Impact of a highly contaminated river on a more important hydrologic system: changes in organic markers.

The Fensch River is a tributary of the Moselle River. It is a highly contaminated river that drains an industrial area. The objective of this preliminary study is to determine its impact on the Moselle River by analysing the extractable organic matter (EOM) coming from the sediments at the molecular scale. EOM is described in term of aromatic hydrocarbons, aliphatic hydrocarbons and polar compounds. EOM coming from Fensch River sediments is mainly composed of anthropogenic molecules. Aromatic hydrocarbons are dominated by parent Polycyclic Aromatic Hydrocarbons (PAHs) underlining the pyrogenic origin of this fraction. Aliphatic hydrocarbons consist of diagenetic hopanes and a broad UCM that are characteristics of thermal mature organic matter. Upstream the confluence the EOM of the Moselle River is mainly from vegetal origin. It is composed of high molecular weight n-alkanes with an odd over even predominance, degredation products of phytol and stigmasterol. The occurrence of PAHs and diagenetic hopanes underlines that the Moselle River is already contaminated before the confluence. The Fensch River input drastically changes the EOM of the Moselle River. Amount of PAHs is doubled and the fingerprints of both aliphatic hydrocarbons and polar compounds highlight the combination of both natural and anthropogenic sources.