Articles | Volume 7, issue 12
Research article
08 Dec 2014
Research article |  | 08 Dec 2014

Prerequisites for application of hyperbolic relaxed eddy accumulation on managed grasslands and alternative net ecosystem exchange flux partitioning

M. Riederer, J. Hübner, J. Ruppert, W. A. Brand, and T. Foken

Abstract. Relaxed eddy accumulation is still applied in ecosystem sciences for measuring trace gas fluxes. On managed grasslands, the length of time between management events and the application of relaxed eddy accumulation has an essential influence on the determination of the proportionality factor b and thus on the resulting flux. In this study this effect is discussed for the first time. Also, scalar similarity between proxy scalars and scalars of interest is affected until the ecosystem has completely recovered. Against this background, CO2 fluxes were continuously measured and 13CO2 isofluxes were determined with a high measurement precision on two representative days in summer 2010.

Moreover, a common method for the partitioning of the net ecosystem exchange into assimilation and respiration based on temperature and light response was compared with an isotopic approach directly based on the isotope discrimination of the biosphere. This approach worked well on the grassland site and could enhance flux partitioning results by better reproducing the environmental conditions.

Short summary
The REA technique cannot be applied on grassland shortly after management without the risk of REA-flux errors due to large uncertainties of b-factors and lacking scalar similarity. The NEE flux partitioning model based on REA measurement results is complex but can enhance results of common partitioning by considering ecosystem discrimination of 13C and wind velocity.