Carbon budgets of a composite ecosystem.

Mediterranean type ecosystems (MTE) are suffering from human disturbance, land use changes and climate change. Given such a scenario, actions to monitor mass and energy fluxes are a priority. The possibility to assess C-fluxes depends on the capacity to scale up observations, made with eddy correlation (EC) ground stations, to the landscape or regional scale. MTEs are mosaics of different land use types and up-scaling can only be obtained by the integration of approaches ranging from ecosystem physiology to remote sensing and modelling. In the last few years new methods have been considered, including boundary layer (CBL) budgeting and the use of instrumented aircraft. More recently the idea developed to use a small island (SI) as a model system. SI provide an analogue for the main land and a unique opportunity to work on systems with little external disturbance and to measure atmospheric profiles easily. EC C-fluxes can be combined with atmospheric budgeting methods and aircraft measurements as, under conditions of relatively constant and unidirectional wind, it is reasonable to expect significant differences in the atmospheric CO2 profiles measured at the upwind and the downwind side of a SI. Perturbation in CO2 concentrations caused by vegetation activity are therefore likely to be observed as CO2 depletion or enrichment of the air that passed over the island. Finally, differences in vertical profiles must reflect the sum of the individual contributions of the different land patches. In the spring of 2002 PianosaLab, a multidisciplinary project, started continuous monitoring of C and water fluxes by means of an eddy covariance (EC) tower placed in the centre of the island. To validate and extend EC data, an atmospheric profiling system was devised, aimed at calculating C budget by applying the mass balance concept - on the basis of wind, CO2 and H2O profiles. The set-up consisted in a 12 m high pneumatic mast - for measurements at 3, 6 and 12 m - and an 8 m3 tethered balloon for heights up to 125 m, which is typically outside the CBL of the island. Preliminary results from CBL budgets are reported and comparisons are made with EC C fluxes during late spring and summer.