RAPID: Collaborative Research: Tracking the Flood Pulse of a Record Discharge of the Brazos River in the Gulf of Mexico

河流携带沉积物到沿海海洋的运输和命运具有重要的生态和社会意义。河流输入是海洋环境陆源沉积物的主要来源。这些颗粒对沿海生态系统的健康以及沿海海洋和航道的地质和水深测量有重大影响。它们直接或间接地影响渔业和航运。这项研究的重点是在飓风哈维期间发生的前所未有的降雨和洪水事件中，通过布拉索斯河进入墨西哥湾的沉积物的运动。布拉索斯河是墨西哥湾的第二大营养物和有机物来源，仅次于密西西比河。然而，与密西西比河不同的是，从布拉索斯河输送到墨西哥湾的大部分沉积物是在洪水事件期间携带的，比如伴随哈维飓风的洪水。人们对这些沉积物的命运知之甚少。目前尚不清楚它是否被保留在海岸带，其携带的营养物质和化学物质会影响海岸带环境，还是被带到近海并沉积在墨西哥湾的深水中。通过对布拉索斯河入海口附近的沉积物进行密集采样，并进一步对墨西哥湾的德克萨斯州泥毯进行采样，该项目将确定德克萨斯州一条主要河流向墨西哥湾西部输送沉积物的主要储存库。本研究的总体目标是调查一种假设，即来自布拉索斯河的洪水沉积物最初沉积在海岸带，随后被动员并携带到近海，其中很大一部分沉积在德克萨斯泥毯中。这项工作建立在对2017年哈维飓风引发的洪水期间收集的海底沉积物样本的分析基础上。这个新项目将包括两次抽样巡航，以增强已经收集到的数据。第一次巡航将需要获得约25个岩心，这些岩心将表明布拉索斯河口附近近岸地区的沉积物沉积和运输。初步工作表明，布拉索斯河沉积物的大部分初始沉积发生在原始采样区域的东部。第二次巡航将收集更多的Brazos地区岩心，并将采样范围扩大到德克萨斯州泥毯，目的是记录飓风哈维洪水造成的Brazos沉积物沉积的变化。在两次航行期间，将收集互补的水文数据。这包括水柱速度和悬浮泥沙负荷。沉积物样本和箱形岩心中的单个层的来源将通过完整岩心板的数字照片和x射线照片来确定，这些照片显示了沉积物的结构和结构。为了区分墨西哥湾和布拉索斯河沉积物，收集的岩心子样本将进行地球化学分析，并对短寿命放射性同位素地质年代学、含水量、粒度分布、汞和碳酸盐含量进行剖面分析。这些指标将有助于确定沉积在该系统中的沉积物的来源。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The transport and fate of sediment carried by rivers to the coastal ocean is of great ecological and societal importance. River input is the primary source of land-derived sediment to the marine environment. These particles have significant impacts on the health of coastal ecosystems and the geology and bathymetry of coastal oceans and shipping channels. They directly and indirectly affect fisheries and navigation. This research focuses on the movement of sediments carried into the Gulf of Mexico, via the Brazos River, during the unprecedented rainfall and flooding event that occurred during Hurricane Harvey. The Brazos River ranks as the second largest contributor of nutrients and organic matter to the Gulf of Mexico, after the Mississippi River. Unlike the Mississippi, however, most sediment delivered to the Gulf of Mexico from the Brazos is carried during flooding events like that which accompanied Hurricane Harvey. Little is known about the fate of this sediment. It is not clear if it is retained in the coastal zone, where the nutrients and chemicals it carries affect the coastal environment, or is carried offshore and deposited in the deep waters of the Gulf of Mexico. Through intensive sampling of sediments just offshore the mouth of the Brazos River and further offshore in the Gulf of Mexico in what is known as the Texas Mud Blanket, this project will determine the principal repository of sediments delivered to the western Gulf of Mexico by a major Texas river. The overall goal of this research is to investigate the hypothesis that flood-borne sediment from the Brazos River is initially deposited in the coastal zone and subsequently mobilized and carried offshore with a large fraction of it being deposited in the Texas Mud Blanket. The work builds on the analysis of sea-bottom sediment samples collected in 2017 during flooding associated with Hurricane Harvey. This new program will include two sampling cruises to augment already collected data. The first cruise will entail acquisition of ~25 cores that will indicate sediment deposition and transport in the near-shore region near the Brazos River mouth. Preliminary work indicates that much of the initial deposition of Brazos River sediment occurred east of the original sampling region. The second cruise in will collect additional Brazos region cores and expand sampling into the Texas Mud Blanket, with the goal of documenting changes in Brazos sediment deposition from the Hurricane Harvey flooding. During both cruises, complementary hydrography data will be collected. This includes water column velocities and suspended sediment loads. Provenance of individual layers, within the sediment samples and box cores, will be determined by digital photos and x-radiographs of intact core slabs that show sediment fabric and structures. To differentiate Gulf of Mexico from Brazos River sediments, sub-samples of collected cores will be geochemically analyzed and profiled for short-lived-radioisotope geochronology, water content, grainsize distribution, and mercury and carbonate content. These indicators will help identify the origin of the sediments deposited in the system.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.