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Science Initiative IV: Estuary Turbidity Maxima


The Estuarine Turbidity Maxima (ETM) science initiative aims to advance the understanding of ETM physical and biogeochemical processes in order to refine our theoretical understanding of ETM dynamics and contribution to the function of the estuarine bioreactor.

  • Develop highly skilled modeling capability for the detailed dynamics of estuarine turbidity maxima events in the North Channel, South Channel and Entrance of the estuary.
  • Compare the biogeochemistry and microbiology of the three estuarine turbidity maxima, to enhance understanding and prediction of the role of estuarine turbidity maxima in ecosystem organization and production in the estuarine bioreactor.

Conceptual diagram of an estuarine turbidity maximum  in the estuary.Conceptual diagram of an estuarine turbidity maximum (ETM) in the estuary illustrating the geographic origin of materials and microbes to the ETM, biological and chemical processes affecting those materials and microbes (in blue), and physical features and processes that influence. Not represented is the seasonal variability of the sources of sediments to the ETM. (Enlarge)

Estuarine turbidity maxima

Estuarine turbidity maxima are transient events, whose formation and physical dynamics respond to sediment supply and settling velocity, and to tidal mixing and estuarine stratification. Being central features of virtually all river-dominated estuaries, they represent a hotspot of biological activity in the Columbia River estuary, where microbial metabolic processes consume and alter terrestrial and marine materials. Estuarine turbidity maxima increase the residence time of particles in the estuary, but are particularly important because they also concentrate particles long enough to accelerate metabolic processes and energy transfers. An NSF-LMER interdisciplinary study (CRETM, 1990-2000) identified regular estuarine turbidity maxima events in three general regions of the Columbia River estuary and advanced the understanding on how estuarine turbidity maxima trap particles and promote biogeochemical, microbial and ecological processes that sustain a dominant network in the Columbia River estuary's food web.

CRETM recognized that estuarine turbidity maxima particles are aggregates of material from multiple sources, but concluded from then-available data that the river provides most Estuarine turbidity maxima material. CMOP analysis of estuarine turbidity maxima eukaryotes suggested that sometimes most phytoplankton-derived organic matter in the estuarine turbidity maxima originates from the ocean, not the river. A new conceptual model is developing in which the fuel for estuarine turbidity maxima food webs is supplied by a seasonally shifting combination of materials from river, ocean and lateral bays. CRETM described estuarine turbidity maxima as perpetual hotspots of microbiological activity within the fast-moving estuarine water column. CMOP used advanced molecular techniques to provide a detailed description of the space-time variation of microbial communities and patterns in gene expression in the estuary, revealing that microbial communities remained remarkably similar 10 years after the initial CRETM studies. CMOP also demonstrated remarkable similarity in bacterial gene expression patterns along salinity gradients, despite dramatic shifts in diversity. The transient and dynamic nature of the three CRE estuarine turbidity maximas, and the complexity of the sources and nature of sediments and organisms that are entrained into the estuarine turbidity maxima, demands advanced modeling approaches in order to quantify the role of these hotspots in the ecosystem–and models require the support of long-term, high-resolution observations. CRETM studies were centered on intensive but occasional cruises, and the early-generation circulation models then available were depth-averaged, offering no insight into vertical stratification and trapping mechanisms. This initiative will take Columbia River estuary estuarine turbidity maxima studies to a new level, through multi-platform high-resolution observations of estuarine turbidity maxima dynamics, new biogeochemical and microbial sensors, and advanced interdisciplinary numerical models. Anchoring the new sensing and modeling technologies will be established capabilities (e.g., the SATURN circulation modeling system and interdisciplinary observation network), complemented by intensive field campaigns involving vessels, underwater autonomous vehicles, and/or adaptive sampling from endurance stations.

CMOP scientists will first focus on developing highly skilled numerical models of sediment transport, able to capture detailed estuarine turbidity maxima dynamics (density structure, particle trapping and aggregation, and sediment size classes and supply sources); at the same time, we will develop adaptive microbial sampling and sensing strategies with an Environmental Sampling Processor deployed at select fixed SATURN stations. Then the scientists will concentrate on the biogechemical and microbial characterization of the estuarine turbidity maxima as biological hotspots. The most current metagenomic and metatranscriptomic “next-generation” sequencing techniques will be used to provide a genetic map of the metabolic processes, and to describe the biogeography and gene expression patterns of estuarine turbidity maxima communities. Specific sources of particulate organic matter to estuarine turbidity maximas will be identified through a series of biogeochemical measurements. Integrations of microbial and biogeochemical data will guide model reconstructions of estuarine turbidity maxima metabolic networks.

Science Initiative IV Team

Lead Investigators
Byron Crump (Univ. Maryland) and Tom Sanford (APL-UW)

António Baptista (OHSU),  Craig McNeil (APL-UW),  Holly Simon (OHSU), Yvette Spitz (OSU)

Students, Post-Docs, and Staff
Clara Llebot (OHSU) Jesse Lopez (OHSU) Lindy Fine (Univ. Maryland), Mariya Smith (OHSU)

Winched Profiler and Sigma Profiler Team
Jim Carlson (APL-UW), John Dunlap (APL-UW), Avery Snyder (APL-UW), Keaton Snyder (APL-UW)

Operational Team Support
Astoria Field Team: Michael Wilkin (OHSU), Katie Rathmell (OHSU), Jo Goodman (OHSU)
Cyber Team: Charles Seaton (OHSU), Paul Turner (OHSU)
Clatsop Community College: Faculty and students of the Maritime Science Program and Integrated Technologies Program