Jn. Mcnair et al., TURBULENT TRANSPORT OF SUSPENDED PARTICLES AND DISPERSING BENTHIC ORGANISMS - HOW LONG TO HIT BOTTOM, Journal of theoretical biology, 188(1), 1997, pp. 29-52
Turbulence plays an important role in the transport of particles in ma
ny aquatic systems. In addition to various types of inorganic sediment
(silt, sand, etc.), these particles typically include bacteria, algae
, invertebrates, and fine organic debris. In this paper, we focus on o
ne aspect of turbulent particle transport; namely, the average time re
quired for a suspended particle to reach the bottom of a waterbody fro
m a specified initial elevation. This is the mean hitting-time problem
, and it is important in determining, for example, the effect of turbu
lence on downstream transport of organic particles, dispersal times an
d dispersal distances of benthic invertebrates, and the utility of swi
mming by neutrally buoyant dispersal propagules. We approach this prob
lem by developing a stochastic diffusion model of particle transport c
alled the Local Exchange Model, which is an extension of a model posed
by Denny & Shibata (1989) in an earlier study of the same problem. We
show how the mean hitting-time of the Local Exchange Model varies wit
h factors such as a particle's fall velocity and the shape of the vert
ical profile in turbulent mixing. We also show how the mean hitting-ti
me is related to both the vertical profile in current velocity and the
vertical profile in concentration of suspended particles, and how the
se relationships can be exploited in testing the model. Among other th
ings, our results predict that, with the sole exception of neutrally b
uoyant particles that do not swim downward, there is always a region o
f the water-column in which turbulence increases rather than decreases
the mean hitting-time. We discuss the significance of this and other
results for dispersal by benthic organisms. (C) 1997 Academic Press Li
mited.