Nutrient Limitation in the Sea: Dynamics, Identification, and Significance1

A mathematical model has been constructed to provide a theoretical framework for the investigation and discussion of nutrient limitation in the sea. The euphotic zone is divided into nutrient‐limited and light‐limited regions. For simplicity, the regeneration term is ignored, and a steady state is assumed. The uptake of major nutrients is assumed to follow the Michaelis‐Menton expression, and some data indicate that the assumption is probably correct. Also assuming a dominant phytoplankton population, with characteristic Michaelis‐Menton kinetic parameters, it is demonstrated that the size of the population, fractional growth rate, the rate of production, and the concentration of limiting nutrient are determined by the sum of the fractional loss rates for the phytoplankton. The role of micronutrient components of enzymes is developed theoretically using the effect of molybdenum on a nitrate‐limited system as an example. For the sea, the significance of nutrient limitation theory is primarily in the study of phytoplankton competition and succession. Applications to lakes are discussed, and it appears that the effects of micronutrient deficiencies are more likely to be observed there than in the sea.