Interactions between algal-bacterial populations and trace metals in fjord surface waters during a nutrient-stimulated summer bloom

Francois L. L. Muller, Aud Larsen, Colin Stedmon, Morten Søndergaard

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

We examined how variations in algal-bacterial community structure relate to Cu, Zn, and Mn speciation during a diatom-rich bloom that was induced by daily additions of inorganic macronutrients to fjord waters in August 2002. The experiments were carried out in 11-m(3) floating mesocosm bags deployed in the Rauneljord, near Bergen, Norway, and operated in a chemostat (flow-through) mode. Copper speciation was controlled by the formation of very strong organic complexes (log K-1' = 15.2-15.8; log K-2' = 13.0-13.4) whose likely source was the cyanobacterium Synechococcus sp. Strong ligand concentrations were comparable to dissolved Cu levels. This covariation kept the free Cu2+ concentration within the range of 10(-12.4) to 10(-11.2) mol L-1, i.e., below the toxicity threshold for Synechococcus. Weaker ligands (log K-3' = 8.2-9.4) were released during-and up to 4 d following-the exponential growth of algae. During this period, the weaker Cu-binding ligands appeared to have the same source or production process as the proteinlike fluorophores detected in these coastal waters. Zinc speciation was controlled by complexation with a single class of organic ligands that appeared to be released inadvertently upon the death and/or grazing of phytoplankton. Labile manganese fluctuations were inversely synchronized with the abundance of heterotrophic bacteria until the coastal waters experienced a massive rain event on day 17 of the experiment. The rainfall, which was a source of nitrogen and micronutrients, appeared to stimulate the growth of larger cells (diatoms) but to inhibit that of the smaller cells (heterotrophic bacteria and cyanobacteria).
Original languageEnglish
JournalLimnology and Oceanography
Volume50
Issue number6
Pages (from-to)1855-1871
ISSN0024-3590
Publication statusPublished - 2005
Externally publishedYes

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