Empirical estimations of CO2flux component over different ecosystems

Vertical CO2fluxes are the result of the net exchange between an ecosystem and the overlying atmosphere. The complex balance among biogenic and anthropogenic components varies from site to site and can be observed by using the micrometeorological Eddy Covariance (EC) technique. Different approaches can be used then to partition the EC flux measurements in order to understand the influence of each contribution to the flux.The general aim of this PhD thesis is to relate carbon balance of different ecosystems to the main controlling factors and to look for general and empirical relations that allow to estimate CO2flux components by using environmental variables and the percentage of vegetation cover.The work is organized into three main parts: the first is about CO2flux partitioning over three Mediterranean sites by using literature-based empirical relations and a new combined approach. The second part is about estimating anthropogenic components of the CO2flux. A review of empirical methods is presented, as well as the recent improvements of the processbased model ACASA and its evaluation over a suburban site. Finally, the third part combines the results of previous chapters to present a new developed empirical simple model, based on land cover fraction and environmental variables. It can simulates the daily mean trend of CO2flux over different ecosystems, and a first validation of the biogenic module, both over a natural and a suburban site, is presented.