricultural catchments in central and southern Sweden have increased their riverine N export up to tenfold compared to the inferred background flux. Although the relatively unperturbed northernmost catchments receive significant N loads from atmospheric deposition, these catchments do not show significantly elevated riverine N export. The fact that nitrogen export in Swedish catchments appears to be higher in proportion to NANI at higher loads suggests that N retention may be saturating as loading rates increase. In northern and western Sweden the export of nitrogen is largely controlled by the hydraulic load, i.e., the riverine discharge normalized by water surface area, which has units of distance time(-1). Besides hydraulic load the percent total forest cover also affects the nitrogen export primarily in the northern and western catchments.

  • 24.
    Frings, Patrick J
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Clymans, Wim
    Jeppesen, Erik
    Lauridsen, Torben L
    Struyf, Eric
    Conley, Daniel J
    Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration2014In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 117, no 2-3, p. 255-277Article in journal (Refereed)
    Download full text (pdf)
    fulltext
  • 25.
    Frings, Patrick
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Nantke, Carla
    Stadmark, Johanna
    Si cycling in transition zones: a study of Si isotopes and biogenic silica accumulation in the Chesapeake Bay through the Holocene2019In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 146, no 2, p. 145-170Article in journal (Refereed)
  • 26.
    Giesler, Reiner
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Esberg, Camilla
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lagerström, Anna
    Graae, Bente J
    Phosphorus availability and microbial respiration across different tundra vegetation types2012In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 108, no 1-3, p. 429-445Article in journal (Refereed)
    Abstract [en]

    Phosphorus (P) is an important nutrient in tundra ecosystems that co-limits or in some cases limits primary production. The availability of P is largely driven by soil characteristics, e.g., pH, organic carbon, and abundance of P-sorbing elements such as aluminium (Al) or iron (Fe). We tested how vegetation and soil properties relate to P availability across different tundra vegetation types. The different soil P fractions in the organic horizon were measured and plant foliar nitrogen (N) to P ratio and a plant bioassay was used as indicators of plant nutrient status. Microbial bioassays were used to study microbial respiration kinetics and in response to carbon, N, and P amendments. The distribution of P fractions differed significantly across vegetation types; labile fractions of P were less abundant in meadow sites compared to heath sites. Calcium-phosphates seemed to be an important P-fraction in meadows, but were only found in lower concentrations in the heath. There were only small differences in NaOH–extractable P between the vegetation types and this correlated with the distribution of oxalate-extractable Al. Plant N:P ratios and the plant bioassay indicated decreasing P availability from dry heath to mesic heath to mesic meadow. The microbial bioassay suggests that the heterotrophic microbial community is C-limited with N as a secondary limiting nutrient although there were indications that microbial P availability was lower in the meadow sites. Overall, we suggest that the observed variations in soil P across vegetation types are affecting both plant and microbial function although the differences seem to be relatively small.

  • 27.
    Guelland, Kathi
    et al.
    Institute of biogeochemistry and pollutant dynamics, ETH Zurich.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Göransson, H.
    Bernasconi, S. M.
    Hajdas, I.
    Kretzschmar, R.
    Evolution of carbon fluxes during initial soil formation along the forefield of Damma glacier, Switzerland2013In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 113, no 1-3, p. 545-561Article in journal (Refereed)
    Abstract [en]

    Soil carbon (C) fluxes, soil respiration and dissolved organic carbon (DOC) leaching were explored along the young Damma glacier forefield chronosequence (7-128 years) over a three-year period. To gain insight into the sources of soil CO2 effluxes, radiocarbon signatures of respired CO2 were measured and a vegetation-clipping experiment was performed. Our results showed a clear increase in soil CO2 effluxes with increasing site age from 9 +/- A 1 to 160 +/- A 67 g CO2-C m(-2) year(-1), which was linked to soil C accumulation and development of vegetation cover. Seasonal variations of soil respiration were mainly driven by temperature; between 62 and 70 % of annual CO2 effluxes were respired during the 4-month long summer season. Sources of soil CO2 effluxes changed along the glacier forefield. For most recently deglaciated sites, radiocarbon-based age estimates indicated ancient C to be the dominant source of soil-respired CO2. At intermediate site age (58-78 years), the contribution of new plant-fixed C via rhizosphere respiration amounted up to 90 %, while with further soil formation, heterotrophically respired C probably from accumulated 'older' soil organic carbon (SOC) became increasingly important. In comparison with soil respiration, DOC leaching at 10 cm depth was small, but increased similarly from 0.4 +/- A 0.02 to 7.4 +/- A 1.6 g DOC m(-2) year(-1) over the chronosequence. A strong rise of the ratio of SOC to secondary iron and aluminium oxides strongly suggests that increasing DOC leaching with site age results from a faster increase of the DOC source, SOC, than of the DOC sink, reactive mineral surfaces. Overall, C losses from soil by soil respiration and DOC leaching increased from 9 +/- A 1 to 70 +/- A 17 and further to 168 +/- A 68 g C m(-2) year(-1) at the < 10, 58-78, and 110-128 year old sites. By comparison, total ecosystem C stocks increased from 0.2 to 1.1 and to 3.1 kg C m(-2) from the young to intermediate and old sites. Therefore, the ecosystem evolved from a dominance of C accumulation in the initial phase to a high throughput system. We suggest that the relatively strong increase in soil C stocks compared to C fluxes is a characteristic feature of initial soil formation on freshly exposed rocks.

