Fluxos hidrogeoquímicos em águas fluviais de microbacias do nordeste paraense e a sua relação com o uso da terra

Abstract

The Northeast of Pará is characterized by the Amazonian old settlements, where the slash and burn small farming and large pastures are predominant. Its landscape is dominated by secondary vegetation at a widely succession stage and very few mature forest remnant, which are generally situated along the rivers and streams. In this context, the present study was conducted in fourteen small catchments under different land use and four other small catchments in forested areas under low anthropic impact, with the objective of evaluating the fluvial hydrogeochemistry to support two mesobasins management in the studied region. It was detected that the chemical composition of the evaluated small stream waters is being affected by the agriculture practices adopted in their drainage areas. Hydrogeochemical changing signals were observed for the small catchments where the predominant land uses are: slash-and-burn small farming; crops with irrigation and agrochemical; and cattle farming. Moreover, we observed the importance of the forested catchments for nitrate, chloride and sodium inputs to the studied stream ecosystems. In addition, it was verified a seasonal fluvial hydrogeochemistry variation and strong effects of agriculture systems, especially cattle farming, to the monitored physic-chemical parameters, as the dissolved oxygen concentration decrease, besides the increasing of temperature, pH and electric conductivity. By the results of the present research we can infer that riparian forest is indispensable to mitigate the impacts of the agriculture systems to the water resources, and should be pointed as an important tool in the watershed management, as well as the substitution of slash-and-burn for more sustainable agriculture practices as chop-and-mulching for instance. Finally, we suggest that some of the analyzed parameters can be recommended, according to the focused land use, as environment sustainable indicators of the agriculture systems along the local watershed management in the region.