Wave-Driven Porewater-Seawater Exchange in Sandy Coastal Sediments

在透水性砂质沉积物（即粒径大于~80 um的砂质沉积物）上方传播的浅水表面波，可大大增强沉积物-水界面的混合以及沉积物内部水和颗粒的快速输运。因此，近岸和大陆架水域的沙质沉积物的水动力运输可以预期：(1)通过增加向沉积物提供的氧气和颗粒物，大大增加沉积物中发生的生化过程的速率；(2)显著增加降解产物（如营养物）返回水柱的速率，从而增加水柱和底栖生物的初级生产。砂质沉积物中孔隙水和颗粒的快速运输使得使用传统的基于扩散的模型计算底栖生物通量无效，从而混淆了对沿海地区和大陆架上收集的化学剖面的解释。在这个项目中，夏威夷大学的研究人员将进行研究，以描述和量化沙质沉积物中溶质和颗粒物的运输。通过实地调查，他们将证实或反驳现有的水力通过沉积物孔隙的理论模型的有效性，并评估水动力泵送机制的重要性和时间尺度。他们建议(1)在一系列波浪条件下测量波浪引起的孔隙水运动/弥散；(2)利用这些测量结果评估波浪增强孔隙水运动/分散和交换的现有理论；(3)在现场建立物理传感器阵列，收集一系列波浪条件下的天气数据；(4)测量整个阵列中生物地球化学重要成分的孔隙水浓度；(5)计算孔隙水-海水通量作为波浪条件的函数；(6)将这些孔隙-海水通量与实测222Rn分布和涡动相关技术计算的通量进行比较；(7)测量沙质沉积物中波浪引起的颗粒输运率，作为颗粒大小和波浪条件的函数；(8)研究了河床形态对孔隙水和颗粒输运的影响。这项研究将在夏威夷瓦胡岛南岸的沙质沉积物中进行，这是一个受到广泛和可预测的波浪条件影响的地方。目前缺乏适当的工具来量化砂质沉积物中的孔隙水和颗粒运动，包括沉积物-水通量。提出的研究旨在提供实用的方法来克服这一限制，并发展一种通用的过程理解，这将允许在用于代表砂质沉积物成岩作用的生物地球化学模型中估计间隙运输速率。

ABSTRACTOCE-0327332Shallow-water surface waves traveling above permeable sandy sediments (i.e., those with grains coarser than ~80 um) can induce greatly enhanced mixing across the sediment-water interface and rapid transport of water and particles within the sediment. Thus, hydrodynamic transport in sandy sediments in nearshore and continental shelf waters can be expected to (1) substantially increase the rates of biochemical processes occurring in sediments by increasing the supply of oxygen and particulate matter to the sediment, and (2) significantly increase the rate of return of degradation products such as nutrients to the water column, thereby increasing water-column and benthic primary production. The rapid transport of porewater and particles in sandy sediments renders the calculation of benthic fluxes using conventional diffusion-based models invalid and thus confounds the interpretation of chemical profiles collected in coastal areas and on the continental shelf.In this project, researchers at the University of Hawaii will conduct studies to describe and quantify the transport of solutes and particulate matter in sandy sediments. Using field investigations, they will confirm or refute the validity of available theoretical models of hydraulic transport through sediment pores and evaluate the importance and timescales of the hydrodynamic pumping mechanisms. They propose to (1) measure wave-induced porewater movement/dispersion under a range of wave conditions; (2) evaluate current theories of wave-enhanced porewater movement/dispersion and exchange using the results of these measurements; (3) establish an array of physical sensors at the field site, and collect synoptic data over a range of wave conditions; (4) measure porewater concentrations of biogeochemically important constituents across the array; (5) compute porewater-seawater fluxes as functions of wave conditions; (6) compare these porewater-seawater fluxes with those calculated using measured 222Rn distributions and eddy correlation techniques; (7) measure wave-induced particle transport rates into and within sandy sediments, as a function of particle size and wave conditions; and (8) investigate the effect of bedforms on porewater and particle transport. This research will be conducted in sandy sediment off the south shore of Oahu, Hawaii, a site that is subject to a wide and predictable range of wave conditions.There is presently a lack of suitable tools for quantifying porewater and particle motion, including sediment-water fluxes, in sandy sediments. The proposed research aims to provide practical methodologies to overcome this limitation and to develop a generic process understanding that will allow the estimation of interstitial transport rates in biogeochemical models used to represent diagenesis in sandy sediments.