The Irish Sea: nutrient status and phytoplankton.

Gowen, Richard J and Stewart, B M (2005) The Irish Sea: nutrient status and phytoplankton. Journal of Sea Research, 54 (1). pp. 36-50. ISSN 1385 1101

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    Historical nutrient and phytoplankton data from the Irish Sea are reviewed in the light of recent studies. Mean late winter concentrations of dissolved inorganic nitrogen (DIN as NO3− + NO2−), dissolved inorganic phosphate (DIP as PO43 −) and silica (Si as SiO2) in offshore near-surface waters are 8.3, 0.7 and 6.6 μM, respectively. Concentrations in inshore waters of the eastern Irish Sea can reach 57 μM DIN, 5 μM DIP and 17 μM Si. The northwards residual flow through the Irish Sea (≈ 5 km− 3 d− 1) is estimated to deliver ≈ 82 × 103 t DIN and 12 × 103 t DIP during the winter period. The annual freshwater inputs of DIN (including ammonium) and DIP are 123 and 9 × 103 t, respectively. Offshore waters of the western Irish Sea are enriched with DIN and DIP (≈ 3.0 and 0.4 μM, respectively) relative to Celtic Sea shelf break concentrations but salinity DIN relationships show that measured winter concentrations are lower than predicted. Denitrification is considered a key process limiting nitrogen enrichment of the Irish Sea.

    The onset and duration of the production season is controlled by the sub-surface light climate. Differences in depth and tidal mixing in the Irish Sea give rise to regional variation in the timing and length of the production season. Maximum spring bloom biomass in coastal and offshore waters of the western Irish Sea (23 and 16 mg chlorophyll m− 3, respectively) compares with values of up to 44 mg chlorophyll m− 3 in Liverpool Bay and elevated production and biomass in the latter is attributed to enrichment. There is no evidence that enrichment and changes in nutrient ratios have caused major shifts in phytoplankton composition in Liverpool Bay. Species of Phaeocystis are found throughout the region in most years and together with other microflagellates can dominate the spring bloom. Red tides of dinoflagellates are rare events in the Irish Sea but regular monitoring of phytoplankton in the vicinity of shellfish beds has revealed the presence of toxin-producing dinoflagellates in the Irish Sea.

    Item Type: Article
    Print ISSN: 1385 1101
    Uncontrolled Keywords: Dissolved inorganic nutrients; Enrichment; Eutrophication; Phytoplankton; Irish Sea
    Dewey Decimal Subjects: 500 Science > 550 Earth sciences & geology
    500 Science > 570 Life sciences; biology > 570 Life sciences; biology
    Library of Congress Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
    Q Science > QH Natural history > QH301 Biology
    G Geography. Anthropology. Recreation > GC Oceanography
    Item ID: 1689
    Depositing User: RAE Import
    Date Deposited: 07 Jul 2008 11:19
    Last Modified: 05 Mar 2015 10:35

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