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Marine Ecology Progress Series

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MEPS 120:123-133 (1995)  -  doi:10.3354/meps120123

Nitrate and ammonium depletion rates and preferences during a Baltic spring bloom

Tamminen, T.

Nitrate and ammonium depletion potential of the planktonic community was studied during a spring bloom off the SW coast of Finland in the Baltic Sea. Depletion rates were measured after nutrient enrichments with different concentrations and combinations of NO3, NH4 and PO4. Depletion kinetics, N source preferences, mutual inhibition, utilization efficiency and P stimulation of N depletion were estimated. During the bloom peak, the community showed a depletion potential over 24 h equivalent to the total wintertime accumulation of inorganic nitrogen. A clear succession in N source preferences, mutual inhibition and utilization efficiency illustrated the shift from NO3 to NH4 as the basis for nitrogenous nutrition of the community. The succession of these potential qualities was gradual, in sharp contrast to the abrupt depletion of NO3 from the water column and to profound changes in the species composition of the phytoplankton community. This gradual succession allowed the community to effectively utilize both NO3 and NH4 as N sources according to their availability. The relative proportions of new and regenerated production seem therefore to be regulated mainly by relative supply rates of NO3 through physical transport and NH4 through mineralization processes within the community, while inherent preferences of the community play a subordinate role.

Phytoplankton . Nitrogen sources . Depletion rate . Preference . Inhibition . Spring bloom . Baltic Sea

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