Velocity and concentration distributions in turbulent odor plumes in the presence of vegetation mimics: a flume study

Abstract

Many marine animals use olfaction to search for vital resources (e.g. food, mates), and their success depends on the complex structure of turbulent odor plumes. To better understand chem- ically mediated interactions it is necessary to empirically measure the relationship between turbulent water flow and odor distribution in a variety of settings. Marsh edge habitats are important nursery and foraging areas for resident and transient estuarine species. The presence of emergent vegetation in these habitats can have a strong influence on the ambient turbulence regime, as well as the dis- persal of water-borne odors. To quantify the effects of vegetation-like structure on odor dispersal, I measured velocity and concentration fluctuations in artificial 'odor' plumes created in a laboratory flume. Time-series measurements of velocity and concentration were made simultaneously at the same spatial location using a thermistor flowmeter combined with a conductivity microprobe. Flow speed (advection) controlled odor dilution and odor filament dispersal throughout the plume; plumes generated in 5 cm s -1 flows had higher mean concentrations, and were characterized by fewer odor filaments that were more concentrated and of longer duration than plumes generated in 12 cm s -1 flows. In contrast, adding Spartina alterniflora mimics upstream of the plume source primarily altered odor filament properties; the presence of upstream structure created more abundant odor filaments that were more dilute and of shorter duration relative to smooth-bottomed treatments. Importantly, such changes to the odor plume structure can alter the success of odor mediated search, although further studies are needed to show if this effect will be positive or negative.