Loading...
3 results
Search Results
Now showing 1 - 3 of 3
- The yield of microphytobenthic chlorophyll from nutrients: enriched experiments in microcosmsPublication . Brito, Ana; Newton, Alice; Tett, Paul; Icely, John; Fernandes, TeresaThe yield of phytoplankton chlorophyll from nitrogen is a useful parameter in the study of eutrophication of coastal waters, providing the link between chlorophyll formation and nutrient consumption. This parameter has been estimated for microphytobenthos from Ria Formosa lagoon on the south coast of Portugal with a series of three experiments conducted in May and September 2007. Six sediment cores were collected from Ria Formosa in acrylic cylinders and cork stoppers were placed in the bottom. Water samples were collected in large containers and prepared (filtered and enriched) to be pumped to the top of the sediment inside the acrylic cylinders, which are the microcosms of the experiments. Microcosms were isolated to avoid water exchanges and placed in large tanks full of water to maintain temperature stability. Experiments were run for 5 to 9 days in a continuous diluted nutrient enriched system. One of the experiments was carried out with half the microcosms in the dark to evaluate the nutrient fluxes between the sediment and the water column, when no algal growth is expected. Nutrient fluxes of muddy sediments, during the two last days of the experiment in the dark were estimated to be 0.1015 μmol cm−2d−1 for nitrogen, −0.0015 μmol cm−2d−1 for phosphorus, and 0.1395 μmol cm−2d−1 for silicon. The yield of chlorophyll was determined to be between 3.65 and 4.11 μg chl (μmol N)−1 from nitrogen and between 4.03 and 4.77 μg chl (μmol Si)−1 for silicon in muddy sediments. It was not possible to determine the yield from phosphorus. These values are higher than for phytoplankton which may be due to physiological reasons, or due to the presence of a smaller fraction of microheterotrophs, which would divert nutrients. For sand, smaller yields were obtained but it is likely that this was mainly due to the fact that the values of the sediment fluxes used were the ones obtained for mud, which are higher than they should be for sand. This extra input of nutrients is considered to be taken up by algae, thereby decreasing the value of the yield. Therefore, reliable chlorophyll yield estimates for sand could not be obtained.
- Oceanographic applications to eutrophication in tidal, coastal lagoons: the Ria Formosa, PortugalPublication . Newton, Alice; Icely, JohnPhysical and biogeochemical processes control the impact of eutrophication in tidal, coastal lagoons and the ecosystem response to nutrient enrichment. Ascreening model of eutrophication in a tidal, coastal lagoon considers a well-mixed box, exchanging with the ocean at a daily rate determined by physical processes and converting nutrient to phytoplankton chlorophyll at a fixed yield. The model uses nutrient levels to estimate maximum biomass, that may be limited by light-controlled growth in turbid, turbulent, highly-diluted or heavily-grazed system. The components of the box model were tested using field data from the Ria Formosa, a mesotidal coastal lagoon in southern Portugal. Sampling coincided with equinox spring tides, in spring and autumn, as well as solstice neap tides, in summer and winter, to cover the full range of tidal exchange. Discrete sampling coincided with high water, mid-ebb, low water and mid-flood to exemplify the different tidal states. Sampling stations included the ocean boundary (lagoon inlet), and two different landward boundary situations: the shallow westernmost “blind end” of the lagoon, and one near to a major sewage outlets. Results show that nutrient loading in the Ria Formosa is sufficiently diluted and flushed by the tides to limit the effects of eutrophication in the outer lagoon. Flushing, however, is insufficient in the inner lagoon. In conclusion, basin-scale parameters in simple box models can be derived from detailed research models and the results of process studies to provide end-users with simple, transparent, screening models for eutrophication and related aspects of water quality.
- The yield of chlorophyll from nitrogen: a comparison between the shallow Ria Formosa lagoon and the deep oceanic conditions at Sagres along southern coast of PortugalPublication . Edwards, Vivien; Icely, John; Newton, Alice; Webster, RuthThe yield of chlorophyll from dissolved inorganic nitrogen (DIN) has been shown to be a potentially useful parameter for predicting eutrophication, particularly, in the northerly, coastal waters of the North East Atlantic (NEA). This study investigates whether this parameter might also be appropriate for the southerly, coastal waters of the NEA. Nitrogen enrichment experiments were carried out using microcosms to determine the microplanktonic yield of chlorophyll from DIN in waters from the Ria Formosa (April 2002) and from Sagres (September 2002) on the south coast of Portugal. Continuous culture techniques enabled experiments to be run for 7 days after enrichment so that changes in the cumulative yield over time could be calculated. Yields from the Sagres experiment were consistently higher than those from the Ria Formosa experiment, with respective maximum yields of 4.7 and 2.1 mg chl (mmol N) 1, and respective steady-state yields of 3.1 and 0.9 mg chl (mmol N) 1. In addition, regressions carried out on historical data sets from the two study sites showed poor correlation between chlorophyll and nitrate. Other differences between the microcosm experiments at the two sites, included: background concentrations of DIN, silicate and phosphate that were, respectively, 5.6 mM, 8.1 mM, and 0.3 mMhigher in the Ria; chlorophyll concentrations at Sagres that were double those of the Ria; accumulation of particulate nitrogen that was both more rapid and more substantial at Sagres; a different community structure for the diatoms at the two sites; more numerous autotrophic dinoflagellates, flagellates and cyanobacteria, as well as more numerous protozoan grazers, at Sagres. These differences may explain why the yield of chlorophyll from DIN at Sagres is one of the highest reported in the literature. This yield parameter requires further study under a range of seasonal conditions and with a range of microplankton communities before it could be considered useful for predicting eutrophication throughout the coastal waters of the NEA.