1. To measure the relevant greenhouse gas fluxes above three different surface types in the catchment.
2. To identify the main driving factors for the exchange of greenhouse gases between the land surface and the atmosphere.
Task 1: Eddy flux measurements of greenhouse gases
Sonic anemometers and infrared gas analysers for the detection of H2O and CO2 have been installed permanently at all 3 sites in collaboration with WP2. The meadow site at Skjern Enge has been equipped with an ICOS (integrated-cavity output spectroscopy) laser to detect CH4. At the agricultural site an Off-Axis ICOS LGR laser gas analyser is measuring N2O and CO. The eddy covariance technique is applied to calculate the fluxes of all greenhouse gases. The high-frequency raw data is processed using the Alteddy software (Wageningen University and Research Centre, The Netherlands).
Task 2: Partitioning of the CO2 fluxes
At the forest site the vertical within-canopy CO2 profile is monitored, and 4 soil respiration chambers have been installed for continuous measurements of the CO2 flux between the soil and the canopy air. Leaf level photosynthesis chambers will be applied on occasion at all three sites. Meteorological sensors measuring the microclimate in and above the vegetation accompany the investigations.
Task 3: Feedbacks between carbon and water cycle
The exchange rates of H2O and CO2 between the vegetation and the atmosphere are closely linked through the action of the stomata in the leaves. Therefore the study aims to develop a robust description of the stomatal resistance of the three vegetation types and its response to environmental factors. The water use efficiency, being the ratio between the CO2 uptake and the water loss, is monitored continuously at the canopy scale, and the CH4 fluxes at the meadow site will be compared to the depth of the water table.
Task 4: Upscaling
Based on the knowledge about the distribution of the different land use and soil types in the Skjern Å catchment, the total greenhouse gas balance for the catchment will be calculated in collaboration with the ECOCLIM project. The extensive data set from the three sites provide an excellent tool for estimation of a full GHG budget for the catchment as well as to establish a better understanding of the key factors controlling the exchange on long and short time basis. As such, references to results on the relative importance of GHGs from individual sites and effects of management on CH4 emission can be found under publications.