| 1. |
- Alewell, C, et al.
(författare)
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Stable carbon isotopes as indicators for environmental change inpalsa peats
- 2011
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Ingår i: Biogeosciences. - Kaltenburg-Lindau : European Geosciences Union. - 1726-4170 .- 1726-4189. ; 8, s. 1769-1778
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Alewell, C, et al.
(författare)
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Stable carbon isotopes as indicators for micro-geomorphic changes in palsa peats
- 2011
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Ingår i: Biogeosciences Discussions. - : Copernicus GmbH. - 1810-6277 .- 1810-6285. ; 8:1, s. 527-548
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
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| 4. |
- Bartels, Pia, et al.
(författare)
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Allochthonous Organic Matter Supports Benthic but Not Pelagic Food Webs in Shallow Coastal Ecosystems
- 2018
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Ingår i: Ecosystems (New York. Print). - : Springer. - 1432-9840 .- 1435-0629. ; 21:7, s. 1459-1470
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Berggren, Martin, et al.
(författare)
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Lake secondary production fueled by rapid transfer of low molecular weight organic carbon from terrestrial sources to aquatic consumers
- 2010
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 13:7, s. 870-880
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Tidskriftsartikel (refereegranskat)abstract
- P>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-km2 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.
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| 6. |
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| 7. |
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| 8. |
- Björk, Robert G., 1974, et al.
(författare)
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Nitrification and Denitrification Enzyme Activity: a successful tool in Arctic and Alpine soil ecology
- 2007
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Ingår i: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Nitrogen is consideration to be a limiting factor for plants and microbes in arctic and alpine ecosystems and the rates of mineralization, nitrification, and denitrifi¬cation are known to be generally low. However, Climate Change is expected to alter the nitrogen availability and dynamics and, as a consequence, affect plant community composition and production. The general consensus today is that increased temperature will lead to greater microbial activity and more plant-available nitrogen. Nevertheless, nitrification and denitrification are restricted by a number of environmental factors such as low tem¬perature and low pH. The C/N ratio and the water content of the soils also play an important role in determining the rates of nitrification and denitrification. Since 2002 microbial studies has been undertaken at Latnjajure, and comprise several microbial techniques, e.g. Nitrification Enzyme Activity (NEA), Denitrification Enzyme Activity (DEA), Phospholipid fatty acid analysis (PFLA), and Temperature Gradient Gel Electrophoresis (TGGE). These studies focuses on the interaction between plants and microbes along natural environmental gradients, both within plant communities and within the landscape, but also entails the OTCs used in the ITEX studies at Latnjajaure. Here we present the techniques NEA and DEA and give some brief results from how these have been successfully applied at Latnjajaure. In ecosystems with low nitrification activity, small amounts of NO3-/NO2- will be formed and it is thus difficult to measure low fluxes. However, NO3-/NO2- can be converted to N2O and then analysed by gas chromatography, whereby the detection limit is increased at least 1000 times compared to the spectroscopical technique. These techniques are referred to Nitrification (NEA) and Denitrification Enzyme Activity (DEA) and give a potential measure on the nitrification and denitrification rates, which goes back to the actual populations of nitrifiers and denitrifiers in the soil. For instance, NEA has been proved to better correlate with extractable NH4+ concentration than net nitrification does, and still after twelve weeks show a strong correlation with the initial extractable NH4+ concentration. Therefore, these variables, in particular NEA, have the advantage of being a much more stable variable than, for instance, extractable N concentrations and net nitrification, and NEA and DEA are therefore suitable when working in fringe environments with restricted logistics like the Latnjajaure catchment. NEA is measured using a two-step incubation technique; first by incubate the soil with a nutrient solution for 24 hours in darkness, at room temperature on a rotary shaker. Sub-samples are then withdrawn after a specified time schedule. The second step allows NO3- to be reduced to N2O by adding a modified denitrifying bacterium, Pseudomonas chlororaphis ATCC 43928, together with a carbon source. This strain of bacteria lacks the enzyme to reduce N2O to N2. The samples are then again incubated in darkness, at room temperature for 24 hours, and analysed by gas chromatography. This method was first used by Lensi et al. (1985, 1986), to study nitrification potentials in forest soils. Furthermore, the method has been developed for soils with low pH and small amounts of NO3- and the analysis makes the quantification without interference of organic matter, which makes it