  • 28.
    Gustafsson, Erik
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Savchuck, Oleg P.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Müller-Karulis, Bärbel
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Key processes in the coupled carbon, nitrogen, and phosphorus cycling of the Baltic Sea2017In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 134, no 3, p. 301-317Article in journal (Refereed)
    Abstract [en]

    In this study we examine pools of carbon (C), nitrogen (N), and phosphorus (P) in the Baltic Sea, both simulated and reconstructed from observations. We further quantify key fluxes in the C, N, and P cycling. Our calculations include pelagic reservoirs as well as the storage in the active sediment layer, which allows a complete coverage of the overall C, N, and P cycling on a system-scale. A striking property of C versus N and P cycling is that while the external supplies of total N and P (TN and TP) are largely balanced by internal removal processes, the total carbon (TC) supply is mainly compensated by a net export out of the system. In other words, external inputs of TN and TP are, in contrast to TC, rather efficiently filtered within the Baltic Sea. Further, there is a net export of TN and TP out of the system, but a net import of dissolved inorganic N and P (DIN and DIP). There is on the contrary a net export of both the organic and inorganic fractions of TC. While the pelagic pools of TC and TP are dominated by inorganic compounds, TN largely consists of organic N because allochthonous organic N is poorly degradable. There are however large basin-wise differences in C, N, and P elemental ratios as well as in inorganic versus organic fractions. These differences reflect both the differing ratios in external loads and differing oxygen conditions determining the redox-dependent fluxes of DIN and DIP.

    Download full text (pdf)
    fulltext
  • 29.
    Gómez-Gener, Lluís
    et al.
    Department of Ecology, University of Barcelona.
    Obrador, Biel
    Department of Ecology, University of Barcelona.
    von Schiller, Daniel
    Department of Plant Biology and Ecology, Faculty of Science and Technology, University of the Basque Country.
    Marcé, Rafael
    Catalan Institute for Water Research, Scientific and Technological Park of the University of Girona.
    Casas-Ruiz, Joan Pere
    Catalan Institute for Water Research, Scientific and Technological Park of the University of Girona.
    Proia, Lorenzo
    Catalan Institute for Water Research, Scientific and Technological Park of the University of Girona.
    Acuña, Vicenç
    Catalan Institute for Water Research, Scientific and Technological Park of the University of Girona.
    Catalán, Núria
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Muñoz, Isabel
    Department of Ecology, University of Barcelona.
    Koschorreck, Matthias
    Department Lake Research, Helmholtz Centre for Environmental Research.
    Hot spots for carbon emissions from Mediterranean fluvial networks during summer drought2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 125, no 3, p. 409-426Article in journal (Refereed)
    Abstract [en]

    During summer drought, Mediterranean fluvial networks are transformed into highly heterogeneous landscapes characterized by different environments (i.e., running and impounded waters, isolated river pools and dry beds). This hydrological setting defines novel biogeochemically active areas that could potentially increase the rates of carbon emissions from the fluvial network to the atmosphere. Using chamber methods, we aimed to identify hot spots for carbon dioxide (CO2) and methane (CH4) emissions from two typical Mediterranean fluvial networks during summer drought. The CO2 efflux from dry beds (mean ± SE = 209 ± 10 mmol CO2 m−2 d−1) was comparable to that from running waters (120 ± 33 mmol m−2 d−1) and significantly higher than from impounded waters (36.6 ± 8.5 mmol m−2 d−1) and isolated pools (17.2 ± 0.9 mmol m−2 d−1). In contrast, the CH4 efflux did not significantly differ among environments, although the CH4 efflux was notable in some impounded waters (13.9 ± 10.1 mmol CH4 m−2 d−1) and almost negligible in the remaining environments (mean <0.3 mmol m−2 d−1). Diffusion was the only mechanism driving CO2 efflux in all environments and was most likely responsible for CH4 efflux in running waters, isolated pools and dry beds. In contrast, the CH4 efflux in impounded waters was primarily ebullition-based. Using a simple heuristic approach to simulate potential changes in carbon emissions from Mediterranean fluvial networks under future hydrological scenarios, we show that an extreme drying out (i.e., a four-fold increase of the surface area of dry beds) would double the CO2 efflux from the fluvial network. Correspondingly, an extreme transformation of running waters into impounded waters (i.e., a twofold increase of the surface area of impounded waters) would triple the CH4 efflux. Thus, carbon emissions from dry beds and impounded waters should be explicitly considered in carbon assessments of fluvial networks, particularly under predicted global change scenarios, which are expected to increase the spatial and temporal extent of these environments.

  • 30.
    Haei, Mahsa
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Öquist, Mats G.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Ilstedt, Ulrik
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    The influence of soil frost on the quality of dissolved organic carbon in a boreal forest soil: combining field and laboratory experiments2012In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 107, no 1-3, p. 95-106Article in journal (Refereed)
    Abstract [en]

    Riparian soils exert a major control on stream water dissolved organic carbon (DOC) in northern latitudes. As the winter climate in northern regions is predicted to be particularly affected by climate change, we tested the sensitivity of DOC formation to winter conditions in riparian soils using an 8 year field-scale soil frost manipulation experiment in northern Sweden. In conjunction with the field experiment, we also carried out a laboratory experiment based on three levels of four winter climatic factors: frost intensity, soil water content, frost duration and frequency of freeze–thaw cycles. We evaluated changes in lability of DOC in soil solution from lysimeter samples taken at different depths (10–80 cm) as well as from DOC extracted from soils in the laboratory, using carbon-specific ultraviolet absorbance at 254 nm (sUVA254). In the field, significantly more labile DOC was observed during the spring and summer from upper horizons of frost-exposed soils, when compared to controls. In addition, the amount of labile DOC was positively correlated with frost duration at a soil depth of 10 cm. In the laboratory, frost intensity was the factor that had the greatest positive influence on DOC lability; it also reduced the C:N ratio which may indicate a microbial origin of the DOC. The laboratory experiment also demonstrated significant interactions between some of the applied climatic factors, such as frost intensity interacting with water content. In combination, field and laboratory experiments demonstrate that winter soil conditions have profound effects on DOC-concentration and quality during subsequent seasons.

