© 1987 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
The dynamics of nutrient regeneration and simulation studies of the nutrient cycle
DAFS Marine Laboratory P.O. Box 101, Victoria Road, Aberdeen AB98DB, Scotland
Attempts to simulate the annual cycle in a mixed water column, 50 m deep, assumed to be independent of adjacent water masses, lead to a number of important conclusions.
A large part of the winter nitrate nitrogen is in the form of dead organic matter during the summer. This is because the decrease in nitrate nitrogen from winter to summer appears to be four or five times greater than the corresponding increase in animals and plants. An understanding of the formation and breakdown of dead organic matter is therefore essential for an understanding of the nutrient cycle.
After the spring bloom there is a period of about 100 days during which the relative magnitudes of the various nitrogen pools do not appear to vary significantly. Average values have been determined for the principal fluxes during this period, and it is deduced that to maintain a balance, the bacterial uptake of inorganic nitrogen, in association with the breakdown of soluble carbon produced by plants, must be larger than the uptake of nitrogen by plants associated with particulate primary production.
The associated microbial loop, from bacteria-to-protozoa-to-zooplankton, could increase zooplankton food intake, but only by less than 7%. Food for zooplankton via this source could be further increased, theoretically, but only by further increasing he rate of soluble carbon production by plants.
Towards the end of the low nutrient summer period, plants may be limited either by nutrients or by grazing. The fact that an autumn bloom only occurs sometimes, can be explained by postulating variation in the balance between these two opposing factors.
The inclusion of refractory material requiring more than a year to be broken down created problems in the model, and these are discussed, as are problems associated with variations in the total nitrogen in the model.