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Nitrogen uptake of phytoplankton assemblages under contrasting upwelling and downwelling conditions: The Ría de Vigo, NW Iberia

Nitrogen uptake of phytoplankton assemblages under contrasting upwelling and downwelling conditions: The Ría de Vigo, NW Iberia
Nitrogen uptake of phytoplankton assemblages under contrasting upwelling and downwelling conditions: The Ría de Vigo, NW Iberia
Regenerated production (including organic nitrogen) is shown here to be important in the Ría de Vigo (Galicia, NW Iberia) in supporting both harmful algal bloom communities during the downwelling season, but also (to a lesser extent) diatom communities during stratified periods of weak to moderate upwelling. The Galician Rías, situated in the Iberian upwelling system, are regularly affected by blooms of toxic dinoflagellates, which pose serious threats to the local mussel farming industry. These tend to occur towards the end of summer, during the transition from upwelling to downwelling favourable seasons, when cold bottom shelf waters in the rías are replaced by warm surface shelf waters. Nitrate, ammonium and urea uptake rates were measured in the Ría de Vigo during a downwelling event in September 2006 and during an upwelling event in June 2007. In September the ría was well mixed, with a downwelling front observed towards the middle of the ría and relatively high nutrient concentrations (1.0 - 2.6 μmol L-1 nitrate; 1.0 - 5.6 μmol L-1 ammonium; 0.1 - e0.8 μmol L-1 phosphate; 2.0 - 9.0 μmol L-1 silicic acid) were present throughout the water column. Ammonium represented more than 80% of the nitrogenous nutrients, and the phytoplankton assemblage was dominated by dinoflagellates and small flagellates. In June the water column was stratified, with nutrient-rich, upwelled water below the thermocline and warm, nutrient-depleted water in the surface. At this time, nitrate represented more than 80% of the nitrogenous nutrients, and a mixed diatom assemblage was present. Primary phytoplankton production during both events was mainly sustained by regenerated nitrogen, with ammonium uptake rates of 0.035 - 0.063 μmol N L-1 h-1 in September and 0.078 - 0.188 μmol N L-1 h-1 in June. Although f-ratios were generally low (<0.2) in both June and September, a maximum of 0.61 was reached in June due to higher nitrate uptake (0.225μmol N L-1 h-1). Total nitrogen uptake was also higher during the upwelling event (0.153 - 0.366 in June and 0.053 - 0.096 μmol N L-1 h-1 in September). Nitrogen uptake kinetics demonstrated a strong preference for ammonium and urea over nitrate in June.
harmful algal blooms, new production, phytoplankton ecology, regenerated production Ría de Vigo Spain, upwelling
0272-7714
1-12
Seeyave, Sophie
6a164d70-1fab-4ec0-8dc9-de7d7d56a15b
Probyn, Trevor
d5a69b25-2df2-4928-8413-a469afdb4985
Álvarez-Salgado, Xosé Antón
c1111fff-5252-4e37-a6c4-9921df939260
Figueiras, Francisco G.
71197a0c-9b0c-4a54-a4b5-4ecc785e6846
Purdie, Duncan A.
18820b32-185a-467a-8019-01f245191cd8
Barton, Eric D.
110173cc-5723-467e-bbef-eb797200cc5b
Lucas, Michael
b340b075-ea73-4348-b576-d2a6979ce1e2
Seeyave, Sophie
6a164d70-1fab-4ec0-8dc9-de7d7d56a15b
Probyn, Trevor
d5a69b25-2df2-4928-8413-a469afdb4985
Álvarez-Salgado, Xosé Antón
c1111fff-5252-4e37-a6c4-9921df939260
Figueiras, Francisco G.
71197a0c-9b0c-4a54-a4b5-4ecc785e6846
Purdie, Duncan A.
18820b32-185a-467a-8019-01f245191cd8
Barton, Eric D.
110173cc-5723-467e-bbef-eb797200cc5b
Lucas, Michael
b340b075-ea73-4348-b576-d2a6979ce1e2

Seeyave, Sophie, Probyn, Trevor, Álvarez-Salgado, Xosé Antón, Figueiras, Francisco G., Purdie, Duncan A., Barton, Eric D. and Lucas, Michael (2013) Nitrogen uptake of phytoplankton assemblages under contrasting upwelling and downwelling conditions: The Ría de Vigo, NW Iberia. Estuarine, Coastal and Shelf Science, 124, 1-12. (doi:10.1016/j.ecss.2013.03.004).

Record type: Article

Abstract

Regenerated production (including organic nitrogen) is shown here to be important in the Ría de Vigo (Galicia, NW Iberia) in supporting both harmful algal bloom communities during the downwelling season, but also (to a lesser extent) diatom communities during stratified periods of weak to moderate upwelling. The Galician Rías, situated in the Iberian upwelling system, are regularly affected by blooms of toxic dinoflagellates, which pose serious threats to the local mussel farming industry. These tend to occur towards the end of summer, during the transition from upwelling to downwelling favourable seasons, when cold bottom shelf waters in the rías are replaced by warm surface shelf waters. Nitrate, ammonium and urea uptake rates were measured in the Ría de Vigo during a downwelling event in September 2006 and during an upwelling event in June 2007. In September the ría was well mixed, with a downwelling front observed towards the middle of the ría and relatively high nutrient concentrations (1.0 - 2.6 μmol L-1 nitrate; 1.0 - 5.6 μmol L-1 ammonium; 0.1 - e0.8 μmol L-1 phosphate; 2.0 - 9.0 μmol L-1 silicic acid) were present throughout the water column. Ammonium represented more than 80% of the nitrogenous nutrients, and the phytoplankton assemblage was dominated by dinoflagellates and small flagellates. In June the water column was stratified, with nutrient-rich, upwelled water below the thermocline and warm, nutrient-depleted water in the surface. At this time, nitrate represented more than 80% of the nitrogenous nutrients, and a mixed diatom assemblage was present. Primary phytoplankton production during both events was mainly sustained by regenerated nitrogen, with ammonium uptake rates of 0.035 - 0.063 μmol N L-1 h-1 in September and 0.078 - 0.188 μmol N L-1 h-1 in June. Although f-ratios were generally low (<0.2) in both June and September, a maximum of 0.61 was reached in June due to higher nitrate uptake (0.225μmol N L-1 h-1). Total nitrogen uptake was also higher during the upwelling event (0.153 - 0.366 in June and 0.053 - 0.096 μmol N L-1 h-1 in September). Nitrogen uptake kinetics demonstrated a strong preference for ammonium and urea over nitrate in June.

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More information

Published date: 10 June 2013
Keywords: harmful algal blooms, new production, phytoplankton ecology, regenerated production Ría de Vigo Spain, upwelling
Organisations: Ocean Biochemistry & Ecosystems

Identifiers

Local EPrints ID: 351277
URI: http://eprints.soton.ac.uk/id/eprint/351277
ISSN: 0272-7714
PURE UUID: 986ec15e-4746-4568-a7e9-34090a575d46
ORCID for Duncan A. Purdie: ORCID iD orcid.org/0000-0001-6672-1722

Catalogue record

Date deposited: 01 May 2013 08:46
Last modified: 15 Mar 2024 02:32

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Contributors

Author: Sophie Seeyave
Author: Trevor Probyn
Author: Xosé Antón Álvarez-Salgado
Author: Francisco G. Figueiras
Author: Eric D. Barton
Author: Michael Lucas

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