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  • 1.
    Alewell, C
    et al.
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Leifeld, J
    Agroscope Reckenholz-Tanikon Research Station ART, Switzerland.
    Rollog, M
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Stable carbon isotopes as indicators for environmental change inpalsa peats2011Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, s. 1769-1778Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Palsa peats are unique northern ecosystems formed under an arctic climate and characterized by a high biodiversity and sensitive ecology. The stability of the palsas are seriously threatened by climate warming which will change the permafrost dynamic and induce a degradation of the mires.

    We used stable carbon isotope depth profiles in two palsa mires of Northern Sweden to track environmental change during the formation of the mires. Soils dominated by aerobic degradation can be expected to have a clear increase of carbon isotopes (δ13C) with depth, due to preferential release of 12C during aerobic mineralization. In soils with suppressed degradation due to anoxic conditions, stable carbon isotope depth profiles are either more or less uniform indicating no or very low degradation or depth profiles turn to lighter values due to an enrichment of recalcitrant organic substances during anaerobic mineralisation which are depleted in 13C.

    The isotope depth profile of the peat in the water saturated depressions (hollows) at the yet undisturbed mire Storflaket indicated very low to no degradation but increased rates of anaerobic degradation at the Stordalen site. The latter might be induced by degradation of the permafrost cores in the uplifted areas (hummocks) and subsequent breaking and submerging of the hummock peat into the hollows due to climate warming. Carbon isotope depth profiles of hummocks indicated a turn from aerobic mineralisation to anaerobic degradation at a peat depth between 4 and 25 cm. The age of these turning points was 14C dated between 150 and 670 yr and could thus not be caused by anthropogenically induced climate change. We found the uplifting of the hummocks due to permafrost heave the most likely explanation for our findings. We thus concluded that differences in carbon isotope profiles of the hollows might point to the disturbance of the mires due to climate warming or due to differences in hydrology. The characteristic profiles of the hummocks are indicators for micro-geomorphic change during permafrost up heaving.

  • 2.
    Alewell, C
    et al.
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Leifeld, J
    Agroscope Reckenholz-Tänikon Research Station ART, Switzerland.
    Rollog, M
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Stable carbon isotopes as indicators for micro-geomorphic changes in palsa peats2011Ingår i: Biogeoscience Discussions, ISSN 1810-6277, Vol. 8, nr 1, s. 527-548Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Palsa peats are unique northern ecosystems formed under an arctic climate and characterizedby an unique biodiversity and ecology. The stability of the palsas are seriouslythreatened by climate warming which will change the permafrost dynamic and5 results in degradation of the mires. We used stable carbon isotope depth profiles intwo palsa mires of Northern Sweden to track environmental change during the formationof the mires. Carbon isotope (13C) depth profile of the yet undisturbed mireStorflaket indicated very low to no degradation of the peat in the water saturated depressions(hollows) but increased rates of anaerobic degradation at the Stordalen site.10 The latter might be induced by degradation of the permafrost cores in the uplifted areas(hummocks) and subsequent braking and submerging of the hummock peat intothe hollows due to climate warming. Carbon isotope depth profiles of hummocks indicateda turn from aerobic mineralisation to anaerobic degradation at a peat depthbetween 4 to 25 cm. The age of these turning point was 14C dated between 150 and15 670 years and could thus not be caused by anthropogenically induced climate change.We found the uplifting of the hummocks due to permafrost heave the most likely explanationfor our findings. We thus concluded that differences in carbon isotope profiles ofthe hollows might point to the disturbance of the mires due to climate warming or dueto differences in hydrology. The characteristic profiles of the hummocks are indicators20 for micro-geomorphic change during permafrost up heaving.

  • 3.
    Andersson, Tove
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Lövgren, Lars
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Persson, Per
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Giesler, Reiner
    Ekologi, miljö och geovetenskap.
    Adsorption of Monomethyl Phosphate to the Goethite (-FeOOH)/water Interface2002Konferensbidrag (Övrigt vetenskapligt)
  • 4.
    Bartels, Pia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ask, Jenny
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Andersson, Agneta
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Climate Impacts Research Centre (CIRC), Department of Ecology and Environmental Science, Umeå University, Abisko, Sweden.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Climate Impacts Research Centre (CIRC), Department of Ecology and Environmental Science, Umeå University, Abisko, Sweden.
    Allochthonous Organic Matter Supports Benthic but Not Pelagic Food Webs in Shallow Coastal Ecosystems2018Ingår i: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 21, nr 7, s. 1459-1470Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rivers transport large amounts of allochthonous organic matter (OM) to the ocean every year, but there are still fundamental gaps in how allochthonous OM is processed in the marine environment. Here, we estimated the relative contribution of allochthonous OM (allochthony) to the biomass of benthic and pelagic consumers in a shallow coastal ecosystem in the northern Baltic Sea. We used deuterium as a tracer of allochthony and assessed both temporal variation (monthly from May to August) and spatial variation (within and outside river plume). We found variability in allochthony in space and time and across species, with overall higher values for zoobenthos (26.2 +/- 20.9%) than for zooplankton (0.8 +/- 0.3%). Zooplankton allochthony was highest in May and very low during the other months, likely as a result of high inputs of allochthonous OM during the spring flood that fueled the pelagic food chain for a short period. In contrast, zoobenthos allochthony was only lower in June and remained high during the other months. Allochthony of zoobenthos was generally higher close to the river mouth than outside of the river plume, whereas it did not vary spatially for zooplankton. Last, zoobenthos allochthony was higher in deeper than in shallower areas, indicating that allochthonous OM might be more important when autochthonous resources are limited. Our results suggest that climate change predictions of increasing inputs of allochthonous OM to coastal ecosystems may affect basal energy sources supporting coastal food webs.

  • 5.
    Berggren, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ström, L
    Laudon, H
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jonsson, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lake secondary production fueled by rapid transfer of low molecular weight organic carbon from terrestrial sources to aquatic consumers2010Ingår i: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 13, nr 7, s. 870-880Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ecology Letters (2010) Abstract Carbon of terrestrial origin often makes up a significant share of consumer biomass in unproductive lake ecosystems. However, the mechanisms for terrestrial support of lake secondary production are largely unclear. By using a modelling approach, we show that terrestrial export of dissolved labile low molecular weight carbon (LMWC) compounds supported 80% (34-95%), 54% (19-90%) and 23% (7-45%) of the secondary production by bacteria, protozoa and metazoa, respectively, in a 7-km(2) boreal lake (conservative to liberal estimates in brackets). Bacterial growth on LMWC was of similar magnitude as that of primary production (PP), and grazing on bacteria effectively channelled the LMWC carbon to higher trophic levels. We suggest that rapid turnover of forest LMWC pools enables continuous export of fresh photosynthates and other labile metabolites to aquatic systems, and that substantial transfer of LMWC from terrestrial sources to lake consumers can occur within a few days. Sequestration of LMWC of terrestrial origin, thus, helps explain high shares of terrestrial carbon in lake organisms and implies that lake food webs can be closely dependent on recent terrestrial PP.

