Hydrogeochemical fluxes in river waters of microcatchments under different farming systems in the Eastern Amazon
DOI:
https://doi.org/10.6008/CBPC2179-6858.2018.003.0017Keywords:
Hydrogeochemical Fluxes, Stream Water, Agricultural Systems, CatchmentsAbstract
This article presents the influence of agricultural systems on the hydrogeochemical fluxes in stream waters, of eighteen small catchments under different land use in the Eastern Amazon. The Northeast of Pará is one of the oldest areas of agricultural colonization in the Eastern Amazon and its landscape is dominated by the presence of farming systems, especially a family-based subsistence agriculture, large pasture areas and, more recently, a monoculture of palm oil trees. In addition, the landscape is also caractherized by secondary forests in various stages of succession and a few fragments of primary forest, usually located close to streams and rivers. The study was carried out in nine catchments located in the municipalities of Marapanim, Igarapé-açu and São Francisco do Pará, inserted in the Marapanim River Basin and in nine micro-basins located in the municipalities of Mãe do Rio Irituia and Capitão Poço, inserted in the Guamá River Basin. The four catchments in São Francisco and Capitão Poço served as references, in which the forest occupies at least 85% their drainage areas. Field campaigns occurred during one year, from October 2009 to September 2010. Streamwater samples were collected and transported in ice boxes to the laboratory, where later water ionic concentrations were quantified. During the field campaigns, channell bathymetry were done and current speed was measured to calculate the instantaneous discharge. It was confirmed the influence of the agricultural systems which use fire (pastures and crops in the slash-and-burn system) on the fluxes of calcium, magnesium and potassium. We also observed a large influence of pasture on ammonium fluxes, especially in the watersheds where cattle enter into the streams to drink water. In the catchment where there is a more technician agricultures apply irrigation and nitrogen fertilizers, it was observed a higher nitrate flux. It was also possible to observe some influence of the forests in the fluxes of sodium, chloride, sulfate and nitrate. Thus, it was evident that the agricultural activities in the microbasins in the Eastern Amazon alter the natural nutrient cycles, promoting higher fluxes of these nutrients in the streamwater. Statistical analyzes confirmed such influences: it was observed a direct correlation of agricultural activities with streamwater ionic concentrations in the studied catchments.
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