| 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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