  • 6. Björk, R G
    et al.
    Klemendtsson, L
    Molau, Ulf
    Harndorf, J
    Ödman, A
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Linkages between N turnover and plant community structure in a tundra landscape2007Ingår i: Plant and Soil, Vol. 294, s. 247-261Artikel i tidskrift (Refereegranskat)
  • 7. Björkvald, L
    et al.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Humborg, C
    Mörth, C-M
    Landscape variations in stream water SO4 and d34S-SO4 in a boreal stream network2009Ingår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, s. 4648-4660Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite reduced anthropogenic deposition during the last decades, deposition sulphate may still play an important role in the biogeochemical cycles of S and many catchments may act as net sources of S that may remain for several decades. The aim of this study is to elucidate the temporal and spatial dynamics of both SO42− and δ34SSO4 in stream water from catchments with varying percentage of wetland and forest coverage and to determine their relative importance for catchment losses of S. Stream water samples were collected from 15 subcatchments ranging in size from 3 to 6780 ha, in a boreal stream network, northern Sweden. In forested catchments (<2% wetland cover) S–SO42− concentrations in stream water averaged 1.7 mg L−1 whereas in wetland dominated catchments (>30% wetland cover) the concentrations averaged 0.3 mg L−1. A significant negative relationship was observed between S–SO42− and percentage wetland coverage (r2 = 0.77, p < 0.001) and the annual export of stream water SO42− and wetland coverage (r2 = 0.76, p < 0.001). The percentage forest coverage was on the other hand positively related to stream water SO42− concentrations and the annual export of stream water SO42− (r2 = 0.77 and r2 = 0.79, respectively). The annual average δ34SSO4 value in wetland dominated streams was +7.6‰ and in streams of forested catchments +6.7‰. At spring flood the δ34SSO4 values decreased in all streams by 1‰ to 5‰. The δ34SSO4 values in all streams were higher than the δ34SSO4 value of +4.7‰ in precipitation (snow). The export of S ranged from 0.5 kg S ha−1 yr−1 (wetland headwater stream) to 3.8 kg S ha−1 yr−1 (forested headwater stream). With an average S deposition in open field of 1.3 kg S ha−1 yr−1 (2002–2006) the mass balance results in a net export of S from all catchments, except in catchments with >30% wetland. The high temporal and spatial resolution of this study demonstrates that the reducing environments of wetlands play a key role for the biogeochemistry of S in boreal landscapes and are net sinks of S. Forested areas, on the other hand were net sources of S.

  • 8. Campeau, Audrey
    et al.
    Wallin, Marcus B.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Löfgren, Stefan
    Mörth, Carl-Magnus
    Schiff, Sherry
    Venkiteswaran, Jason J.
    Bishop, Kevin
    Multiple sources and sinks of dissolved inorganic carbon across Swedish streams, refocusing the lens of stable C isotopes2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikel-id 9158Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is well established that stream dissolved inorganic carbon (DIC) fluxes play a central role in the global C cycle, yet the sources of stream DIC remain to a large extent unresolved. Here, we explore large-scale patterns in δ13C-DIC from streams across Sweden to separate and further quantify the sources and sinks of stream DIC. We found that stream DIC is governed by a variety of sources and sinks including biogenic and geogenic sources, CO2 evasion, as well as in-stream processes. Although soil respiration was the main source of DIC across all streams, a geogenic DIC influence was identified in the northernmost region. All streams were affected by various degrees of atmospheric CO2 evasion, but residual variance in δ13C-DIC also indicated a significant influence of in-stream metabolism and anaerobic processes. Due to those multiple sources and sinks, we emphasize that simply quantifying aquatic DIC fluxes will not be sufficient to characterise their role in the global C cycle.

  • 9. Creed, Irena F.
    et al.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Trick, Charles G.
    Grimm, Nancy B.
    Hessen, Dag O.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Kidd, Karen A.
    Kritzberg, Emma
    McKnight, Diane M.
    Freeman, Erika C.
    Senar, Oscar E.
    Andersson, Agneta
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ask, Jenny
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Berggren, Martin
    Cherif, Mehdi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Hotchkiss, Erin R.
    Kortelainen, Pirkko
    Palta, Monica M.
    Vrede, Tobias
    Weyhenmeyer, Gesa A.
    Global change-driven effects on dissolved organic matter composition: Implications for food webs of northern lakes2018Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, nr 8, s. 3692-3714Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.

  • 10. De Long, Jonathan R.
    et al.
    Sundqvist, Maja K.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Center for Macroecology, Evolution and Climate, The Natural History Museum of Denmark, University of Copenhagen, 2100 Copenhagen, Denmark.
    Gundale, Michael J.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Climate Impacts Research Centre, Department of Ecology and Environmental Sciences, Umeå University, SE-981 07 Abisko, Sweden.
    Wardle, David A.
    Effects of elevation and nitrogen and phosphorus fertilization on plant defence compounds in subarctic tundra heath vegetation2016Ingår i: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 30, nr 2, s. 314-325Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Plant chemical and structural defence compounds are well known to impact upon herbivory of fresh leaves and influence decomposition rates after leaf senescence. A number of theories predict that alleviating nutrient limitation and reducing other environmental stressors will result in decreased production of plant chemical defences. In this study, we measured plant defence properties [total polyphenols (TP), condensed tannins (CT) and lignin concentrations, and protein complexation capacity (PCC)] in both fresh and senesced plant leaves in a fully factorial N and P fertilization experiment set-up at each of three elevations along an elevational gradient in Swedish subarctic tundra heath vegetation. Further, we performed a decomposition of variance analysis on community-weighted averages (CWAs) of plant defence properties to determine the relative contributions of interspecific and intraspecific variation to the total variation observed in response to elevation and nutrient addition. We hypothesized that N fertilization would reduce plant defence properties and that this reduction would be greater at higher elevations, while the effects of P fertilization would have no effect at any elevation. At the community level, N addition reduced CT and PCC in both fresh and senesced leaves and TP in senesced leaves, while P addition had few effects, broadly in line with our hypothesis. The effects of N addition frequently varied with elevation, but in contrast to our hypothesis, the said effects were strongest at the lowest elevations. The effects of N addition and the interactive effect of N with elevation were primarily driven by intraspecific, rather than interspecific, variation. Our findings suggest that as temperatures warm and N availability increases due to global climate change, secondary metabolites in subarctic heath vegetation will decline particularly within species. Our results highlight the need to consider the effects of both nutrient availability and temperature, and their interaction, in driving subarctic plant defence.

