Long-term accumulation of metals and persistent pollutants (PAHs, PCBs, organochlorine pesticides) from Eure river watershed (France) in sediments: possible consequences of a dam removal

Abstract : The Dam of Martot in Eure (France) will be destroyed in order to restore the ecological continuity but removal impacts of such small structures remain poorly studied. The aim of this study is (i) to characterize the variability and the origin of the hydro-sedimentary transfers, (ii) to determine the history, at a decadal scale, of the pollution emitted in the watershed of the Eure River, by analyzing the sediment stored in the Martot’s pond upstream the dam and (iii) to predict the hazards of the dam removal.Present day sedimentary transfers were assessed from high frequency measurements from two sampling sites while past transfers were reconstructed by analyzing sediment archives taken from the Martot’s pond (hydraulic annex). The analysis of present day hydro-sedimentary transfers showed a strong variability of water and sediment discharges where main forcing are rainfall, water depth and tidal cycles from the Seine estuary. On sedimentary archives, sedimentological analysis (macroscopic description, spectrophotometry, magnetic susceptibility…) identified two heterogeneous facies. The use of radionuclides for dating the sediment suggests that this transition date of 1942. This change is related to river management policy that led the annex first to trap sediments from the Seine River, and then those from the Eure River. High resolution analysis of the metal composition of the sediments by X-ray fluorescence showed two origins of the sedimentary transfers: one component is linked to soil erosion and a second highlight an anthropic contribution. It appeared that the sedimentation rate remains unchanged since the 40’s suggesting a simple relationship between the sediment depth and the year of contamination.XRF core scanning is not quantitative, it allowed to compare different levels of metal contamination, but not to determine accurate quantification. So other methods were developed to quantify some metallic and persistent organic pollutants accumulated in the sedimentary archive before and after 1942. Extractions or wet digestion were carried out in a micro-wave extractor. The analyses of organic pollutants (PAH, PCB and organochlorine pesticides) were performed with GC-MS, and heavy metals with ICP-OES. Our results showed that the most polluted fractions in the sediment core correspond to the Eure signal, with however a different timing according to the pollutant: a majority of them were particularly concentrated in the fractions accumulated in the 50’s (economic development after the World War II), whereas the lead was more concentrated on the top of the sediment core. Some other pollutants, such as PCB or Lindane, presented unusual high punctual pollution peaks around their prohibition of sale.In conclusion, this archive can track the human impact on the watershed since 1942. However, it is strongly expected that the dam removal would provoke some significant changes in the hydro-sedimentary characteristics of the Eure River. So the pollutants stored in sediments could be remobilized in the river. As a consequence, it will be necessary to evaluate the overall pollutants stock in the Martot’s pond, as well as the sediments dynamics and the risk of contamination of the Eure River after the dam removal
Complete list of metadatas

https://hal.archives-ouvertes.fr/hal-01855438
Contributor : Thomas Gardes <>
Submitted on : Tuesday, August 7, 2018 - 8:14:32 PM
Last modification on : Friday, April 5, 2019 - 8:08:47 PM

Identifiers

  • HAL Id : hal-01855438, version 1

Citation

Thomas Gardes, Yan Laberdesque, Edouard Patault, Maxime Debret, Yoann Copard, et al.. Long-term accumulation of metals and persistent pollutants (PAHs, PCBs, organochlorine pesticides) from Eure river watershed (France) in sediments: possible consequences of a dam removal. 16th ICCE 2017, Jun 2017, Oslo, Norway. ⟨hal-01855438⟩

Share

Metrics

Record views

263

Files downloads

15