Interactions of Estuarine Physics, Sediment, and Organic Matter in Determining Suspended Particle Properties, Their Spatial and Temporal Distribution, and Resulting Water Clarity

海岸和河口系统的水质清澈度影响生态系统动态，影响许多物种关键生命阶段的基本栖息地，对美学和娱乐也很有价值。在切萨皮克湾，水的透明度似乎对管理措施特别不敏感，近几十年来一直在下降。奇怪的是，在无机沉积物浓度相对较低的地区，透明度的下降幅度大于河流沉积物负荷增加的地区。在这里，它建议，在切萨皮克湾和许多其他河口的水的透明度和沉积物的输入之间的明显断开有关的共同河口流模式与过量有机物的存在下的相互作用。通过改进的观察，建模和河口物理与悬浮有机物和无机沉积物的相互作用的分析，本研究的目的是改变对河口水质清澈度的控制的理解。 切萨皮克湾流域的各州将在未来十年投资数十亿美元，以进一步减少养分和沉积物的径流。未来，全国河口流域可能需要类似的投资。通过评估河口物理，有机物和沉积物如何相互作用，影响水的清晰度，这项研究将提供有效地投资这些资金有价值的指导。 该项目将资助两名博士生进行与社会相关的论文项目，并为本科研究人员提供引人入胜的项目。在许多沿海环境中，确定水的透明度的相互作用是敏感的颗粒浓度，大小，密度，成分，有机物含量和沉降速度，但很少有研究明确考虑这些连接到广义河口湍流和环流模式。这项研究的主要目的是更好地了解小规模和大规模的河口物理与无机沉积物和有机物的混合物典型的部分混合系统的相互作用。将开发新的实地观测和数值模型来测试这些想法，并将重点放在约克河口，一个后勤上有吸引力的，具有广泛代表性的，部分混合的分支的切萨皮克湾。实地观测将描述物理海洋学（环流、分层和湍流）以及颗粒群（包括大小分布、浓度、密度、沉降速度和有机成分）的特征。开源，社区支持的数值模型将被实施，以进一步调查河口水动力学，有机物含量和沉积物动力学之间的反馈，将多种颗粒大小和密度，以及新的配方成分依赖的絮凝，以及国家的最先进的配方粘性床行为。这项工作将测试以下新的假设：（H1）：有机材料的添加进一步提高了水平和垂直颗粒分选的物理特性的部分混合河口。(H2)将有机物质添加到低浓度的无机固体中会产生相对较小的低密度絮凝物，其沉降速度较慢（1型絮凝物）。相反，向高浓度的无机絮凝物中加入有机物有利于更大、更高密度的絮凝物，并增加沉降速度（2型絮凝物）。(H3)富含有机物的絮凝体（1型）在衰减阳光方面特别有效，因为它们悬浮在水柱的高处，每单位质量的横截面积很大。与河口物理相互作用的最终结果是，有机物的河口降低水的透明度在较低的河口和提高水的透明度在河口上游，更接近河口最大浑浊度。

Water clarity in coastal and estuarine systems impacts ecosystem dynamics, influences essential habitat for key life stages of many species, and is also valuable for aesthetics and recreation. In Chesapeake Bay, water clarity has seemed particularly unresponsive to management practices, and has continued to decline over recent decades. Paradoxically, clarity has decreased more in areas with relatively low concentrations of inorganic sediment than in locations where riverine sediment loads have increased. Here it is proposed that the apparent disconnect between water clarity and input of sediment in the Chesapeake Bay and many other estuaries is related to the interaction of common estuarine flow patterns with the presence of excess organic matter. Through improved observation, modeling, and analysis of the interaction of estuarine physics with suspended organic matter and inorganic sediment, this study aims to transform understanding of the controls on water clarity in estuaries. States in the Chesapeake Bay watershed will invest billions of dollars over the next decade to further reduce runoff of nutrients and sediment. In the future, analogous investments may be required for estuarine watersheds nationwide. By evaluating how estuarine physics, organics, and sediment interact to influence water clarity, this study will provide valuable guidance on effectively investing these funds. This project will fund two PhD students on societally-relevant dissertation projects and provide engaging projects for undergraduate researchers. In many coastal settings, the interactions that determine water clarity are sensitive to particle concentration, size, density, composition, organic content, and settling velocity, yet few studies have explicitly considered how these connect to generalized estuarine turbulence and circulation patterns. The main objective of the study is to better understand the interaction of small and large scale estuarine physics with mixtures of inorganic sediment and organic matter typical of partially-mixed systems. Novel field observations and numerical models will be developed to test these ideas and focus on the York River estuary, a logistically attractive, broadly representative, partially-mixed branch of the Chesapeake Bay. Field observations will characterize physical oceanography (circulation, stratification, and turbulence), as well as particle populations (including size distribution, concentration, density, settling velocity and organic constituents). Open-source, community-supported numerical models will be implemented to further investigate feedbacks between estuarine hydrodynamics, organic content, and sediment dynamics, incorporating multiple particle sizes and densities, and new formulations for composition-dependent flocculation, as well as state-of-the-art formulations for cohesive bed behavior. This work will test the following novel hypotheses: (H1): Addition of organic material further enhances the horizontal and vertical particle sorting that characteristic to the physics of partially-mixed estuaries. (H2): Organic matter added to low concentrations of inorganic solids results in relatively small, low density flocs having slow settling velocities (Type 1 flocs). Conversely, adding organic matter to high concentrations of inorganic flocs favors larger, higher density flocs, with increased settling velocity (Type 2 flocs). (H3): Organic rich flocs (Type 1) are especially effective at attenuating sunlight because they are suspended high in the water column and have a large cross-sectional area per unit mass. The end result of interactions with estuarine physics is that the addition of organic matter to the estuary degrades water clarity in the lower estuary and improves water clarity in the upper estuary, closer to the estuarine turbidity maximum.