Rainfall chemistry composition in two ecosystems in the northeastern Brazilian Amazon (Amapa State)

The rainfall chemical composition in two Amazonian ecosystems, a "terra firme" forest (dense tropical rain forest) and the "cerrado" (savanna) are presented. Both areas are located in the northeast Brazilian Amazon (Amapa State). This study evaluated the statistical differences in the rainfall chemistry, as well as the deposition through rainfall, for each ecosystem. The chemical species evaluated in the rainwater were Na+, K+, Mg2+, Ca2+, NH4+, Cl-, NO3-, SO42-, Fe3+, Al3+, Zn2+, and Mn2+ for both ecosystems. Factor analysis for the terra fume ecosystem indicated that there is a significant difference between the dry and wet periods in the rainfall chemical composition, indicating a biomass-burning signature (K+ in association with Zn2+. High deposition of solutes, except for Mn2+ and Cl+, was also observed during the dry period. Comparison between the terra fume and cerrado rainfall chemistry showed statistical differences in concentration for the marine species (Nac and CU and for the soil dust species (Al3+, Fe3+, and Mn2+. The sea-salt and biogenic sources of chemical species in terra fume forest rainwater are equally important. The site nearer to the sea (cerrado) has rainfall chemistry dominated by species having marine origins. The terra firme forest also has rainfall chemistry dominated by marine origin species, although the biogenic and soil dust origin species are highly significant at this site. Also in the terra firme a biomass-burning signature was observed. The amount of sea salt deposited was more than 50% larger in the cerrado owing to its proximity to the shore.