  • 31.
    Hansson, Sophia V.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kaste, James M.
    College of William & Mary.
    Chen, Keyao
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bindler, Richard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Beryllium-7 as a natural tracer for short-term downwash in peat2014In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 119, no 1-3, p. 329-339Article in journal (Refereed)
    Abstract [en]

    Several factors can affect the integrity of natural archives such as peat records, e.g., decomposition and nutrient cycling, and it has also been hypothesized that some rapid downward transport of atmospherically derived elements may occur. We test this hypothesis by analyzing the short-lived, natural tracer beryllium-7 (tA1/2A = 53.4 days) in five cores from two peatlands. In triplicate hummock cores from a raised bog in southern Sweden, Be-7 could be measured to 20, 18 and 8 cm depth, and in a nutrient-poor mire in northern Sweden to a depth of 16 cm in a Sphagnum lawn core, but only 4 cm in the dominant, more-decomposed fen peat, indicating some spatial variability both within and between sites. Total Be-7 inventories were 320-450 Bq m(-2) in the bog, and 150 Bq m(-2) (lawn) and 240 Bq m(-2) (fen peat) in the mire. 25-79 % of the total inventory of Be-7 was located in the upper 2-cm layer. To further test downwashing, in the laboratory we applied a CuBr-solution to two cores and a Cu-solution to one core taken from the mire Sphagnum lawn, all with low water table conditions. About 50 % of the added Cu and similar to 35 % of the added Br were retained in the surface (2 cm) layer; 1-3 % of the Cu was found at 8-12 cm depth and similar to 1 % of the Br was measured in the lowest level (20-22 cm). Based on our novel approach using Be-7 and experimental work we show that short-term downwashing can occur in peatlands and we suggest the depth of this will depend on the properties of the peat, e.g., bulk density and decomposition, as well as hydrology.

  • 32. Hodgkins, Suzanne B.
    et al.
    Chanton, Jeffrey P.
    Langford, Lauren C.
    McCalley, Carmody K.
    Saleska, Scott R.
    Rich, Virginia I.
    Crill, Patrick M.
    Cooper, William T.
    Soil incubations reproduce field methane dynamics in a subarctic wetland2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 126, no 1, p. 241-249Article in journal (Refereed)
    Abstract [en]

    A major challenge in peatland carbon cycle modeling is the estimation of subsurface methane (CH4) and carbon dioxide (CO2) production and consumption rates and pathways. The most common methods for modeling these processes are soil incubations and stable isotope modeling, both of which may involve departures from field conditions. To explore the impacts of these departures, we measured CH4/CO2 concentration ratios and 13C fractionation factors (αC, indicating CH4 production pathways) in field pore water from a thawing subarctic peatland, and compared these values to those observed in incubations of corresponding peat samples. Incubation CH4/CO2 production ratios were significantly and positively correlated with observed field CH4/CO2 concentration ratios, though observed field ratios were ~20 % of those in incubations due to CH4’s lower solubility in pore water. After correcting the field ratios for CH4 loss with an isotope mass balance model, the incubation CH4/CO2 ratios and αC were both significantly positively correlated with field ratios and αC (respectively), both with slopes indistinguishable from 1. Although CH4/CO2 ratios and αC were slightly higher in the incubations, these shifts were consistent along the thaw progression, indicating that ex situ incubations can replicate trends in in situ CH4 production.

  • 33. Hodgkins, Suzanne B.
    et al.
    Chanton, Jeffrey P.
    Langford, Lauren C.
    McCalley, Carmody K.
    Saleska, Scott R.
    Rich, Virginia I.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cooper, William T.
    Soil incubations reproduce field methane dynamics in a subarctic wetland2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 126, no 1-2, p. 241-249Article in journal (Refereed)
    Abstract [en]

    A major challenge in peatland carbon cycle modeling is the estimation of subsurface methane (CH4) and carbon dioxide (CO2) production and consumption rates and pathways. The most common methods for modeling these processes are soil incubations and stable isotope modeling, both of which may involve departures from field conditions. To explore the impacts of these departures, we measured CH4/CO2 concentration ratios and C-13 fractionation factors (alpha(C), indicating CH4 production pathways) in field pore water from a thawing subarctic peatland, and compared these values to those observed in incubations of corresponding peat samples. Incubation CH4/CO2 production ratios were significantly and positively correlated with observed field CH4/CO2 concentration ratios, though observed field ratios were similar to 20 % of those in incubations due to CH4's lower solubility in pore water. After correcting the field ratios for CH4 loss with an isotope mass balance model, the incubation CH4/CO2 ratios and alpha(C) were both significantly positively correlated with field ratios and alpha(C) (respectively), both with slopes indistinguishable from 1. Although CH4/CO2 ratios and alpha(C) were slightly higher in the incubations, these shifts were consistent along the thaw progression, indicating that ex situ incubations can replicate trends in in situ CH4 production.

  • 34. Hodson, Andy
    et al.
    Roberts, Tjarda Jane
    Engvall, Anne-Christin
    Stockholm University, Faculty of Science, Department of Meteorology .
    Holmen, Kim
    Mumford, Paul
    Glacier ecosystem response to episodic nitrogen enrichment in Svalbard, European High Arctic2010In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 98, no 03-jan, p. 171-184Article in journal (Refereed)
    Abstract [en]

    We describe the climatology, hydrology and biogeochemistry of an extreme nitrogen deposition event that occurred in the highly glacierised environment of the European High Arctic during June 1999. Meteorological analysis, three-dimensional air mass trajectories and a 3D transport model show that blocking high pressures over Scandinavia and the rapid advection of western European pollution toward Svalbard were sufficient to cause the most concentrated (1.15 ppm NO3-N and 1.20 ppm NH4-N), high magnitude (total 26 mm and up to 2.4 mm h(-1) at 30 m above sea level) nitrogen deposition event on record in this sensitive, high Arctic environment (78.91A degrees A N, 11.93A degrees A E). Since the event occurred when much of the catchment remained frozen or under snow cover, microbial utilisation of nitrogen within snowpacks and perennially unfrozen subglacial sediments, rather than soils, were mostly responsible for reducing N export. The rainfall event occurred long before the annual subglacial outburst flood and so prolonged (ca. 10 day) water storage at the glacier bed further enhanced the microbial assimilation. When the subglacial outburst eventually occurred, high runoff and concentrations of NO3 (-) (but not NH4 (+)) returned in the downstream rivers. Assimilation accounted for between 53 and 72% of the total inorganic nitrogen deposited during the event, but the annual NO3 (-) and NH4 (+) runoff yields were still enhanced by up to 5 and 40 times respectively. Episodic atmospheric inputs of reactive nitrogen can therefore directly influence the biogeochemical functioning of High Arctic catchments, even when microbial activity takes place beneath a glacier at a time when terrestrial soil ecosystems remain frozen and unresponsive.

