Nitrogen balance in paired small catchments (forest vs. pasture) in Rondonia state. / Balanço de nitrogênio em microbacias pareadas (floresta vs. pastagem) no estado de Rondônia.

AUTOR(ES)

Adriana Lucia Castellanos Bonilla

DATA DE PUBLICAÇÃO

2005

RESUMO

The nitrogen cycle has been altered by anthropogenic activities, in response to the increment of cultures such, as the leguminous, fossil fuel use, and deforestation for agricultural uses and cattle raising. In temperate regions, there is considerable information about the biogeochemical cycle of nitrogen and the role of anthropogenic alterations on this cycle. However, in tropical regions, where deforestation rates are significant, there is little available information about these processes. The objective of the present work was to provide information on possible alterations in nitrogen forms transported in small catchments (igarapés) of tropical regions, after the conversion of forests into pastures. Two small catchments, one covered by primary forest, and another one covered by pasture, were selected in Rondonia State (Cacaulândia). At both catchments, balances of nitrogen forms and of quantities transported from the rain water to the rivers were calculated, employing a rain event approach. Sampling was done during the wet season, from January 21 to February 27, 2004. We observed: (1) higher discharges at pasture catchment, which resulted in larger nitrogen fluxes; (2) differences in the predominant nitrogen forms at each studied compartment. Dissolved organic nitrogen predominated in the internal precipitation, overland flow, and stream water, while ammonium predominated in the subsurface water and groundwater; (3) differences in the predominat dissolved inorganic nitrogen forms in stream waters of each catchment, nitrate in the forest, and ammonium in the pasture; (4) Dissolved organic nitrogen in the pasture stream comes primarily from overland flow but, for the forest stream, it was not possible to clearly identify the main source of this nitrogen form. This study shows significant changes in nitrogen cycling in small tropical catchments, as a result of deforestation for pasture.

ASSUNTO(S)

microbacia hidrográfica ecologia floresta deforestation pastagem ciclo de nitrogênio pasture ecology small catchment forest nitrogen cycle desmatamento

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