Radionuclide deposition in the Rhône River Prodelta (NW Mediterranean sea) in response to the December 2003 extreme flood

The extreme Rhône River flood that peaked in early December 2003 with water discharges as high as 11,500 m3 s− 1, induced major damage in southern France and transferred large amounts of radionuclides that were associated with suspended particulate matter such as 7Be, 137Cs and 210Pb. Specific marine locations in the close vicinity of the Rhône River Mouth were sampled three times in December 2003, February 2004 and April 2004 in order to quantify the consequences of flood events in the Rhône River Prodelta and to investigate the sedimentary depositional patterns through time. The 210Pbxs profile analyses in sediment revealed the existence of two particulate matter inputs, one that was related to the December extreme flood and the other to a peak flood of 4000 m3 s− 1 of water discharge that occurred in January 2004. The December event net deposition was assessed at 75 ± 19 GBq of 210Pbxs and 27 ± 2 GBq of 137Cs. The net deposition in response to the January 2004 flood event, although less damaging, is of the same order of magnitude to the December 2003 deposition, i.e. 71 ± 21 GBq of 210Pbxs and 16 ± 5 GBq of 137Cs. The sedimentary records of the December flood exhibited from the cores collected in December 2003, February 2004 and April 2004 are similar arguing for good environmental signal preservation through time but, the standard deviation of flood deposition estimate increases with time after the December flood event indicating a loss of accuracy with time.