Organic compounds and Trace Metal Elements in the Eure River Watershed: Past and actual records of anthropogenic impacts

Abstract : The Eure River (Normandie, France) is the main tributary of the Seine River downstream. Formerly the Martot Dam blocked the Eure River waters less than 1 km upstream the Eure-Seine Rivers confluence. But, in the context of the European Water Framework Directive (2000/60/EC), the French Authorities removed the Martot Dam in October 2017. A hydraulic annex (called the Martot Pond) is located ~300 m upstream the ex-location of the Martot Dam, wherein sediments are stored since several decades.The study aims to evaluate the dam removal impacts on (i.) re-suspension of contaminated sediments stored in the Martot Pond and the Eure River’s channel and (ii.) hydro-sedimentary transfers in Eure River.Concerning past transfers and sediments accumulation in the Eure River Watershed, sedimentary archives have been cored, before dam removal, at the Martot Pond and the Les Damps Pond (located 10 km upstream the latter). Dating of sedimentary cores for both ponds indicates a sedimentation rate around 1 cm y-1. Organic compounds (PAHs, PCBs and Organochlorine Pesticides) and Trace Metal Elements (TME) showed a wide contamination with highest concentrations evidenced during the 1950-1960’s and the 1990-2000’s. These variations of concentrations along cores can be associated with agricultural and industrial past of the Eure River Watershed and sources of contamination could be identified. Concerning actual transfers, Suspended Particulate Matter (SPM) are monthly sampled using Time-Integrated Mass-flux Sediments Samplers (TIMS Samplers). Suspended Particulate Matter sampling in the Eure River began before dam removal in two sites: between the Martot Dam and the Martot Pond and at Les Damps site. Particulate concentrations of organic compounds and TME allow us to determine (i.) actual SPM transfers quality (ii.) contaminants fluxes before, during and after dam removal and (iii.) contaminated sediments re-suspension from the Martot Pond and the Eure River’s channel.