Quantifying the resuspension of sediment and associated metallic contaminants with fallout radionuclide measurements in a channelized river draining an industrial catchment

Abstract

Contamination of river sediment reaches problematic levels in industrialised regions. This study investigates the relevance of using beryllium-7 (7Be), a short-lived environmental radionuclide (53 days half-life), for quantifying the deposition and resuspension of sediment and associated metallic contaminants in a heavily polluted channelized river of Northern France (The Lower Scarpe River). Activities in 7Be were measured in bed and suspended sediments collected each month over a hydrological year. Suspended sediments were analysed for metal contents (Pb, Zn, Cd, Cu). The determination of short-term sediment dynamics is based on the variation of total 7Be inventory between two successive samplings. Total inventory of 7Be consists of two components, i.e., the residual inventory and the new inventory. Inventories of 7Be in sediment varied from 1 to 135 mBq cm−2. Observed spatial and temporal variations reflected the dynamic behaviour of sediment in the studied channel section. The succession of sediment deposition and resuspension periods was demonstrated during the study, with maximum deposition and erosion rates of 0.3 ± 0.2 and −0.46 ± 0.05 g cm−2 month−1, respectively. A sediment resuspension rate of 0.06 g cm−2 month−1 supplied to the water column a flux of 12, 13, 23 and 145 μg cm−2 month−1 of Cd, Cu, Pb and Zn, respectively. During this 15-month study, 28 to 50 % of Pb that was deposited in the riverbed sediment was resuspended, thereby contributing to the (short term) degradation of water quality. The present work provides a useful tool for examining the role of sediment as a sink or source of contamination for the water column. It produces knowledge of how sediment processes affect the fate and the transport of contaminants and the implications for future downstream fluxes.