6 Research projects
6.4 Collaboration on permafrost – soil – vegetation studies
Bo Elberling, Hanne H. Christiansen, Anders Michelsen, Peter Kuhry, Daan Blok, Carsten Suhr Jacobsen, Christian J. Jørgensen, Ulla Kokfelt, Jordan R. Mertes, Stefanie Härtel, Katrine M.L. Johansen, Daiga Smeke and Ulrich Neumann
Activities within the newly established Centre for Permafrost (CENPERM), Uni-versity of Copenhagen, the 7th framework EU research project PAGE21 (Changing Permafrost in the Arctic and its Global Effects in the 21st Century) and the Nordic Centre of Excellence, DEFROST (Biogeo-chemistry in a changing cryosphere –
Days since 28 May 2012
ΔNorth (m)ΔEast (m)ΔUp (m)
0 1 2 3 4 5 6 7 8
–0.4 -0.3 –0.2 –0.1 0 0.1
–0.1 0 0.1 0.2 0.3 0.4
–0.4 –0.3 –0.2 –0.1 0 0.1
Figure 6.9 Horizontal components (N, E) and vertical component (U) of a representa-tive GPS station for the period of 28 May to 4 June 2012. Horizontal components show an acceleration and vertical component a lowering. Blue shaded periods mark the switch of P1 to P2 (fi gure 6.8).
depicting ecosystem-climate feedbacks as affected by changes in permafrost, snow and ice distribution) were coordinated and resulted in several subprojects from mid-July to mid-September 2012 in Zacken-berg. In these various projects researchers and students from the University Centre in Longyearbyen (UNIS), Stockholm University and University of Copenhagen were working closely together. With the support from the EU infrastructure project INTERACT Transnational Access it was possible to bring all involved collaborating researchers, students and technical staff to work together in Zackenberg.
Methane dynamics using mobile chambers (July-September) Aerobic methane-oxidizing bacteria (methanotrophs) are distinguished by their ability to use methane (CH4) as their sole source of metabolic energy and structural carbon. In this study, we focussed on the methanotrophs inhabits across a variety of plant ecosystems within the Zackenberg valley. The project focus on in situ CH4 oxidation rates from well-drained soil types and the importance of CH4 oxidation on the annual CH4 budget for the Zackenberg area and further north.
The work was carried out from 11 July to 16 September 2012.
Data collection consisted of transparent and dark chamber measurements of CH4, CO2 and N2O as well as depth-specifi c soil water contents and soil temperatures. A methane analyser (LGR-DLT100) was used to provide high precision and resolution data at low concentrations.
The sites chosen and established for CH4 oxidation assessment were based on hydrological regimes and in relation to al-ready established sites. The latter included ITEX (International Tundra Experiment) sites established in 2007 (Cassiope tetragona
and Salix arctica). Additional sites were established along a hydrological gradient representing a downward sloping topo-graphy: from vegetation-free sites, dry heath vegetated by mountain avens Dryas octopetala and into a fen area dominated by mosses, sedge Carex bigelowii and Arctic cottongrass Eriophorum scheuchzeri.
In order to assess the potential CH4 dynamics within the active layer, Cassiope and Salix sites were manipulated in fi ve replicates: i) control, ii) removal of vegeta-tion and top soil (10 cm) and iii) exposed permafrost (removal of entire active layer).
The effect of increased temperature on CH4 processes were also assessed based on fi ve replicate measurements on ITEX which has setups of i) control and ii) heated plots on both Cassiope and Salix.
Preliminary results of three different vegetation types and bare soil (fi gure 6.10) show differences in average CH4 uptake.
Over the two months of measurements Dryas has an average CH4 uptake of 8.5 ± 5 µmol m-2 h-1 which is signifi cant higher than Cassiope and Salix which were 3.4 ± 1 and 3.0 ± 0.6 µmol m-2 h-1, respectively.
Surprisingly, uptake rate observed at vege-tation-free ground (7.63 ± 1.9 µmol CH4 m-2 h-1) were similar to rates observed for Dryas. The relatively high oxidation rates observed at Dryas and vegetation-free sites will be used for upscaling, as these landforms are the dominant types in the ice-free part of Greenland further north.
