Seasonal characterization of the waters of the estuarine system of the Caeté (Bragança-PA) / Caracterização sazonal das águas do sistema estuarino do Caeté (Bragança-PA)

ABSTRACT

The effect of Spring tides on the physical, chemical and biological quality of tidal water channels (called furos) was investigated, taking into account the regional seasonality and the spatial distribution of the Furo do Taici and the Furo da Estiva in the estuary of the Caeté. The abiotic variables were determined in situ during the diurnal cycle of the tide. The nutrients and chlorophyll-a were determined spectrophotometrically. In the Taici, there was a significant increase in salinity (18.57 ± 2.78) and in nitrite (12.93 ± 7,92μM) in the dry season, while in the rainy season, high turbidity (> 900UNT) and chlorophyll-a (12.09 ± 5,72μg L-1) were recorded. In the Estiva, the values of salinity were different in the dry season (36.20 ± 0.90) and in the rainy season (23.23 ± 6.19). When there was flooding, pH (7.72 ± 0.18) and dissolved oxygen (6.62 ± 0.54 mg L-1) were recorded which were higher than those of the ebb tide. The temperature (29.26 ± 1.08°C), phosphate (1.73 ± 1,43μM) and chlorophyll-a (33.6 ± 14,74 μg L-1) had higher values during the ebb tide. Coastal waters had an influence on the Furo da Estiva and the waters of the Furo do Taici were influenced by drainage from the mangrove.

RESUMO

Investigou-se o efeito das marés de sizígia na qualidade física, química e biológica da água de canais-de-maré, considerando a sazonalidade regional e a distribuição espacial do furo do Taici e do furo da Estiva no estuário do Caeté. As variáveis abióticas foram determinadas in situ durante o ciclo diurno da maré. Os nutrientes e a clorofila–a foram determinados por espectrofotometria. Em Taici houve aumento significativo da salinidade (18,57±2,78) e do nitrito (12,93±7,92 µM) no período seco, enquanto que no chuvoso foram registradas elevadas turbidez (>900UNT) e clorofilaa (12,09±5,72 µg L-1). Em Estiva, a salinidade apresentou valores distintos no período seco (36,84±1,37) e no chuvoso (21,56±5,54). Na enchente foram registrados valores de pH (7,72±0,18) e oxigênio dissolvido (6,62±0,54 mg L-1) superiores aos da vazante. Os valores da temperatura (29,26±1,08°C), fosfato (1,73±1,43 µM) e clorofila-a (33,6±14,74 µg L-1) foram mais elevados na vazante. O furo da Estiva sofreu influência de águas costeiras, e o do Taici, influência da drenagem do manguezal.