  • 11.
    Esberg, Camilla
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    du Toit, Ben
    Department of Forest and Wood Science, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
    Olsson, Rickard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ilstedt, Ulrik
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Microbial responses to P addition in six South African forest soils2010Ingår i: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 329, nr 1/2, s. 209-225Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Forests growing on highly weathered soils are often phosphorus (P) limited and competition between geochemical and biological sinks affects their soil P dynamics. In an attempt to elucidate the factors controlling the relative importance of these two sinks, we investigated the relationship of between soil microbial growth kinetics and soil chemical properties following amendments with C, N and P in six South African forest soils. Microbial growth kinetics were determined from respiration curves derived from measurements of CO2 effluxes from soil samples in laboratory incubations. We found that microbial growth rates after C + N additions were positively related to NaOH-extractable P and decreased with soil depth, whereas the lag time (the time between substrate addition and exponential growth) was negatively related to extractable P. However, the growth rate and lag time were unrelated to the soil’s sorption properties or Al and Fe contents. Our results indicate that at least some of the NaOH-extractable inorganic P may be biologically available within a relatively short time (days to weeks) and might be more labile than previously thought. Our results also show that microbial utilization of C + N only seemed to be constrained by P in the deeper part of the soil profiles.

  • 12.
    Esberg, Camilla
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lagerström, Anna
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Graae, Bente J.
    Department of Biology, NTNU, Høgskoleringen 5, 7491 Trondheim, Norway.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Phosphorus availability and microbial respiration across different tundra vegetation typesManuskript (preprint) (Övrigt vetenskapligt)
    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 top soil were measured and plant foliar nitrogen (N) to P ratio was used as an indicator of plant nutrient status. Microbial and plant bioassays were used to study microbial respiration kinetics and plant biomass 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 sorbed P between the vegetation types and this corroborated with the distribution of Al+Fe. Plant N: P ratios and the plant bioassay indicated decreasing P availability from dry heath to mesic heath to mesic meadow. Our results showed that vegetation type was related to soil chemistry and P availability; however, in contrast to other studies, this effect was not related to redistribution of Fe and Al. We conclude that in this tundra ecosystem plants are generally co-limited by N and P, and P availability varies between different vegetation types, which is reflected in both above- and belowground ecosystem processes.

  • 13.
    Esberg, Camilla
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nilsson, Mats
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Microbial indices of P availability across a forest productivity gradient in South AfricaManuskript (preprint) (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    Soil microorganisms have the capability to solubilize different fractions of phosphorus (P) and can probably access P fractions unavailable to plants in the short term. However, there are few studies available that attempt to estimate the potentially available microbial P. We compare a wet-chemical extraction procedure for P with a microbial bioassay based on respiration kinetics after amending carbon (C), nitrogen (N), and sub-saturation levels of P in laboratory incubations across a plantation forest productivity gradient in South Africa. We found that the estimated microbial available P was at least 10-fold higher than P fractions conventionally defined as easily plant available based on wet-chemical methods. The microbial P was strongly positively related to sorbed P (i.e. NaOH extractable P) P (r2=0.63, p<0.001) and indicates that this P fraction contributes to the microbial P utilization within a relatively short time frame (<300 hrs) when C and N are not limiting. This was further emphasized by the change in respiration kinetics when the amendment of C and N were combined with phosphate. Addition of phosphate-P increased the growth and maximum respiration (max resp) rates and decreased the amount of time needed to reach max resp in comparison to amendments with only C and N. Our study indicates that sorbed P), a dominant P fraction in highly weathered soils, is most likely accessible to microorganisms.

  • 14. Eshetu, Z
    et al.
    Giesler, R
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Högberg, P
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Historical land use pattern affects the chemistry of forest soils in the Ethiopian highlands2004Ingår i: Geoderma, Vol. 118, s. 149-165Artikel i tidskrift (Refereegranskat)
  • 15. George, T. S.
    et al.
    Giles, C. D.
    Menezes-Blackburn, D.
    Condron, L. M.
    Gama-Rodrigues, A. C.
    Jaisi, D.
    Lang, F.
    Neal, A. L.
    Stutter, M. , I
    Almeida, D. S.
    Bol, R.
    Cabugao, K. G.
    Celi, L.
    Cotner, J. B.
    Feng, G.
    Goll, D. S.
    Hallama, M.
    Krueger, J.
    Plassard, C.
    Rosling, A.
    Darch, T.
    Fraser, T.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Richardson, A. E.
    Tamburini, F.
    Shand, C. A.
    Lumsdon, D. G.
    Zhang, H.
    Blackwell, M. S. A.
    Wearing, C.
    Mezeli, M. M.
    Almas, A. R.
    Audette, Y.
    Bertrand, I
    Beyhaut, E.
    Boitt, G.
    Bradshaw, N.
    Brearley, C. A.
    Bruulsema, T. W.
    Ciais, P.
    Cozzolino, V
    Duran, P. C.
    Mora, M. L.
    de Menezes, A. B.
    Dodd, R. J.
    Dunfield, K.
    Engl, C.
    Frazao, J. J.
    Garland, G.
    Jimenez, J. L. Gonzalez
    Graca, J.
    Granger, S. J.
    Harrison, A. F.
    Heuck, C.
    Hou, E. Q.
    Johnes, P. J.
    Kaiser, K.
    Kjaer, H. A.
    Klumpp, E.
    Lamb, A. L.
    Macintosh, K. A.
    Mackay, E. B.
    McGrath, J.
    McIntyre, C.
    McLaren, T.
    Meszaros, E.
    Missong, A.
    Mooshammer, M.
    Negron, C. P.
    Nelson, L. A.
    Pfahler, V
    Poblete-Grant, P.
    Randall, M.
    Seguel, A.
    Seth, K.
    Smith, A. C.
    Smits, M. M.
    Sobarzo, J. A.
    Spohn, M.
    Tawaraya, K.
    Tibbett, M.
    Voroney, P.
    Wallander, H.
    Wang, L.
    Wasaki, J.
    Haygarth, P. M.
    Organic phosphorus in the terrestrial environment: a perspective on the state of the art and future priorities2018Ingår i: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 427, nr 1-2, s. 191-208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: The dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (P-o) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction.

    Scope: We asked a group of experts to consider the global issues associated with P-o in the terrestrial environment, methodological strengths and weaknesses, benefits to be gained from understanding the P-o cycle, and to set priorities for P-o research.

    Conclusions: We identified seven key opportunities for P-o research including: the need for integrated, quality controlled and functionally based methodologies; assessment of stoichiometry with other elements in organic matter; understanding the dynamics of P-o in natural and managed systems; the role of microorganisms in controlling P-o cycles; the implications of nanoparticles in the environment and the need for better modelling and communication of the research. Each priority is discussed and a statement of intent for the P-o research community is made that highlights there are key contributions to be made toward understanding biogeochemical cycles, dynamics and function of natural ecosystems and the management of agricultural systems.

