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

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