  • 35.
    Holmström, Sara
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Lundström, Ulla
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Finlay, Roger
    van Hees, Patrick
    Siderophores in forest soil solution2004In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 71, no 2, p. 247-258Article in journal (Refereed)
    Abstract [en]

    Siderophores in soil solution of coniferous forest soils have been chemically identified for the first time. We have identified the siderophores ferrichrome and ferricrocin in soil solution of the upper organic layer by High Performance Liquid Chromatography Mass Spectrometry (HPLC-MS). The soil solutions were sampled from mor layers of podzolic soils from the south and the north of Sweden and from a mor layer overlying granitic rock and intensively colonised by ectomycorrhizal hyphae. Ferrichrome was found in nanomolar concentrations in all soil solutions investigated and ferricrocin only in the soil solution from the mor layer covering a rock and in the soil solution from the north of Sweden. The findings are discussed in relation to the possible role of fungal hyphae and siderophores in weathering minerals in podzolic soils under coniferous forests. Citric and oxalic acid are able to dissolve minerals via complexation of cations from the mineral. Siderophores should be, kinetically and thermodynamically even more efficient complexing agents for trivalent cations than oxalic and citric acid. The present study provides direct for presence of siderophores in soil solution.

  • 36. Hong, Bongghi
    et al.
    Swaney, Dennis P.
    McCrackin, Michelle
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Svanbäck, Annika
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Gustafsson, Bo
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Yershova, Alexandra
    Pakhomau, Aliaksandr
    Advances in NANI and NAPI accounting for the Baltic drainage basin: spatial and temporal trends and relationships to watershed TN and TP fluxes2017In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 133, no 3, p. 245-261Article in journal (Refereed)
    Abstract [en]

    In order to assess the progress toward eutrophication management goals, it is important to understand trends in land-based nutrient use. Here we present net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI, respectively) for 2000 and 2010 for the Baltic Sea watershed. Overall, across the entire Baltic, between the 5-year periods centered on 2000 and 2010, NANI and NAPI decreased modestly by -6 and -4%, respectively, but with substantial regional variation, including major increases in the Gulf of Riga drainage basin (+19 and +58%, respectively) and decreases in the Danish Straits drainage basin (-25 and -40% respectively). The changes were due primarily to changes in mineral fertilizer use. Mineral fertilizers dominated inputs, at 57% of both NANI and NAPI in 2000, increasing to 68 and 70%, respectively, by 2010. Net food and feed imports declined over that period, corresponding to increased crop production; either fewer imports of food and feedstocks were required to feed humans and livestock, or more of these commodities were exported. A strong linear relationship exists between regional net nutrient inputs and riverine nutrient fluxes for both periods. About 17% of NANI and 4.7% of NAPI were exported to the sea in 2000; these relationships did not significantly differ from those for 2010. Changes in NANI from 2000 to 2010 across basins were directly proportional rather than linearly related to changes in total N (TN) fluxes to the sea (i.e., no change in NANI suggests no change in TN flux). Similarly, for all basins except those draining to the Baltic Proper, changes in NAPI were proportional to changes in total P (TP) fluxes. The Danish Straits decreased most between 2000 and 2010, where NANI and NAPI declined by 25 and 40%, respectively, and corresponding fluxes of TN and TP declined 31 and 18%, respectively. For the Baltic Proper, NAPI was relatively unchanged between 2000 and 2010, while riverine TP fluxes decreased 25%, due possibly to lagged effects of fertilizer reduction resulting from socio-political changes in the early 1990s or improvements in sewage treatment capabilities. For most regions, further reductions in NANI and NAPI could be achieved by more efficient production and greater substitution of manure for imported mineral fertilizers.

  • 37.
    Isles, Peter D. F.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Rubenstein Ecosystem Science Laboratory, University of Vermont, Burlington, VT, USA; Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington, VT, USA; Vermont EPSCoR, University of Vermont, Burlington, VT, USA.
    Xu, Yaoyang
    Stockwell, Jason D.
    Schroth, Andrew W.
    Climate-driven changes in energy and mass inputs systematically alter nutrient concentration and stoichiometry in deep and shallow regions of Lake Champlain2017In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 133, no 2, p. 201-217Article in journal (Refereed)
    Abstract [en]

    Concentrations of nitrogen (N) and phosphorus (P) in lakes may be differentially impacted by climate-driven changes in nutrient loading and by direct impacts of temperature and wind speed on internal nutrient cycling. Such changes may result in systematic shifts in lake N:P under future climate warming. We used 21 years of monitoring data to compare long-term and intra-annual trends in total N (TN), total P (TP) and TN:TP at 15 sites in Lake Champlain to concurrent measurements of watershed nutrient inputs and meteorological drivers. TN:TP declined sharply lake-wide, particularly in the past decade, yet the drivers of this trend varied based on site depth. In deep sites, declines were driven by changes in watershed loading of dissolved P and N and (in some cases) by decreases in hypolimnetic dissolved oxygen. In shallow sites, declines in TN:TP were primarily driven by long-term increases in temperature and decreases in wind speed, and exhibited systematic seasonal variability in TN:TP due to the timing of sediment P loading, N removal processes, and external nutrient inputs. We developed a conceptual model to explain the observed trends, and suggest that while climate drivers have affected nutrient dynamics in shallow and deep sites differently, both deep and shallow sites are likely to experience further declines in N:P and increases in cyanobacteria dominance if recent climate trends continue.

