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Temporal variability of chlorophyll-a in the S o Vicente estuary

Keywords: Padr es temporais , Descarga de água doce , Biomassa fitoplanct nica , Estuários controlados por maré , Temporal pattern , Freshwater runoff , Phytoplankton biomass , Tide regulated estuaries

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Abstract:

Estuaries are extremely dynamic environments that are vulnerable to anthropogenic alterations. Thus, monitoring phytoplankton abundances and composition is an essential tool for the prediction of eutrophication and its effects on coastal ecosystems. Phytoplankton biomass, as chlorophyll-a, in the S o Vicente estuary (Brazil) varies in response to tidal cycles and seasonal rainfall. Objectives. To present two datasets designed to assess the relationship between chlorophyll-a and changes in water turbidity driven by tide and rain. Methods. Weekly observations were made in the shallow embayment (February to September 2008; site 1) and observations recorded on alternate days (summer 2010, site 2). Results. At site 1, turbidity differed between high and low tides, but on most days was over 3000 RU, maintaining moderate chlorophyll-a levels (4 mg.m-3) and only two blooms developed during low turbidity. Site 2 mean turbidity was 1500 RU, nutrient level was higher during neap tides and phytoplankton blooms were mainly observed at the end of neap tides at 15-day intervals, dominated by chain-forming diatoms and occasionally flagellates and pennate diatoms. Conclusions. Taxonomic composition of the blooms was different and their frequency altered by events characterized by intense freshwater discharges from the Henry Borden Hydroelectric Dam (> 9*106.m3), inhibiting phytoplankton accumulation during neap tide periods. Estuários s o ambientes dinamicos e susceptíveis a altera es antropogênicas. Nesses ambientes, torna-se imprescindível monitoramento do fitoplancton na previs o da eutrofiza o e de seus efeitos para o ecossistema. No estuário de S o Vicente (Brasil) a biomassa fitoplanct nica, como clorofila-a, varia sazonalmente em resposta às chuvas e marés. O presente estudo visa apresentar dois programas de monitoramento para detectar flora es fitoplanct nicas em rela o a turbidez da água guiada pelas marés e chuvas. Métodos. As observa es foram semanais na por o rasa (Fevereiro a Setembro de 2008; área 1) e observa es em dias alternados no canal (ver o de 2010; área 2). Os resultados mostram que a área 1, turbidez acima de 3000 RU manteve níveis de clorofila-a médios (4 mg.m-3) e duas flora es ocorreram apenas em baixa turbidez, sendo esta diferente entre marés alta e baixa. Na área 2, a turbidez manteve-se entre 1500 RU, os nutrientes foram maiores durante as marés de quadratura, e as flora es tiveram frequência de aproximadamente 15 dias, no final da quadratura, predominando diatomáceas em cadeia e eventualmente flagelados e diatomáceas penadas. A co

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