  • 16.
    Giesler , Reiner
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Björkvald , L
    Laudon , Hjalmar
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Mörth , CM
    Spatial and Seasonal Variations in Stream Water delta S-34-Dissolved Organic Matter in Northern Sweden2009Ingår i: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 43, nr 2, s. 447-452Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The discharge of terrestrial dissolved organic matter (DOM) by streams is an important cross-system linkage that strongly influences downstream aquatic ecosystems. Isotopic tracers are important tools that can help to unravel the source of DOM from different terrestrial compartments in the landscape. Here we demonstrate the spatial and seasonal variation of delta S-34 of DOM in 70 boreal streams to test if the tracer could provide new insights into the origin of DOM. We found large spatial and seasonal variations in stream water delta S-34-DOM values ranging from -5.2 parts per thousand to + 9.6 parts per thousand with an average of +4.0 +/- 0.6 (N=62; average and 95% confidence interval). Large seasonal variations were found in stream water delta S-34-DOM values: for example, a shift of more than 10 parts per thousand during the spring snowmelt in a wetland-dominated stream. Spatial differences were also observed during the winter base flow with higher delta S-34-DOM values in the fourth-order Krycklan stream at the outlet of the 68 km(2) compared to the small (<1 km(2)) headwater streams. Our data clearly show that the delta S-34-DOM values have the potential to be used as a tracer to identify and generate new insights about terrestrial DOM sources in the boreal landscape.

  • 17.
    Giesler, R
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Morth, C
    Mellqvist, E
    Torssander, P
    The humus layer determines SO42 isotope values in the mineral soil2005Ingår i: Biogeochemistry, Vol. 74, s. 3-20Artikel i tidskrift (Refereegranskat)
  • 18.
    Giesler, R
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Satoh, F
    Ilstedt, U
    Nordgren, A
    Microbially available phosphorus in boreal forests: Effects of aluminum and iron accumulation in the humus layer2004Ingår i: Ecosystems, Vol. 7, s. 208-217Artikel i tidskrift (Refereegranskat)
  • 19.
    Giesler, Reiner
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Andersson, Tove
    Kemi.
    Lövgren, Lars
    Kemi.
    Phosphate adsorption in aluminum and iron rich humus soils from forested groundwater discharge areas2000Konferensbidrag (Övrigt vetenskapligt)
  • 20.
    Giesler, Reiner
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Andersson, Tove
    Kemi.
    Lövgren, Lars
    Kemi.
    Persson, Per
    Kemi.
    Phosphate sorption in aluminum- and iron-rich humus soils2005Ingår i: Soil Science Society of America Journal, Vol. 69, nr 1, s. 77-86Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Groundwater discharge areas in boreal forest ecosystems can potentially be areas where Fe and Al accumulate in the forest floor and affect the solubility of P. This study was conducted to determine phosphate sorption properties using humus soils containing high native amounts of Al and Fe. Humus soils were collected from two different forested groundwater discharge areas varying in pH and amount and distribution of At and Fe species. The phosphate sorption capacities were 265 and 216 mmol P kg(-1) dry wt. soil, respectively, for the two humus soils. Pyrophosphate extractable Al and Fe dominated in the first soil, 738 mmol kg(-1) dry wt. The concentration of pyrophosphate extractable Al and Fe in the second soil was 317 mmol kg(-1) dry wt.. whereas citrate-dithionite (CD) extracted 548 mmol Al and Fe kg(-1) dry wt. Using 0.1 mol dm(-3) NaCl as ionic medium gave a higher phosphate sorption compared with deionized water at the midrange additions, but no difference at the highest addition. Phosphate sorption was pH independent when 0.1 mol dm(-3) NaCl was used, whereas deionized water gave a sorption minimum at approximately pH 6. Dissolved organic carbon (DOC) release in solution was positively correlated with phosphate sorption, especially in 0.1 mol dm(-3) NaCl ionic medium. However, dissolved organic P (DOP) was unaffected by the phosphate sorption. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) indicated that precipitation of Al and Fe phosphates dominated at higher phosphate additions in the soil with mainly organically bound At and Fe, whereas both surface sorption and precipitation occurs in the soil with a larger amount of CD-extractable Fe.

  • 21.
    Giesler, Reiner
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Esberg, Camilla
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lagerström, Anna
    Graae, Bente J
    Phosphorus availability and microbial respiration across different tundra vegetation types2012Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 108, nr 1-3, s. 429-445Artikel i tidskrift (Refereegranskat)
    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.

  • 22.
    Giesler, Reiner
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Högberg, M N
    Strobel, B W
    Richter, A
    Nordgren, A
    Högberg, P
    Production of dissolved organic carbon and low-molecular weight organic acids in soil solution driven by recent tree photosynthate2007Ingår i: Biogeochemistry, Vol. 84, s. 1-12Artikel i tidskrift (Refereegranskat)
  • 23.
    Giesler, Reiner
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karina, E. Clemmensen
    Wardle, David A.
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Boreal Forests Sequester Large Amounts of Mercury over Millennial Time Scales in the Absence of Wildfire2017Ingår i: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 51, nr 5, s. 2621-2627Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alterations in fire activity due to climate change and fire suppression may have profound effects on the balance between storage and release of carbon (C) and associated volatile elements. Stored soil mercury (Hg) is known to volatilize due to wildfires and this could substantially affect the land air exchange of Hg; conversely the absence of fires and human disturbance may increase the time period over which Hg is sequestered. Here we show for a wildfire chronosequence spanning over more than 5000 years in boreal forest in northern Sweden that belowground inventories of total Hg are strongly related to soil humus C accumulation (R-2 = 0.94, p < 0.001). Our data clearly show that northern boreal forest soils have a strong sink capacity for Hg, and indicate that the sequestered Hg is bound in soil organic matter pools accumulating over millennia. Our results also suggest that more than half of the Hg stock in the sites with the longest time since fire originates from deposition predating the onset of large-scale anthropogenic emissions. This study emphasizes the importance of boreal forest humus soils for Hg storage and reveals that this pool is likely to persist over millennial time scales in the prolonged absence of fire.

  • 24.
    Giesler, Reiner
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lyon, S. W.
    Morth, C-M
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, E. M.
    Jantze, E. J.
    Destouni, G.
    Humborg, C.
    Catchment-scale dissolved carbon concentrations and export estimates across six subarctic streams in northern Sweden2014Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, nr 2, s. 525-537Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climatic change is currently enhancing permafrost thawing and the flow of water through the landscape in subarctic and arctic catchments, with major consequences for the carbon export to aquatic ecosystems. We studied stream water carbon export in several tundra-dominated catchments in northern Sweden. There were clear seasonal differences in both dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations. The highest DOC concentrations occurred during the spring freshet while the highest DIC concentrations were always observed during winter baseflow conditions for the six catchments considered in this study. Long-term trends for the period 1982 to 2010 for one of the streams showed that DIC concentrations has increased by 9% during the 28 yr of measurement while no clear trend was found for DOC. Similar increasing trends were also found for conductivity, Ca and Mg. When trends were discretized into individual months, we found a significant linear increase in DIC concentrations with time for September, November and December. In these subarctic catchments, the annual mass of C exported as DIC was in the same order of magnitude as DOC; the average proportion of DIC to the total dissolved C exported was 61% for the six streams. Furthermore, there was a direct relationship between total runoff and annual dissolved carbon fluxes for these six catchments. These relationships were more prevalent for annual DIC exports than annual DOC exports in this region. Our results also highlight that both DOC and DIC can be important in high-latitude ecosystems. This is particularly relevant in environments where thawing permafrost and changes to subsurface ice due to global warming can influence stream water fluxes of C. The large proportion of stream water DIC flux also has implications on regional C budgets and needs to be considered in order to understand climate-induced feedback mechanisms across the landscape.

