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

这项拟议的研究旨在研究河流中的水流和泥沙输送过程如何与挖在河床中的淡水贻贝(贻贝科)相互作用。淡水贻贝是北美最受威胁的水生生物之一，人们已经进行了大量的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一段时间(长达几十年)，即使在有大量泥沙流动的高流量事件中也是如此。为了做到这一点，贻贝可能具有特殊的适应能力，使它们能够在高流量阶段保持在河床上。实地调查、数值模拟和实验设施将证明河床上的贻贝可以在相对较长的时间内保持在原地，以表明将贻贝移出洞穴所需的力高于预期值，并说明贻贝可以改变河流中的水流，以帮助它们长期生存。这项工作寻求提供有关使贻贝在河流中茁壮成长的过程的关键信息，然后这些信息可以用于帮助保护工作。研究生和本科生将接受在河流和水生态中使用的野外、实验和数值方法方面的培训，为他们未来的职业生涯提供必要的技能。最后，将组建一个创新的跨学科研究小组，以促进对水生生物如何与河流流动相互作用的基本理解。淡水贻贝是北美河流中最危险的水生生物之一，人们花费了大量努力来了解它们的急剧下降。目前的模式是，河床在很长一段时间(几十年)内的相对稳定(不动)是贻贝生态成功和弹性的关键组成部分。然而，这些信息与人们对自我形成的河流的核心理解形成了鲜明对比。这项研究计划旨在研究沙砾河床和底栖生物栖息的不稳定河床中近床面湍流和泥沙输送之间的基本相互作用。这项研究的重点是一种濒临灭绝的淡水贻贝，它可以被认为是一名“生态工程师”。假设(1)像淡水贻贝这样的底栖生物可以在具有不稳定河床的动态的自制河流系统中在相对较长的一段时间(大约几十年)内茁壮成长，并且这些相同的河段经常经历河道形成的排放，(2)由于生物物理适应(生态工程)，选定的活的底栖生物在不稳定的河床中的夹带阈值可测量地大于完全等效的无粘性沉积物颗粒，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紧急现象，即“引爆点”，“这增加了相对高水位时不稳定河床的稳定性。首先，将在两条具有历史和生态意义的贻贝种群的选定河段进行实地调查和数值模拟，以明确地证明贻贝床在不稳定的河道中的持久性。其次，实验室实验，也得到数值模拟的支持，将直接测量作用于穴居贻贝的升力和阻力，包括主动过滤和不主动过滤，以评估夹带阈值和近床流体动力学。第三，一个实验和数值模拟相结合的运动将量化流体动力学“临界点”的出现，在这个临界点上，作用在贻贝覆盖的河床上的流体阻力通过可变边界条件的建设性干扰而减少。这项工作试图证明，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.