Summer algal blooms in a coastal ecosystem: the role of atmospheric deposition versus entrainment fluxes

• Published in: Estuarine, coastal and shelf science Vol. 62; no. 4; pp. 595 - 608
• Main Authors: Carstensen, Jacob, Frohn, Lise Marie, Hasager, Charlotte Bay, Gustafsson, Bo G.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.03.2005; Elsevier
• Subjects: advective transport; Animal and plant ecology; Animal, plant and microbial ecology; baltic sea; Biological and medical sciences; Brackish; Brackish water ecosystems; Earth and Related Environmental Sciences; eutrophication; frontal systems; Fundamental and applied biological sciences. Psychology; Geovetenskap och miljövetenskap; inorganic nitrogen; input; kattegat; nitrogen deposition; nitrogen pulses; north-sea; nutrient-limitation; phytoplankton growth; river estuary; Synecology; the Kattegat; upwelling; frontal systems; nitrogen pulses; upwelling; eutrophication; the Kattegat; advective transport; Brackish water environment; Algae; Ecosystem; Bloom; Thallophyta
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1016/j.ecss.2004.09.026

The nitrogen inputs from atmospheric deposition and bottom water entrainment to the surface layer were modelled in the summer period (May–September) over a 11-year period (1989–1999) and compared to investigate the significance of these fluxes for generating blooms in the Kattegat. In the summer periods the average atmospheric deposition was 2.81 mg N m −2 d −1 compared to average entrainment fluxes of 5.42 mg N m −2 d −1, 1.21 mg N m −2 d −1 and 1.15 mg N m −2 d −1 for the northern, central and southern part of the Kattegat, respectively. Atmospheric nitrogen deposition alone could not sustain biomass increases associated with observed blooms and entrainment fluxes dominated the high nitrogen inputs to the surface layer. The potential for a bloom through growth was typically obtained after several days of high nitrogen inputs from entrainment in the frontal area of the northern Kattegat and to some extent from atmospheric deposition. The modelled nitrogen input in this area could account directly for 30% of the observed blooms in the Northern sub-basin, and through advective transport 24% and 19% of the observed blooms in the central and southern Kattegat. The direct nitrogen inputs through atmospheric deposition and entrainment to the central and southern sub-basins were small and could not be linked to any bloom observation.