  • 25.
    Giesler, Reiner
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Morth, Carl-Magnus
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lundin, Erik J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lyon, Steve W.
    Humborg, Christoph
    Spatiotemporal variations of pCO(2) and delta C-13-DIC in subarctic streams in northern Sweden2013Ingår i: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 27, nr 1, s. 176-186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Current predictions of climate-related changes in high-latitude environments suggest major effects on the C export in streams and rivers. To what extent this will also affect the stream water CO2 concentrations is poorly understood. In this study we examined the spatiotemporal variation in partial pressure of CO2 (pCO(2)) and in stable isotopic composition of dissolved inorganic carbon (delta C-13-DIC) in subarctic streams in northern Sweden. The selected watersheds are characterized by large variations in high-latitude boreal forest and tundra and differences in bedrock. We found that all streams generally were supersaturated in pCO(2) with an average concentration of 850 mu atm. The variability in pCO(2) across streams was poorly related to vegetation cover, and carbonaceous bedrock influence was manifested in high DIC concentrations but not reflected in either stream pCO(2) or delta C-13-DIC. Stream water pCO(2) values were highest during winter base flow when we also observed the lowest delta C-13-DIC values, and this pattern is interpreted as a high contribution from CO2 from soil respiration. Summer base flow delta C-13-DIC values probably are more affected by in situ stream processes such as aquatic production/respiration and degassing. A challenge for further studies will be to disentangle the origin of stream water CO2 and quantify their relative importance.

  • 26. Humborg, Christoph
    et al.
    Mörth, Carl-Magnus
    Sundblom, Marcus
    Borg, Hans
    Blenckner, Thorsten
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ittekot, Venugopalan
    CO2 supersaturation along the aquatic conduit in Swedish watersheds as constrained by terrestrial respiration, aquatic respiration and weathering2010Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 16, nr 7, s. 1966-1978Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We tested the hypothesis that CO2 supersaturation along the aquatic conduit over Sweden can be explained by processes other than aquatic respiration. A first generalized-additive model (GAM) analysis evaluating the relationships between single water chemistry variables and pCO2 in lakes and streams revealed that water chemistry variables typical for groundwater input, e.g., dissolved silicate (DSi) and Mg2+ had explanatory power similar to total organic carbon (TOC). Further GAM analyses on various lake size classes and stream orders corroborated the slightly higher explanatory power for DSi in lakes and Mg2+ for streams compared with TOC. Both DSi and TOC explained 22–46% of the pCO2 variability in various lake classes (0.01–>100 km2) and Mg2+ and TOC explained 11–41% of the pCO2 variability in the various stream orders. This suggests that aquatic pCO2 has a strong groundwater signature. Terrestrial respiration is a significant source of the observed supersaturation and we may assume that both terrestrial respiration and aquatic respiration contributed equally to pCO2 efflux. pCO2 and TOC concentrations decreased with lake size suggesting that the longer water residence time allow greater equilibration of CO2 with the atmosphere and in-lake mineralization of TOC. For streams, we observed a decreasing trend in pCO2 with stream orders between 3 and 6. We calculated the total CO2 efflux from all Swedish lakes and streams to be 2.58 Tg C yr−1. Our analyses also demonstrated that 0.70 Tg C yr−1 are exported to the ocean by Swedish watersheds as HCO3 and CO32− of which about 0.56 Tg C yr−1 is also a residual from terrestrial respiration and constitute a long-term sink for atmospheric CO2. Taking all dissolved inorganic carbon (DIC) fluxes along the aquatic conduit into account will lower the estimated net ecosystem C exchange (NEE) by 2.02 Tg C yr−1, which corresponds to 10% of the NEE in Sweden.

  • 27.
    Högberg, Mona N.
    et al.
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umea.
    Myrold, David D.
    Department of Crop and Soil Science, Oregon State University, Corvallis, USA.
    Giesler, Reiner
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umeå.
    Högberg, Peter
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umeå.
    Contrasting patterns of soil N-cycling in model ecosystems of Fennoscandian boreal forests2006Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 147, nr 1, s. 96-107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The low plant productivity of boreal forests ingeneral has been attributed to low soil N supply and lowtemperatures. Exceptionally high productivity occurs intoe-slope positions, and has been ascribed to influx of Nfrom surrounding areas and higher rates of soil Nturnover in situ. Despite large apparent natural variationsin forest productivity, rates of gross soil N mineralizationand gross nitrification have never beencompared in Fennoscandian boreal forests of contrastingproductivity. We report contrasting patterns of soilN turnover in three model ecosystems, representing therange in soil C-to-N ratios (19–41) in Fennoscandianboreal forests and differences in forest productivity by afactor close to 3. Gross N mineralization was seventimes higher when soil, microbial, and plant C-to-Nratios were the lowest compared to the highest. Thisprocess, nitrification and potential denitrification correlatedwith inorganic, total and microbial biomass N, butnot microbial C. There was a constant ratio between soiland microbial C-to-N ratio of 3.7±0.2, across wide ratiosof soil C-to-N and fungi-to-bacteria. Soil N-cyclingshould be controlled by the supplies of C and N to themicrobes. In accordance with plant allocation theory, wediscuss the possibility that the high fungal biomass athigh soil C-to-N ratio reflects a particularly high supplyof plant photosynthates, substrates of high-quality C, tomycorrhizal fungi. Methods to study soil N turnoverand N retention should be developed to take into accountthe impact of mycorrhizal fungi on soil N-cycling.

  • 28.
    Johansson, Otilia
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Palmqvist, Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lichen responses to nitrogen and phosphorus additions can be explained by the different symbiont responses2011Ingår i: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 191, nr 3, s. 795-805Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Responses to simulated nitrogen (N) deposition with or without added phosphorus (P) were investigated for three contrasting lichen species – the N-sensitive Alectoria sarmentosa, the more N-tolerant Platismatia glauca and the N2-fixing Lobaria pulmonaria– in a field experiment.

    To examine whether nutrient limitation differed between the photobiont and the mycobiont within the lichen, the biomass responses of the respective bionts were estimated.

    The lichenized algal cells were generally N-limited, because N-stimulated algal growth in all three species. The mycobiont was P-limited in one species (A. sarmentosa), but the growth response of the mycobionts was complex, as fungal growth is also dependent on a reliable carbon export from the photobiont, which may have been the reason for the decrease of the mycobiont with N addition in P. glauca.