    Download full text (pdf)
    fulltext
  • 38.
    Jansson, Per-Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Svensson, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Berggren Kleja, Dan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Simulated climate change impacts on fluxes of carbon in Norway spruce ecosystems along a climatic transect in Sweden2008In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 89, no 1, p. 81-94Article in journal (Refereed)
    Abstract [en]

    A simulation study based on recent regional climate scenarios for Sweden investigated possible changes in carbon (C) dynamics and net ecosystem exchange (NEE) of Swedish Norway spruce forest ecosystems. Four sites, representative of well-drained soils in four regions, were included. Stand development was simulated for a 100-year rotation period using a coupled model describing abiotic and biotic processes in the soil-plant-atmosphere system. Two IPCC climate change scenarios, corresponding to a mean annual temperature increase of about 2 degrees C (A2) or 3 degrees C (B2) from the reference period 1961-1990 to a new period 2061-2090, were considered. Annual maximum snow depth decreased with the increase in air temperature, whereas maximum soil frost depth and mean annual soil temperature showed only small changes, especially for the sites in northern Sweden. Simulations suggested that in the warmer climate, gross primary production (GPP) increased by 24-32% in northern Sweden and by 32-43% in the south. In the north, the increase was related to the combined effect of air and soil temperature extending the growing season, whereas in the south it was mainly governed by increased N availability due to increased soil temperature. NEE increased by about 20% (A2) or 25% (B2) at all sites, more or less solely due to increased accumulation of C in the tree biomass (including harvest residues), since changes in soil C were small compared with the current climate. Both light use efficiency and water use efficiency were improved in the future climate scenarios, despite increases in atmospheric CO2 not being considered.

  • 39.
    Johnsen, Anders R.
    et al.
    Geol Survey Denmark & Greenland GEUS, Dept Geochemistry, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark..
    Jacobsen, Ole S.
    Geol Survey Denmark & Greenland GEUS, Dept Geochemistry, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark..
    Gudmundsson, Lasse
    Geol Survey Denmark & Greenland GEUS, Dept Geochemistry, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark..
    Albers, Christian N.
    Geol Survey Denmark & Greenland GEUS, Dept Geochemistry, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.;Univ Copenhagen, Dept Geosci & Nat Resource Management, Ctr Permafrost CENPERM, Copenhagen K, Denmark..
    Chloroform emissions from arctic and subarctic ecosystems in Greenland and Northern Scandinavia2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 130, no 1-2, p. 53-65Article in journal (Refereed)
    Abstract [en]

    The aim of our study was to estimate emissions of natural chloroform from soil in arctic and subarctic ecosystems. We therefore determined the seasonal and spatial variation in soil-to-air fluxes of chloroform at 11 sites representing typical vegetation types in Greenland (Narsarsuaq, Kangerlussuaq and Disko Island) and northern Scandinavia (Abisko). Fluxes of chloroform showed a large variation, ranging from 4 to 2850 ng m(-2) h(-1). The local variation within a 12-m transect at each site was frequently five to tenfold, which emphasizes the need for multiple measurements even within field plots that seem homogenous. At one site, the transect was extended to 58 m and 40 measurements and a large number of environmental parameters were recorded as well. In this transect, collars separated by 60 cm distances were in most cases similar but at 3 m distance variation was as big as between collars with greater separation. CO2 flux was the parameter that showed the most correlation to the chloroform flux in the extended transect. Chloroform fluxes also varied over the year, but this variation was smaller than the variation between the five collars of each site and much smaller than the variation between sites. All arctic sites except a non-tussock sedge wetland showed low fluxes. A subarctic pine forest had by far the highest fluxes. Subarctic and boreal coniferous forests generally seem to be important global sources of biogenic chloroform to the troposphere. The future spatial extent of coniferous forest in the subarctic to arctic region, in response to climate change, may be the key driver of future chloroform emissions from these areas.

  • 40. Jones, K
    et al.
    Berggren, M
    Sjöstedt, Johanna
    Lund University, Lund, Sweden.
    Seasonal variation and importance of catchment area composition for transport of bioavailable carbon to the Baltic Sea2023In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 165, no 3Article in journal (Refereed)
  • 41.
    Klaminder, Jonatan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bindler, Richard
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Emteryd, Ove
    Appleby, Peter
    Grip, Harald
    Estimating the mean residence time of lead in the organic horizon of boreal forest soils using 210-lead, stable lead and a soil chronosequence2006In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 78, no 1, p. 31-49Article in journal (Refereed)
    Abstract [en]

    Knowledge about the residence time of lead in the organic horizon (mor layer; O-horizon) overlaying forest mineral soils is important for the prediction of past and future lead levels in the boreal environment. To estimate the mean residence time (MRT) of lead in the mor layer, we use in this study from Northern Sweden three different approaches: (1) lead-210 is applied as a tracer of lead migration; (2) estimations of loss rates of stable lead (concentrations and 206Pb/207Pb ratios) from the mor layer at an undisturbed forest setting, and (3) a study of lead in a soil series with sites of different age (a chronosequence of 20–220 years). In the last two approaches we compared measured inventories in the soil with estimated inventories derived using analyses of lake sediments. The results suggested a MRT of about 250 years in the mor layer in the mature forest and in the older parts of the chronosequence it was at least >170 years. The agreement between the three different approaches gives good credibility to this estimate. It is also supported by a modeling of trends in the 206Pb/207Pb ratio both between single cores and with depth in the mor layer. Our results suggest that it will take centuries for the deeper parts of the mor layer of undisturbed boreal forest soils to fully respond to decreased atmospheric lead pollution. However, data from the chronosequence indicate that the response could be much faster (MRT<50 years) in the mor layer at early stages of forest succession where graminoid and broadleaved litter fall dominates over conifer litter.