suitable for arctic and alpine ecosystems. To analyse DEA an anaerobic incubation technique is used, based on acetylene inhibition of the N2O-reductase resulting in N2O as the only end product. The soil sample is evacuated and flushed with N2. Thereafter acetylene is inserted to a final acetylene concentration of 10%, and the samples are shaken continuously and gas samples are withdrawn after a specified time schedule, which is then analysed by gas chromatography. This provides an estimate of the maximum concentration of functional denitrifying enzymes in the soil. Denitrifiers, in contrast to nitrifiers, are heterotrophs and can switch from using NO3- as an alternative electron acceptor to O2 under aerobic conditions. This makes other factors in the soil important determinants of DEA, e.g. availability of oxygen and C. Hence, the presence of denitrifiers is rarely a limitation for denitrification and they usually make up a reasonably large fraction of the soil bacteria. At Latnjajaure NEA shows a larger differentiation across plant communities than DEA. However, the spatial variability in the landscape, at the meso-scale, was in the same range in both variables and increased with altitude from 1000 to 1365 m a.s.l, particularly in heath plant communities. This result suggests that the decrease in mean annual temperature with altitude (0.6ºC with every one hundred meters) did not reduce nitrification and denitrification rates, as one might have expected. None of the other variable studied could explain the altitudinal increase in all cases, and the factors controlling the nitrification and denitrification rates seem to vary with the vegetation type. Furthermore, neither NEA nor DEA exhibited any changes between the ambient and warmed plots in the warming experiments. However, the warming experiment in the dry heath exhibited a change in root morphology via increased specific root length (SRL; m gDM-1) and specific root area (SRA; m2 kgDM -1). As both heterotrophic microbes and plants out-compete nitrifiers for NH4+, a change in root morphology, as seen in the warming experiment, may also explain the increased activity of nitrifying and denitrifying microbes with altitude.
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| 9. |
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| 10. |
- Björkvald, Louise, et al.
(författare)
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Landscape variations in stream water SO42- and delta S-34(SO4) in a boreal stream network
- 2009
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 73:16, s. 4648-4660
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Tidskriftsartikel (refereegranskat)abstract
- 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 delta S-34(SO4) 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 (r(2) = 0.77, p 0.001) and the annual export of stream water SO42- and wetland coverage (r(2) = 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- (r(2) = 0.77 and r(2) = 0.79, respectively). The annual average delta S-34(SO4) value in wetland dominated streams was +7.6%omicron. and in streams of forested catchments +6.7%omicron. At spring flood the delta S-34(SO4) values decreased in all streams by 1%omicron to 5%omicron. The delta S-34(SO4) values in all streams were higher than the delta S-34(SO4) value of +4.7%omicron 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.
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| 11. |
- Campeau, Audrey, et al.
(författare)
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Multiple sources and sinks of dissolved inorganic carbon across Swedish streams, refocusing the lens of stable C isotopes
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- It is well established that stream dissolved inorganic carbon (DIC) fluxes play a central role in the global C cycle, yet the sources of stream DIC remain to a large extent unresolved. Here, we explore large-scale patterns in delta C-13-DIC from streams across Sweden to separate and further quantify the sources and sinks of stream DIC. We found that stream DIC is governed by a variety of sources and sinks including biogenic and geogenic sources, CO2 evasion, as well as in-stream processes. Although soil respiration was the main source of DIC across all streams, a geogenic DIC influence was identified in the northernmost region. All streams were affected by various degrees of atmospheric CO2 evasion, but residual variance in delta C-13-DIC also indicated a significant influence of in-stream metabolism and anaerobic processes. Due to those multiple sources and sinks, we emphasize that simply quantifying aquatic DIC fluxes will not be sufficient to characterise their role in the global C cycle.
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| 12. |
- Creed, Irena F., et al.
(författare)
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Global change-driven effects on dissolved organic matter composition : Implications for food webs of northern lakes
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:8, s. 3692-3714
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Forskningsöversikt (refereegranskat)abstract
- Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.
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| 13. |
- De Long, Jonathan, et al.
(författare)
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Effects of elevation and nitrogen and phosphorus fertilization on plant defence compounds in subarctic tundra heath vegetation
- 2016
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 30:2, s. 314-325
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 14. |
- Ehnvall, Betty, et al.
