The Tapajós National Forest, FLONA Tapajós, with 600.000 ha of protected forest is located at the km 50 south of Santarém, Pará, Brazil. Soils are highly weathered and deep, well drained, kaolinitc, classified as Yellow Latosol and according to north American classification as Oxisol (Haplustox), with a acidic pH (4.5) and free of duripans and lateritic concretions. In a ecosystem like a humid tropical forest, nutrients are being cycled. This cycling involves inputs from atmosphere and from the weathering of rocks and minerais present in the soil, with output through drainage water and internai circulation of the system. This circulation involves the transfer of nutrients from vegetation to the soil through the washing (throughfall and runoff on the bole), where there is no intervention by decomposers. Concentrations of ions Cl-, NO3-, PO4-3, SO4-2, Na+, NH4+, K+, Mg+2 and Ca+2 were analyzed by liquid chromatography using a Dionex DX - 120. For gas sampling, stainless steel tubings were installed on the lateral walls of three profiles dig on the ground at the following depths of 5, 15, 30, 50, 100 and 200 centimeters. The concentrations of N20 and CO2 were analyzed by gas chromatography using electron capture detector (ECD), whereas CH4 concentrations were measured using a flame ionization detector (FID). The chromatographs were calibrated using 3 different leveis of synthetic air standards. As results, we observed: The station has strong influence on the basic cation concentration; throughfall is one of the most important ways for nutrient inputs pt the FLONA Tapajós; there is a significant arrival of macronutrients together with Chlorine and sodium coming from the intensive grain agriculture. We observed the greatest volume of precipitation over the last 20 years. Dry deposition is the most important process of water enrichment that reaches the forest soil. The duration of the previous dry period is predominant to determine the input of nutrients into the Tapajós National forest. Within the dry period occur the greatest variations among the ions analyzed. Convection processes that accumulate the nutrients over the FLONA area, due to the breeze of the Tapajós river, favor the increase in the amount of the studied elements; the analyzes of the main components facilitate the interpretation of water characterization from precipitation, showing in this study, the influence of anthropogenic sources (agriculture, biomass burning) and dust; The process of nitrification plays a major role on chemistry,of water from precipitation and should be more studied. About the studied gases, we verified fluxes at a 15 cm depth during the dry period lower than the fluxes observed during the wet period at the same depth. For the other depths, the fluxes during the dry period are always greater than the fluxes during wet period, showing that moisture at depths deeper than 15 cm is enough to promote'the prodúction and emissjon of those gases, not constraining the soil diffusion. We observed sensible seasonal variation among the fluxes of N2O and CO2, with the lowest rates taking place during the dry period. The fluxes, in kg ha-1 year-1, showed 182.1, 22. 97 and 14.08 for CO2, N2O, and CH4, respectively. Strong seasonal variation was observed for soil water content between dry and wet seasons. The soil shows a deficit for available water during dry period when we consider the depth down to 100 cm. At the 100 cm layer down to 200 cm, there was observed no deficit. There was significant correlation between soil water content and N2O flux. No evident variation in soil temperature along the various depths studied. There was no olear seasonal variation in soil temperature between dry and wet periods. Degradable organic material and nitrogen are, together with moisture and soil temperature major factors determining the production and emission of N2O and CO2.
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