Collaborative Research: Regulation of plankton and nutrient dynamics by hydrodynamics and profundal filter feeders

底栖滤食动物，如蛤和贻贝，影响浅海和淡水系统中的浮游生物和营养动态，但它们的作用通常被认为在大型深海系统中是次要的。然而，最近的证据表明，深海斑马贻贝（Dreissena rostriformis bugensis）极大地改变了劳伦森五大湖和其他大型深海水生系统的能量流动和营养循环，对食物网的许多其他组成部分产生了负面影响。以前，这些湖泊的管理策略依赖于预测湖泊对磷负荷反应的数值模型。湖泊中底栖滤食动物的激增似乎从根本上改变了磷循环和能量流动的动态，因此这些模型不再有效。该项目测量密歇根湖的能量流动和营养循环过程，重点关注斑驴贻贝在这些过程中的作用，并利用这些测量数据开发数值模型，以指导有关营养负荷和鱼类放养的管理决策。除了支持三名博士生的教育和为本科生提供研究培训外，该项目还通过为学生举办跨学科研究和建模研讨会，并通过开放访问项目网站提供研讨会讲座，促进未来水生科学家的教育。这个生物物理合作项目围绕两个主要问题展开：1)深海贻贝在大湖碳和营养循环中扮演什么角色？2)从毫米（底栖边界层）到米（整个水柱）的尺度上，水动力学如何调节贻贝的放牧和贻贝循环的营养物质的命运？研究人员假设，颗粒输送到湖底的明显增强是由于高过滤能力和垂直混合过程，浮游植物从透光区平流到近底层。然而，流体力学的作用尚不清楚，因为这些过程在整个低阴离子和近底层中都没有得到很好的表征。此外，对浮游植物和营养动态的影响尚不清楚，因为贻贝既是食草动物又是营养循环者。最先进的仪器和分析工具，包括粒子图像测速仪、声学多普勒电流分析器和营养微量分析器，正在密歇根湖部署，以量化这些关键的动态过程，包括边界层湍流、贻贝放牧、排泄和排泄，以及底栖生物的碳和磷通量。结果数据用于校准三维流体动力学-生物地球化学模型，该模型用于解决具有丰富深层滤食性动物的大型深湖中浮游生物和营养动力学与先前模型所描述的传统范式的差异这一首要问题。该项目还提供了对底部边界层物理的见解，适用于其他大型湖泊，潮汐沿海海和深海。

Benthic filter feeders such as clams and mussels influence plankton and nutrient dynamics in shallow marine and freshwater systems, but their role is generally considered to be minor in large, deep systems. However, recent evidence indicates that profundal quagga mussels (Dreissena rostriformis bugensis) have dramatically altered energy flow and nutrient cycling in the Laurentian Great Lakes and other large, deep aquatic systems, with negative consequences for many other components of the food web. Previously, management strategies for these lakes relied on numerical models that predicted the lake's response to phosphorus loading. The proliferation of benthic filter feeders in the lakes appears to have fundamentally altered the dynamics of phosphorus cycling and energy flow, so that these models are no longer valid. This project measures energy flow and nutrient cycling processes in Lake Michigan, with a focus on the role of quagga mussels in these processes, and uses these measurements to develop numerical models to guide management decisions with regard to nutrient loading and fish stocking. In addition to supporting the education of three Ph.D. students and providing research training for undergraduate students, the project promotes education of future aquatic scientists by hosting a workshop on interdisciplinary research and modeling for students and making workshop lectures available through an open-access project website.This collaborative biophysical project is structured around two primary questions: 1) What role do profundal dreissenid mussels play in large lake carbon and nutrient cycles? 2) How are mussel grazing and the fate of nutrients recycled by mussels modulated by hydrodynamics at scales ranging from mm (benthic boundary layer) to meters (entire water column)? The investigators hypothesize that the apparent enhanced particle deliver rate to the lake bottom results from high filtration capacity combined with vertical mixing processes that advect phytoplankton from the euphotic zone to the near bottom layer. However, the role of hydrodynamics is unclear, because these processes are poorly characterized both within the hypolimnion as a whole and within the near-bottom layer. In addition, the implications for phytoplankton and nutrient dynamics are unclear, as mussels are both grazers and nutrient recyclers. State-of-the-art instruments and analytical tools, including particle image velocimetry, acoustic Doppler current profilers, and nutrient micro-profilers, are being deployed in Lake Michigan to quantify these critical dynamic processes, including boundary layer turbulence, mussel grazing, excretion and egestion, and benthic fluxes of carbon and phosphorus. Resulting data are used to calibrate a 3D hydrodynamic-biogeochemical model, which is used to address the overarching question of how plankton and nutrient dynamics in large, deep lakes with abundant profundal filter feeders differ from the conventional paradigm described by previous models. The project also provides insight into bottom boundary layer physics, with applicability to other large lakes, atidal coastal seas, and the deep ocean.