  • 42. Klemedtsson, Leif
    et al.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Karlberg, Louise
    Weslien, Per
    von Arnold, Karin
    Ernfors, Maria
    Langvall, Ola
    Lindroth, Anders
    Bayesian calibration method used to elucidate carbon turnover in forest on drained organic soil2008In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 89, no 1, p. 61-79Article in journal (Refereed)
    Abstract [en]

    Depending on the balance between sink and source processes for C, drained organic forest soil ecosystems can be in balance or act as net sinks or sources of CO2 to the atmosphere. In order to study the effect of groundwater level and soil temperature on C-flux, the CoupModel was calibrated (climate data, groundwater levels, soil CO2 flux, net ecosystem fluxes of CO2-exchange, sensible heat flux and latent heat flux, forest production etc.) for a drained forest in Sweden. Bayesian calibration techniques were used to elucidate how different parameters and variables were interlinked in C-circulation. The calibrated model reproduced abiotic and biotic variables reasonably well except for root respiration, which was largely underestimated. Bayesian calibration reduced the uncertainties in the model and highlighted the fact that calibrations should be performed with a high number of parameters instead of specific parameter values.

  • 43.
    Koehler, Birgit
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Corre, Marife D
    Steger, Kristin
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Well, Reinhard
    Zehe, Erwin
    Sueta, Juvia P.
    Veldkamp, Edzo
    An in-depth look into tropical lowland forest soil: nitrogen-addition effects on the content of N2O, CO2 and CH4 ad N2O isotopic signatures down to 2-m depth2012In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 111, no 1-3, p. 695-713Article in journal (Refereed)
    Abstract [en]

    Atmospheric nitrogen (N) deposition is rapidly increasing in tropical regions. We investigated how a decade of experimental N addition (125 kg N ha−1 year−1) to a seasonal lowland forest affected depth distribution and contents of soil nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4), as well as natural abundance isotopic signatures of N2O, nitrate (NO3 ) and ammonium (NH4 +). In the control plots during dry season, we deduced limited N2O production by denitrification in the topsoil (0.05–0.40 m) as indicated by: ambient N2O concentrations and ambient 15N-N2O signatures, low water-filled pore space (35–60%), and similar 15N signatures of N2O and NO3 . In the subsoil (0.40–2.00 m), we detected evidence of N2O reduction to N2 during upward diffusion, indicating denitrification activity. During wet season, we found that N2O at 0.05–2.00 m was mainly produced by denitrification with substantial further reduction to N2, as indicated by: lighter 15N-N2O than 15N-NO3 throughout the profile, and increasing N2O concentrations with simultaneously decreasing 15N-N2O enrichment with depth. These interpretations were supported by an isotopomer map and by a positive correlation between 18O-N2O and 15N-N2O site preferences. Long-term N addition did not affect dry-season soil N2O-N contents, doubled wet-season soil N2O-N contents, did not affect 15N signatures of NO3 , and reduced wet-season 15N signatures of N2O compared to the control plots. These suggest that the increased NO3 concentrations have stimulated N2O production and decreased N2O-to-N2 reduction. Soil CO2-C contents did not differ between treatments, implying that N addition essentially did not influence soil C cycling. The pronounced seasonality in soil respiration was largely attributable to enhanced topsoil respiration as indicated by a wet-season increase in the topsoil CO2-C contents. The N-addition plots showed reduced dry-season soil CH4-C contents and threshold CH4 concentrations were reached at a shallower depth compared to the control plots, revealing an N-induced stimulation of methanotrophic activity. However, the net soil CH4 uptake rates remained similar between treatments possibly because diffusive CH4 supply from the atmosphere largely limited CH4 oxidation.

  • 44. Korth, Frederike
    et al.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Liskow, Iris
    Voss, Maren
    Uptake of dissolved organic nitrogen by size-fractionated plankton along a salinity gradient from the North Sea to the Baltic Sea2012In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 111, no 1-3, p. 347-360Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea is known for its ecological problems due to eutrophication caused by high nutrient input via nitrogen fixation and rivers, which deliver up to 70% of nitrogen in the form of dissolved organic nitrogen (DON) compounds. We therefore measured organic nitrogen uptake rates using self produced N-15 labeled allochthonous (derived from Brassica napus and Phragmites sp.) and autochthonous (derived from Skeletonema costatum) DON at twelve stations along a salinity gradient (34 to 2) from the North Sea to the Baltic Sea in August/September 2009. Both labeled DON sources were exploited by the size fractions 0.2-1.6 mu m (bacteria size fraction) and > 1.6 mu m (phytoplankton size fraction). Higher DON uptake rates were measured in the Baltic Sea compared to the North Sea, with rates of up to 1213 nmol N l(-1) h(-1). The autochthonous DON was the dominant nitrogen form used by the phytoplankton size fraction, whereas the heterotrophic bacteria size fraction preferred the allochthonous DON. We detected a moderate shift from > 1.6 mu m plankton dominated DON uptake in the North Sea and central Baltic Sea towards a 0.2-1.6 mu m dominated DON uptake in the Bothnian Bay and a weak positive relationship between DON concentrations and uptake. These findings indicate that DON is an important component of plankton nutrition and can fuel primary production. It may therefore also contribute substantially to eutrophication in the Baltic Sea especially when inorganic nitrogen sources are depleted.

