Aporte de carbono orgânico sob diferentes condições hidrológicas no rio Tapajós (PA), Amazônia, Brasil

EnglishThe Tapajos River is a clear-water tributary on the right shore of the Amazon River, draining an area of 492.263 km2 from the central region of Brazil to the central portion of the Para state. The objective of this study is to determine the concentrations of organic carbon (POC and DOC) transported by the Tapajos river in near the city of Itaituba/PA, evaluating the influence of the discharge and the seasonal hydrological changes on the transport of these compounds. Monthly samples of surface river water were collected in 2016 and biogeochemical parameters (e.g., pH, electrical conductivity, dissolved oxygen and temperature) were measured in situ. The concentration in sediment were analyzed through statistical tests in relation to the hydrological data (precipitation, quota and flow) provided by INMET and HyBam database. POC has an annual mean of 14±10.0 mg L-1 , with mean of 20.8 mg L-1 for the high discharge and of 7.9 mg L-1 for the low discharge period. The DOC has an annual mean of 3.8±2.2 mg L-1 , with mean value of 5 mg L-1 for the high discharge period and of 2.3 mg L-1 for the low discharge period. The results suggest that, seasonal hydrological changes are the main cause for the variation in the concentration of the sediments transported by the Tapajos river, with possible associations to the mining activities and other anthropogenic actions along its tributaries. portuguesO rio Tapajos e um afluente de aguas claras da margem direita do rio Amazonas, drenando uma area de 492.263 km2 da regiao central do Brasil para a porcao central do estado do Para. O objetivo deste estudo e determinar as concentracoes de carbono orgânico (COP e COD) transportados no rio Tapajos proximo a cidade de Itaituba/PA, avaliando a influencia da vazao e as mudancas hidrologicas sazonais no transporte destes compostos. Amostras mensais de agua da superficie do rio foram coletadas em 2016 e os parâmetros biogeoquimicos (pH, condutividade eletrica, oxigenio dissolvido e temperatura) foram medidos in situ. As concentracoes de sedimento foram analisados atraves de testes estatisticos em relacao aos dados hidrologicos (precipitacao, cota e vazao) fornecidos pelo INMET e banco de dados HyBam. COP teve uma media anual de 14±10,0 mg L-1 , com media de 20,8 mg L-1 na fase de cheia e de 7,9 mg L-1 na fase de seca. O COD teve media anual de 3,8±2,2 mg L-1 , com media de 5,0 mg L-1 na cheia e de 2,3 mg L-1 na seca. Os resultados obtidos sugerem que as mudancas hidrologicas sazonais sao a principal causa das variacoes na concentracao de sedimentos transportados pelo rio Tapajos, com possiveis associacoes as atividades de mineracao e outras acoes antropicas ao longo de seus afluentes.