Long term observations of land-atmosphere interactions in Amazonia: The role of land use change on the functioning of the Amazonian ecosystem
Abstract:In the wet season, a large portion of the Amazon region constitutes one of the most pristine continental areas. However, land use change modifies the biosphere-atmosphere interactions in such a way that key processes that maintain the functioning of Amazonia are substantially altered. In order to monitor this process, six years of continuous aerosols and trace gases measurements in Central Amazonia were performed at the TT34 site North of Manaus. Additionally, observations were also done at a heavily biomass burning impacted site in southwestern Amazonia (PVH-Porto Velho). Amazonian aerosols were characterized in detail, including aerosol size distributions, aerosol light absorption and scattering, optical depth and aerosol inorganic and organic composition, among others properties. Trace gases measurements include CO, CO2, O3, VOCs and others.
The central Amazonia site (TT34) showed very low aerosol concentrations (PM2.5 of 1.3 µg m-3 and 3.4 µg m-3 in the wet and dry seasons, respectively. At the impacted site (PVH), aerosol loadings were one order of magnitude higher (PM2.5 of 10.2 µg m-3 and 33.0 µg m-3 in the wet and dry seasons, respectively). The aerosol number concentration at the impacted site ranged from 680 cm-3 in the wet season up to 20,000 cm‑3 in the dry season. Organic aerosol dominates the composition with 81% to the PM1 aerosol loading at TT34, while biomass-burning aerosols at PVH shows a 93% organic particles content. Aerosol optical properties changed dramatically due to land use change.
Long term remote sensing observations from several AERONET sites and from MODIS since 1999, provides a regional and temporal overview of atmospheric aerosol loading. These changes in aerosol loading and in the radiation balance caused a significant increase of Net Ecosystem Exchange (NEE) of 18-29%. There clear observations that the hydrological cycle is being enhanced, while the extent of the dry season is increasing. From this analysis, it is clear that land use change in Amazonia shows alterations of many atmospheric properties, and these changes are affecting the functioning of the Amazonian ecosystem in significant ways. Climate change may also play a role and is important to monitor these changes in a critically important tropical region.