Date of Award

Fall 2021

Project Type


Program or Major

Earth Sciences

Degree Name

Doctor of Philosophy

First Advisor

Thomas Lippmann

Second Advisor

James Pringle

Third Advisor

Robert Letscher


This thesis examines the role of transport and environmental variables in determining the occurrence or suppression of harmful algal blooms (HABs). In the first part, a simple 2-D diagnostic model is used to hindcast HABs occurring off the coast of Korea using observations of averaged environmental factors including nutrient concentration. Hindcasting results using the model show that physical transport of HABs is of the same order of importance as the environmental conditions in controlling HABs. The model reproduces the interannual variability of the observe HABs off the coast of Korea. The relative importance of the environmental factors based on limiting functional analysis suggest that phosphate, ammonium, and temperature are the most important (in that order), and that nitrate and light limitations have very little influence on the behavior of HABs.In the second part, a modified version of the NPZD ecosystem model is used to examine the effects of species competition and nutrient limitation in the development of HABs. Solutions to the NPZD system of equations show that steady state (equilibrium) conditions cannot occur for two phytoplankton groups (one normal and one HAB) without the presence of zooplankton which effectively acts to replenish the nitrogen pool. When the zooplankton prefer different phytoplankton groups, different equilibrium states are found and depend on a threshold for nitrogen level that depends on functional group parameters (like growth and mortality rates). Solutions explain details of population dynamics underlying HABs and should be useful to find best-fit mode coefficients. In the third part, the NPZD model is modified to include a bottom boundary condition describing sediment nitrification-denitrification process that necessitates both the inclusion of a functional phytoplankton group that fixes nitrogen, and the phosphorus cycle. The model shows why previous models that do not include specified bottom boundary conditions unrealistically predict oligotrophic water in coastal regions, whereas inclusions of denitrification and nitrogen fixing group lead to phytoplankton spatial distributions consistent with observations.