Temporal variability of chlorophyll-a in the São Vicente estuary

• Published in: Brazilian journal of oceanography 2012-12, Vol.60 (4), p.485-499
• Main Authors: Bucci, André Francisco, Ciotti, Áurea Maria, Pollery, Ricardo Cesar Gonçalves, Carvalho, Renan de, Albuquerque, Heitor Cavalcanti de, Simões, Leonardo Tomida Spalletti
• Format: Article
• Language: English
• Subjects: Bacillariophyceae; Biomassa fitoplanctônica; Descarga de água doce; Estuários controlados por maré; Freshwater runoff; MARINE & FRESHWATER BIOLOGY; OCEANOGRAPHY; Padrões temporais; Phytoplankton biomass; Temporal pattern; Tide regulated estuaries
• ISSN: 1679-8759; 1982-436X; 1679-8759; 1982-436X
• DOI: 10.1590/S1679-87592012000400007

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 São 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 são ambientes dinâmicos e susceptíveis a alterações antropogênicas. Nesses ambientes, torna-se imprescindível monitoramento do fitoplâncton na previsão da eutrofização e de seus efeitos para o ecossistema. No estuário de São Vicente (Brasil) a biomassa fitoplanctônica, como clorofila-a, varia sazonalmente em resposta às chuvas e marés. O presente estudo visa apresentar dois programas de monitoramento para detectar florações fitoplanctônicas em relação a turbidez da água guiada pelas marés e chuvas. Métodos. As observações foram semanais na porção rasa (Fevereiro a Setembro de 2008; área 1) e observações em dias alternados no canal (verão 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 florações 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 florações tiveram frequência de aproximadamente 15 dias, no final da qu