reduced (Fig. 2b), with P balance becoming even negative in recent periods (Fig. 9a),
but the legacy of accumulated P is large enough to keep sustaining high crop
productivity for one decade or more [44].
Comparing the regional estimates of cumulated P storage with the data reported
by Delmas et al. [43], providing the distribution of measured total P concentration in
agricultural soil at the scale of France (Fig. 9c), reveals that the inherited amount of P
in cropland accounts for 7–80% of the total stock, with an average value of 23% over
the Seine basin (Fig. 9d).
5 Hydrosystem Response to Agricultural Trajectories
Groundwater quality closely reflects the trends of agriculture changes, particularly
regarding nitrate concentration, but also pesticide contamination which is dealt with
in detail in chapter “How Should Agricultural Practices Be Integrated to Understand
and Simulate Long-Term Pesticide Contamination in the Seine River Basin?” As far
as surface water quality is concerned, both diffuse sources from agriculture and point
sources from urban wastewater together determine their level of contamination. All
along the continuum from land to river and to sea, a cascade of transfer, retention and
elimination processes affects the budget of nutrients and their ultimate delivery at the
outlet of the watershed.
-200
0
200
400
600
800
1000
1850
1900
1950
2000
stock P, kgP/ha
cumulated cropland P balance
(corrected for erosion)
Br
N-PdC
L Am
LC
L Av
Pic
B
M
SM
CO
Gde L
IdF
E
E&L
Current stock
(<30cm):
3865 kgP/ha
pre-industrial
stock:
2970 kgP/ha
Br
L Am
LC
L Av
Pic
B
M
SM
CO
Gde L
IdF
E
E&L
% du stock actuel
< 5 %
5 – 15 %
15 – 25 %
25 – 50 %
50 – 75 %
75 – 100%
Inherited fraction of current Pstock
Ptot
mgP/kgsol
< 600
600 - 700
700 - 800
800 - 900
900 - 1000
> 1000
Current P Stock
(<30cm)
% current P stock
a.
b.
c.
d.
inherited: 23%
-10
0
10
20
30
40
50
1850
1900
1950
2000
P balance, kgP/ha/y
Cropland P balance
Fig. 9 (a) P balance of cropland soils of the Seine watershed estimated from the GRAFS approach
over the 1852–2015 period. (b) Accumulation of P in cropland soil estimated from the cumulated P
balance corrected for net erosion losses. (c) Current total P concentration in cropland soils of the
Seine basin, according to Delmas et al. [43]. (d) Inherited fraction of total P in cropland soils
104
G. Billen et al.
but the legacy of accumulated P is large enough to keep sustaining high crop
productivity for one decade or more [44].
Comparing the regional estimates of cumulated P storage with the data reported
by Delmas et al. [43], providing the distribution of measured total P concentration in
agricultural soil at the scale of France (Fig. 9c), reveals that the inherited amount of P
in cropland accounts for 7–80% of the total stock, with an average value of 23% over
the Seine basin (Fig. 9d).
5 Hydrosystem Response to Agricultural Trajectories
Groundwater quality closely reflects the trends of agriculture changes, particularly
regarding nitrate concentration, but also pesticide contamination which is dealt with
in detail in chapter “How Should Agricultural Practices Be Integrated to Understand
and Simulate Long-Term Pesticide Contamination in the Seine River Basin?” As far
as surface water quality is concerned, both diffuse sources from agriculture and point
sources from urban wastewater together determine their level of contamination. All
along the continuum from land to river and to sea, a cascade of transfer, retention and
elimination processes affects the budget of nutrients and their ultimate delivery at the
outlet of the watershed.
-200
0
200
400
600
800
1000
1850
1900
1950
2000
stock P, kgP/ha
cumulated cropland P balance
(corrected for erosion)
Br
N-PdC
L Am
LC
L Av
Pic
B
M
SM
CO
Gde L
IdF
E
E&L
Current stock
(<30cm):
3865 kgP/ha
pre-industrial
stock:
2970 kgP/ha
Br
L Am
LC
L Av
Pic
B
M
SM
CO
Gde L
IdF
E
E&L
% du stock actuel
< 5 %
5 – 15 %
15 – 25 %
25 – 50 %
50 – 75 %
75 – 100%
Inherited fraction of current Pstock
Ptot
mgP/kgsol
< 600
600 - 700
700 - 800
800 - 900
900 - 1000
> 1000
Current P Stock
(<30cm)
% current P stock
a.
b.
c.
d.
inherited: 23%
-10
0
10
20
30
40
50
1850
1900
1950
2000
P balance, kgP/ha/y
Cropland P balance
Fig. 9 (a) P balance of cropland soils of the Seine watershed estimated from the GRAFS approach
over the 1852–2015 period. (b) Accumulation of P in cropland soil estimated from the cumulated P
balance corrected for net erosion losses. (c) Current total P concentration in cropland soils of the
Seine basin, according to Delmas et al. [43]. (d) Inherited fraction of total P in cropland soils
104
G. Billen et al.