Coupled Energy, Water, Carbon and Nutrient Dynamics of Peatland and Permafrost Landscapes

Arctic Permafrost Landscapes in North-East Siberia

Project Background

In collaboration with Alfred Wegener Institute (AWI), Research Unit Potsdam and other CliSAP research group, we investigate the soil-water-atmosphere system in permafrost landscapes of North-East Siberia. During the CRG, we have participated in five joint Russian-German expeditions to the North-Siberian Lena River Delta. During the expeditions LENA 2009 and LENA 2010, we set up a new, state-of-the-art micrometeorological system in the central Lena River Delta (72°N, 126°E) to determine the land-atmosphere fluxes of energy, water, CO2 and CH4 in this remote permafrost region. This system, which we operate together with Dr. Boike’s group (SPARC, AWI-Potsdam), is now one of the best equipped and most recognised land-atmosphere flux observation systems in the Arctic. These investigations were expanded in LENA 2011, 2012, and 2013 to include measurements of discharge from the island’s central polygon-covered watershed so that the lateral fluxes of water and carbon can be incorporated into budget studies. Other work in North-East Siberia through the DFG-funded Polygon project has focused on spatial variability in nutrient availability in permafrost soils.

Motivation

The CRG’s main research topics are the coupled water, carbon and nutrient dynamics of terrestrial systems under climate and land use changes with a focus on peatlands and permafrost landscapes. Peatland and permafrost soils are long-term repositories for globally significant quantities of carbon, nitrogen and other elements, which have accumulated over centuries to millennia due to water-saturated and cold soil conditions. It is feared that climatic changes could lead to pronounced changes of the energy and water budgets of permafrost soils and to a partial release of the stored carbon and nitrogen either into the atmosphere in the form of greenhouse gases or to the aquatic systems by lateral waterborne element exports.
Due to this positive feedback on climate warming, these carbon-rich systems are considered as tipping elements of the climate system. However, predictions of how these landscapes might develop under a changing climate are still highly uncertain, which is due to (1.) a scarcity of observational data, especially for the Arctic and Russia, (2.) a still insufficient understanding of the many nonlinearly interlinked soil, vegetation and atmosphere processes working on different spatial and temporal scales, and (3.) the missing representation of permafrost and wetland dynamics in most current Earth system models. We approach these three problems in close cooperation with various modelling and measuring working groups at the UHH and other scientific collaborators.

Objectives

  • Vertical (land-atmosphere) fluxes of CO2, CH4, water and energy
  • Lateral (surface-water) fluxes of dissolved organic carbon in a hydrological context
  • Soil variability in nutrient availability

Results

Flux datasets for the Lena River Delta site for ten expedition years (between 2002 and 2013) have been re-processed according to the latest best practice recommendations, and inter-annual flux variability is currently analysed. The data is archived at the European Fluxes Database Cluster.
An in-depth analysis of CO2 flux data from polygonal tundra showed that CO2 emissions through ecosystem respiration are strongly controlled by ground surface temperature. However, improved statistical approaches showed that the temperature sensitivity of ecosystem respiration is smaller than previously reported (Runkle et al., 2013). Furthermore, this study improved our understanding how the CO2 sink function of arctic tundra depends on weather patterns. For example, high surface temperatures (through arctic warming) but also low irradiance (through e.g. higher cloudiness) can turn the tundra into a short-term CO2 source even in summer.

Time series of land-atmosphere fluxes of CH4 (FCH4, blue) and CO2 (FCO2, green) and air temperature (T2m, red) during the shoulder seasons at the polygonal tundra in the Lena River Delta.

In a second arctic study, we analysed how water is re-distributed within and discharged from complex polygonal tundra catchments using a distributed water level sensor network and weir outflow measurements (Helbig et al., 2013). The measurements demonstrated that water discharge is significant for the water balance; however, lateral waterborne carbon fluxes are several orders of magnitude smaller than the vertical carbon fluxes due to very low dissolved organic carbon concentrations in the outflow waters (Runkle et al., in prep.). We learned that the concept of fill-and-spill systems is particularly applicable to polygonal tundra catchments due to their pronounced microtopography, abundant depression storages and seasonally changing connectivity due to soil freeze-thaw processes. Colleagues of the MPI-M (CliSAP Research Topic A2) recently incorporated these field-based findings into a stochastic model for the polygonal tundra based on Poisson-Voronoi Diagrams, which represents a significant step forward to statistically relate large-scale properties of the system to the main small-scale hydrological and biogeochemical processes within the single polygons (Cresto Aleina et al., 2013).

In a third arctic study, we used a biogeochemical stoichiometric approach, based on the N:P:K ratios in the different compartments of the soil-vegetation system, to analyse nutrient limitation relations in polygonal tundra (Beermann et al., submitted). We found that despite large amounts of bulk soil nitrogen there is an excess in plant-available phosphorus and potassium in the soils indicating significant limitation of plant-available nitrogen. Climate warming in the Arctic probably will lead to increased nitrogen mineralization. As there is currently an excess in plant-available phosphorus, increased primary production and changes in the plant-species composition might follow. Another interesting finding was that dissolved inorganic nitrogen is about seven times enriched in permanently frozen ground compared to the active layer (Beermann et al., in prep.). Permafrost thawing will likely make this nitrogen available to the plant roots and microbial biomass in the deepened active layer.

Nutrients of different compartments of the trophic web in all studied top soil horizons (Oi, Oe and Oa) in arctic permafrost affected peat soils.

Additionally, in collaboration with CliSAP Research Topic B1 members S. Zubrzycki and E.-M. Pfeiffer, Kutzbach co-authored several articles on the properties and distribution of permafrost-affected soils and their importance within the arctic carbon cycle (Antcibor et al., 2014; Boike et al., 2013; Kutzbach et al., 2014; Zubrzycki et al., 2012a,b, 2013, 2014 in online review).