UC San Diego

Estuarine environments are uniquely diverse coastal subsystems located at the land-river-ocean interface. Across different systems, carbon dioxide (CO2) parameters and anthropogenic inputs can vary greatly given the heterogeneity between individual estuarine systems, which makes it difficult to characterize coastal ocean systems as a whole. The Agua Hedionda Lagoon (AHL) is a tidal estuary located on the southern California coast, which supports a diverse ecosystem while serving numerous recreation activities, a marine fish hatchery, a shellfish hatchery (Carlsbad Aquafarm, CAF), and the largest desalination plant in the western hemisphere. This dissertation contains three main chapters. Chapter 1 provides the information about sampling design and instrumentation used for data collection at the AHL. The detailed steps and procedures required for quality control and processing of the data are also included. In Chapter 2, a one-year time series of carbon dioxide (CO2) data is used to establish baseline and seasonal average inorganic carbon conditions in the AHL. Based on a mass balance model of the lagoon, we propose that the outer lagoon of the AHL is a source of inorganic carbon to the adjacent ocean, through advective export, and a direct source of CO2 to the atmosphere. In Chapter 3, a time series from autonomous sensors deployed in AHL captured the effects of a massive red tide occurring along the Southern & Baja California coast during the spring of 2020. Biogeochemical data (pH and O2) were examined using an open-source model designed to filter out the influence of tides and estimate net ecosystem metabolism (NEM). Contemporaneous pH and O2 observations allowed simultaneous, independent evaluations of production, respiration and NEM.