This proposal focuses on the highly productive Eastern Boundary Columbia river plume. This plume is sufficiently large to be of regional importance, yet small enough to allow determination of dominant processes affecting river plumes, and to facilitate rate comparisons with regions outside the plume The proposed study will integrate results from the nearby wind-driven CoOP study, as well as with those from nearby GLOBEC and ECOHAB projects to provide definitive new information on alteration of rates of biogeochemical processes by the unique stratification, turbidity, mixing environment and nutrients of a river plume. Moreover, because the Columbia River provides no significant terrigneous nitrate to the plume in the growing season, this study allows plume-endemic processes to be isolated and hence process results can be directly applied to other plumes. Results can also be contrasted with more eutrophic, buoyancy-influenced coastal areas.
The proposed study will address three hypotheses: - During upwelling the growth rate of phytoplankton within the plume exceeds that in nearby areas outside the plume being fueled by the same upwelling macronutrients. - The plume enhances cross-margin transport of plankton and nutrients. - Plume-specific nutrients (Fe and SiO4) alter and enhance productivity on nearby shelves.
The proposed strategy is to compare production rates within the plume and outside the plume, on the more productive shelf to the north of the river mouth (Washington) and the less productive shelf to the south (Oregon). Results from this study address important question as to why a shelf with weaker upwelling winds is more highly productive than a shelf with stronger winds.