Collaborative Research: Near-bed flow, turbulence, and emergent hydrodynamics of biologically-conditioned labile river channels

这项拟议中的研究旨在研究如何在河流中的流动和沉积物运输过程中相互作用的淡水贻贝（蚌科）钻入河床。 淡水贻贝是北美最受威胁的水生生物之一，人们已经做了很多工作来了解和保护它们。 这里假设淡水贻贝可以在给定的河流位置存活相对较长的时间（长达几十年），即使在高流量事件与大量沉积物的运动。 为了做到这一点，贻贝可能有特殊的适应能力，使它们能够在高流量阶段留在河床上。 实地调查，数值模拟和实验设施将证明，河蚌在河床上可以保持在相对较长的时间内，以表明所需的力量，以移动贻贝的洞穴高于预期值，并说明贻贝可以改变河流内的流量，以帮助他们的长期生存。 这项工作旨在提供有关使贻贝在河流中茁壮成长的过程的关键信息，然后可以用来帮助保护工作。 研究生和本科生将接受河流和水生生态学领域，实验和数值方法的培训，为他们未来的职业生涯提供必要的技能。 最后，一个创新的跨学科研究团队将组装，以推进水生生物如何与河流流量相互作用的基本理解。淡水贻贝（蚌科）是北美河流中最危险的水生生物之一，人们已经花费了大量精力来了解它们的急剧下降。 目前的范式是，相对稳定（不动）的河床在很长一段时间（几十年）是一个关键组成部分的生态成功和弹性的贻贝。 然而，这些信息与自我形成的河流的核心理解形成鲜明对比。 这项研究计划的目的是研究近床湍流和泥沙输运砂和砾石层河流与底栖生物居住的不稳定床之间的基本相互作用。 这项研究的重点是一种濒危的淡水贻贝，它可以被认为是一个“生态工程师”。“据推测，（1）像淡水贻贝这样的底栖生物可以在相对较长的时间内茁壮成长（约100年）。10年），在具有不稳定河床的动态自制河流系统中，这些相同的河段经常经历形成河道的排放，（2）由于生物物理适应，不稳定河床中选定的活底栖生物的夹带阈值明显大于完全等效的非粘性沉积物颗粒（生态工程），以及（3）近床流、湍流、粗糙度和生态工程适应的建设性干扰产生了水动力学涌现现象，即“临界点，他说：“在相对较高的流量阶段，可增加不稳定河床的稳定性。 首先，实地调查和数值模拟将在选定的两个流与历史和生态显着的贻贝种群，以明确地证明贻贝床在不稳定的河道的持久性。 第二，实验室实验，也支持数值模拟，将直接测量的升力和阻力作用于挖洞贻贝，有和没有主动过滤，以评估夹带阈值和近床流体动力学。 第三，结合实验和数值模拟活动将量化的流体动力学的“临界点”的出现，其中流体阻力作用在贻贝覆盖的床变得减少，通过建设性的可变边界条件的干扰。 这项工作旨在证明，进化适应促进水动力条件有利于贻贝在河流中的持久性和生存。

This proposed research is designed to examine how flow and sediment transport processes in rivers interact with freshwater mussels (Unionidae) burrowed into the river's bed. Freshwater mussels are one of the most threatened aquatic organisms in North America, and much work has been conducted to understand and conserve them. It is hypothesized here that freshwater mussels can survive for relatively long time periods (up to several decades) at a given river location even during high flow events with much sediment in motion. To do this, mussels may have special adaptations that enable them to remain in place on a river bed during high flow stages. Field surveys, numerical modeling, and experimental facilities will demonstrate that mussels on river beds can remain in place for relatively long time periods, to show that the forces required to move mussels out of their burrows are higher than expected values, and to illustrate that mussels can alter the flow within a river to aid in their long-term survival. This work seeks to provide critical information on those processes that enable mussels to thrive in rivers, which then could be used to aid conservation efforts. Graduate and undergraduate students will be trained in field, experimental, and numerical methods employed in rivers and aquatic ecology, providing them the necessary skills for their future careers. Lastly, an innovative interdisciplinary research team will be assembled to advance the fundamental understanding of how aquatic organisms interact with river flow.Freshwater mussels (Unionidae) are one of the most imperiled aquatic organisms in North American rivers and much effort has been expended to understand their precipitous decline. The current paradigm is that the relative stability (immobility) of river beds over long time periods (decades) is a critical component to the ecological success and resiliency of mussels. Yet such information is in stark contrast to the central understanding of self-formed rivers. This research program is designed to examine the fundamental interactions between near-bed turbulent flow and sediment transport within sand- and gravel-bedded rivers with labile beds populated by benthic organisms. The focus for this study is an imperiled freshwater mussel, which can be considered an "ecologic engineer." It is hypothesized that (1) benthic organisms like freshwater mussels can thrive for relatively long time periods (ca. decades) at-a-station in dynamic, self-made river systems with labile channel beds, and that these same reaches often experience channel-forming discharges, (2) entrainment thresholds for selected live benthic organisms in labile river beds are measurably greater than fully-equivalent non-cohesive sediment particles due to biophysical adaptations (ecological engineering), and (3) the constructive interference of near-bed flow, turbulence, roughness, and ecological engineering adaptations create a hydrodynamic emergent phenomenon, a "tipping-point," that increases the stability of labile river beds at relatively high flow stages. First, field surveys and numerical modeling will be employed at selected reaches of two streams with historically- and ecologically-significant mussel populations to demonstrate unequivocally the persistence of mussel beds in labile river channels. Second, laboratory experiments, also supported by numerical modeling, will directly measure the lift and drag forces acting on burrowed mussels, with and without active filtering, to assess entrainment thresholds and near-bed hydrodynamics. Third, a combined experimental and numerical modeling campaign will quantify the emergence of a hydrodynamic "tipping-point" wherein the fluid drag acting on a mussel-covered bed becomes reduced through the constructive interference of variable boundary conditions. This work seeks to demonstrate that evolutionary adaptations promote hydrodynamic conditions beneficial to the persistence and survival of mussels in rivers.