sources, particularly from major chemical industries, including P fertiliser production from phosphogypsum. The atmospheric inputs of contaminants are greater at the
core sites URB to EST [58].
Floodplain sites store the fraction of the sediment flux circulating during floods,
usually during winter, and act as a temporary sediment trap. The SPM transported by
high-flow and flood events in the Seine River, i.e. 10% of the time, was estimated for
the Marne River (12,900 km
2 ) at 60% of the total annual flux [30], and samples from
floodplains are therefore interesting candidates for the estimation of yearly fluxes.
At the Bassée floodplain, downstream of Troyes (URB), the sedimentation rate
35 m from the river channel is 10 mm year
À1 on average (5 mm year
À1 at 70 m), and
the flooding frequency is 1.6 year
À1 [30]. The Bouafles site, at the basin outlet
(OUT 1 ), underwent particular study, and 12 cores were retrieved between 2003 and
2010. It was clear in the field that the site was under active accretion, with large trees
buried above their roots. Unfortunately, in 2016, the inundated prairie was ploughed,
evidencing the issue of on-site conservation of the archives in strongly anthropic
basins.
The sampling strategy is completed by the assessment of the natural backgrounds.
For organic pollutants, the PRI core can be considered. For metals, a prehistoric
reference sediment (REF 1 ) is considered (Marne–Seine Rivers confluence at ParisBercy, dated 5,000 years BP). It is similar to another prehistoric estuarine sediment
(REF 2 ) [59].
3.4 Core Dating
With the notable exception of the cores from Chatou for which no age model could
be drawn, the cores exhibiting a clear chronology based on the measurement of
radioactive tracers,
137 Cs and
210 Pb (and
238 Pu for EST), were selected. All cores
were checked for a regular and fine-grain sedimentation profile. Core analyses are
detailed in the published papers quoted here.
4 The Evolution of the Seine River Basin Contamination
(1910–2015) Unveiled from Sediment Cores
4.1 Temporal Evolution of Persistent Organic Pollutants
at the Basin Outlet and in the Estuary
4.1.1 Evolution of the River Basin at Its Outlet
The vertical profiles are represented for a set of different pollutants in Fig. 3. Since
analyses provide multielemental contents for a given chemical family for each
sample, the individual results are often clustered and given as “sum of”. As the
280
S. Ayrault et al.
core sites URB to EST [58].
Floodplain sites store the fraction of the sediment flux circulating during floods,
usually during winter, and act as a temporary sediment trap. The SPM transported by
high-flow and flood events in the Seine River, i.e. 10% of the time, was estimated for
the Marne River (12,900 km
2 ) at 60% of the total annual flux [30], and samples from
floodplains are therefore interesting candidates for the estimation of yearly fluxes.
At the Bassée floodplain, downstream of Troyes (URB), the sedimentation rate
35 m from the river channel is 10 mm year
À1 on average (5 mm year
À1 at 70 m), and
the flooding frequency is 1.6 year
À1 [30]. The Bouafles site, at the basin outlet
(OUT 1 ), underwent particular study, and 12 cores were retrieved between 2003 and
2010. It was clear in the field that the site was under active accretion, with large trees
buried above their roots. Unfortunately, in 2016, the inundated prairie was ploughed,
evidencing the issue of on-site conservation of the archives in strongly anthropic
basins.
The sampling strategy is completed by the assessment of the natural backgrounds.
For organic pollutants, the PRI core can be considered. For metals, a prehistoric
reference sediment (REF 1 ) is considered (Marne–Seine Rivers confluence at ParisBercy, dated 5,000 years BP). It is similar to another prehistoric estuarine sediment
(REF 2 ) [59].
3.4 Core Dating
With the notable exception of the cores from Chatou for which no age model could
be drawn, the cores exhibiting a clear chronology based on the measurement of
radioactive tracers,
137 Cs and
210 Pb (and
238 Pu for EST), were selected. All cores
were checked for a regular and fine-grain sedimentation profile. Core analyses are
detailed in the published papers quoted here.
4 The Evolution of the Seine River Basin Contamination
(1910–2015) Unveiled from Sediment Cores
4.1 Temporal Evolution of Persistent Organic Pollutants
at the Basin Outlet and in the Estuary
4.1.1 Evolution of the River Basin at Its Outlet
The vertical profiles are represented for a set of different pollutants in Fig. 3. Since
analyses provide multielemental contents for a given chemical family for each
sample, the individual results are often clustered and given as “sum of”. As the
280
S. Ayrault et al.