Santa Margarita Lagoon Water Quality Monitoring Data

Abstract

Abstract : This report describes water quality monitoring data collected in the Santa Margarita Lagoon in between February 2010 and February 2011 by the Navy's Environmental Sciences Branch of the Space and Naval Warfare Systems Center Pacific. The data collection was requested by watershed stakeholders to fulfill a San Diego Regional Water Quality Control Board Investigative Order related to potential eutrophication impairment. The objectives of the project were to provide a long-term water quality dataset that can be used for calibrating a hydrodynamic and eutrophication numeric model of the lagoon and to gain a more complete understanding of lagoon dynamics and physiochemical processes. The general technical approach followed the work plan developed by Investigative Order. The technical elements included collecting a one-year water quality dataset including depth, temperature, conductivity, pH, and dissolved oxygen using electronic sensors at a fixed location, and collecting discrete nutrient water samples, benthic algae, and performing spatial mapping during two index periods. The data showed a lagoon that was strongly dominated by its connection with tidal flow from the ocean. The lagoon had strong seasonal variations in water quality conditions driven by decreasing freshwater flow, summertime heating, longer aylight hours, and a reduction in tidal flow as a result of natural berm building at the lagoon-ocean boundary. Seasonal changes in nutrient concentrations reflected changes in sources and uptake and transformations by the biota. The observed seasonal changes generally were much greater than the spatial variations observed between the lower and upper lagoon. Based on the Basin Plan limits of N, P, and dissolved oxygen, the lagoon can be classified as intermittently impaired from eutrophication.