    Our findings showed that P availability was an important factor when studying effects of N deposition, as P supply can both mitigate and intensify the negative effects of N on epiphytic lichens.

  • 29.
    Karlsson, Jan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Global Change and the High-Latitude Environment2008Ingår i: EOS: Transactions, ISSN 0096-3941, E-ISSN 2324-9250, Vol. 89, nr 10, s. 97-97Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    High Latitude Terrestrial and Freshwater Ecosystems: Interactions and Response to Environmental Change; Abisko, Sweden, 11–14 September 2007; Terrestrial and aquatic scientists took part in a workshop in Sweden to discuss cross-system linkages that strongly influence the structure and function of terrestrial and aquatic ecosystems, which effects may be altered by future environmental change. Sixty-five researchers, mainly from northern Europe and North America, attended the meeting.

  • 30.
    Karlsson, Jan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persson, Jenny
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lundin, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    High emission of carbon dioxide and methane during ice thaw in high latitude lakes2013Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, nr 6, s. 1123-1127Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The winter period is seldom included in the estimates of aquatic-atmospheric carbon exchange. In this study we quantified the flux of carbon dioxide (CO2) and methane (CH4) over 3 years from 12 small subarctic lakes. The lakes accumulated consistent and high amounts of CO2 and CH4 (56–97% as CO2) over the winter, resulting in a high flux during ice thaw. The CO2 flux during ice thaw increased with increasing mean depth of the lakes, while the CH4 flux was high in lakes surrounded by mires. The ice thaw period was quantitatively important to the annual gas balances of the lakes. For nine of the lakes, 11 to 55% of the annual flux occurred during thaw. For three of the lakes with an apparent net annual CO2 uptake, including the thaw period reversed the balance from sink to source. Our results suggest that the ice thaw period is critically important for the emissions of CO2 and CH4 in small lakes.

  • 31.
    Karlsson, Torbjörn
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Persson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Skyllberg, Ulf
    Mörth, Carl-Magnus
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Characterization of Iron(III) in Organic Soils Using Extended X-ray Absorption Fine Structure Spectroscopy2008Ingår i: Environmental Science & Technology, Vol. 42, nr 15, s. 5449-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The distribution of different iron (Fe) species in soils, sediments, and surface waters has a large influence on the mobility and availability of Fe, other nutrients, and potentially toxic trace elements. However, the knowledge about the specific forms of Fe that occurs in these systems is limited, especially regarding associations of Fe with natural organic matter (NOM). In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to characterize Fe(III) in organic soils (pH 4.6-6.0) with varying natural Fe content. The EXAFS data were subjected to wavelet transform analysis, to facilitate the identification of the nature of backscattering atoms, and to conventional EXAFS data fitting. The collective results showed the existence of two pools of iron: mononuclear Fe(III)-NOM complexes and precipitated Fe(III) (hydr)oxides. In the soil with lowest pH (4.6) and Fe content mononuclear organic complexes were the completely dominating fraction whereas in soils with higher pH and Fe content increasing amounts of Fe (hydr)oxides were detected. These results are of environmental importance, as the different iron pools most likely have markedly different reactivities.

  • 32.
    Klaminder, J
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Yoo, K
    Giesler, R
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Soil carbon accumulation in the dry tundra: Important role played by precipitation2009Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, s. G04005-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A positive relationship between the mean annual precipitation (MAP) and soil organic carbon (SOC) is found in most surveys covering the subarctic and boreal region. In this paper we assess mechanisms behind variable SOC pools in dry tundra soils developed along a 50 km long subarctic precipitation (snow) gradient in northern Sweden. Lead 210 is used to infer SOC accumulation rates in the O horizon. Despite an unchanged or even slightly decreasing accumulation rate of SOC in the O horizon (range 0.02–0.06 kg C m−2 yr−1) along with increasing MAP and a relative constant litter input (∼0.04 kg C m−2 yr−1), the SOC pool in the upper 1 m increase significantly with increasing MAP. This trend is mainly due to a progressively buildup of SOC in the mineral soil and argued to be the result of an accelerated vertical translocation of SOC at sites overlain by a thick snowpack. Furthermore, the loss of SOC from the O horizon through wind erosion appears to be more pronounced at snow-poor sites. We estimate that vegetated heath soil may loose >0.02 kg C m−2 yr−1 (∼half of the annual litter fall) due to wind erosion in snow-poor areas. We stress that lateral and vertical translocation processes inherent by precipitation regimes may be of fundamental importance for the long-term SOC accumulation in tundra soil.

  • 33.
    Klaminder, Jonatan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Makoto, Kobayashi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Physical mixing between humus and mineral matter found in cryoturbated soils increases short-term heterotrophic respiration rates2013Ingår i: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 57, s. 922-924Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cryoturbation is an important mechanism in the most recent large-scale model describing the build-up of soil organic carbon (SOC) in arctic soils. In this paper, we hypothesize that the physical mixing of humus and mineral soil generated by this process causes previously unconsidered effects on respiration rates. Through laboratory incubations we found that mixing of humus into mineral soil from cryoturbated soils primed heterotrophic respiration rates by about 40%, which was of the same magnitude as the effect generated by a rise in soil temperature from 5 degrees C to 10 degrees C. Our result indicates that cryogenic mixing, if complete, may generate short-term positive effects on heterotrophic respiration rates as long as the mixing does not translocate carbon into much colder soil layers. (C) 2012 Elsevier Ltd. All rights reserved.

  • 34.
    Klaminder, Jonatan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Yoo, K.
    Rydberg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    An explorative study of mercury export from a thawing palsa mire2008Ingår i: Journal of Geophysical Research, Vol. 113, s. G04034-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thawing of permafrost and a subsequent accelerated loss of mercury from the soil constitute a possible threat to the quality of high-latitude surface waters. In this paper we estimate the export of mercury generated by a thawing palsa mire in northern Sweden, by assessing net mercury storage changes along thermokarst erosion gradients. Lower mercury inventories in inundated hummocks covered by water (≤3.1 mg Hg m−2) than in noneroding hummocks (between 5.5 and 8 mg Hg m−2) suggests a release of ~40–95% of the mercury pool from hummock peat experiencing subsidence and submerging. The documented expansion of submerged areas between 1970 and 2000 in the studied system indicates that permafrost thawing has initiated a mobilization of 34 to 50 g mercury. We stress the need of further assessing the fate of this mercury because the size of the mobilized mercury pool might be highly significant for subarctic surface waters.

