A Nutrient-Phytoplankton-Zooplankton Model for Classifying Estuaries Based on Susceptibility to Nitrogen Loads
A NUTRIENT-PHYTOPLANKTON-ZOOPLANKTON MODEL FOR CLASSIFYING ESTUARIES BASED ON SUSCEPTIBILITY TO NITROGEN LOADS By Yuntao Zhou A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (Natural Resources and Environment) in the University of Michigan April 18, 2006 Thesis Committee: Professor Donald Scavia, Chair Professor J. David Allan Abstract Estuarine responses to nutrient loads can be remarkably different. Many driving variables including light, water residence time, physical stratification, and temperature are responsible for the diversity of the response. To classify estuaries based on their susceptibility to nutrient loads, a nutrient- phytoplankton- zooplankton (NPZ) model was developed and applied to river-dominated, well-mixed estuaries. Estuaries are classified as having low, medium, high and hyper eutrophic conditions by the model. The result of the model suggests that water residence time is an important controlling variable in the process of achieving a steady-state response to nutrient loads. Although phytoplankton responses to residence time vary under different loads, they have the same positive trend. Phytoplankton responses are almost linear with water residence time initially, then decrease, and eventually plateau. i Table of Contents Part1. Introduction……………………………………………………………………1 Light availability………………………………………………………………………………..2 Water residence time……………………………………………………………………………3 Physical Stratification…………………………………………………………………………..3 Temperature…………………………………………………………………………………….4 Part 2. Modeling Approaches…………………………………………………………5 A simple plankton model (Steele and Henderson, 1981)……………………………………...7 Coastal ecosystem sensitivity to light and nutrient enrichment (Cloern 1999)……………..8 A model for partially mixed estuary (Peterson and Festa, 1984)………………………….....9 CSTT (Comprehensive Studies Task Team) model (Tett, 2003)…………………………….10 ASSETS (Assessment of Estuarine Trophic Status) model (Bricker, 2003) ………………..11 Part 3.
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