Lagrangian coherent structures are associated with fluctuations in airborne microbial populations

Abstract

Many microorganisms are advected in the lower atmosphere from one habitat to another with scales of motion being hundreds to thousands of kilometers. The concentration of these microbes in the lower atmosphere at a single geographic location can show rapid temporal changes. We used autonomous unmanned aerial vehicles equipped with microbe-sampling devices to collect fungi in the genus Fusarium 100 m above ground level at a single sampling location in Blacksburg, Virginia, USA. Some Fusarium species are important plant and animal pathogens, others saprophytes, and still others are producers of dangerous toxins. We correlated punctuated changes in the concentration of Fusarium to the movement of atmospheric transport barriers identified as finite-time Lyapunov exponent-based Lagrangian coherent structures (LCSs). An analysis of the finite-time Lyapunov exponent field for periods surrounding 73 individual flight collections of Fusarium showed a relationship between punctuated changes in concentrations of Fusarium and the passage times of LCSs, particularly repelling LCSs. This work has implications for understanding the atmospheric transport of invasive microbial species into previously unexposed regions and may contribute to information systems for pest management and disease control in the future. We consider the nonlinear dynamics underlying fluctuations of airborne microbe populations, via hypothesis testing combining theoretical considerations of atmospheric dynamical structures with atmospheric sampling and microbiological analysis. Our goal is to provide a new language for discussion of transport and mixing of atmospheric pathogens, paving the way for new modeling and management strategies for the spread of infectious diseases affecting plants, domestic animals, and humans. The hypotheses considered are built on the observation that in environmental flows, chaotic dynamical structure makes efficient movement and dispersal of agents possible, whether these agents are biological, chemical, or engineered devices like sensor platforms or delivery vehicles. Despite the flow complexity, our results suggest that atmospheric Lagrangian coherent structures play a significant role in geometrically organizing the motion of long-range microbe transport.

Lagrangian coherent structures and inertial particle dynamics

“…Previous studies have investigated inertial particles using FTLE for varying Stokes number for airborne microbes [55,56], urban flows [58,57], accumulation of inertial particles in the wake of a square cylinder [25], dissipative transport in the ocean [9], evasive motion of plankton fleeing predators [38], and identifying inertial slow manifolds in hurricane dynamics [48]. It is noteworthy to mention the more general treatment of these techniques by Haller and Sapsis [24].…”

Lagrangian based methods for coherent structure detection

“…Another atmospheric application of FTLE ridges looked into the impact of Lagrangian transport structures on airborne microbial populations. 70 In conjunction with atmospheric calculations, a remote control aircraft was flown through different regions collecting samples of the microbial populations; the authors were able to identify significant shifts in the population sizes either side of an FTLE surface. Because atmospheric Lagrangian structures can play a significant role in airborne transport, further studies were made investigating the uncertainty of the FTLE calculation and the contributions of unresolved turbulence and other forecast uncertainties.…”

Detection of a surrogate biological agent with a portable surface plasmon resonance sensor onboard an unmanned aircraft system

“…Fast response time is essential for sampling activities ranging from localized spore tracking to large-scale contaminant mapping, improving our ability to predict the spread of airborne constituents (Koch et al 2000). In recent studies, various BTAs have been shown to travel great distances within the atmospheric boundary layer in short amounts of time, underscoring the importance of fast-response sensing methods (Schmale et al 2008;Tallapragada et al 2011). An anthrax attack simulation conducted by Wein et al (2003) showed that an improved detection time would directly result in a lower fatality rate given a release near a populated area.…”