TY - JOUR A1 - Scheidweiler, David A1 - Mendoza‐Lera, Clara A1 - Mutz, Michael A1 - Risse‐Buhl, Ute T1 - Overlooked Implication of Sediment Transport at Low Flow: Migrating Ripples Modulate Streambed Phototrophic and Heterotrophic Microbial Activity Y1 - 2021-03-17 VL - 57 IS - 3 JF - Water Resources Research DO - 10.23689/fidgeo-4404 N2 - Sandy streambeds are mobile even at low flow velocities at which sediments can be transported as bedload, more specifically as migrating ripples. Small variations in discharge can result in transitions between sediment transport and no‐transport. Despite being inherent processes of streams and rivers, the effect of sediment transport and transport regime transition on the phototrophic and heterotrophic activity of streambed microbial communities remains unclear. We performed a microcosm experiment mimicking sediment transport as migrating ripples (i.e., migrating) and no sediment transport (i.e., stationary), and their transition to observe the response of the phototrophic and heterotrophic microbial community. Both net community production and community respiration were respectively 77% and 40% suppressed in migrating sediments compared to stationary sediments. In migrating sediments, a combination of mechanical stress, light limitation, and limited habitable area likely hampered microbial metabolism. Stationary conditions facilitated an active community of phototrophs, mainly diatoms, as indicated by high net community production, high rates of dissolved organic carbon release and silicon retention. After transitioning migrating to stationary and vice versa, differences were maintained regardless of the change in mechanical stress and associated stressors, most likely as a result of the interaction between their antecedent transport conditions and developmental stage that shaped the microbial community. Our results indicate that sediment transported as migrating ripples at low flow velocity can strongly modulate streambed metabolism, and discharge oscillations resulting in sediment transport transitions will result in a mosaic of microbial activity and biomass that will emerge at larger scales determining reach‐scale metabolism. N2 - Key Points: A microcosm approach was used to identify the effect of ripple migration on the metabolism and composition of microbial communities. Migrating ripples hampered the phototrophic and heterotrophic community respiration, net production, and composition. The influence of transition from (to) migrating ripple to (from) stationary sediment was modulated by community developmental stage. UR - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/8750 ER -