An expanded Eulerian model of phytoplankton environmental response

An Eulerian approach to modeling plankton physiological responses to enviro nmental factors is developed wherein the time history of cell exposure to t wo external environmental fields over specified time intervals are utilized as independent variables along with position and time to help characterize the cell population. We seek to find the concentration of cells per unit v olume as a function of depth, time, and the time histories of exposure to P AR (photosynthetically active radiation) as it influences internal cellular carbon through phototsynthesis and to nitrate as it influences internal ce llular nitrogen through nutrient assimilation. The response under considera tion here, vertical swimming, is taken to depend on historical exposure to the external PAR and nitrate fields. The model can be readily extended to o ther external fields and to more than the one historical time scale here as sociated with each external held. This type of model joins Lagrangian model s as most beneficial when phytoplankton physiology responds to environmenta l factors in a nonlinear fashion, i.e. when the mean response does not depe nd on the mean exposure. A simple example is discussed and the impact of wi nd-driven mixing is explored. (C) 1999 Elsevier Science B.V. All rights res erved.