(författare)
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Catchment characteristics control boreal mire nutrient regime and vegetation patterns over ~5000 years of landscape development
- 2023
-
Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 895
-
Tidskriftsartikel (refereegranskat)abstract
- Vegetation holds the key to many properties that make natural mires unique, such as surface microtopography, high biodiversity values, effective carbon sequestration and regulation of water and nutrient fluxes across the landscape. Despite this, landscape controls behind mire vegetation patterns have previously been poorly described at large spatial scales, which limits the understanding of basic drivers underpinning mire ecosystem services. We studied catchment controls on mire nutrient regimes and vegetation patterns using a geographically constrained natural mire chronosequence along the isostatically rising coastline in Northern Sweden. By comparing mires of different ages, we can partition vegetation patterns caused by long-term mire succession (<5000 years) and present-day vegetation responses to catchment eco-hydrological settings. We used the remote sensing based normalized difference vegetation index (NDVI) to describe mire vegetation and combined peat physicochemical measures with catchment properties to identify the most important factors that determine mire NDVI. We found strong evidence that mire NDVI depends on nutrient inputs from the catchment area or underlying mineral soil, especially concerning phosphorus and potassium concentrations. Steep mire and catchment slopes, dry conditions and large catchment areas relative to mire areas were associated with higher NDVI. We also found long-term successional patterns, with lower NDVI in older mires. Importantly, the NDVI should be used to describe mire vegetation patterns in open mires if the focus is on surface vegetation, since the canopy cover in tree-covered mires completely dominated the NDVI signal. With our study approach, we can quantitatively describe the connection between landscape properties and mire nutrient regime. Our results confirm that mire vegetation responds to the upslope catchment area, but importantly, also suggest that mire and catchment aging can override the role of catchment influence. This effect was clear across mires of all ages, but was strongest in younger mires.
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| 15. |
- Erhagen, Björn, et al.
(författare)
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Bioavailability of stream dissolved organic carbon (DOC) during spring flood and base flow in high-latitude streams
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An important component of the carbon cycle is the lateral flow of dissolved organic carbon (DOC) from terrestrial ecosystems to streams and rivers. The fate of this carbon depends very much on the bioavailability of DOC (BDOC), which may determine whether DOC is returned to the atmosphere as CO2 or deposited in sediments. This study focuses on the linkages between stream DOC composition, optical characteristics and bioavailability along vegetation gradients in subarctic Sweden. We sampled streams from tundra, birch forest, and boreal forest ecoregions, which encompass large differences in C:N ratios (6.4-30.1) and spectroscopic characteristics, all related to variation in landscape properties. The DOC bioavailability was determined through laboratory bioassays carried out twice during the year (spring-flood and base flow). During spring flood, DOC concentration varied between 0.5 - 6.7 mg L-1 and the BDOC ranged between 3- 24 %, with the highest BDOC from birch forest/tundra and tundra streams. Results suggest that broad-scale transitions in vegetation structure across sub-arctic landscapes have important implications for the quantity and quality of DOC delivered to aquatic ecosystems.
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| 16. |
- Esberg, Camilla, 1977-, et al.
(författare)
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Microbial indices of P availability across a forest productivity gradient in South Africa
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Annan publikation (populärvet., debatt m.m.)abstract
- 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.
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| 17. |
- Esberg, Camilla, 1977-, et al.
(författare)
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Microbial responses to P addition in six South African forest soils
- 2010
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Ingår i: Plant and Soil. - : Springer. - 0032-079X .- 1573-5036. ; 329:1/2, s. 209-225
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 18. |
- Esberg, Camilla, 1977-
(författare)
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Phosphorus availability and microbial respiration across biomes : from plantation forest to tundra
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phosphorus is the main limiting nutrient for plant growth in large areas of the world and the availability of phosphorus to plants and microbes can be strongly affected by soil properties. Even though the phosphorus cycle has been studied extensively, much remains unknown about the key processes governing phosphorus availability in different environments.In this thesis the complex dynamics of soil phosphorus and its availability were studied by relating various phosphorus fractions and soil characteristics to microbial respiration kinetics. The soils used represent a range of aluminium, iron, carbon and total phosphorus content, and were located in four different biomes: subtropical forest, warm temperate forest, boreal forest and tundra.The results showed that NaOH extractable phosphorus, a fraction previously considered to be available to plants only over long time scales, can be accessed by microbes in days or weeks. Microbial phosphorus availability was not related to aluminium or iron content in any of the studied systems, not even in highly weathered soils with high aluminium and iron content. This is in contrast with other studies of soils with high sorption capacity and shows the variability of factors that govern phosphorus availability in different environments.In the boreal forest chronosequence, no difference could be seen with age in total phosphorus content or concentrations of occluded phosphorus forms. However, there were lower concentrations of labile phosphorus forms in older systems, which were correlated with a decrease in microbial respiration. This was most likely related to organic matter quality in the system, and not to geochemical factors.Phosphorus availability was linked to differences in topography (water regime) and vegetation in the tundra ecosystems. The results suggest that the availability of phosphorus, both for microbes and plants, was lower on the meadow vegetation sites compared to the two types of heath vegetation.Many factors are important for phosphorus availability in soils, but these results suggest that microbes can access less available phosphorus if not restricted by carbon, and this may be important in regard to forest management practices as well as effects of environmental change.
