A Regional Survey of the Extent and Magnitude of Eutrophication in Mediterranean Estuaries of Southern California, USA

(Abstract) The magnitude and extent of eutrophication was assessed at 27 segments in 23 estuaries in the Southern California Bight (SCB) between October 2008 and 2009. We applied thresholds from the existing assessment frameworks from both the European Union and the U.S. National Eutrophication Assessment to measurements of three indicators [macroalgae biomass and cover, phytoplankton biomass, and dissolved oxygen (DO) concentration] to categorize eutrophic condition in each estuary. Based on these frameworks, a large fraction of segments had moderate or worse eutrophic condition—78 % based on macroalgae, 39 % for phytoplankton, and 63 % for DO. Macroalgal biomass exceeding 70 g dw m−2 and 25 % cover was found at 52 % of sites during any sampling event and in 33 % of segments for 8 weeks or longer, a duration found to negatively impact benthic infauna. Duration of hypoxic events (DO