Trajectories of river chemical quality issues over the Longue Durée: the Seine River (1900S-2010).

River quality trajectories are presented for (i) organic pollution, (ii) eutrophication, (iii) nitrate pollution, and (iv) metal contamination over the Longue Durée (130 to 70 years). They are defined by a quantified state indicator (S) specific to each issue, compared to drivers (D) or pressures (P) and to social responses (R) that reflect the complex interactions between society and river quality. The Lower Seine River, naturally sensitive to anthropogenic pressures, greatly impacted by Paris urban growth, industrialization, and intensive agriculture, and well documented by the PIREN-Seine 25-year research program, was chosen to illustrate these trajectories. State indicators, dissolved oxygen, algal pigments, nitrate, and heavy metals (Cd, Cr, Hg, Pb, Zn) in sediments have only been monitored by river basin authorities since 1971. Therefore, their past changes have been reconstructed using three approaches: (i) reassessment of historical sources, (ii) pressure-state models that reconstruct past water quality, and (iii) sedimentary archives of past persistent contamination from dated floodplain cores. The indicators were then transformed into river quality status using contemporary water quality criteria throughout these records. Each environmental issue shows specific trajectories because each has its own relationship between the issue evidence and the social response, but all are characterized by very poor quality in the past, largely ignored: the long-term summer hypoxia (<1880-1995), the summer eutrophication peak (1965-2005), the growing nitrate level since the 1950s, recently stabilized but still high, and the extreme metal contamination (>1935-2000) that peaked in the 1960s. The efficiency of social responses has been highly variable but more efficient in the last 15-25 years.

Severe and contrasted polymetallic contamination patterns (1900-2009) in the Loire River sediments (France).

The Loire River basin (117,800 km(2), France) has been exposed to multiple sources of metals during the last 150 years, originating from major mining districts (coal and non-ferrous metals) and their associated industrial activities. Geochemical archives are established here from the analysis of a 4m sediment core in the downstream floodplain and then compared to stream bed sediments from pristine monolithological sub-basins and from bed and bank sediments in impacted tributaries. The contamination is assessed for 55 major and trace elements through their enrichment factors to Al (EF), normalized to the pre-anthropogenic background. Archives from 1900 to 2009 show enrichment (EF<1.3) not only for Ba, Be, Cs, Ga, Rb, REE, Sr, V, and Zr but also for U and Th, despite U mining activities until the 1990s. From 1900 to 1950, the level of contamination is severe for Hg, Au, Ag (10