Colloquium: Dr. Steven G. Ackleson
ABSTRACT: The San Francisco Estuary (SFE) is the largest wetland habitat on the Pacific Coast of the United States and serves as an ecologically important system that links freshwater and marine environments and provides habitat for key fisheries. The Sacramento river watershed is the primary source of fresh water to the SFE and provides drinking water to over 25 million people and irrigation water to the highly productive California Central Valley. The SFE and Sacramento River are heavily impacted by human activities. Over the past 150 years the estuary and hydrology of the connecting waterways have been substantially exploited and altered for human and agricultural use. Population within the region is increasing at the rate of .7 million per decade, creating greater demand for SFE services, and future climate change is expected to impact the system with drier conditions on average and higher sea level. An ecosystem model, the SFE Model, is under development that will link physical, biological and optical processes in realistic ways with the goal of providing scientists and resource managers more accurate predictive tools. The purpose of this seminar is to describe the overall SFE Model construct and to present details of the optical component of the model, SFE-O, focused on the northern portion of the San Francisco Estuary, including the lower reaches of the Sacramento River and Delta. SFE-O is formulated based on three primary water constituents; phytoplankton, suspended sediments, and colored dissolved organic matter. Field measurements of optical properties (P) and constituent concentration (C), are used to establish P-C relationships using data-directed mass-specific constants (P') and stable spectral functions (F). The optical model, combined with known pure water optical properties, defines the total absorption (a), light scatter (b), and fractional backscatter. Modeled values of a, b, and fractional backscatter are used to simulate the SFE light field and to test SFE-O output against independent observations of water reflectance (Rw) and the depth where light intensity decreases to 1% of surface photosynthetically active radiation. Applications of the SFE Model will be discussed for dynamic ecosystem modeling and remote sensing algorithm development.