Publication Date

Fall 2023

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


Thomas Connolly; Maxime Grand; Nick Nidzieko


Four years of observational data for Moro Cojo Slough (MCS), a Mediterranean climate estuary in central California, linked anthropogenic nutrient loading and hydrological modifications to a shift in net ecosystem metabolism (NEM) that differs from the characteristic net heterotrophic behavior of most estuarine systems. A lack of precipitation and limited flushing during the dry seasons, as evidenced from hypersaline waters, contribute to high ecosystem respiration rates that drove NEM to nearly balanced or net autotrophic. During the wet seasons, increased runoff and nutrient loading due to precipitation elevated primary production rates within MCS, characterizing the system as net autotrophic. Box models developed for the estuary determined that: 1) salinity was primarily controlled by advection, runoff, and evaporation, 2) high nitrate fluxes were advected into the slough in the wet seasons and out of the slough during the dry seasons, and 3) the processes that dominate DO fluxes were biological processes and gas exchange. Field deployments of DO loggers further reinforced this dependence on daytime primary production and nighttime ecosystem respiration, as observed in the diurnal variabilities in DO. With anthropogenic factors playing a critical role in MCS’s net autotrophic characterization, the results of this study suggest that heavily modified systems may exhibit a shift in metabolic behavior and ultimately act as a net source of carbon.