Flux of water vapor and carbon dioxide from a tall tower in a complex landscape

Flux observations from a tall tower in the Southeastern US are analyzed to determine the flux from vegetation types surrounding the tower. Daytime flux averages for one-hour periods, measured at 33, 68 and 329m above a landscape of mixed pine/hardwood, commercial pine forest, residential, pasture, and corn/soybean crops, were analyzed for the months of March, April and July. The flux variation with height, sector and season is discussed qualitatively, related to rainfall and temperature and compared with fluxes above a nearby continuous pine forest. Quantitative analysis of the fluxes is carried out by decomposing each flux into the weighted fluxes from each vegetation type with the aid of a footprint model and a digitized land-use map. The uncertainty in inferred fluxes from each vegetation type is reduced by combining several days of data at a time. It was found that the flux contributions from the various vegetation types were difficult to determine accurately because of the small patch size and the widespread occurrence of mixed pine and hardwood throughout the landscape. Methods to refine the analysis, e.g., by normalizing fluxes, are discussed.