ABSTRACT
Coastal river plumes represent one of the final stages of material transport across the land-sea interface. Most studies, however have focused on the behavior of medium to large sized river plumes of coastal-shelf waters, whereas small sized river plumes acting within estuaries have been neglected. This study addressed the behavior of suspended particulate matter (SPM), dissolved inorganic nutrients (DIN, DIP and DSi) and Chlorophyll a (Chl. a) of a small sized river plume derived from the closely lain São Francisco and Guandú river channels, set in the Sepetiba Bay estuary, SE-Brazil. Two surface water sampling campaigns were conducted, one in January 2003 (humid summer conditions) and the other in June 2003 (dry winter conditions). On both occasions, the plumes dispersed in a SE direction towards the inner portion of the bay. The "wet" event plume was more turbid, nutrient rich and dispersed beyond nearshore waters, whereas the "dry" event plume proliferated as a narrow, less turbid and more nutrient poor film alongshore. Both exhibited a marked degree of patchiness, induced by the differential input of materials from the river sources and resuspension processes from the shallow nearshore bottom. The São Francisco river channel was the main source of freshwater, SPM and nutrients, except for ammonia (NH4+-N) derived from domestic effluents of the Guandú river. The mesohaline portion of the estuarine mixing zone of the plumes behaved as a slight source for SPM, DSi and DIP, due to bottom resuspension processes. N:P molar ratios ranged between 80:1 and 20:1 along the estuarine gradient, being higher in the summer than in the winter event, indicating that DIP was the potential nutrient limiting primary production. Chl. a concentrations increased at the outer premises of the plume, suggesting that the short residence times and turbidity of the plume waters, hampered primary production nearshore, particularly during the summer occasion...
A extensão, forma e as concentrações da matéria das plumas de pequena escala geradas pelos canais dos rios São Francisco e Guandu, se diferenciaram consideravelmente entre os eventos de alta e baixa descarga. A pluma durante o evento de alta descarga apresentou maior potencial de fertilização da parte central interna da Baía de Sepetiba, enquanto a pluma de baixa descarga fluvial reteve materiais próximo da costa em área rasa. As plumas foram impactadas por múltiplas fontes de materiais, incluindo o aporte lateral fluvial e os sedimentos do fundo. A baixa profundidade da área foi responsável pelo acoplamento nítido da água e do sedimento. O bombeamento da maré com, provavelmente, o atrito no fundo gerado pelo fluxo fluvial, foram responsáveis pela ressuspensão de matéria em suspensão e a liberação de nutrientes dos sedimentos superficiais. As plumas apresentaram um desacoplamento nítido entre as zonas de turbidez e a clorofila, e um acoplamento entre as zonas de turbidez e de mistura estuarina, geralmente não observado em plumas de médio a grande porte que se proliferam na costa e plataforma continental.
ABSTRACT
The mangrove cockle Anadara grandis (Broderip and Sowerby, 1829) is a potential candidate for aquaculture and for bioremediation of aquaculture effluents in the tropical and subtropical coastal areas of the eastern Pacific Ocean. Laboratory-produced spat are available, but there is no information on their responses to the range of environmental conditions to which they might be subject during the growth cycle. The aim of this study was to evaluate the filtration and clearance rates ofA. grandis spat (shell length 9.50+/-0.37 mm) with a food concentration (7.5 mgxl(-1)) at four different temperatures (22, 25, 28 and 31 degrees C, with pH=7.5+/-0.2 and O2 concentration of 6.4+/-0.5 mgxl(-1); experiment one); and with a temperature (25 degrees C) and five concentrations of suspended matter (from 7.5 to 29 mgxl(-1) and pH and O2 values of 7.9+/-0.2 and 6.8+/-0.4 mgxl(-1); experiment two). Filtration and clearance rates were highest at 25 degrees C and significantly different (p<.05) from those obtained at 22, 28 and 31 degrees C; the clearance rates had the same tendency but the differences were not significant (p>.05). In the second experiment filtration increased according to the amount of food available, but there were no significant differences (p>.05) between 7.5 and 11 mgxl(-1) and from 22.4 to 29 mgxl(-1). The trend was similar for clearance, and in this case significant differences were found (p<.05) between 7.5, 22.4 and 29 mgxl(-1). Filtration at 31 degrees C was close to 80% at the optimum temperature of 25 degrees C, which indicates that A. grandis is a good candidate for tropical aquaculture. Clearance increased with high concentrations of suspended solids, but the production of biodeposits could be a source of environmental concern. Therefore, the possibility of using this species for bioremediation of aquaculture effluents should be studied with larger specimens and at higher seston concentrations.
La almeja Anadara grandis (Broderip and Sowerby, 1829) es un candidato potencial para la acuicultura y la biorremediación de efluentes acuícolas en las áreas costeras tropicales y subtropicales del océano Pacífico oriental. Se dispone de semilla producida en laboratorio, sin embargo no hay información sobre sus respuestas a los intervalos de las condiciones ambientales a las cuales puede estar sujeta durante el periodo de crecimiento. El objetivo de este estudio fue evaluar las tasas de filtración y de clarificación de semilla de A. grandis (largo de la concha= 9.50±0.37 mm) con una concentración de alimento (7.5 mg∙l-1) y cuatro diferentes temperaturas (22, 25, 28 y 31 °C con pH= 7.5±0.2, concentración de O2 de 6.4±0.5 mg∙l-1; experimento uno); y con una temperatura (25 °C) y cinco concentraciones de material suspendido (de 7.5 a 29 mg∙l-1 y niveles de pH y O2 de 7.9±0.2 y 6.8±0.4 mg∙l-1, experimento dos). Las tasas de filtración y de clarificación fueron máximas a 25 °C y significativamente diferentes (p<.05) de las obtenidas a 22, 28 y 31 ºC; la tasa de clarificación presentó la misma tendencia, pero las diferencias no fueron significativas (p>.05). En el segundo experimento, se registró un incremento de la filtración, de acuerdo a la concentración de alimento, pero sin diferencias significativas (p>.05) en los intervalos 7.5 a 11 mg·l-1 y 22.4 a 29 mg·l-1. La clarificación mostró la misma tendencia y en este caso se encontraron diferencias significativas (p<.05) entre 7.5, 22.4 y 29 mg·l-1. La cantidad de sólidos ingeridos a 31 °C representó más del 80% de la filtración a 25 °C, que indica que A. grandis es un buen candidato para la acuicultura tropical. Con altas concentraciones de sólidos la clarificación aumentó, pero se notó una producción de pseudoheces que pudieran ser fuente de problemas ambientales, por lo cual se sugiere que la posibilidad de utilizar esta especie para la biorremediación de efluentes debería ser investigada con...