Sediment resuspension effects on dissolved organic carbon fluxes and microbial metabolic potentials in reservoirs

Sediment resuspension can affect water quality in lakes and reservoirs. We investigated the effect of sediment resuspension on benthic fluxes of dissolved organic carbon (DOC), metals (Fe, Mn), and nutrients (N, P) in three drinking water reservoirs using sediment core incubations. Measurement of Fe and Mn fluxes, and of microbial potentials to degrade organic substrates (Biolog EcoPlates T) were employed to understand mechanisms regulating DOC exchange after sediment resuspension. Single sediment resuspension events resulted in DOC fluxes [-104 (into sediment) to 46 (release) mmol m(-2) event(-1)] equal to 9-17 days of diffusive fluxes, making them a relevant process. Shallow reservoir sites were more likely to immobilize DOC after resuspension than deep sites. Sediment resuspension under anoxia always led to increases of DOC and metals in the overlying water. Resuspension did not necessarily mobilize nitrate or phosphorus even under anoxia, while ammonium was released after resuspension. Sediment resuspension increased hypolimnetic microbial potentials to utilize organic substrates in both spring and summer. However microbial cells counts and biomass either remained constant or decreased in summer. Adsorption to Fe minerals seemed to play a role in DOC immobilization as evidenced by a decrease in DOC: Fe molar ratios after resuspension in Fe limited sites and constant ratios in Fe rich sites. The results demonstrate a potential for DOC immobilization mainly by Fe minerals and to some extent by benthic microbes. Therefore, sediment resuspension can be beneficial for water quality in low nutrient, iron rich systems.