Temporal variability of chlorophyll-a in the São Vicente estuary

Abstract

A B S T R A C TEstuaries 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.m 3 ), inhibiting phytoplankton accumulation during neap tide periods. R E S U M OEstuários 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 quadratura, predominando diatomáceas em cadeia e eventualmente flagelados e diatomáceas penadas. A composição taxonômica variou entre florações e o padrão quinzenal foi significativamente alterado durante eventos com alta descarga de água doce oriundos da usina hidroelétrica Henry Borden (> 9*106.m 3 ) o que impediu o acúmulo de fitoplâncton no período das quadraturas.

Variability in the light absorption coefficients of phytoplankton, non-algal particles, and colored dissolved organic matter in a subtropical bay (Brazil)

“…This lack of correlation was also verified in the São Vicente Estuarine Channel, which is connected to Santos Bay as well (Bucci et al, 2012).…”

Bio-Optical Properties of the Inner Continental Shelf off Santos Estuarine System, Southeastern Brazil, and their Implications for Ocean Color Algorithm Performance

“…Thus it is to be expected that their relative contributions be reflected in the optical properties of the estuarine plume formed within Santos Bay, which can be identified as distinct types and monitored by remote sensing spectral reflectances. Some studies on the optical properties of the Santos estuary and Santos Bay have discussed the role of spring tides in the resuspension of inorganic sediments and the estuarine input of organic particles and CDOM during neap tides, whereas CDOM optical properties are not good predictors of surface salinity (BUCCI et al, 2012). Other surveys have shown that summer phytoplankton blooms inside the Santos estuarine complex may produce optical dominance of phytoplankton and are modulated by tides (MOSER et al, 2005;BUCCI et al, 2012), wind patterns (MOSER et al, 2012) and fresh water discharges.…”

The use of CBERS (China-Brazil Earth Resources Satellite) to trace the dynamics of total suspended matter at an urbanized coastal area

“…On the other hand, the true-color composite (Figure 8a) suggests that the water with low TSM indexes found in the center of the bay were associated with a brownish water color forming a plume from the main estuarine channel towards the bay. This is probably a result of a very high contribution of Colored Dissolved Organic Matter (CDOM), which has been previously reported in this region (BUCCI et al, 2012;FERRARI et al, 2014), and could trace the estuarine discharge. In estuarine plumes, the decrease in TSM, or CDOM, towards offshore is not a simple process of dilution (OUBELKHEIR et al, 2006), particles size and their chemical composition will also change, leading to biogeochemical and optical changes (BUKATA, 2005;BURD;JACKSON, 2009;CHEN et al, 2005;FETTWEIS et al, 2006).…”

“…Since a high precipitation event was registered in the city of São Paulo two days before the neap tide sampling (CPTEC/INPE 2007), outflows from the power plant to the estuary could explain the anomalous data. Unfortunately, no official discharge data from Henry Borden were available for this period; however, the importance of the Henry Border plant in the study area is discussed in BUCCI et al (2012). Regardless the source of freshwater, our results showed a significant estuarine contribution in both September 2007 campaigns.…”

“…Because of that, Santos Bay receives organic and inorganic materials from several sources, which include estuarine outflows, sewage runoff (e.g. BUCCI et al, 2012) and a submarine sewage outflow (ABESSA et al, 2005), as well as adjacent coastal and continental shelf waters.…”