4
8
12
16
mg O
2 l -1
1971
1975
1980
1985
1990
1995
2000
2005
2010
2015
2
4
6
8
10
mg N-NO
3 l -1
1971
1975
1980
1985
1990
1995
2000
2005
2010
2015
0
2
4
6
8
10
mg N-NH
4 l -1
0
2
4
6
8
0
1971
1975
1980
1985
1990
1995
2000
2005
2010
2015
0.5
1.0
1.5
2.0
2.5
mg P-PO
4 l -1
1971
1975
1980
1985
1990
1995
2000
2005
2010
2015
0
50
100
150
200
µg Chla l -1
1971
1975
1980
1985
1990
1995
2000
2005
2010
2015
2
4
6
8
10
mg Si l -1
1971
1975
1980
1985
1990
1995
2000
2005
2010
2015
0
0.0
0
0
Fig. 5 Long-term variations in observed concentrations of water quality (1971–2017) at the outlet
of the Seine basin (Poses): oxygen, nitrate, ammonium, phosphates, dissolved silica, phytoplankton
biomass (in chlorophyll a, Chla)
200
J. Garnier et al.