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

任何水生系统中的化学循环都受到通过该系统的颗粒输送的强烈影响，特别需要更好地了解湖泊和浅海系统中的颗粒动力学，因为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，但量化不足。我们目前的理解粒子通量和衰减通过水柱主要依赖于使用沉积物陷阱和自然发生的粒子反应性放射性核素。然而，颗粒动力学在浅水系统中长期研究不足，主要是因为方法的限制。在浅水沃茨中颗粒物质的向下迁移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（210 Pb）和其子体铋-210（210 Bi）的联合测量可用于确定在一个浅的和动态的水生系统中的颗粒通量。210 Bi/210 Pb示踪剂的全面演示和测试是必要的，然后再进行任何一般应用的示踪剂，研究过程速率。该项目将支持两名本科生作为现场和实验室助理在夏季和一个MS研究生在本项目的持续时间。样品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：（一）证明测量水生系统中210 Pb-210 Bi-210 Po放射性核素三重组合的简单技术的实用性;（ii）表明在一个动态和“校准”的近岸系统中，210 Bi/210 Pb衍生粒子通量与234 Th/238 U衍生粒子通量是一致的;和（iii）表明在不同的颗粒浓度和有机质含量的条件下，在溶解氧浓度梯度上，210 Bi的原位Kd大于210 Pb的原位Kd。由于方法的限制，近岸清除过程长期研究不足。基于210 Bi/210 Pb不平衡，开发一种相对容易测量和广泛存在的粒子示踪剂，将允许未来动态粒子循环的过程研究，这对于理解全系统化学以及与营养状态、缺氧、有害藻华管理相关的实际问题至关重要。该奖项反映了NSF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.