O papel ecológico das bactérias planctônicas para a dinâmica da matéria orgânica na zona de confluência dos Rios Negro e Solimões (AM)

Abstract

In order to evaluated the role of bacterial metabolism for the organic matter (OM) dynamics on the confluence zone of Negro and Solimões rivers, it was estimated in spatial scale: bacterial production (BP), bacterial respiration (BR), bacterial carbon demand (BCD), bacterial growth efficiency (BGE), in addition, chemical and physical variables, such as inorganic nutrients, dissolved organic carbon (DOC), stoichiometric ratio of nutrients, conductivity and turbidity. An experiment was conducted to estimate the contribution of bacterial activity and sorption process of OM to the DOC decay on the mixing waters. The metabolic rates showed longitudinal and lateral variability along Negro and Solimões rivers. However, it was observed in the metabolic rates with the increase of mixing waters in situ. The BP ranged between 0,03 and 0,56 μgC L-1 h-1 and the BR between 38,8 and 78,73 μgC L-1 h-1, reflecting in low BGE rates, average 0,236%, which means the heterotrophic bacteria allocated major part of OM available to the cells catabolic process, resulting in a quick remineralization of carbon and nutrients on these systems. In general, the nutrients and the quality and quantity of OM were the factors that most contributed to bacterial metabolism in the studied site. The bacterial metabolism showed as major component to the DOC decay, however, the OM sorption process is very important to the OM processing, mainly on water mixing zone. The results of this study showed that planktonic bacteria significantly contributed to the processing of OM, and high BR rates highlight the important role of planktonic bacteria for the carbon and nutrient remineralization on the confluence zone of the Negro and Solimões rivers.