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| 19. |
- Esberg, Camilla, 1977-, et al.
(författare)
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Phosphorus availability and microbial respiration across different tundra vegetation types
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 20. |
- Fischer, Sandra, et al.
(författare)
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Drivers, magnitudes, and trends of microbial sulfate reduction (MSR) in freshwater systems
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Microbial sulfate reduction (MSR), which transforms sulfate into sulfide through the consumption of organic matter, plays an integral part in sulfur and carbon cycling. Yet, its magnitude beyond snap-shot conditions in specific surface water systems such as individual wetlands or lakes is with few exceptions unknown. We use stream water samples and a sulfur isotopic fractionation and mixing scheme to derive MSR at relatively large scales, both within and between five study areas located between southern Sweden and the Kola Peninsula, Russia. Results showed that the freshwater MSR ranged from 0 to 79% within the catchments and from 2 to 28% between the catchments, displaying a catchment-average value of 13%. The MSR-values showed differences between seasons, in particular in wetland/lake catchments where they were high during the spring flood, which is consistent with the mobilization of water that under low-flow winter periods can have developed anoxic conditions needed by the sulfate-reducing microorganisms (SRM). The combined abundance or deficiency of several landscape elements were found to indicate relatively well whether or not catchment-scale MSR would be high, such as the percentage of forest cover that can support MSR by the provision of organic matter to the SRM, and the areal percentage of lakes/wetlands providing longer hydrological residence times and the anoxic conditions needed by the SRM. This study, for the first time, shows compelling evidence in multiple catchments of MSR at levels around 10%, which is unaccounted for in global weathering budgets, implying for instance that the terrestrial pyrite oxidation may be underestimated.
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| 21. |
- Fischer, Sandra, et al.
(författare)
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Wide-spread microbial sulfate reduction (MSR) in northern European freshwater systems : drivers, magnitudes and seasonality
- 2023
-
Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 889
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Tidskriftsartikel (refereegranskat)abstract
- Microbial sulfate reduction (MSR), which transforms sulfate into sulfide through the consumption of organic matter, is an integral part of sulfur and carbon cycling. Yet, the knowledge on MSR magnitudes is limited and mostly restricted to snap-shot conditions in specific surface water bodies. Potential impacts of MSR have consequently been unaccounted for, e.g., in regional or global weathering budgets. Here, we synthesize results from previous studies on sulfur isotope dynamics in stream water samples and apply a sulfur isotopic fractionation and mixing scheme combined with Monte Carlo simulations to derive MSR in entire hydrological catchments. This allowed comparison of magnitudes both within and between five study areas located between southern Sweden and the Kola Peninsula, Russia. Our results showed that the freshwater MSR ranged from 0 to 79 % (interquartile range of 19 percentage units) locally within the catchments, with average values from 2 to 28 % between the catchments, displaying a non-negligible catchment-average value of 13 %. The combined abundance or deficiency of several landscape elements (e.g., the areal percentage of forest and lakes/wetlands) were found to indicate relatively well whether or not catchment-scale MSR would be high. A regression analysis showed specifically that average slope was the individual element that best reflected the MSR magnitude, both at sub-catchment scale and between the different study areas. However, the regression results of individual parameters were generally weak. The MSR-values additionally showed differences between seasons, in particular in wetland/lake dominated catchments. Here MSR was high during the spring flood, which is consistent with the mobilization of water that under low-flow winter periods have developed the needed anoxic conditions for sulfate-reducing microorganisms. This study presents for the first time compelling evidence from multiple catchments of wide-spread MSR at levels slightly above 10 %, implying that the terrestrial pyrite oxidation may be underestimated in global weathering budgets.
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| 22. |
- George, T. S., et al.
(författare)
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Organic phosphorus in the terrestrial environment : a perspective on the state of the art and future priorities
- 2018
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Ingår i: Plant and Soil. - : Springer Netherlands. - 0032-079X .- 1573-5036. ; 427:1-2, s. 191-208
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 23. |
- Giesler, Reiner, et al.
(författare)
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Boreal Forests Sequester Large Amounts of Mercury over Millennial Time Scales in the Absence of Wildfire
- 2017
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 51:5, s. 2621-2627
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 24. |
- Giesler, Reiner, et al.
(författare)
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Catchment-scale dissolved carbon concentrations and exportestimates across six subarctic streams in northern Sweden
- 2014
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 11:2, s. 525-537
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 25. |
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