Phytoplankton dynamics in a highly eutrophic estuary in tropical Brazil

Abstract

A B S T R A C TThe port of Recife in northeastern Brazil is an important ecological and social area but little is known about its environmental quality. Observations, sampling and measurements of phytoplankton were performed during spring and neap tides in the dry (January-February, 2005) and rainy (June, 2005) seasons to assess the environmental quality of the port of Recife. The area had chlorophyll-a concentrations ranging from 3.30 to 54.40 mg m -3 , the highest values occurring at low tide during the dry season. A total of 129 species were identified: 53 of them in the dry season and 97 in the rainy season. Diatoms were the most diverse group and comprised 75.47% of the phytoplankton collected in the dry season and 60.82% of those collected in the rainy season. The dry season was characterized by Coscinodiscus sp. and Helicotheca tamesis; the rainy season by Oscillatoria sp. and Coscinodiscus centralis. Species diversity indices varied from 1.06 to 3.74 bits cel -1 . Low indices were related to the dominance of Helicotheca tamesis, Coscinodiscus centralis, Coscinodiscus sp. and Aulacoseira granulata. Seasonal forcing, rather than the estuarine flux, determined the phytoplankton community structure. The area is exposed to seasonally varying negative impacts due to metropolitan degradation and the high level of eutrophication. R E S U M OPara avaliar a qualidade ambiental Porto do Recife (Nordeste do Brasil), uma área ecológica e socialmente importante mas pouco investigada, observações, medições e amostragem do fitoplâncton foram realizadas durante as marés de sizígia e quadratura no período de estiagem (janeiro-fevereiro / 2005) e chuvoso (junho/2005). A área apresentou concentração de clorofila a variando de 3,30 a 54,40 mg m -3 , com maiores valores registrados durante a maré baixa no período de estiagem. Um total de 129 espécies foi identificada com 53 espécies durante o período de estiagem e 97 espécies no chuvoso. As diatomáceas formaram o grupo mais diverso, com 75,47% no período de estiagem e 60,82% no chuvoso. Coscinodiscus sp. e Helicotheca tamesis caracterizaram o período de estiagem e Oscillatoria sp. e Coscinodiscus centralis o período chuvoso. A diversidade de espécie variou de 1,06 a 3,74 bits cel -1 . Os baixos índices foram relacionados com a dominância de Helicotheca tamesis, Coscinodiscus centralis, Coscinodiscus sp. e Aulacoseira granulata. A sazonalidade determinou a estrutura da comunidade fitoplanctônica, em vez do fluxo estuarino. A área é exposta sazonalmente a vários impactos negativos, devido à degradação metropolitana e ao elevado nível de eutrofização.

Influence of river discharge on phytoplankton structure and nutrient concentrations in four tropical semiarid estuaries

“…This is in agreement with findings for other tropical estuaries in northeastern Brazil where the phytoplankton composition in the rainy season is strongly influenced by the input of freshwater species (SILVA et al, 2009;SANTIAGO et al, 2010).…”

“…In addition, the decrease in phytoplankton biomass may be associated with a decrease in the inorganic forms of nitrogen and phosphorus. SANTIAGO et al (2010), who studied the phytoplankton dynamics in a highly eutrophic estuary in northeastern Brazil found that phytoplankton biomass and phosphate concentrations were higher in the dry season. In addition to the influence of point sources, which according to SANTIAGO et al (2010) are responsible for an enhanced eutrophication process in the dry season, the nutrients from runoff events in the rainy period may fuel phytoplankton blooms commonly occurring during the next dry season, when the river discharges decrease significantly.…”

“…SANTIAGO et al (2010), who studied the phytoplankton dynamics in a highly eutrophic estuary in northeastern Brazil found that phytoplankton biomass and phosphate concentrations were higher in the dry season. In addition to the influence of point sources, which according to SANTIAGO et al (2010) are responsible for an enhanced eutrophication process in the dry season, the nutrients from runoff events in the rainy period may fuel phytoplankton blooms commonly occurring during the next dry season, when the river discharges decrease significantly. Particularly, in CO and CE, the large difference in nutrient concentrations between the dry and rainy periods suggest that the anthropogenic point source discharges of N and P are considerably higher in the dry season than during increased runoff events in the rainy period.…”

Phytoplankton in a tropical estuary, Northeast Brazil: composition and life forms

“…T. musica and G. balticum are tycoplanktonic estuarine diatoms. Both species are present in other tropical estuaries in Brazil (Fujita and Odebrecht 2007;Leão et al 2008;Santiago et al 2010;Masuda et al 2011), while F. capucina is the only tycoplanktonic freshwater form in the present study, commonly reported in other benthonic substrates (Roberts et al 2004;Antoniades et al 2005). The three diatoms mentioned are in water column due to the high dynamism of the estuarine ecosystem, which induces mixture and resuspension of organisms from the bottom (Fujita and Odebrecht 2007).…”

“…It is explained by the higher levels of silicate in these waters and thus, its benefits the diatom population (Santiago et al 2010;Borges et al 2012). In addition, our results suggest that the greater occurrence of diatoms in estuaries, comparing with other groups, is due to the different life forms that this population can assume (Table 1).…”