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- Microplankton composition, production and upwelling dynamics in Sagres (SW Portugal) during summer 2001Publication . Loureiro, Sofia; Newton, Alice; Icely, JohnMicroplankton community, production, and respiration were studied alongside physical and chemical conditions at Sagres (SW Portugal) during the upwelling season, from May to September 2001. The sampling station was 5 km east of the upwelling center off Cabo S. Vicente, and 2 km of an offshore installation for bivalve aquaculture.
- Enrichment experiments and primary production at Sagres (S.W. Portugal)Publication . Loureiro, Sofia; Icely, John; Newton, AliceWater was collected from the Sagres station (SW Portugal) in September 2002, at a site adjacent to the upwelling centre of Cabo São Vicente, during relaxation of upwelling conditions. Surface and depth samples were enriched with inorganic nutrients in order to evaluate their relative influence on the microalgal assemblage. Small-scale, short-term bioassays involved separate in vitro additions of nitrogen and phosphorus. Enrichments with nitrogen led to a general increase of primary production, suggesting nitrogen as the primary potential nutrient limiting microalgal growth during this period, as well as altering the relative microplanktonic composition in favour of diatoms.
- Effects of nutrients enrichements on primary production in the Ria Formosa Coastal Lagoon (Southern Portugal)Publication . Loureiro, Sofia; Newton, Alice; Icely, JohnSmall-scale, short-term enrichment experiments were conducted in the Ria Formosa coastal lagoon (southern Portugal), to assess the effects of nutrient availability on primary productivity, biomass (as chlorophyll a), and algal composition. Samples were collected from natural communities at three different sites in the western lagoon: Barra, oceanic inlet; Ramalhete, adjacent to a urban waste water treatment plant; and Ponte, an upstream channel used for recreation and bivalve farming. These samples were enriched separately with nitrogen and phosphorous during the extreme neap tides of the summer solstice at both high (HW) and low water (LW). The experiment was repeated during the autumnal equinox to test for seasonality, and during the following summer solstice to test for replication. The addition of nitrogen consistently stimulated the productivity and biomass during summer experiments at the two sites within the lagoon, identifying N as the most likely primary ‘‘potentially limiting nutrient’’ in the western part of the lagoon for this period. No stimulation of biomass and productivity occurred in September at the same two sites indicating the importance of other factors such as light, sedimentation or grazing pressure, as controlling the pelagic community. However, these outcomes were reversed at the oceanic inlet (Barra-HW) where there was no stimulation by nitrogen during the summer months, but there was in September, suggesting that there is a different nutritional requirement for the coastal community in comparison with the lagoon community. In samples where productivity was stimulated, diatoms were the group mostsensitive to enrichment.
- Boundary conditions for the European Water Framework Directive in the Ria Formosa lagoon, Portugal (physico-chemical and phytoplankton quality elements)Publication . Loureiro, Sofia; Newton, Alice; Icely, JohnThe dynamics between nutrients, the microplankton assemblage and physical factors were evaluated in the Ria Formosa (S. Portugal) coastal lagoon. Water samples were collected from Ramalhete and Ponte within the lagoon and compared with the conditions at Barra, an oceanic inlet. The two lagoon stations represent the boundary conditions of two different water bodies that have been registered as intercalibration sites for the European Water Framework Directive. Sampling coincided with high and low water conditions, at the summer and winter solstice, and at the spring and autumn equinox between June 2001 and July 2002. Chlorophyll a values, with a maximum of 5.1 mg l 1 during growing season, were lower than those reported for similar systems. The maximal winter values of 5.99 mM for total inorganic nitrogen, 0.53 mM for phosphate, and 6.34 mM for silicate, were also lower than previously reported for this area. Microplankton peaked during the summer solstices of June 2001 and July 2002, with maximal abundances of 12 105 cells l 1 and 7 105 cells l 1 for total microplankton, respectively: these communities were dominated by diatoms. At the autumn and spring equinox (September 2001 and April 2002), the maximal abundances were 4.9 105 cells l 1 and 2.6 105 cells l 1 total microplankton, respectively: these communities were more evenly distributed between diatoms, dinoflagellates, nanoflagellates and ciliates. At the winter solstice (December 2001), the microplankton were at their lowest with a maximal abundance of 1.0 105 cells l 1: these communities were dominated by small organisms, particularly nanoflagellates. The oceanic microplankton community at the Barra inlet was generally less numerous and differed in composition from the lagoonal communities at Ramalhete and Ponte. Multivariate analysis clustered the microplankton assemblage according to season. Changes in the microplankton community were related mainly to variations in temperature, solar radiation and salinity, and to the availability of the reduced forms of nitrogen. The differences between the parameters observed at the entrance of the lagoon during the summer solstice of 2001 and 2002 may be due, respectively, to the colder upwelled water during 2001 and the much warmer water observed in 2002. Nutrient enrichment was possible both from coastal waters and from internal lagoonal processes. Consequent accumulation of biomass may occur in inner regions where water circulation is restricted, which may lead to episodes of water quality degradation. This study does not alter the boundary conditions for Ramalhete and Ponte registered at the European Commission, respectively, as ‘good/moderate’ and ‘high/good’.