  • 45. Kristensen, Jeppe A.
    et al.
    Metcalfe, Daniel B.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
    Rousk, Johannes
    The biogeochemical consequences of litter transformation by insect herbivory in the Subarctic: a microcosm simulation experiment2018In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 138, no 3, p. 323-336Article in journal (Refereed)
    Abstract [en]

    Warming may increase the extent and intensity of insect defoliations within Arctic ecosystems. A thorough understanding of the implications of this for litter decomposition is essential to make predictions of soil-atmosphere carbon (C) feedbacks. Soil nitrogen (N) and C cycles naturally are interlinked, but we lack a detailed understanding of how insect herbivores impact these cycles. In a laboratory microcosm study, we investigated the growth responses of heterotrophic soil fungi and bacteria as well as C and N mineralisation to simulated defoliator outbreaks (frass addition), long-term increased insect herbivory (litter addition at higher background N-level) and non-outbreak conditions (litter addition only) in soils from a Subarctic birch forest. Larger amounts of the added organic matter were mineralised in the outbreak simulations compared to a normal year; yet, the fungal and bacterial growth rates and biomass were not significantly different. In the simulation of long-term increased herbivory, less litter C was respired per unit mineralised N (C:N of mineralisation decreased to 20 +/- 1 from 38 +/- 3 for pure litter), which suggests a directed microbial mining for N-rich substrates. This was accompanied by higher fungal dominance relative to bacteria and lower total microbial biomass. In conclusion, while a higher fraction of foliar C will be respired by insects and microbes during outbreak years, predicted long-term increases in herbivory linked to climate change may facilitate soil C-accumulation, as less foliar C is respired per unit mineralised N. Further work elucidating animal-plant-soil interactions is needed to improve model predictions of C-sink capacity in high latitude forest ecosystems.

    Download full text (pdf)
    fulltext
  • 46. Kristensen, Jeppe A.
    et al.
    Metcalfe, Daniel B.
    Rousk, Johannes
    The biogeochemical consequences of litter transformation by insect herbivory in the Subarctic: a microcosm simulation experiment2018In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 138, no 3, p. 323-336Article in journal (Refereed)
    Abstract [en]

    Warming may increase the extent and intensity of insect defoliations within Arctic ecosystems. A thorough understanding of the implications of this for litter decomposition is essential to make predictions of soil-atmosphere carbon (C) feedbacks. Soil nitrogen (N) and C cycles naturally are interlinked, but we lack a detailed understanding of how insect herbivores impact these cycles. In a laboratory microcosm study, we investigated the growth responses of heterotrophic soil fungi and bacteria as well as C and N mineralisation to simulated defoliator outbreaks (frass addition), long-term increased insect herbivory (litter addition at higher background N-level) and non-outbreak conditions (litter addition only) in soils from a Subarctic birch forest. Larger amounts of the added organic matter were mineralised in the outbreak simulations compared to a normal year; yet, the fungal and bacterial growth rates and biomass were not significantly different. In the simulation of long-term increased herbivory, less litter C was respired per unit mineralised N (C:N of mineralisation decreased to 20 ± 1 from 38 ± 3 for pure litter), which suggests a directed microbial mining for N-rich substrates. This was accompanied by higher fungal dominance relative to bacteria and lower total microbial biomass. In conclusion, while a higher fraction of foliar C will be respired by insects and microbes during outbreak years, predicted long-term increases in herbivory linked to climate change may facilitate soil C-accumulation, as less foliar C is respired per unit mineralised N. Further work elucidating animal-plant-soil interactions is needed to improve model predictions of C-sink capacity in high latitude forest ecosystems.

  • 47.
    Lagerström, Anna
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Esberg, Camilla
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Soil phosphorus and microbial response to a long-term wildfire chronosequence in northern Sweden2009In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 95, no 2/3, p. 199-213Article in journal (Refereed)
    Abstract [en]

    In the prolonged absence of major disturbances, ecosystems may enter a stage of retrogression, which is characterized by decreased ecosystem process rates both above and belowground, and often reduced availability of phosphorus (P). Disturbance through wildfire can increase soil P losses through leaching or erosion, but in the long-term absence of fire, soil P could potentially become increasingly bound in more stable forms that are less available to microbes. We studied forms of P and microbial respiration kinetics in the humus layer of a group of islands that vary considerably in wildfire frequency (40–5,300 years since last fire), and which are known to enter retrogression in the prolonged absence of fire. We found a decrease in labile P with decreasing fire frequency but no change in total P. Soil microorganisms responded more strongly to N than to P addition, and microbial biomass N:P ratios remained unchanged across the gradient. However, the concentration of labile P was the best predictor of microbial respiration responses across the islands, and this provides some evidence that declining access to P could contribute to the decline in soil microbial activity during retrogression. Our results show that even though N is arguably the main limiting nutrient during retrogression in this chronosequence, long term absence of fire also causes a decline in P availability which negatively affects microbial activity. This in turn could potentially impair microbially driven processes such as decomposition and mineralization and further contribute to the reduced availability of soil nutrients during retrogression.

  • 48.
    Laturnus, Frank
    et al.
    Linköping University, Faculty of Arts and Sciences. Linköping University, The Tema Institute.
    Haselmann, KF
    Linkoping Univ, Dept Themat Studies, Environm Sci Programme, S-60174 Norrkoping, Sweden Univ So Denmark, Dept Chem, DK-5230 Odense, Denmark Montana State Univ, Ctr Biofilm Engn, Bozeman, MT 59717 USA Eurofins AS, DK-2970 Horsholm, Denmark.
    Borch, T
    Linkoping Univ, Dept Themat Studies, Environm Sci Programme, S-60174 Norrkoping, Sweden Univ So Denmark, Dept Chem, DK-5230 Odense, Denmark Montana State Univ, Ctr Biofilm Engn, Bozeman, MT 59717 USA Eurofins AS, DK-2970 Horsholm, Denmark.
    Gron, C
    Linkoping Univ, Dept Themat Studies, Environm Sci Programme, S-60174 Norrkoping, Sweden Univ So Denmark, Dept Chem, DK-5230 Odense, Denmark Montana State Univ, Ctr Biofilm Engn, Bozeman, MT 59717 USA Eurofins AS, DK-2970 Horsholm, Denmark.
    Terrestrial natural sources of trichloromethane (chloroform, CHCl3) - An overview2002In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 60, no 2, p. 121-139Article in journal (Refereed)
    Abstract [en]

