Major Ions Fluxes and DOC in Rainfall and Throughfall at the Tapajos National Forest - Belterra, Para, Brazil

The Tapajós National Forest -(FLONA Tapajós), an area of 600,000 ha of protected forest, is located 50km south Santarem (Pará, Brasil). The FLONA receives approximately 2000 mm.y-1 of rainfall and the forest is evergreen. The tropical forest nutrient cycle depends upon inputs from the atmosphere and from rock weathering. Internally, throughfall and stemflow transfer nutrients from the vegetation to the ground. We collected rainfall and throughfall from [starting date] through [ending date]. Concentrations of the ions Cl-, NO3-, PO4-3, SO4-2, Na+, NH4+, K+, Mg+2 and Ca+2 were analyzed using a Dionex DX-120 ion chromatograph. Total carbon and dissolved organic carbon were analyzed by a Shimadzu TOC V - CSN. Ionic fluxes were calculated from volume-weighted concentrations. The fluxes in precipitation followed the sequence: NH4+ (7.1 kg.ha-1.y-1) > Ca+2 (6.31 kg.ha-1.y-1) > Na+ (6.11 kg.ha-1.y-1) > K+ (4.41 kg.ha-1.y-1) > Cl- (3.61 kg.ha-1.y-1) > SO4-2 (3.11 kg.ha-1.y-1) > NO3- (1.31 kg.ha-1.y-1) > PO4-3 (1.11 kg.ha-1.y-1) > Mg+2 (1.01 kg.ha-1.y-1). In the throughfall, the fluxes were in the sequence: NO3- (31.8 kg.ha-1.y-1) > K+ (27.6 kg.ha-1.y-1) > NH4+ (25.5 kg.ha-1.y-1) > Na+ (17.4 kg.ha-1.y-1) > SO4-2 (15.6 kg.ha-1.y-1) > Cl- (14.5 kg.ha-1.y-1) > Ca+2 (12.7 kg.ha-1.y-1) > Mg+2 (11.1 kg.ha-1.y-1) > PO4-3 (10.8 kg.ha-1.y-1). The seasonality of cation and anion inputs suggests that intensive fertilized grain agricultural activity upwind of the site is contributing a substantial nutrient input to the forest. The fluxes of the total organic carbon for April 2003, May 2003 and February 2004 reached amounts of the 23, 18 and 34 kg.ha-1.y-1, respectively.