Permafrost cryo-stratigraphy and ground thermal observations (Au-gust-September)
Two Ph.D. projects co-fi nanced by DE-FROST, PAGE21 and CENPERM/Univer-sity of Copenhagen and the UniverCENPERM/Univer-sity Centre in Svalbard focus on permafrost cryostratigraphy and ground temperatures down to 10-20 metres at two landforms: on the bottom moraine surface near ZERO-CALM1 and at a snow patch site south of the runway near ZEROCALM2 site.
Drilling was carried out using a medi-um-sized UNIS-based drill rig using air compression, which allows intact perma-frost cores to be collected as part of the drilling. Three deeper boreholes were drilled. Two of the deep boreholes were cased to a depth of 18.3 and 18.5 m respec-tively, allowing installation of thermistor strings. Both have a steel casing with no fi lling. The third bore hole was a replicate of the ZEROCALM1 borehole.
CH4 uptake (mmol m2 hr-1)
0 4 8 12 16
Dryas Cassiope Salix Bare soil
Figure 6.10 Average CH4 uptake during the snow-free season 2012 at three vegetation types (n = 5) and bare soil (n = 3).
The ZEROCALM1 borehole has one 20 m temperature string with 20 sensors to a depth of 18.3 m. The ZEROCALM2 site has two 10 m thermistor strings hanging one above the other, resulting in 30 sensors to a depth of 18.5 m. Thermistors were located to have higher spatial resolution within the active layer and top permafrost (approxi-mately seven sensors within the top 2 m).
Two shorter 2.5 m deep boreholes were hand-drilled to obtain additional cores of the permafrost top cryostratigraphy, in a large nival fan and in the Zackenberg delta.
In the Zackenberg lowland seven ad-ditional boreholes were made for carbon assessment and for obtaining a wider spatial coverage of the variations in the top permafrost ground temperature. These boreholes are located along a north-south transect and covers different landforms, microclimatic regimes as well as vegeta-tion zones. All boreholes were instrumen-ted with GeoPrecision thermistor strings hanging for observation of the annual ground thermal regime.
Initial data from September to Novem-ber 2012 were collected by the GeoBasis staff at Zackenberg. These fi rst data al-lows a snapshot of the variability of the relatively cold ground thermal regime (fi gure 6.11) with some of the lowest permafrost temperatures recorded in the Arctic area so far. Data shows the end of summer and autumn freeze up of the active layer and its variability among the landforms observed, and that the active layer thickness variability is between 0.5 to 1.25 m.
Soil and permafrost distribution and characteristics (September)
Focus on the spatial-distribution of soil carbon, nitrogen storage and permafrost characteristics within the top 1-2 m of the ground is a key issue in PAGE21. A continuation of work previously carried out in Zackenberg (1996, 1999, 2000, 2008 and 2009) by Bo Elberling, Peter Kuhry and colleagues. Cores were obtained by simply hammering metal tubes into the active layer/permafrost as far as pos-sible from the surface at 15-20 sites and by using hand drilling equipment, which can be carried around by 1-2 persons.
The aims are to quantify the pool of C and N buried in the top permafrost, to complete the permafrost map and link the quality of C to burial history.
Particular emphasis was put on i) obtain-ing cores from previously under-sampled land cover classes, such as higher eleva-tion sites and small ponds, ii) obtaining deeper cores down to 2-3 m (see section on permafrost drilling) in the most heavily cryoturbated land cover types (fens and grasslands), to estimate deep C storage and, iii) in cooperation with University of Copenhagen, obtain additional deep peat cores from palsas and pounus to assess pale environmental changes in the peat land ecosystems. Figure 6.12 presents prelimi-nary results from an exposure in a naval fan, showing an alternation of dynamic deposition of slope materials and periods of surface stabilisation with soil development.
Additional intact permafrost cores were collected from one soil pit in order to pro-duced replicate permafrost subsamples to be inserted in two different depths within the active layer. This was carried out in both ambient and ITEX warmed plot in both a Salix and Cassiope heath ecosystem.
Finally, intact cores from the drilling cam-paigns and manipulated vegetation plots have been kept at ambient temperatures until DNA/RNA extraction were com-pleted at Zackenberg Research Station.
