  When turbulent flow is laden with negatively buoyant particles, their mean
distribution over the direction of gravity can induce stable density gradients
that penalize turbulent fluctuations. This effect is studied numerically for
shear-driven flow with dilute non-inertial sediment. The turbulent dynamics and
sediment transport depend critically on particle settling velocity $v_s$,
splitting into two regimes: homogeneous weakly stratified turbulence and flow
with developed turbulence atop an intermittent boundary layer. At intermediate
$v_s$, neither state can be sustained and the flow laminarizes.
