Origins and trend of radionuclides within the lower Rhône River over the last decades

Abstract

-Geological and climatic diversity leads to significant spatial variability of naturally occurring radioactivity levels, whether in soils, sediments or natural waters. The activity level of Rhône sediments is estimated at 1450 Bq/kg, between the levels observed in the Loire (1925 Bq/kg) and Seine (730 Bq/kg). The largest amounts of radioactive effluent from nuclear facilities concern tritium, for which activity levels are currently 1000 times higher than the sum of artificial gamma emitters discharged. The proportions of naturally occurring 14 C and 3 H in the lower reaches of the River Rhône are estimated at 50 to 70% and <5%, respectively, with the remaining amount coming from nuclear facilities. Long-term records from River Rhône monitoring show that the level of radioactive contamination from artificial sources declined sharply starting in the early 90s, with the level divided by 10 to 100 depending on the element. Radioactivity of natural origin remained unchanged as expected.

Origin of remineralized organic matter in sediments from the Rhone River prodelta (NW Mediterranean) traced by Δ 14 C and δ 13 C signatures of pore water DIC

“…Cathalot et al (2013) reported a range between À90 and +150‰ for river flows above 2000 m 3 /s, but in extreme cases with low water discharge, enrichments up to +596‰ have been measured (Toussaint, 2013). Eyrolle et al (2015) reported maximal activities of +300‰ in the Rhone River POM. The comparison of the d 13 C and D 14 C signatures of pore waters, surface sediment and SPM in the Rhone River and in the delta together with literature data shows that the organic matter mineralized in prodelta sediments lies outside the known pools (Fig.…”

“…Its drainage basin is dominated by ancient soils and carbonates that lead to a naturally low D 14 C signature of DIC and suspended particles. The natural D 14 C signature of riverine primary production, which should be low, is actually increased by the presence of nuclear power plants that release 14 C-rich effluents mostly under the DIC form into the Rhone River (Eyrolle et al, 2015), which can rapidly be incorporated into POC by photosynthesis in the river as shown in the Loire River (Coularis, 2016).…”

“…The release of radiogenic material into the river basin is legally allowed at discrete time intervals (149 GBq in 2010; Eyrolle et al, 2015) but data about the periods of such releases are not available and quantifying their impacts is therefore very difficult. In the absence of similar studies in the Rhone River, we can only suppose that the same phenomenon occurs as a consequence of nuclear activities, and that the D 14 C signature of the riverine POM deposited in proximal sediments can be high at certain periods.…”

“…The Rhone River is the largest contributor of water and terrestrial POM to the NW Mediterranean (Pont et al, 2002) and discharges in the Gulf of Lions (Sempéré et al, 2000;UNEP/MAP/ MED-POL, 2003). Its drainage basin hosts 14 nuclear power reactors grouped in 4 nuclear plants and a former reprocessing plant which legally discharge effluents containing 14 C in the Rhone River (Eyrolle et al, 2015). This enriched 14 C (mostly in the form of DIC) can be transferred to vegetation and river phytoplankton (Fontugne et al, 2002;Coularis, 2016) and can be used as a tracer of in stream production.…”

Isotopic Signature (δ13C, ∆14C) of DIC in Sediment Pore Waters: An Example from the Rhone River Delta

“…The Rhone River is one of the most nuclearized rivers in Europe. Fourteen nuclear power reactors grouped in four nuclear plants are located all along the Rhone River and legally discharge cooling water containing 14 C enriched dissolved inorganic carbon (DIC) (Eyrolle et al 2015; Jean-Baptiste et al 2018a). The isotopic signature of this DIC can be rapidly transferred to the autotrophic OM pool of the river by photosynthesis of plankton and algae (Fontugne et al 2002; Coularis et al 2016).…”