Evaluating the impact of oscillating light and mechanics on bacterial community composition in migrating and stable riverbed forms

In lowland streams, sandy sediments can be transported in the form of migrating ripples. Microorganisms living on these sandy grains are affected by two main environmental factors: mechanical stress during migration, which causes biofilm abrasion, and alternating light-dark cycles during periods of rest. We conducted two laboratory experiments to determine the impact of ripple migration and alternating light on the biofilm activity and community structure. Sediment samples were collected from the Spree river in Germany in May and July. The first experiment examined the effect of three different migration velocities under similar light conditions. The second experiment compared migrating and stationary sediments under constant or oscillating light exposure.