Bismuth-210: A tracer of dynamic scavenging in aquatic systems.

任何水生系统的化学循环都受到粒子通过该系统的运输的强烈影响，对湖泊和浅海系统的粒子动力学有更好的了解是特别需要的，它们在全球生物地球化学循环中发挥着不成比例的巨大作用，但却缺乏量化。我们目前对颗粒通量和通过水柱的衰减的理解在很大程度上依赖于沉积物捕集器和自然产生的颗粒反应性放射性核素的使用。然而，由于方法上的限制，颗粒动力学在浅水系统中的研究长期不足。浅水中微粒物质的向下输送不能用底部系留沉积物捕集器可靠地量化，在高通量和淡水系统中放射性核素示踪剂的选择受到严重限制。这项拟议工作的主要目标是证明天然放射性核素铅-210 （210Pb）及其子元素铋-210 （210Bi）的联合测量可用于确定浅水动态水生系统中的颗粒通量。在对210Bi/210Pb示踪剂进行任何常规应用以研究过程速率之前，必须对该示踪剂进行彻底的演示和测试。该项目将在夏季期间支持两名本科生担任现场和实验室助理，并在项目期间支持一名硕士研究生。样本收集和实地工作将在密歇根湖进行，并将纳入研究生实地课程。这项拟议工作的目标是：(i)证明在水生系统中测量210Pb-210Bi-210Po三种放射性核素的简单技术的实用性；（ii）在动态校准的近岸体系中，210Bi/210Pb衍生粒子通量与234 /238U衍生粒子通量一致；（iii）表明，在不同颗粒浓度和有机质含量条件下，在不同溶解氧浓度梯度下，210Bi的原位Kd大于210Pb。由于方法上的限制，对近岸清除过程的研究长期不足。开发一种相对容易测量和广泛存在的基于210Bi/210Pb不平衡的颗粒示踪剂将允许未来动态颗粒循环过程研究，这对于理解全系统化学以及与营养状态、缺氧、有害藻华和污染物的管理相关的实际问题至关重要。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。

Chemical cycling in any aquatic system is strongly affected by the transport of particles through that system, and a better understanding of particle dynamics is particularly needed in lakes and shallow marine systems, which play a disproportionately large, yet poorly quantified role in global biogeochemical cycling. Our current understanding of particle flux and attenuation down through the water column has largely relied on the use of sediment traps and naturally occurring particle-reactive radionuclides. However, particle dynamics are chronically understudied in shallow aquatic systems largely because of methodological limitations. The downward transport of particulate matter in shallow waters cannot be reliably quantified with a bottom tethered sediment trap and the choice of radionuclide tracers in high flux and freshwater systems is severely limited. The primary goal of this proposed work is to demonstrate that combined measurements of the natural radionuclide lead-210 (210Pb) and its daughter bismuth-210 (210Bi) can be used to determine particulate flux in a shallow and dynamic aquatic system. A thorough demonstration and testing of the 210Bi/210Pb tracer is imperative before any general application of the tracer is made to study process rates. The project will support two undergraduate students as field and laboratory assistants during summer months and one MS graduate student for the duration of this project. Sample collection and field work will take place in Lake Michigan and will be incorporated into a graduate field course.The goals of this proposed work are to: (i) demonstrate the practicality of a simple technique for measuring the 210Pb-210Bi-210Po radionuclide trio in aquatic systems; (ii) show that 210Bi/210Pb derived particle fluxes are concordant with 234Th/238U derived particle fluxes in a dynamic and “calibrated” nearshore system; and (iii) show that the in situ Kd of 210Bi is greater than that of 210Pb under varying conditions of particle concentration and organic matter content, across a gradient of dissolved oxygen concentrations. Nearshore scavenging processes are chronically understudied due to methodological limitations. Developing a relatively easy to measure and widely occurring particle tracer based on 210Bi/210Pb disequilibria will allow for future process studies of dynamic particle cycling that are critical to understanding system-wide chemistry as well as practical problems associated with the management of trophic status, hypoxia, harmful algal blooms, and contaminant fate and transport.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.