  • 35.
    Kuhn, McKenzie
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Renewable Resources, University of Alberta, 116 St & 85 Ave, Edmonton, AB, CA, T6G 2R3, Canada.
    Lundin, Erik J
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Swedish Polar Research Secretariat, Abisko Scientific Research Station, SE-981 07, Abisko, Sweden.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Johansson, Margareta
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Emissions from thaw ponds largely offset the carbon sink of northern permafrost wetlands2018Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, artikel-id 9535Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Northern regions have received considerable attention not only because the effects of climate change are amplified at high latitudes but also because this region holds vast amounts of carbon (C) stored in permafrost. These carbon stocks are vulnerable to warming temperatures and increased permafrost thaw and the breakdown and release of soil C in the form of carbon dioxide (CO2) and methane (CH4). The majority of research has focused on quantifying and upscaling the effects of thaw on CO2 and CH4 emissions from terrestrial systems. However, small ponds formed in permafrost wetlands following thawing have been recognized as hotspots for C emissions. Here, we examined the importance of small ponds for C fluxes in two permafrost wetland ecosystems in northern Sweden. Detailed flux estimates of thaw ponds during the growing season show that ponds emit, on average (±SD), 279 ± 415 and 7 ± 11 mmol C m−2 d−1 of CO2 and CH4, respectively. Importantly, addition of pond emissions to the total C budget of the wetland decreases the C sink by ~39%. Our results emphasize the need for integrated research linking C cycling on land and in water in order to make correct assessments of contemporary C balances.

  • 36.
    Kupryianchyk, Darya
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bidleman, Terry F.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Liljelind, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lau, Danny Chun Pong
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Sponseller, Ryan A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Andersson, Patrik L.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Industrial and natural compounds in filter-feeding black fly larvae and water in 3 tundra streams2018Ingår i: Environmental Toxicology and Chemistry, ISSN 0730-7268, E-ISSN 1552-8618, Vol. 37, nr 12, s. 3011-3017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report concentrations of polychlorinated biphenyls, polybrominated diphenyl ethers, novel flame retardants, and naturally occurring bromoanisoles in water and filter-feeding black fly (Simuliidae) larvae in 3 tundra streams in northern Sweden. The results demonstrate that black fly larvae accumulate a wide range of organic contaminants and can be used as bioindicators of water pollution in Arctic streams.

  • 37.
    Lagerström, Anna
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Esberg, Camilla
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wardle, David A.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Soil phosphorus and microbial response to a long-term wildfire chronosequence in northern Sweden2009Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 95, nr 2/3, s. 199-213Artikel i tidskrift (Refereegranskat)
    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.

  • 38.
    Lundin, Erik
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Christensen, Torben
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Heliasz, Michal
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persson, Andreas
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    A weak C sink at high latitudes: support from an integrated terrestrial – aquatic C balanceManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    High latitude ecosystems have served as net sinks of atmospheric carbon (C) in the Holocene time perspective. However, the ongoing climate warming makes it questionable if high latitude landscapes still function as net C sinks. In this study we used multiyear high resolution C flux data to estimate an integrated terrestrial-aquatic C balance of a sub-arctic catchment. The results indicate large inter annual variability in C fluxes and suggest that the C sink function of this landscape is weak, especially when also accounting for the often neglected C losses from aquatic systems. In fact, our results suggest that it is more likely that the studied catchment serves as a net source of C rather than a net sink. These results highlight the importance of inland waters in the C cycle and that the strength of the C sequestering in the contemporary sub-arctic environment is much weaker than often assumed.

  • 39.
    Lundin, Erik J.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persson, Andreas
    Thompson, Megan S.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Integrating carbon emissions from lakes and streams in a subarctic catchment2013Ingår i: Journal of Geophysical Research: Biogeosciences, ISSN 2169-8953, Vol. 118, nr 3, s. 1200-1207Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Northern inland waters emit CO2 and CH4 to the atmosphere but the importance of these emissions is poorly understood due to a lack of integrated catchment-scale estimates of carbon (C) emissions from lakes and streams. In this study we quantified the annual emission of CO2 and CH4 from 27 lakes and 23 stream segments in a 15km(2) subarctic catchment in northern Sweden. All lakes and streams were net sources of C to the atmosphere on an annual basis. Streams dominated (96%) the aquatic CO2 emission while lakes (61%) dominated the aquatic CH4 emission. Total aquatic C emission from the catchment was estimated to be 9.1gCm(-2)yr(-1) (98% as CO2). Although streams only accounted for 4% of the aquatic area in the catchment, they accounted for 95% of the total emission. The C emissions from lakes and streams were considerably larger than previously reported downstream waterborne export of C from the catchment, indicating that the atmospheric losses of C in the aquatic systems are an important component in the catchment C balance.

  • 40.
    Lundin, Erik J
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University, Stockholm, Sweden.
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persson, Andreas
    Olefeldt, David
    Heliasz, Michal
    Christensen, Torben R.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Is the subarctic landscape still a carbon sink?: Evidence from a detailed catchment balance2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 5, s. 1988-1995Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate warming raises the question whether high-latitude landscape still function as net carbon (C) sinks. By compiling an integrated C balance for an intensely studied subarctic catchment, we show that this catchment's C balance is not likely to be a strong current sink of C, a commonly held assumption. In fact, it is more plausible (71% probability) that the studied catchment functions as a C source (-1120gCm(-2)yr(-1)). Analyses of individual fluxes indicate that soil and aquatic C losses offset C sequestering in other landscape components (e.g., peatlands and aboveground forest biomass). Our results stress the importance of fully integrated catchment C balance estimates and highlight the importance of upland soils and their interaction with the aquatic network for the catchment C balance.

  • 41. Lyon, Steve W.
    et al.
    Ploum, Stefan W.
    van der Velde, Ype
    Rocher-Ros, Gerard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Mörth, Carl-Magnus
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lessons learned from monitoring the stable water isotopic variability in precipitation and streamflow across a snow-dominated subarctic catchment2018Ingår i: Arctic, Antarctic and Alpine research, ISSN 1523-0430, E-ISSN 1938-4246, Vol. 50, nr 1, artikel-id e1454778Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This empirical study explores shifts in stable water isotopic composition for a subarctic catchment located in northern Sweden as it transitions from spring freshet to summer low flows. Relative changes in the isotopic composition of streamflow across the main catchment and fifteen nested subcatchments are characterized in relation to the isotopic composition of precipitation. With our sampling campaign, we explore the variability in stream-water isotopic composition that originates from precipitation as the input shifts from snow to rain and as landscape flow pathways change across scales. The isotopic similarity of high-elevation snowpack water and early season rainfall water seen through our sampling scheme made it difficult to truly isolate the impact of seasonal precipitation phase change on stream-water isotopic response. This highlights the need to explicitly consider the complexity of arctic and alpine landscapes when designing sampling strategies to characterize hydrological variability via stable water isotopes. Results show a potential influence of evaporation and source water mixing both spatially (variations with elevation) and temporally (variations from post-freshet to summer flows) on the composition of stream water across Miellajokka. As such, the data collected in this empirical study allow for initial conceptualization of the relative importance of, for example, hydrological connectivity within this mountainous, subarctic landscape.

