The role of estuaries in modulating the export of particle-bound biogenic materials by small mountainous rivers to Cascadia Margin

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When subject to seasonal floods, small mountain river (SRM) systems can be responsible for freshwater discharge volumes comparable to that of large continental rivers and recently have been recognized as an important "line-source" of land-derived material to the ocean. Unfortunately, accurate quantification of their contribution to the marine environment has not been possible because we lack quantitative knowledge of the alterations these materials undergo during estuarine transport. Researchers from Oregon State University propose to determine how the composition, magnitude, and timing of sediment, particulate organic matter, and trace metal fluxes are modified by estuarine processes during flood events in Alsea Bay, a typical SRM. To accomplish their goals, the researchers plan to carry out event-response sampling (variable combinations of freshwater discharge, tides, and winds), geochemical analyses (grain size, mineral surface area, organic carbon and nitrogen content, stable carbon and nitrogen isotopic signatures, terrigenous and marine biomarker compositions, total metal contents, and fraction of reactive Fe), in-situ monitoring (water level, currents, salinity and turbidity at the fluvial/estuary and estuary/ocean interfaces), and physical transport modeling. The sampling scheme and the geochemical data will be used to monitor changes in the concentration and compositions of particle-bound organic matter and trace metals during the periods following different flood events. To calculate the net flux of sediment, organic matter, and metals, as well as determine the modulation by physical forcings such as river discharge, tidal amplitude, coastal setup and local winds, the research will rely on the combined in-situ measurements and the geochemical data. Lastly, a three-dimensional circulation and sediment transport model will be developed for Alsea Bay and adjacent coastal waters to predict estuarine circulation, particle export, and within-estuary trapping. The model will be validated by results obtained in the field and then used to quantify patterns of temporary estuarine storage and export to the coastal ocean under a range of scenarios not covered by their observations. As regards the outreach efforts, the proponents will work with the Centers for Ocean Sciences Education Excellence Pacific Partnership and community colleges in Oregon to carry out instructional workshops and develop curricular materials for their classes, as well as work with the Port of Alsea and the city of Waldport to create materials from the project for their website and visitor's center. Lastly, they plan to continue their collaboration with the Oregon State University Hatfield Center and the Oregon Coast Aquarium in Newport via presentations about the study's outcome. One graduate and one undergraduate student will be supported and trained as part of this project. It is anticipated that the students will be recruited via the Oregon State University Native Americans in Science, Engineering, and Natural Resources program. The proponents also plan to attract out-of-state students to the College of Ocean and Atmospheric Sciences Research Experience for Undergraduates program and have them work on the project in the summer months. In addition to funds allocated in the budget for the undergraduate student and the out-of-state student, the budget includes funds for the Saturday Academy's Apprenticeship in Science and Engineering to fund one high school student for an 8 weeks summer internship to work on geochemical or hydrodynamic data analysis collected as part of the study.