    The widespread use of volatile chlorinated compounds like chloroform, trichloroethene and tetrachloroethene in industrialized societies causes a large annual release of these compounds into the environment. Due to their role as a source for halogen radicals involved in various catalytic atmospheric reaction cycles, including the regulation of the stratospheric and tropospheric ozone layers, these compounds also constitute a risk for drinking water resources as they can be transported to the groundwater from contaminated field sites or even from atmospheric deposition. Therefore, identification and investigation of sources and sinks of volatile chlorinated compounds are of particular interest. Chloroform, a major contributor to natural gaseous chlorine, was found to be emitted by several anthropogenic and natural sources including the oceans and terrestrial areas. The origin of chloroform in the terrestrial environment can be anthropogenic point sources, atmospheric deposition, release by vegetation and production directly in the soil. The calculated annual biogenic global chloroform emission is 700 Gg, and marine and terrestrial environments are nearly equal contributors. The estimated emissions from anthropogenic sources account for less than 10% of the estimated total emissions from all sources. Among terrestrial sources, forests have recently been identified as contributing to the release of chloroform into the environment. With the data available, annual emissions of chloroform to the atmosphere from forest sites were calculated and compared to other natural sources. At present knowledge, forests are only a minor source in the total biogenic flux of chloroform, contributing less than 1% to the annual global atmospheric input. However, it should be noted that data are available for Northern temperate forests only. The large tropical forest areas may provide a yet unknown input of chloroform.

  • 49.
    Liénart, Camilla
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Garbaras, Andrius
    Qvarfordt, Susanne
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Walve, Jakob
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Karlson, Agnes M. L.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Spatio-temporal variation in stable isotope and elemental composition of key-species reflect environmental changes in the Baltic Sea2022In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 157, no 2, p. 149-170Article in journal (Refereed)
    Abstract [en]

    Carbon and nitrogen stable isotope ratios are increasingly used to study long-term change in food web structure and nutrient cycling. We retrospectively analyse elemental composition (C, N and P) and stable isotopes (δ13C, δ15N) in archived monitoring samples of two important taxa from the bottom of the food web; the filamentous ephemeral macroalgae Cladophora spp. and the blue mussel Mytilus edulis trossulus from three contrasting regions in the Baltic Sea (coastal Bothnian Sea and Baltic Proper, open sea central Baltic). The aim is to statistically link the observed spatial and interannual (8–24 years’ time-series) variability in elemental and isotope baselines with their biomass trends and to the oceanographic monitoring data reflecting the ongoing environmental changes (i.e., eutrophication and climate) in this system. We find clear differences in isotope baselines between the two major Baltic Sea basins. However, the temporal variation in Mytilus δ13C was similar among regions and, at the open sea station, mussels and algae δ13C also correlated over time, likely reflecting a global (Suess) effect, whereas δ15N of both taxa varied with local and regional dissolved nitrogen concentrations in water. δ15N in source amino acids allowed detection of diazotrophic N in Mytilus, which was masked in bulk δ15N. Finally, Cladophora N:P reflected regional nutrient levels in the water while P%, which differed for both taxa, was linked to food quality for Mytilus. This study highlights the potential of a multi-taxa and multi-stable isotope approach to understand nutrient dynamics and monitor long-term environmental changes.

  • 50.
    Manasypov, R.M.
    et al.
    BIO-GEO-CLIM Laboratory, Tomsk State University, 36, Lenina Av., Tomsk, Russian Federation.
    Lim, A.G.
    BIO-GEO-CLIM Laboratory, Tomsk State University, 36, Lenina Av., Tomsk, Russian Federation.
    Krickov, I.V.
    BIO-GEO-CLIM Laboratory, Tomsk State University, 36, Lenina Av., Tomsk, Russian Federation.
    Shirokova, L.S.
    GET UMR 5563 CNRS University of Toulouse, 14, Avenue Edouard Belin, Toulouse, France; Federal Center for Integrated Arctic Research, Institute of Ecological Problem of the North, 23, Nab. Severnoi Dviny, Arkhangel’sk, Russian Federation.
    Shevchenko, V.P.
    Shirshov Institute of Oceanology, Russian Academy of Sciences, 36, Nakhimovsky Prospect, Moscow, Russian Federation.
    Aliev, R.A.
    Chemistry Department, Lomonosov Moscow State University, 1, Leninskie Gory, Moscow, Russian Federation.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre (CIRC), Umeå University, Umeå, Sweden.
    Pokrovsky, O.S.
    BIO-GEO-CLIM Laboratory, Tomsk State University, 36, Lenina Av., Tomsk, Russian Federation; GET UMR 5563 CNRS University of Toulouse, 14, Avenue Edouard Belin, Toulouse, France; Federal Center for Integrated Arctic Research, Institute of Ecological Problem of the North, 23, Nab. Severnoi Dviny, Arkhangel’sk, Russian Federation.
    Carbon storage and burial in thermokarst lakes of permafrost peatlands2022In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 159, no 1, p. 69-86Article in journal (Refereed)
    Abstract [en]

    Thermokarst (thaw) lakes of the Western Siberian Lowland (WSL), the World´s largest permafrost peatland, contain important but poorly constrained stocks of organic carbon (OC) and nitrogen. These lakes are highly vulnerable to climate warming and permafrost thaw. The present work aims to quantify the OC and total nitrogen (TN) stocks and accumulation rates in sediments of 11 thermokarst lakes in the WSL across a permafrost gradient, from isolated to discontinuous and continuous permafrost. We found an increase in OC and TN stocks in lake sediments (0–30 cm) from the northern taiga with sporadic permafrost (285 Tg C and 10.5 Tg N) to the tundra zone with continuous permafrost (628 Tg C and 26 Tg N). The upper 30 cm thermokarst lake sediments of the permafrost-affected WSL store 1250 ± 35 Tg C and 50 ± 1.4 Tg N). The OC accumulation rates in thermokarst lake sediments ranged from 36 to 250 g C m−2 year−1, which is 5 to 10 times higher than C accumulation rates in peatlands of western Siberia. The total OC accumulation in lakes of WSL is 7.8 ± 0.7 Tg C year−1. This is about 24–47% of the C emission from the WSL thermokarst lakes, implying that it represents an important factor in the C budget to consider in order to understand impacts of climate change and permafrost thaw on the C cycle.

123 1 - 50 of 106
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf