Revista de Gestão Costeira Integrada
Volume 15, Número 4, Dezembro 2015, Páginas 523-532

DOI: 10.5894/rgci560
* Submission: 9 OCT 2014; Peer review: 16 NOV 2014; Revised: 31 MAR 2015; Accepted: 12 MAY 2015; Available on-line: 14 MAY 2015

Water mass characteristics in a shallow bank
highly influenced by river discharges: the Sofala Bank in Mozambique *  

Fialho P.J. Nehama^{@, a}; Muhamade Ali Lemos^b;
Hélder Arlindo Machaieie^a

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@ - Corresponding author, to whom correspondence should be addressed: <fialho.nehama@uem.mz>
a - Escola Superior de Ciências Marinhas e Costeiras, Universidade Eduardo Mondlane, C.P. 128, Chuabo-Dembe, Quelimane, Mozambique
b - Instituto Nacional de Investigação Pesqueira, Delegação de Nampula, Mozambique 

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ABSTRACT
Hydrological data collected between 2003 and 2007 were analysed in order to describe the water masses of the Sofala Bank in Mozambique Channel, a region under the influence of outflow from the Zambezi River. The data analysis consisted in the visual inspection of temperature and salinity combined with the analysis of variance for unbalanced data. Four water masses were identified, which differ in their location, temperature, and mainly salinity. These water masses are: (i) LSSW-low salinity shelf water that occurs at the upper 15m and within 40 km from the coastline; (ii) WOSW- warmer oceanic surface waters that occurs throughout the bank at depths not exceeding 70m; (iii) DOW- deep oceanic waters that occur from the sub-surface layer to the seabed; and (iv) HSSW- high salinity shelf water that occurs offshore from 40 km at depths greater than 15m. In general, the water masses are well oxygenated with the lower limit of oxygen being 13, 7 and 5.7 mL/L for the LSSW, WOSW, and the HSSW, respectively. Fluorescence levels are low and almost homogeneous in the LSSW, but it varies with depth in the other oceanic waters. The presence of four different water masses in the Sofala Bank is likely to have ecological and management implications.

Keywords: Water mass, Sofala Bank, Zambezi, Dissolved Oxygen, Fluorescence.

Características das massas de água num banco pouco profundo altamente influenciado por descargas fluviais: o Banco de
Sofala, em Moçambique.

RESUMO
Dados hidrológicos colhidos entre 2003 e 2007 foram analisados com o intuito de descrever as massas de água que ocorrem no Banco de Sofala no Canal de Moçambique, uma região sob influência das descargas do Rio Zambeze. A análise desses dados consistiu na inspecção visual da temperatura e salinidade combinada com a análise de variância para dados de tamanhos diferentes. Foram identificadas quatro massas de água, que se diferenciam pelo local de ocorrência, temperatura, e principalmente salinidade. As massas de água são: (i) LSSW- águas costeiras de baixa salinidade que ocorrem nos primeiros 15m de profundidade e a 40 km da costa; (ii) WOSW- águas superficiais oceânicas de alta temperatura que ocorrem em todo banco a uma profundidade máxima de 70m; (iii) DOW- águas oceânicas profundas de baixa temperatura que ocorrem desde a camada subsuperficial até ao fundo; e (iv) HSSW- águas da plataforma com salinidade elevada que ocorrem a partir dos 40 km da costa a uma profundidade não inferior a 15m. No geral, as massas são bem oxigenadas, sendo o limite inferior de oxigénio de 13, 7 e 5.7 mL/L para a LSSW, WOSW, e a HSSW, respectivamente. Os níveis de fluorescência são baixos e a distribuição é quase homogénea para LSSW, mas variável em profundidade nas águas oceânicas. A presença de quatro massas de água diferentes no Banco de Sofala tem provavelmente implicações ecológicas e de gestão de recursos. 

Palavras-chave: Massas de água, Banco de Sofala, Zambeze, Oxigénio, Fluorescência.

 

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