Collaborative Research: Are Buried Paleochannels Effective Reactors for Water and Solute Transport in a Deltaic Subterranean Estuary?

合作研究：埋藏古河道是三角洲地下河口水和溶质输送的有效反应器吗？

• 批准号: 1141685
• 负责人: Jaye Cable
• 金额: $ 25.56万
• 依托单位: University of North Carolina at Chapel Hill
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-03-01 至 2016-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1141685&HistoricalAwards=false
• 关键词: Collaborative; Research; Buried; Paleochannels; Effective

COLLABORATIVE RESEARCH:ARE BURIED PALEOCHANNELS EFFECTIVE REACTORS FOR WATER AND SOLUTE TRANSPORT IN THE DELTAIC SUBTERRANEAN ESTUARY?Alexander Kolker, Louisiana Universities Marine ConsortiumKaren Johannesson, Tulane UniversityJaye Cable, University of North Carolina-Chapel HillRivers deltas are one of the largest stores of minerals and organic-rich sediments on earth. Their low relief and close proximity to the ocean also make them one of the best systems to study how coastal ecosystems will respond to climate change and sea-level rise in the coming decades. A wealth of previous studies focused on the role deltas play in cycling carbon, nutrients, metals and other elements. However, very little of this research has investigated the subsurface connections between the main river and adjacent bays and wetlands. Hydrological models of coastal bays associated with river deltas suggest more freshwater is entering these systems than expected. This study will investigate whether this missing component is groundwater discharge through buried ancient channels in these deltas. Modern deltas consist of bays and bayous, sedimentary deposits, and marshes formed and abandoned as the river changed course throughout the Holocene. Over time, sandy-bottom bayous are buried and may leave only a trace of their former existence at the surface. These buried channels commonly retain a hydraulic connection to the main river, thus acting as a conduit for discharge to adjacent bays during the annual spring/summer high river stage. Within the Mississippi River Delta (MRD) system, this hydraulic connection may be enhanced by 20 to 40 ft as a consequence of flood control levees which may produce a river stage (i.e. head) as much as 15 to 22 ft above the adjacent bay water levels. The central hypothesis of this research is that buried ancient channels in deltas act as a vast network of subterranean estuaries, which play a critical role in the transport of groundwater, nutrients, and some metals to deltaic bays and ultimately the ocean. The research addresses several major questions: Is deltaic submarine groundwater discharge sufficient to satisfy current deltaic hydrologic and biogeochemical budgets? How effective are paleochannel networks in the delivery of water and elemental mass fluxes to the coastal ocean? These questions will be addressed using geophysical surveys that can produce images of the structure of the delta sediments and their salinity, as determined through sonars and electrical conductivity. These studies will be conducted in concert with studies of geochemical tracers (e.g. salt, radioactive and stable isotopes) and detailed a study of hydraulic gradients between the river and a paleochannel system (e.g. piezometers, pressure loggers, flow nets). Using the assembled understanding of hydrogeologic flow patterns and rates, we will estimate the biogeochemical mass fluxes associated with seasonal groundwater flow through this paleochannel/subterranean estuary network (e.g. N, C, P, Si, Fe). Results should improve the understanding of the role that the delta?s geology plays in its hydrology and chemistry and how fluxes of water, nutrients and metals vary over space and time. This work will then add to the understanding of how deltas and other coastal ecosystems function, particularly in light of sea-level rise predictions for the next 50 years.Rivers have long been recognized a playing an important role global chemical cycles. Despite this recognition, relatively little is know about how these chemical cycles function below the sea floor, and the implications this has for the chemistry of the coastal zone. The proposed study will examine these processes in the Mississippi River Delta. This delta sits at the mouth of the largest river in North America, and is the entry point to one of the most important economic pathways in the United States. The Mississippi River Delta also has a long history of scientific research, government water quality monitoring, and stakeholder involvement. This provides the team with excellent baseline information and opportunities to link findings to the needs of society. The work will contribute to the education of three graduate students and several undergraduate students. These students will study at leading research universities and have the opportunity to work at a marine laboratory.

合作研究：埋藏古河道是三角洲地下河口水和溶质运移的有效反应器吗？亚历山大·科尔克，路易斯安那大学海洋联盟，卡伦·约翰内森，杜兰大学，杰伊·凯博，北卡罗来纳大学教堂山，河流三角洲是地球上最大的矿物和富含有机物的沉积物储存地之一。它们地势低，靠近海洋，也使它们成为研究未来几十年沿海生态系统如何应对气候变化和海平面上升的最佳系统之一。以前的大量研究集中在三角洲在碳、营养物质、金属和其他元素的循环中所起的作用。然而，很少有研究调查了主要河流与邻近海湾和湿地之间的地下联系。与河流三角洲相关的沿海海湾的水文模型表明，进入这些系统的淡水比预期的要多。本研究将探讨这一缺失的成分是否是通过这些三角洲埋藏的古河道排出的地下水。现代三角洲由海湾、河口、沉积物和沼泽组成，它们是在全新世河流改道时形成和废弃的。随着时间的推移，砂底河口被掩埋，可能只会在地表留下它们以前存在的痕迹。这些埋在地下的河道通常与主河保持水力连接，因此在每年的春夏高水位期间充当向邻近海湾排放的管道。在密西西比河三角洲（MRD）系统中，由于防洪堤的存在，这种水力连接可能会增加20到40英尺，因为防洪堤可能会产生比邻近海湾水位高出15到22英尺的河段（即水头）。这项研究的中心假设是，在三角洲中埋藏的古河道充当着一个巨大的地下河口网络，在将地下水、营养物质和一些金属输送到三角洲海湾并最终进入海洋方面发挥着关键作用。该研究解决了几个主要问题：三角洲海底地下水排放是否足以满足目前的三角洲水文和生物地球化学预算？古河道网络在向沿海海洋输送水和元素质量通量方面有多有效？这些问题将通过地球物理调查来解决，地球物理调查可以产生三角洲沉积物结构及其盐度的图像，通过声纳和电导率来确定。这些研究将与地球化学示踪剂（如盐、放射性和稳定同位素）的研究一起进行，并详细研究河流和古河道系统之间的水力梯度（如压力计、压力记录仪、流网）。利用对水文地质流动模式和速率的综合理解，我们将估算与季节性地下水流动相关的生物地球化学物质通量，通过这个古河道/地下河口网络（如N， C， P, Si, Fe）。结果应提高对三角洲的作用的认识？美国的地质学在其水文学和化学中发挥作用，以及水、营养物质和金属的通量如何随空间和时间而变化。这项工作将增加对三角洲和其他沿海生态系统如何运作的理解，特别是考虑到未来50年海平面上升的预测。长期以来，河流一直被认为在全球化学循环中发挥着重要作用。尽管认识到了这一点，但相对而言，人们对这些化学循环在海底以下是如何运作的，以及这对海岸带化学的影响知之甚少。拟议的研究将检查密西西比河三角洲的这些过程。这个三角洲位于北美最大河流的入海口，是美国最重要的经济通道之一的入口。密西西比河三角洲在科学研究、政府水质监测和利益相关者参与方面也有着悠久的历史。这为团队提供了极好的基线信息，并有机会将研究结果与社会需求联系起来。这项工作将有助于三名研究生和几名本科生的教育。这些学生将在一流的研究型大学学习，并有机会在海洋实验室工作。