Temporal variability of chlorophyll-a in the São Vicente estuary

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

Disponibilidade e distribuição dos nutrientes e clorofila - A nas águas adjacentes a península antártica

The Antarctic ecosystem has long been characterised as a region with high nutrient concentrations and low Chlorophyll concentration, in what constitutes the antarctic paradox . However, many authors have shown that despite the low concentration of phytoplankton in some regions, this biomass may be high in others, especially if it is associated with lower depth waters causing an water mixture zone or upwelling with no nutrient depletion. To carry out this investigation, water was collected in depths varying from the near surface to 200 metres in the Sea of Weddell, the Sea of Bellinshausen, in the Strait of Gerlache and in the Straight of Bransfield in operations XXI, XX and XXI, Summers of 2000/01, 2001/02 and 2002/03, on the oceanographic vessel Ary Rongel. The nutrient dynamic was quite different in the areas sampled, with Chlorophyll-a values ranging from below detection to high values of 15x10 μg/L, such as in the Straight of Gerlache. Dissolved Inorganic Nitrogen (DIN) and Silicate had similar variations and have high values even when no noticeable consumption of these nutrients by primary production. It was expected that Phosphate would have a similar distribution as that of DIN and Silicate but in some regions, the high Phosphate concentrations coincided with higher values of Chlorophyll-a, and in one specific region of the Sea of Weddell, very low concentrations of Phosphate coincided with very low values of Chlorophyll-a which led us to believe in a certain control of primary productivity by Phosphorus. The different nutrient distribution found in the areas studied show us various subsystems, where conditions vary according to local depth proximity to islands or the continent, wind regime, ice cover, among other physical, chemical and biological variables. The project of this investigation currently is under the Grupo de Oceanografia de Altas Latitudes (GOAL), of Rede 1 (Antártica, Mudanças Globais e Teleconexões com o Continente Sul-americano) of the Brazilian Antarctic Program (PROANTAR). GOAL proposes a systematic sampling and analysis plan of physical, chemical and biological components of the Austral Ocean in order to contribute to relevant processes investigation, to understand the impact of global changes in this ecosystem as well as possible connections with the coastal zone of Brasil.Conselho Nacional de Desenvolvimento Cientifico e TecnológicoO ecossistema Antártico há muito vem sendo caracterizado como uma região de alta concentração de nutrientes e baixas concentrações de clorofila, constituindo o paradoxo antártico . Muitos autores, porém vem mostrando que embora a biomassa fitoplanctônica seja baixa em algumas regiões, em outras esta biomassa pode ser bastante elevada, principalmente se associada a águas pouco profundas, ocasionando uma camada de mistura mais ativa ou ressurgências, sem depleção de nutrientes. Para a realização deste trabalho coletou-se água em profundidades que variaram desde a superfície até 200 metros no mar de Weddell,, no mar de Bellingshausen, no estreito de Gerlache e no estreito de Bransfield nas operações XXI, XX e XXI, verões de 2000/01, 2001/02 e 2002/03 no navio de apoio oceanográfico Ary Rongel. A dinâmica de nutrientes foi bastante diferente nas áreas amostradas, com valores de clorofila-a que não chegaram a serem detectados a valores de bastante elevados de 15x10 μg/L, como no estreito de Gerlache. O nitrogênio inorgânico dissolvido (NID) e o silicato tiveram variações semelhantes e encontram-se com valores elevados, mesmo quando houve consumo acentuados destes nutrientes pela produção primária. Esperava-se que o fosfato tivesse distribuição semelhante ao NID e ao silicato, mas em algumas regiões, as concentrações elevadas de fosfato coincidiam com os valores mais elevados de clorofila-a e em uma única região no mar de Weddell, concentrações muito baixas de fosfato coincidiram com valores muito baixos de clorofila-a, o que nos levou a acreditar num certo controle da produtividade primária pelo fosfato. A diferente distribuição de nutrientes encontradas nas regiões amostradas demonstram existir vários subsistemas, onde as condições variam conforme a profundidade local, proximidade de ilhas ou do continente, regime de ventos, cobertura de gelo, dentre outras variáveis físicas, químicas e biológicas. O projeto deste trabalho atualmente encontra-se inserido no Grupo de Oceanografia de Altas Latitudes (GOAL), pertencente à Rede 1 (Antártica, Mudanças Globais e Teleconexões com o Continente Sul-americano) do Programa Antártico Brasileiro (PROANTAR). O GOAL propõe um plano de coleta e análise sistemática dos componentes físicos, químicos e biológicos do Oceano Austral, no intuito de contribuir na investigação de processos relevantes para a compreensão do impacto das mudanças globais neste ecossistema, além de possíveis conexões com a zona costeira do Brasil

Nutrients and chlorophyll-a distribution over the continental margin between Cabo Frio (RJ) and Ubatuba (SP): winter of 2010

Thirty nine oceanographic stations were conducted off Rio de Janeiro and northern São Paulo, encompassing Cabo Frio, Guanabara Bay, Sepetiba Bay and Ubatuba in the winter of 2010. Dissolved inorganic nutrients (ammonium, nitrite, nitrate, phosphate and silicate) and chlorophyll-a data were used to investigate biogeochemical and physical processes occurring on the continental shelf. Four major sources of nutrients were identified: local estuarine plumes; remote origins coastal waters; intrusion of South Atlantic Central Water over the continental shelf; and bottom sediments ressuspension and remineralization processes

Phytoplankton, dissolved inorganic nutrients and hydrography during the ACEx/SIMTECO campaign in the southern Brazilian shelf in June 2012 (SW Atlantic - Winter 2012)

The response of phytoplankton assemblages to hydrographical forcing across the southern Brazilian shelf was studied based on data collected during wintertime (June/2012), complemented with MODIS-Aqua satellite imagery. The in situ data set was comprised by water column structure properties (derived from CTD casts), dissolved inorganic nutrients (ammonium, nitrite, nitrate, phosphate and silicate) and phytoplankton biomass [chlorophyll a (Chl a) concentration] and composition. Phytoplankton assemblages were assessed by both microscopy and HPLC-CHEMTAX approaches. A canonical correspondence analysis associating physical, chemical and phytoplankton composition data at surface evinced a tight coupling between the phytoplankton community and hydrographic conditions, with remarkable environmental gradients across three different domains: the pelagic, outer shelf Tropical Water (TW); the mid shelf domain under influence of Subtropical Shelf Water (STSW); and the inner shelf domain mainly under influence of riverine outflow of the Plata River Plume Water (PPW). Results showed that intrusion of low salinity and nutrient-rich PPW stimulated the phytoplankton growth and diversity within the inner shelf region, with enhanced Chl a levels (>1.3 mg/m**3) and a great abundance of diatoms, ciliates, dinoflagellates, raphidophyceans and cryptophytes. Conversely, other diatoms (e.g. Rhizosolenia clevei), tiny species of prochlorophytes and cyanobacteria and a noticeable contribution of dinoflagellates and other flagellates associated with lower Chl a levels (<0.93 mg/m**3), characterized the TW domain, where low nutrient concentrations and deep upper mixed layer were found. The transitional mid shelf domain showed intermediate levels of both nutrients and Chl a (ranging 1.06-1.59 mg/m**3), and phytoplankton was mainly composed by dinoflagellates, such as Dinophysis spp., and gymnodinioids. Results have shown considerable phytoplankton diversity in winter at that section of the southwestern Atlantic Ocean