Hindcasts of potential harmful algal bloom transport pathways on the Pacific Northwest coast

TitleHindcasts of potential harmful algal bloom transport pathways on the Pacific Northwest coast
Publication TypeJournal Article
Year of Publication2014
AuthorsGiddings S.N, MacCready P., Hickey B.M, Banas N.S, Davis K.A, Siedlecki S.A, Trainer V.L, Kudela R.M, Pelland N.A, Connolly T.P
JournalJournal of Geophysical Research: Oceans
Date Published2014/04
ISBN Number2169-9291
Keywords4217 Coastal processes; 4273 Physical and biogeochemical interactions; 4534 Hydrodynamic modeling; 4805 Biogeochemical cycles, processes, and modeling; 4855 Phytoplankton; algal bloom; harmful algae; numerical simulations; Pacific Northwest; particle tracking; transport

Harmful algal blooms (HABs) pose a significant threat to human and marine organism health, and negatively impact coastal economies around the world. An improved understanding of HAB formation and transport is required to improve forecasting skill. A realistic numerical simulation of the US Pacific Northwest region is used to investigate transport pathways from known HAB formation hot spots, specifically for Pseudo-nitzschia (Pn), to the coast. We show that transport pathways are seasonal, with transport to the Washington (WA) coast from a northern source (the Juan de Fuca Eddy) during the summer/fall upwelling season and from a southern source (Heceta Bank) during the winter/early spring due to the predominant wind-driven currents. Interannual variability in transport from the northern source is related to the degree of wind intermittency with more transport during years with more frequent relaxation/downwelling events. The Columbia River plume acts to mitigate transport to the coast as the plume front blocks onshore transport. The plume's influence on alongshore transport is variable although critical in aiding transport from the southern source to the WA coast via plume entrainment. Overall transport from our simulations captures most observed Pn HAB beach events from 2004 to 2007 (characterized by Pseudo-nitzschia cell abundance); however, numerous false positives occur. We show that incorporating phytoplankton biomass results from a coupled biogeochemical model reduces the number of false positives significantly and thus improves our Pn HAB predictions.


Current methods for predicting harmful algal blooms of Pseudo-nitzschia (Pn) and its toxic impacts along the Pacific Northwest coast are imprecise, contributing to conservative shutdowns of shellfish and planktivorous fish harvesting and economic losses. By modeling and simulating productivity and transport pathways in the region, this method provides more accurate predictions with fewer false positives, which can likely be further enhanced through additional research into Pn and an ongoing monitoring/modeling approach.

Integrated Research Themes: 
Student Publication: 
Research Topics: