Simulation of an Aquatic Ecosystem

Abstract

Kootenay Lake, a large body of water (448 square kilometers) in southeastern British Columbia, has been subject to ever increasing inorganic phosphate pollution from fertilizer plant effluent draining into the Kootenay River. Under a recent treaty between the United States and Canada, Libby Dam is to be constructed in Montana between the pollution source and the lake. In order that the eventual consequences of pollution and damming be better understood and hopefully regulated, information from laboratory and field investigations has been integrated into a model for digital computer simulation. Physical components of the model include seasonal changes in river inflow, phosphate concentration in the river, temperature and phosphate concentration in the lake, and photoperiod. Biological components reference changes in phytoplankton, zooplankton, and landlocked salmon populations relative to changes in physical parameters. The system of differential equations thus formulated has been integrated numerically using constants closely approaching biological reality. Results to date demonstrate that minor changes in a single component do not drastically affect the behavior of the entire complex, and suggest that simulation may prove to be a useful tool in the management of natural ecological systems.