Intermittent riverine resuspension: Effects on phosphorus transformations and heterotrophic bacteria

Andreas Kleeberg, Michael Hupfer, Giselher Gust, Ivette Salka, Kirsten Pohlmann and Hans-Peter Grossart

Limnol. Oceanogr., 58(2), 2013, 635-652 | DOI: 10.4319/lo.2013.58.2.0635

ABSTRACT: Intermittent riverine resuspension (IRR), a common phenomenon, was applied to investigate its effects on sedimentary resources availability and bacteria in the water column. This lab experiment used organic-rich lowland river sediment in a newly designed erosion chamber, the Benthic Water Column Simulator, generating well-defined ratios of shear velocity u* to turbulence intensity. Eight consecutive resuspension events, 1–8, were initiated at u* = 1.1 cm s−1. Sedimentary and phosphorus entrainment decreased from 20.4 g m−2 h−1 and 111.6 mg m−2 h−1 at event 1 to 1.31 g m−2 h−1 and 18.7 mg m−2 h−1 at event 8, suggesting an exhaustion of particulate and dissolved sediment constituents. Entrainment of particle-associated (PA) bacteria (132.7 × 109–251.1 × 109 cells m−2 h−1) was strongly correlated to that of particles. Free-living (FL) bacteria (−27.6 × 109–36.4 × 109 cells m−2 h−1) were fractionally entrained. Numbers of PA bacteria remained low after each event, whereas those of FL bacteria strongly increased 5–15 h after an event because of growth due to increased availability of dissolved organic carbon and inorganic nutrients following each event. FL bacteria community structure also changed during IRR. The systematic changes over consecutive IRR cycles show a strong effect in all considered parameters that elude the typical single-event, steady-state experiments. IRR should thus be considered in two respects: experimental protocols on riverine water quality should be revised. In ecosystem modeling, IRR should be considered to better predict extent and effect of resuspension. Only IRR adequately reflects the natural interplay between hydrodynamics and organisms in rivers.

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