MODELLING THE DYNAMICS OF MARINE ECOSYSTEM USING MOMENT CLOSURE METHOD

Abstract

This thesis constitutes a comprehensive exploration into the intricate dynamics governing the distribution of phytoplankton within planktonic ecosystems, marked by their inherent irregularity. Utilizing the closure approach as a mathematical modeling technique, the research aims to shed light on the complex interplay of variables within ecological systems. The closure approach introduces a novel perspective by segregating state variables into mean and fluctuating components, treating the latter as new variables within the system. This innovative methodology provides a nuanced understanding of the ecological intricacies, setting the stage for a multifaceted inquiry. Building upon these insights, the closure approach is extended to a more intricate NPZ model, encompassing nutrient-phytoplankton-zooplankton interactions. To further enrich the study, fluid dynamics of a one-dimensional water column are seamlessly integrated with the nutrient-phytoplankton closure ecosystem model. This integration not only broadens the scope of the research but also intricately weaves together the physical and biological processes, providing a more holistic representation of the coupled dynamics within the ecosystem. The analytical phase of the study then scrutinizes diverse spatio-temporal patterns of mean phytoplankton biomass and growth rate. These patterns, contingent upon the overall variability levels within the ecosystem, are examined with a particular emphasis on the amalgamated impacts of subscale variability and its dynamic interaction with physical transport processes. To ensure the validity of the theoretical findings, the study meticulously compares all results with real-world observations derived from phytoplankton data collected at various ocean depths near Tokyo Bay, Japan. The data, meticulously gathered by the Yamazaki Group within the Division of Ocean Science at Tokyo University of Marine Science and Technology, serves as a robust benchmark for confirming the accuracy and applicability of the developed mathematical models. Transitioning seamlessly, the study broadens its scope to address the intermittency in phytoplankton distribution using the moment closure methodology. Having laid a comprehensive foundation by exploring the complexities of ecological dynamics, the focus then shifts to understanding the treatment strategy for phytoplankton blooms using algaecides.