ABSTRACT. This work analyzes hydrographic properties (temperature and salinity) obtained from three oceanographic cruises performed along the Amazon continental shelf and adjacent oceanic areas of the western equatorial Atlantic. Field data covered three distinct periods and river discharge situation: the maximum river outflow during boreal spring (May 1999); the transition flow period (maximum to minimum discharges) during summer (August 2001), and minimum river flow during autumn

Abstract.-This paper presents a hydrobiological time series at Barra de Jangadas estuary in Northeastern Brazil. Studies were carried out during seven consecutive days from a spring to a neap tide, in one fixed station during the dry (January) and rainy (July) seasons, in 2001. The meteorology (rainfall, evaporation, wind intensity), hydrology (temperature, salinity, pH, dissolved oxygen-DO and relative saturation, BOD 5 , nutrients (NH 3 + NH 4 , NO 2 -, NO 3 -, PO 4 -3 , SiO 2 )), bathymetry, current intensity and, chlorophyll-a, were studied. The principal component analysis (PCA) explained 80% of the total variance showing an inverse relationship between nutrients and DO, salinity and pH. This analysis showed a positive correlation between low tide and nutrients, indicating anthropogenic pollution. The water temperature presented low seasonal variation, similar to chlorophyll-a, which presented values over 20 mg m -3 , characterizing a eutrophic environment. Higher salt concentrations were registered during the dry season with no vertical stratification. DO varied significantly in both seasons. Total dissolved inorganic nitrogen and dissolved inorganic Phosphorus values in July were in general 2 to 5 times higher than values registered in January, respectively. The average N/ P ratio varied from 35:1 in January to 8:1 in July, being both phosphate and nitrogen limiting for phytoplankton growth. Night/day differences showed that in January, ammonia decreased in higher proportion than the other nitrogen compounds indicating assimilation by the autotrophic organisms during the day. , SiO 2 )), batimetría, intensidad de las corrientes y clorofila-a. El análisis de componentes principales (ACP), explicó el 80% de la varianza total, mostrando una relación inversa entre nutrientes y OD, salinidad y pH. Este análisis mostró una correlación positiva entre la bajamar y los nutrientes, indicativo de polución de origen antropogénica. La temperatura del agua varió poco estacionalmente, similar a la clorofila-a que caracterizó un ambiente eutrófico con valores superiores a 20 mg m -3 . Mayores concentraciones de sal ocurrieron en el mes estival y sin mostrar estratificación vertical. El oxígeno disuelto varió significativamente entre ambos períodos. Los valores totales de nitrógeno y fósforo inorgánico disuelto en julio fueron en promedio 2 y 5 veces superiores a los de enero, respectivamente. Las medias de N:P variaron de 35:1 en enero a 8:1 en julio, siendo ambos, el fosfato y el nitrógeno limitantes para el crecimiento del fitoplancton. Diferencias día/noche evidenciaron que, en enero, el amonio decreció en mayor proporción que el resto de los compuestos nitrogenados, indicativo de la asimilación por los organismos autotróficos durante el día.Palabras clave: Nutrientes, oxígeno disuelto, Barra de Jangadas, eutroficación

Estuarine systems undergo different physical processes that simultaneously control their stratification and mixing dynamics. This energy balance determines both, the estuarine hydrodynamics and the dynamics of water. This article presents a quantitative and comparative analyses between the forces maintaining stratification (surface heating; rainfall precipitation; and differential advection of the longitudinal density gradient due to the vertical velocity field) and those responsible for the vertical mixing (mechanical stirring of botiom tidal stress; mechanical stirring ofsurface wind stress; and surface evaporation) in the lower estuary ofthe Jaboatão River (JE), Pernambuco, NE-Brazil. The energy available to mix the water column at thé lower Jaboatão was 2.2 and 2.0-fold greater than that available to promote stratification, during the dry and rainy seasons, respectively. The botiom shear turbulence caused by the tides was the major source of energy for the vertical mixing. A theoretical analyses revealed that the turbulence decay time-scale in both seasons was much greater (~29min; rainy=25 min) than the stratification time-scale (dry=8 min; rainy=7 min) and than the slack water time-scale (15 min). Thus the estuary was vertically well-mixed even during slack water periods during both, dry and rainy seasons. Theoretical results were confirmed by field data and are in agreement with earlier numerical simulations.

The carbon dioxide flux through the air-water interface of coastal freshwater ecosystems must be quantified to understand the regional balances of carbon and its transport through coastal and estuarine regions. The variations in air-sea CO 2 fluxes in nearshore ecosystems can be caused by the variable influence of rivers. In the present study, the amount of carbon emitted from a tropical coastal river was estimated using climatological and biogeochemical measurements (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) obtained from the basin of the Capibaribe River, which is located in the most populous and industrialized area of the northeast region of Brazil. The results showed a mean CO 2 flux of +225 mmol·m, mainly from organic material from the untreated domestic and industrial wastewaters that are released into the river. This organic material increased the dissolved CO 2 concentration in the river waters, leading to a partial pressure of CO 2 in the aquatic environment that reached 31,000 μatm. The months of April, February and December (the dry period) showed the largest monthly means for the variables associated with the carbonate system ( 3 HCO  , DIC, CO 2(aq) , , TA, temperature and pH). This status reflects the state of permanent pollution in the basin of the Capibaribe River, due, in particular, to the discharge of untreated domestic wastewater, which results in the continuous mineralization of organic material. This mineralization significantly increases the dissolved CO 2 content in the estuarine and coastal waters, which is later released to the atmosphere.