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Marine Ecology Progress Series

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MEPS 208:51-64 (2000)  -  doi:10.3354/meps208051

Production and its fate in two coastal regions of the Irish Sea: the influence of anthropogenic nutrients

R. J. Gowen1,*, D. K. Mills2 , M. Trimmer3,**, D. B. Nedwell3

1Aquatic Systems Group, Agricultural and Environmental Science Division, Department of Agriculture for Northern Ireland, Newforge Lane, Belfast BT9 5PX, United Kingdom
2Centre for Environment, Fisheries and Aquaculture, Lowestoft Laboratory, Lowestoft, Suffolk NR33 OHT, United Kingdom
3School of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ, United Kingdom
*E-mail: **Present address: Department of Biological Sciences, Queen Mary and Westfield College, University of London, Mile End Road, London E1 4NS, United Kingdom

ABSTRACT: Fluvial and sewage loading of N and P to Liverpool Bay (England) elevated winter concentrations of dissolved inorganic N (29.2 µM) and P (1.7 µM) and molar ratios of N:P (17.0) and N:Si (6.0) compared to Irish coastal waters (9.5 µM N, 0.8 µM P; N:P 12.0 N:Si 1.9). At the enriched site in Liverpool Bay, enhanced spring production (up to 3165.8 mg C m-2 d-1) summer production (471.8 to 971.5 mg C m-2 d-1) and biomass (4.1 to 13.6 mg chorophyll m-3) was dominated by diatoms. Annual production at this site was estimated as 182 g C m-2 compared to 97 g C m-2 at the Irish coastal station. Enrichment and shifts in nutrient ratios did not favour flagellate growth compared to growth of diatoms in Liverpool Bay. Low amounts of sediment phytopigments (9.2 to 26 mg m-2), low concentrations of pore water Si (mean, 9.8 µM), and a negligible summer benthic efflux of Si (1.0 µmol m-2 h-1) suggested little phytodetrital input to sediments in Liverpool Bay and that summer diatom production required an allochthonous supply of Si. At the Irish coastal station, coupling between benthic and water-column processes ensured that benthic efflux of Si was sufficient to support the bulk of summer diatom production. Water-column recycling of N was an order of magnitude greater than sediment recycling of N at both coastal sites.

KEY WORDS: Nutrient enrichment · Primary production · Standing stock · Benthic-pelagic coupling

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