Energy balance and time-scales of mixing and stratification in the Jaboatão estuary, NE-Brazil

Abstract

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.

Nutrient budgets (C, N and P) and trophic dynamicsof a Brazilian tropical estuary: Barra das Jangadas

“…Both rivers suffer the impact of domestic and agricultural effluents, mainly from the sugarcane agro-industry, under the form of high Biochemical Oxygen Demand (BOD), especially between November and March (dry season). During the rainy season, the higher freshwater discharge is the product of increased precipitation throughout the hydrographic basin (Araujo et al 1999, Noriega et al 2005a) and the controlled outflow from Pirapama Dam (Araujo et al 2008).…”

Circulation and suspended particulate matter transport in a tidally dominated estuary: caravelas estuary, Bahia, Brazil

“…However, its main hydrodynamic and thermohaline characteristics are little known. Taking into account the main forcing of other tropical estuaries located further north in the states of Pernambuco and Rio Grande do Norte, such as the Itamaracá estuary (MEDEIROS; KJERFVE, 1993), the Jaboatão river estuary (ARAÚJO et. al., 1999) and the Curimataú river estuary (MIRANDA et al, 2005(MIRANDA et al, , 2006ANDUTTA, 2006) it is possible to establish the following hypothesis: the Caravelas estuary is mainly forced by tides, fresh water discharge and the wind, which are responsible for the stratification and circulation through the balance of potential and kinetic energy.…”

Mesozooplâncton do sistema estuarino de Barra das Jangadas, Pernambuco, Brasil

“…Os primeiros estudos ambientais na área analisada ocorreram na década de 60, destacando-se: OKUDA & NÓBREGA (1960), , OTTMANN & OTTMANN (1960), CARNEIRO & COELHO (1960), SILVA & COELHO (1960), OKUDA & CAVALCANTI (1961), OTTMANN et al (1965. Porém, por mais de três décadas esse sistema estuarino não foi investigado, e, somente a partir da década de 90, vários estudos voltaram a ser desenvolvidos, dentre eles, os trabalhos de: SANTOS & SOARES (1999), ARAÚJO et al (1999), COELHO-SANTOS & COELHO (1998), BRANCO et al (2002) e NORIEGA et al (2005.…”