Warming impacts on plant decom-position rates and plant-soil-microbe nitrogen cycling
Increasing evidence emerges for a pan-Arctic positive shrub growth response to rising air temperatures during the last decades. However, it remains unclear as of yet whether observed shrub growth in-creases are a direct response to an increase in air temperature or an indirect effect of warming-induced increases in litter decomposition rates and shrub nitrogen availability. The overall objective of our study is to examine the impacts of summer
Mean ground temperatures (°C) from September-October 2012
Depth (m)
Figure 6.11 Snapshot of the mean ground thermal regime at the two new deeper permafrost boreholes drilled in end of summer 2012. Clearly the snow patch site (ZERO-CALM2) is somewhat warmer than at the more exposed fl at ground mo-raine site (ZEROCALM1).
Figure 6.12 Site ZK12-12 lithology, dating, simple geochemistry and plant macrofossil content.
and winter warming on litter decomtion rates and assess the potential posi-tive feedback to shrub expansion through enhanced nitrogen availability. Here, we measured decomposition rates of deci-duous and evergreen shrub biomass and followed fate of decomposition-released nitrogen in soils, microbes and plants in or-der to answer our main research question:
Does seasonal (summer/winter) warming enhance organic matter decomposition and shrub nitrogen uptake differently in low-, mid-, and high Arctic tundra?
Furthermore, we investigated if local microbial adaptation to litter species identity favours breakdown of plant litter beneath the species from which it is derived compared to decomposition beneath a different species. The hypothesis for such species-identity origin effect on litter decomposability has been termed home-fi eld advantage (HFA) and has been shown to be widespread in forest ecosy-stems. However, it is unclear if HFA also accelerates litter decomposition in tundra ecosystems. Furthermore, it is unclear to which extent HFA is altered by climatic perturbations. Here, we incubated ever-green (Cassiope tetragona) and deciduous (Salix arctica) shrub biomass reciprocally in two mid-Arctic heath sites dominated by either species. Both at the Cassiope and Salix heath, summer temperature and growing season length have been manipu-lated since the start of the experiments in 2004. The close vicinity of the two experi-ments (few hundred meters) and similar experimental setup allows us to assess the importance of HFA in a tundra ecosystem and predict how HFA may be modifi ed by future climatic changes.
Long-term impacts of shading, warm-ing and growwarm-ing season length on the natural abundances of carbon and nitrogen isotopes in a Salix and Cas-siope heath ecosystem
Climatic changes in the Arctic may lead to changes in vegetation community composition through shifts in nitrogen source usage and/or through changes in soil moisture status, which can potentially alter species’ competitive abilities. We investigated changes in soil, root, microbe and leaf natural abundances of nitrogen and carbon after 10 years of manipula-tion of summer temperature, shading level and growing season length in both a Cassiope- and a Salix-dominated heath in
the Zackenberg valley, in order to reveal potential changes in nitrogen source usa-ge, as shown by potential changes in the natural abundance of nitrogen isotopes, and changes in plant water-use-effi ciency, identifi ed by potential changes in the natural abundance of carbon isotopes. We will investigate linkages between shifts in plant community composition and carbon/nitrogen natural abundances, both above- and below-ground, and link this to earlier results from the same sites.
Plant uptake of nitrogen from perma-frost soils
What is the maximum rooting depth of plants, and will they be able to take up nutrients released from thawing perma-frost soils? In order to study the uptake of nitrogen from intact, live Arctic plants in the fi eld, a trace amount of the stable iso-tope 15N was in mid-August 2012 added in the form of 15N labelled ammonium chlo-ride to an open, dry Dryas-Kobresia-Salix heath. To reveal potential plant nitrogen uptake at depth, for instance as N released from thawing permafrost, 15N isotope was injected into the soil at three depths, 10 cm, 45 cm and 90 cm depth, of which the latter is representing the maximum active layer depth at the site, in ten replicates of each depth. The amount of N added is too low to have a fertilizing effect, but plant uptake may be detectable due to use of
15N enriched nitrogen. Leaves of the three dominant species were collected three and seven days after injection, in order to determine potential enrichment in 15N in the leaves. This will be followed up by investigating the long-term 15N concentra-tion in plant leaves after one year.
Figure 6.13 View of snow covered dry heath/semi desert site in early April.
Despite being situated on top of a windswept ridge, snow depth was approximately 20 cm.
Clavering Ø can be seen in the background. Photo:
Casper T. Christiansen.