The dynamics of nutrient regeneration and simulation studies of the nutrient cycle

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. 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. 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. (DBO)