Eddy-Kovarianz Messungen über einem tropischen Regenwald in komplexem Gelände

Carbon budgets of terrestrial ecosystems are of great importance for understanding the global carbon cycle. The region of Southeast Asia is one of the least investigated areas as atmosphere-vegetation interactions are concerned. The region is characterised, however, by world highest harvesting rates of tropical rainforests and therefore has a significant influence on the global carbon cycle. To estimate the effects of the land-use changes on the regional and global climate investigations at the local scale are needed.Remainders of closed rainforests are only present at higher elevations in Central Sulawesi. Measurements of turbulent CO2 fluxes at the elevated rainforest regions are complicated by a heterogeneous terrain. In complex relief nocturnal stable atmospheric stratification in connection with low wind velocities and katabatic flows may lead to significant contributions of advective CO2 fluxes. Therefore turbulent flux measurements over complex terrain should be interpreted with great care and require additional analysis/corrections. This work presents a method to quantify relief-induced uncertainties of measured CO2 fluxes. It serves for the assessment of advective CO2 fluxes, which are overlooked by means of the eddy covariance method. The method classifies the flow regime into three different atmospheric stratifications. The situations are then examined separately both with a numerical flow model and with experimental methods.The investigations showed that neutral and stable stratifications are especially problematic because of the occurrence of advective fluxes. To overcome the problem parts of time series with low friction velocities were excluded (u* filtering) and subsequent standard gap filling were carried out. The quality tests (Aubinet,2000) have shown that within the well mixed surfacelayer at unstable stratification advection could be neglected. As a result of these investigations the most significant carbon-sink of 993 g (C) m-2 a-1 in the examined Indonesian rainforest that was measured by means of eddy-covariance technique was reduced by at least 152 g (C) m-2 a-1.