Export Of Materials Along A Tidal River Channel That Links A Coastal Lagoon To The Adjacent Sea

Export of materials along a tidal river channel that links a coastal lagoon to the adjacent sea

Javier Aldeco Ramírez1,*, Martha Signoret Poillon2,
María Adela Monreal Gómez3 and David Alberto Salas de León4

1,2Universidad Autónoma Metropolitana Unidad Xochimilco - Departamento El Hombre y su Ambiente
(Calz. del Hueso 1100, col. Villa Quietud, Coyoacán, 04960, México, D.F. México)3,4Universidad Nacional Autónoma de México - Instituto de Ciencias del Mar y Limnología
(Ciudad Universitaria s/n, 04510, México, D.F., México)

*Corresponding author: jaldeco@correo.xoc.uam.mx

A b s t r a c t

Intratidal variability and flux of salt, chlorophyll-a and suspended materials were evaluated in a shallow tropical tidal channel linking a coastal lagoon to the western Gulf of Mexico.Velocity, temperature and conductivity were used to calculate the fluxes. Data were recorded during three tidal velocity cycles (tvc) under extreme river discharge conditions. Chlorophyll-a and suspended materials were determined below the surface. In both seasons (dry and rainy), the flow was ebb-dominated and with longer duration than when in flood. Maximum current velocities were 0.30 m s-1 inMay (dry season) and 0.60 m s-1 in September (rainy season). In the dry season the mean chlorophyll-a export was of 7.56 Kg over tvc while the import was of 3.32 Kg. In the rainy season mean export (47.3 Kg) was 6 times greater than the import (7.93 Kg over tvc). Phytoplankton was dominated by organisms of marine origin. The mean of exported, suspended materials in the rainy season (111.3 Kg) was4.6 times greater (859 Kg) than that in the dry season (184.7 Kg over tvc). Tidal velocity asymmetry is an effective mechanism of exportation, introducing relatively warm and saltier water into the river through the tidal channel.


R E S U M O

A variabilidade intramaré, o fluxo de salinidade, a clorofila-a e material em suspensão foram avaliados em um canal superficial de maré tropical emuma lagoa costeira ao oeste do Golfo do México. Os dados de velocidade, temperatura usados para cálculo dos fluxos durante três ciclos de velocidades das marés (tvc) sob condições extremas de descarga. A Clorofila-a e material em suspensão foram determinados abaixo da superfície. Em ambas as estações (seca e chuvosa), o fluxo dominante foi durante o refluxo e com duração maior durante o fluxo deentrada. A máxima velocidade encontrada foi 0.30 m s-1 em maio (estação seca) e 0.60 m s-1 em setembro (estação chuvosa). Durante a época seca se exportou 7.56 Kg de clorofila-a, enquanto a importação foi de 3.32 Kg. Durante a temporada de chuva, a media exportada (47.3 Kg) foi seis vezes maior que a importada (7.93 Kg). A concentração media de material em suspensão exportado durante a época dechuvas (111.3 Kg) foi 4.6 vezes maior (859 Kg) que durante a época seca (184.7 Kg). A assimetria das marés é um mecanismo efetivo de transporte onde à lagoa exporta águas relativamente quentes e mais salgadas ao rio através do canal de maré.

Descriptors: Tidal channel, Intertidal variability, Salt, Chlorophyll-a, Suspended materials, Gulf of México.
Descriptors: Ambiente intermarés, Sais,Clorofila-a, Material em suspensão, Golfo do México.

Introduction

The structure and function of planktonic communities are governed to a large extent by physical forcing on different temporal and spatial scales (MANN; LAZIER, 2006). On small spatial-temporal scales hydrodynamic processes such as tides in the inlets of coastal lagoons and estuaries play an important role in the distribution andabundance of planktonic organisms (LUCAS et al., 1999, 2006; MONBET, 1992). Tidal currents may be the major source of energy for transporting non-living materials and organisms as they are largely passively driven by these physical forces (LUCAS et al., 1999). Transport depends on differences in current magnitude and duration between ebb and flood tidal currents; such differences, “velocity...