Ecological simulation model of Los Angeles Harbor

Abstract

A quasi-steady state numerical ecosystem model was designed to help evaluate the potential impact of various scenarios of effluent treatment and of a landfill on the distribution of phytoplankton and inorganic nutrients in Los Angeles and Long Beach harbors Formulations included (a) tidal circulation, (b) phytoplankton growth and oxygen production as a function of temperature, light, and nutrients, (c) grazing by zooplankton, (d) respiration and nutrient regeneration by the benthos, (e) biochemical oxidation of organics, and (f) nitrification Phytoplankton nitrogen, ammonium, nitrate, and oxygen were the state variables, which were simulated with diel and spatial variability for a range of seasonal conditions. Physical circulation was indicated to be a primary factor governing the distribution of state variables, and the landfill resulted in significant alterations. Simulated phytoplankton stocks approximated the upper range of reported concentrations, indicating a satisfactory prediction of bloom conditions. The model indicated that while light may usually regulate maximum phytoplankton levels, under bloom conditions nutrient limitation may also be important Most of the outer Los Angeles Harbor was affected by the effluent, as shown by comparison to the case with zero input Simulations for secondary versus primary treatment converged a short distance from the outfall in response to high BOD oxidation rates. In general, total phytoplankton crop was not greatly affected by the change from primary to secondary treatment, and predation on phytoplankton was small