  • 42. Lyon, SW
    et al.
    Destouni, G
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Humborg, C
    Mörth, CM
    Seibert, J
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Troch, PA
    Estimation of permafrost thawing rates in a sub-arctic catchment using recession flow analysis2009Ingår i: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 13, nr 5, s. 595-604Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Permafrost thawing is likely to change the flow pathways taken by water as it moves through arctic and sub-arctic landscapes. The location and distribution of these pathways directly influence the carbon and other biogeochemical cycling in northern latitude catchments. While permafrost thawing due to climate change has been observed in the arctic and sub-arctic, direct observations of permafrost depth are difficult to perform at scales larger than a local scale. Using recession flow analysis, it may be possible to detect and estimate the rate of permafrost thawing based on a long-term streamflow record. We demonstrate the application of this approach to the sub-arctic Abiskojokken catchment in northern Sweden. Based on recession flow analysis, we estimate that permafrost in this catchment may be thawing at an average rate of about 0.9 cm/yr during the past 90 years. This estimated thawing rate is consistent with direct observations of permafrost thawing rates, ranging from 0.7 to 1.3 cm/yr over the past 30 years in the region.

  • 43. Lyon, SW
    et al.
    Mörth, M
    Humborg, R
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Destouni, G
    The relationship between subsurface hydrology and dissolved carbon fluxes for a sub-arctic catchment2010Ingår i: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 14, nr 6, s. 941-950Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In recent years, there has been increased interest in carbon cycling in natural systems due to its role in a changing climate. Northern latitude systems are especially important as they may serve as a potentially large source or sink of terrestrial carbon. There are, however, a limited number of investigations reporting on actual flux rates of carbon moving from the subsurface landscape to surface water systems in northern latitudes. In this study, we determined dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) fluxes from the subsurface landscape for a sub-arctic catchment located in northern Sweden. These are based on observed annual flux-averaged concentrations of DOC and DIC for the 566 km2 Abiskojokken catchment. We demonstrate the importance to correctly represent the spatial distribution of the advective solute travel times along the various flow and transport pathways. The fluxes of DOC and DIC from the subsurface landscape to the surface water system were comparable in magnitude. This balance could shift under future climatic changes that influence the hydrological and biogeochemical system.

  • 44.
    Myrstener, Maria
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rocher-Ros, Gerard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Burrows, Ryan M.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Sponseller, Ryan A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persistent nitrogen limitation of stream biofilm communities along climate gradients in the Arctic2018Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, nr 8, s. 3680-3691Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate change is rapidly reshaping Arctic landscapes through shifts in vegetation cover and productivity, soil resource mobilization, and hydrological regimes. The implications of these changes for stream ecosystems and food webs is unclear and will depend largely on microbial biofilm responses to concurrent shifts in temperature, light, and resource supply from land. To study those responses, we used nutrient diffusing substrates to manipulate resource supply to biofilm communities along regional gradients in stream temperature, riparian shading, and dissolved organic carbon (DOC) loading in Arctic Sweden. We found strong nitrogen (N) limitation across this gradient for gross primary production, community respiration and chlorophyll-a accumulation. For unamended biofilms, activity and biomass accrual were not closely related to any single physical or chemical driver across this region. However, the magnitude of biofilm response to N addition was: in tundra streams, biofilm response was constrained by thermal regimes, whereas variation in light availability regulated this response in birch and coniferous forest streams. Furthermore, heterotrophic responses to experimental N addition increased across the region with greater stream water concentrations of DOC relative to inorganic N. Thus, future shifts in resource supply to these ecosystems are likely to interact with other concurrent environmental changes to regulate stream productivity. Indeed, our results suggest that in the absence of increased nutrient inputs, Arctic streams will be less sensitive to future changes in other habitat variables such as temperature and DOC loading.

  • 45. Mörth, C
    et al.
    Laudon, H
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Mellqvist, E
    Torssander, P
    Giesler, R
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Sources of stream water sulfate during the spring snowmelt in boreal streams: Evidence from δ34S isotope measurements2008Ingår i: J. Geophys. Res., Vol. 113, s. G01005-Artikel i tidskrift (Refereegranskat)
  • 46. Mörth, Carl-Magnus
    et al.
    Torssander, Peter
    Kjønaas, O Janne
    Stuanes, Arne O
    Moldan, Filip
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Mineralization of organic sulfur delays recovery from anthropogenic acidification.2005Ingår i: Environ Sci Technol, ISSN 0013-936X, Vol. 39, nr 14, s. 5234-40Artikel i tidskrift (Refereegranskat)
  • 47. Nilsson, Lars Ola
    et al.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Bååth, Erland
    Wallander, Håkan
    Growth and biomass of mycorrhizal mycelia in coniferous forests along short natural nutrient gradients.2005Ingår i: New Phytol, ISSN 0028-646X, Vol. 165, nr 2, s. 613-22Artikel i tidskrift (Refereegranskat)
  • 48. Olefeldt, David
    et al.
    Roulet, Nigel
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Persson, Andreas
    Total waterborne carbon export and DOC composition from ten nested subarctic peatland catchments-importance of peatland cover, groundwater influence, and inter-annual variability of precipitation patterns2013Ingår i: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 27, nr 16, s. 2280-2294Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Waterborne carbon (C) export from terrestrial ecosystems is a potentially important flux for the net catchment C balance and links the biogeochemical C cycling of terrestrial ecosystems to their downstream aquatic ecosystems. We have monitored hydrology and stream chemistry over 3 years in ten nested catchments (0.6–15.1 km2) with variable peatland cover (0%–22%) and groundwater influence in subarctic Sweden. Total waterborne C export, including dissolved and particulate organic carbon (DOC and POC) and dissolved inorganic carbon (DIC), ranged between 2.8 and 7.3 g m–2 year–1, representing ~10%–30% of catchment net ecosystem exchange of CO2. Several characteristics of catchment waterborne C export were affected by interacting effects of peatland cover and groundwater influence, including magnitude and timing, partitioning into DOC, POC, and DIC and chemical composition of the exported DOC. Waterborne C export was greater during the wetter years, equivalent to an average change in export of ~2 g m–2 year–1 per 100 mm of precipitation. Wetter years led to a greater relative increase in DIC export than DOC export due to an inferred relative shift in dominance from shallow organic flow pathways to groundwater sources. Indices of DOC composition (SUVA254 and a250/a365) indicated that DOC aromaticity and average molecular weight increased with catchment peatland cover and decreased with increased groundwater influence. Our results provide examples on how waterborne C export and DOC composition might be affected by climate change.

  • 49. Olsson, P
    et al.
    Linder, S
    Giesler, R
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Högberg, P
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Fertilization of boreal forest reduces both autotrophic and heterotrophic soil respiration2005Ingår i: Global Change Biology, Vol. 11, s. 1-9Artikel i tidskrift (Refereegranskat)
  • 50. Olsson, R
    et al.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Persson, P
    Abiotic hydrolysis of glucose-1-phosphate adsorbed at the water-goethite interface2007Ingår i: Geochimica et Cosmochimica Acta, Vol. 71, s. A739-A739 Suppl. SArtikel i tidskrift (Refereegranskat)
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