Phytoplankton Productivity: Mapping and Modeling Along an Urbanized Floodplain-Estuary Transect
Author: Reed Hoshovsky
Faculty Supervisor: Frances Wilkerson
Department: Biology
A stable isotope of carbon (13C), when incorporated into bicarbonate, can be a powerful analytical tool to trace and quantify the uptake of inorganic carbon by phytoplankton. Fixation of bicarbonate occurs during photosynthesis and can be used as a proxy to determine phytoplankton productivity in aquatic systems. Despite this tool, phytoplankton productivity in the northern San Francisco Estuary (nSFE) is estimated using a linear model calibrated to the system in the 1980s. This model estimates phytoplankton productivity using a composite parameter of chlorophyll biomass and a measure of light availability in the water column. The regression slope of this model is treated as a holistic constant that can be (and has been) broadly applied to a hydrologically variable estuarine system. Recent studies have highlighted complications with doing this and so this study examines assumptions made by the linear model about phytoplankton light utilization. Here we present over 70 fitted light utilization curves along a transect of the Yolo Bypass and nSFE downstream from West Sacramento to Grizzly Bay between March and November of 2023. These curves indicate both the light utilization efficiency and photosynthetic capacity of phytoplankton, and the underlying discrete data can be used to calibrate the linear model.