Collaborative Research: Kelp forest hydrodynamics: observations of drag and cross-shore exchange on the inner shelf

海带森林在许多中纬度海岸都很常见，它们是渔业、娱乐和可能的生物碳固定最有价值的内大陆架栖息地之一。该项目旨在量化波浪相关的阻力和相关的水动力机制，通过这些机制，巨藻可以调节大陆架内部栖息地的流动条件。单个海带植物和整个海带林产生的摩擦阻力强烈影响沿海生境的环流和运输。然而，目前还不可能将这些影响纳入沿海环流模式。高分辨率野外测量将用于在海岸流、表面波和内波存在的情况下开发整个海带森林阻力的参数化，这将适用于内大陆架环流模型。该分析将设法量化海带林对内大陆架跨岸交换的影响程度，并确定在有海带的情况下减轻跨岸交换的机制，以便将研究结果推广到任何海带林环境。这与了解沿海环境流动及其与自然系统中各种水生植被的相互作用以及大规模水产养殖和生态系统管理有关。因此，了解它们的水动力学对于沿海水域的管理以及设计自然恢复区和潜在的水产养殖系统非常重要。考虑到高分辨率环流模式作为海岸带管理决策分析工具的迅速发展，包括海带森林潜在的巨大水动力效应可能是准确预测内陆架流动的必要先决条件。因此，该项目的一个特别重点将是根据平均洋流和波速开发一个新的海带阻力模型，该模型结合了可用于沿海环流模型的海带结构和生物量的简单测量。考虑到水动力学通过对生物地球化学和幼虫运输的影响在塑造海带森林生态中发挥的基本作用，提高我们对海带森林水动力学的理解将对广泛的研究人员和资源机构有所帮助。此外，考虑到大量正在进行的工作集中在洛马海带森林上，以及它对加州沿海海洋的根本重要性，因为它的规模很大，这项研究的结果应该对当地科学家和管理者特别有用。因此，收集的数据也将存档在scos服务器和NODC数据库上。该项目还将支持研究生教育、博士后专业发展和公众宣传。该项目的中心主题将是量化与施加在灵活的营养结构上的水流相关的深度依赖阻力-海带植物在水流和波浪中-其中海带的运动既受到整体水动力条件的影响，反过来又起到中介作用。因此，该研究将揭示跨整个水柱的环境流与水生植被之间复杂的反馈机制。虽然过去在野外和实验室的研究已经检查了这种相互作用的要素，例如海带平均流量或波速场的变化，但这项研究将提供海带森林流体动力学的整体观点，特别是包括海带的运动。然而，在以前的实地研究中，海带阻力总是以特别的方式估计，这里将直接测量。实地观察的定量分析将检验三个关键假设：(1)波浪存在时植物的运动和海带植物密度足够高时产生的遮蔽效应是平均阻力的0(1)决定因素。这一假设意味着整个海带森林的阻力不是单个海带植物数量的简单线性函数，而是取决于单个阻力元素的规模和间距及其在强加流中的运动之间的相互作用。(2)波流相互作用和频率相关的辐射应力改变了海带森林及其周围的流场。这些流动效应以及高频内波和内潮的阻尼和日热分层的增加意味着：（3a）海带森林的存在可以局部增强海带森林和近海海洋环境之间的跨海岸交换；（3b）海带森林作为部分屏障，减少了近海区域和海带近岸区域之间的运输。后一种假设预测，海带森林的存在对改变近海环流和停留时间有重要影响。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。

Kelp forests are common to many mid-latitude coasts, and they are among the most valuable inner shelf habitats for fisheries, recreation, and possibly biological carbon fixation. This project seeks to quantify the wave-dependent drag forces and associated hydrodynamic mechanisms by which giant kelp mediates flow conditions in inner shelf habitats. The frictional drag generated by individual kelp plants and whole kelp forests strongly influence circulation and transport in coastal habitats. However, at present it is not possible to incorporate these effects into coastal circulation models. High-resolution field measurements will be used to develop parameterizations of drag on a whole kelp forest in the presence of coastal currents, surface waves, and internal waves, that will be suitable for use in inner shelf circulation models. The analysis will seek to quantify the magnitude by which kelp forests affect cross-shore exchange on the inner shelf and to determine the mechanisms that mitigate cross-shore exchange in the presence of kelp so that the findings may be generalized to any kelp forest environment. This is relevant to understanding coastal environmental flows and their interactions with a range of types of aquatic vegetation in both natural systems and for large-scale aquaculture and ecosystem management. Understanding their hydrodynamics is thus important to management of coastal waters, as well as to designing natural restoration areas and potential aquaculture systems. Given the rapid development in high resolution circulation models as decision-analysis tools for coastal zone management, including the potentially large hydrodynamic effects of kelp forests can be an essential prerequisite to producing accurate predictions of inner shelf flows. Thus, one particular focus of the project will be to develop a new model for kelp drag in terms of mean currents and wave velocities incorporating simple measures of kelp configuration and biomass that can be used in coastal circulation models. Given the fundamental roles hydrodynamics play in shaping kelp forest ecology through its effects on biogeochemistry and on the transport of larvae, advancing our understanding of kelp forest hydrodynamics will be of use to a wide range of researchers and resource agencies. Moreover, given the large body of ongoing work focused on the Pt. Loma kelp forest, as well as its fundamental importance to the California coastal ocean due to its large size, the results of this study should be of particular use to local scientists and managers. Accordingly, the data collected will also be archived on SCOOS servers as well as on the NODC database. The project will also support graduate education, post-doctoral professional development, and public outreach.The central theme of the project will be to quantify depth-dependent drag associated with flow imposed on flexible vegetative structures – kelp plants in currents and waves – where the movement of the kelp is both influenced by, and in turn mediates, the overall hydrodynamic conditions. Thus, the research will delineate mechanisms of the complex feedbacks between environmental flows and aquatic vegetation that can span the entire water column. While past studies in the field and in the lab have examined elements of this interaction, e.g. changes in mean flows or wave velocity fields by kelp, this study will provide a holistic view of kelp forest hydrodynamics particularly including motion of the kelp. Whereas, in previous field studies kelp drag has always been estimated in ad hoc ways, here it will be measured directly. Quantitative analysis of field observations will test three key hypotheses: (1) Movement of the plants in the presence of waves and sheltering effects that develop when kelp-plant density is sufficiently high are O(1) determinants of mean drag. This hypothesis implies that drag of a whole kelp forest is not a simple linear function of the number of individual kelp plants, but depends on interactions between scale and spacing of individual drag elements and their movement in imposed flows. (2) Wave-current interactions and frequency dependent radiation stress alter the flow field in and around kelp forests. These flow effects along with damping of high frequency internal waves and internal tides and increased diurnal thermal stratification imply that (3a) the presence of a kelp forest can locally enhance cross-shore exchange between the kelp forest and the offshore ocean environment and (3b) a kelp forest acts as a partial barrier that reduces transport between the offshore region and the very near shore region inshore of the kelp. The latter hypothesis predicts the presence of kelp forests can have important consequences for altering circulation and residence time near shore.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.