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

当遭受季节性洪水时，小山河系统的淡水排放量可与大型大陆河流相当，最近已被认为是陆地物质流入海洋的重要“线源”。不幸的是，由于我们缺乏对这些物质在河口运输过程中所经历的变化的定量知识，因此无法准确量化它们对海洋环境的贡献。俄勒冈州立大学（Oregon State University）的研究人员提议，确定阿尔西湾（Alsea Bay）洪水事件期间河口过程如何改变沉积物、颗粒有机物和微量金属通量的组成、大小和时间。为了实现他们的目标，研究人员计划进行事件响应采样（淡水流量、潮汐和风的可变组合）、地球化学分析（粒度、矿物表面积、有机碳和氮含量、稳定碳和氮同位素特征、陆源和海洋生物标志物组成、总金属含量和活性铁的比例）、现场监测(水位、洋流、河流/河口和河口/海洋界面的盐度和浊度)，以及物理输运模型。采样方案和地球化学数据将用于监测在不同洪水事件之后的时期内颗粒结合的有机物质和微量金属的浓度和组成的变化。为了计算沉积物、有机物和金属的净通量，以及确定河流流量、潮汐振幅、海岸设置和局地风等物理强迫的调制作用，研究将依赖于现场测量和地球化学数据的结合。最后，建立了Alsea Bay及邻近海域的三维环流输沙模型，用于预测河口环流、颗粒输出和河口内捕获。该模型将由实地获得的结果加以验证，然后用于在他们的观测未涵盖的一系列情景下量化临时河口储存和向沿海海洋出口的模式。至于外联工作，支持者将与海洋科学教育卓越太平洋伙伴关系中心和俄勒冈州的社区学院合作，开展教学研讨会，为他们的班级开发课程材料，并与阿尔西港和沃尔波特市合作，为他们的网站和游客中心制作项目材料。最后，他们计划通过介绍研究结果，继续与俄勒冈州立大学哈特菲尔德中心和位于纽波特的俄勒冈海岸水族馆合作。作为该项目的一部分，将支持和培训一名研究生和一名本科生。预计这些学生将通过俄勒冈州立大学印第安人科学、工程和自然资源项目招收。支持者还计划吸引州外学生参加海洋与大气科学学院本科生研究经验项目，并让他们在夏季的几个月里参与这个项目。除了预算中分配给本科生和州外学生的资金外，预算还包括周六学院科学与工程学徒计划的资金，用于资助一名高中生进行为期8周的暑期实习，从事作为研究一部分收集的地球化学或流体动力学数据分析。

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.