HOLIVAR2006 Abstracts
Responses of wetland vegetation, water chemistry, and carbon dynamics to past climatic changes in northern Fennoscandia. A contribution to the REBECCA Project.
Jan Weckström1, Minna Väliranta1,2, Sari Juutinen3, Heikki Seppä2 and Eeva-Stiina Tuittila3
1Department of Biological and Environmental Sciences, P.O. Box 65, 00014 University of Helsinki, Finland
2Department of Geology, P.O. Box 64, 00014 University of Helsinki, Finland, 3Department of Forest Ecology, P.O. Box 27, 00014 University of Helsinki, Finland
Contact: Jan Weckström (jan.weckstrom@helsinki.fi)
REBECCA (REsponses of Boreal ECosystem CArbon exchange to changing environment in different spatio-temporal scales) is a Helsinki University Environmental Research Centre (HERC) funded project. It focuses on cross-disciplinary aspects of carbon exchange in boreal ecosystems, at a multitude of spatial and temporal scales. At millennial time-scales, lakes and mires are the principal carbon sinks and sources in the boreal biome. These wetlands are dynamic and sensitive ecosystems that change morphologically and functionally as a complex response to both internal processes, such as peat and sediment accumulation, and external factors, such as climate. Long-term climate dynamics, particularly changes in temperature, precipitation and evapotranspiration, may therefore have an important role in lake ontogeny, terrestrialisation, and mire expansion and, in a more general context, on landscape evolution in high latitudes.
Our aim is to test whether wetland vegetation has responded to a climatic transition from predominantly dry climate towards moister conditions during the Mid to Late Holocene in northern Fennoscandia. We hypothesise that (1) changes in moisture balance and temperature have induced changes in vascular and bryophyte vegetation in lakes and associated wetlands, and (2) vegetation is a key component in terrestrialisation, upland paludification, and carbon dynamics between the ecosystem and atmosphere. We test these hypotheses in a high latitude lake and associated mire in Finnish Lapland.
Present vegetation communities will be described along transects from the open lake area through the littoral zone to the adjacent mire. Holocene vegetation history will be studied by analysing macrofossils from three sediment cores of the lake and five peat cores from the mire collected along the transects. Water chemistry parameters (e.g. pH, TOC/DOC) will quantitatively be reconstructed by employing already existing diatom-based inference models in the area. Annual CH4 emissions and net CO2 exchange for the present vegetation communities and open water surfaces will be derived via chamber measurements along the selected transects. The Holocene carbon dynamics of the lake-mire continuum will be assessed on the basis of past wetland vegetation communities and water chemistry using calibration.
The Holocene vegetation, CO2 and CH4 dynamics, and the sediment accumulation rate will be reconstructed by means of generalising the data obtained from macrofossil analysis and reconstructed water chemistry. The relationship between the development of the wetland basin and climate dynamics will be quantified using a dynamic model of peat accumulation and lateral growth of peatland. The model will be used for simulating the landscape development and its carbon dynamics under different future climate scenarios.