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Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Climate, Snow and Hydrology in Tundra Ecosystems: Patterns, Processes, Feedbacks and Scaling Issues
Bob Baxter1, Brian Huntley2, Richard Harding3, Terry V. Callaghan4
1School of Biological and Biomedical Sciences, University of Durham, Science Laboratories, South Road, Durham, DH1 3LE, UK, Phone +44 191 334 126, Fax +44 191 334 120, Robert.Baxter@durham.ac.uk
2School of Biological and Biomedical Sciences, University of Durham, Science Laboratories, South Road, Durham, DH1 3LE, UK, Phone +44 191 334 412, Fax +44 191 334 120, Brian.Huntley@durham.ac.uk
3Process Hydrology Division, Centre for Ecology and Hydrology, Wallingford, Maclean Building, Crowmarsh Gifford,, Wallingford, Oxford, OX10 8BB, UK, Phone +44 1491692240, Fax +44 1491 692424, rjh@ceh.ac.uk
4Sheffield Centre for Arctic Ecology, University of Sheffield, Tapton Experimental Gardens , 26 Taptonville Road , Sheffield, S10 5BR, UK, Phone +44 114 222 610, Fax +44 114 268 252, T.V.Callaghan@sheffield.ac.uk
Tundra has acted as a long-term carbon sink, sequestering atmospheric carbon in soils that today contain ca. 11 % of total world soil carbon. Few ecosystem-level studies have been conducted in the Arctic and carbon exchange of tundra vegetation types is generally poorly represented in global ecosystem models. The landscape comprises mosaics of vegetation ‘units’ (graminoid, dwarf-shrub or lichen dominated) at scales of tens to hundreds of metres, in relation to topography, soils and hydrology (wet, mesic, dry).
Tundra exhibits hierarchically-scaled spatial heterogeneity, with plant community mosaics at landscape scales and variation in the predominant mosaic elements at regional to Pan-Arctic scales. This heterogeneity reflects hierarchically-scaled spatial and temporal environmental heterogeneity that has not yet been adequately captured by efforts to model the impacts of climate change upon Arctic tundra. This requires spatially- and temporally-explicit process-based modelling at the landscape-scale. Such models must be underpinned by ecosystem studies that will provide the data necessary to achieve adequate representation of landscape processes and of their spatial and temporal variability.
Through a series of measurements at complementary spatial and temporal scales, coupled with suitably robust upscaling and modelling approaches, we will provide an improved spatially and temporally explicit representation of trace-gas and energy flux across the tundra landscape. The project builds upon existing work carried out in programmes in the American Arctic1-5 and the European Arctic 6-11. The scientific advances over previous work are three-fold:
(i) a clarification of spatial scaling issues in trace-gas and energy exchange in tundra ecosystems; (ii) an improved understanding of the seasonal controls over trace gas and energy exchange, particularly the poorly-studied winter and early spring period; (iii) the provision of a northern European perspective on spatial and temporal scaling issues in tundra ecosystems.
MATERIALS AND METHODS
Fieldwork is being carried out on sub-Arctic tundra ca. 7 km from the Swedish Royal Academy of Science Abisko Scientific Research Station (ANS), Sweden (68°21'N, 18°49'E). We are partitioning ‘field-scale’ measurements of net fluxes across the landscape, made by an eddy flux tower, into components relating to the elements of the tundra mosaic by means of series of plot-scale measurements of trace gas fluxes. These measurements sample the fine-scale mosaic across the landscape and through time, in terms of hydrology and soil processes. We are also attempting to predict trace gas fluxes both spatially across the landscape and temporally through the seasons in terms of contributions from identified soil-vegetation-hydrology associations within particular parts of the landscape mosaic.
Plot-scale measurements within specific components of the landscape mosaic, outside the footprint of the eddy flux tower, include a series of manipulations of winter/late spring snow cover. Snow fences are being used to increase snow depth and duration, and early melt of snow to alter growing season length of the tundra vegetation. Impacts of manipulations upon vegetation phenology and physiological development throughout the growing season are being monitored, along with impacts upon C turnover and partitioning (assessed by integrating canopy photosynthesis and ecosystem respiration measurements made using a ‘whole ecosystem’ cuvette). Soil organic matter mineralisation rates and major nutrient (N and P) fluxes are also being assessed, both during the thaw period and throughout the winter season; we regard measurements of winter soil processes, and development of novel techniques in this area, as of particular importance to the project. We are utilising in situ measurements plus controlled laboratory experiments to improve mechanistic understanding of the key processes and the factors affecting rates and fluxes.
Spatial upscaling from the plot-scale to the scale of the eddy correlation tower footprint will be achieved by mapping the plant community mosaic and micro-topography within the footprint. Field-scale fluxes will be modelled as distance- and area-weighted functions of plot-scale fluxes measured for the principal elements of the mosaic. This will provide quantitative estimates of the relative contributions of each element to the overall flux measured at the field scale. In addition, it will enable upscaling of the results of the snow-lie manipulations to provide quantitative estimates of field-scale impacts. The same approach will also be used to upscale from our measurements to estimates of landscape-scale fluxes by mapping the relative extent of each element of the hydro-topographical mosaic. The UK Meterological Office Surface Exchange Scheme (MOSES) is being utilised for surface flux simulations for each landscape element. These will be similarly upscaled to provide landscape- to regional-scale flux estimates, and the importance of explicit partitioning of the fluxes from the landscape elements assessed.
Abstract Categories: Biological Feedbacks
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