that concentrations of the percolating flow to the Chalk aquifer can reach
10 μg L
À1 [39].
8 Perspectives
The reduction of the water resource contamination by pesticides remains a major
issue. The strategy of banning molecules has only shifted the problem to new and
unknown substances for which we have not yet identified the environmental effects.
Improving water quality and reducing impacts are new challenges involving limiting
and banning the use of these new substances. This requires a deep change in
agricultural practices and systems. Organic agriculture is a typical agriculture system
which bans chemical molecules of pesticides as well as mineral fertilisation. However, this agriculture accounts for only 2% of the agricultural land use in the Paris
basin [82].
Even if this solution would be preferable for the environment and human health,
buffer zones and grass strips can be used over the short term to reduce pesticide
transfer [83–85]. In the case of the Seine catchment, about 20% of arable soils are
drained, depending on soil waterlogging characteristics. Sub-surface drained areas
are mainly covered with redoxic or reductic degraded luvisol. In this context, the
management of sub-surface drained water is important to reducing the impact of
agriculture’s activities on water quality. An experiment conducted since 2012 near
the Orgeval basin led to co-constructing, with local stakeholders, a set of four
artificial wetlands implemented between the outlet of sub-surface buried pipes and
the receiving waterbody. The ratio between the area of what the farmers accepted to
convert into artificial wetland and the total cultivated areas (355 ha) was established
at 0.20%. A 3-year evaluation of the removal rate of pesticides from surface water
showed a reduction of about 30% of pesticides from agricultural plots and surface
waterbodies by artificial wetlands, with, however, a high variability depending on
(1) the pesticides’ properties, (2) temperature dependency and (3) the hydraulic
residence time. By extension of this in situ monitoring, the recommended ratio to
adequately design artificial wetlands was evaluated at 1% for an objective of 70%
pesticide removal from drained water. However, even if artificial wetlands are
constructed at the recommended ratio on the Seine basin, it would not be able to
solve pesticide contamination, because a large proportion of pesticides are directly
transferred from fields to groundwater.
A mechanic modelling approach would help assess the risk of pesticide transfer in
a watershed and explore scenarios of changing agriculture. However, several difficulties have been noted: (1) correctly representing past uses, (2) documenting the
long-term behaviour of an active ingredient in a large watershed and (3) identifying
the effect of changes in agricultural practices on pesticide transfer.
In that case, other parameters must be taken into account such as trajectories of
pesticide uses and landscape changes regarding agricultural activities. The new
national BNV-D database indicating sales of pesticides, available since 2008
How Should Agricultural Practices Be Integrated to Understand and. . .
157
10 μg L
À1 [39].
8 Perspectives
The reduction of the water resource contamination by pesticides remains a major
issue. The strategy of banning molecules has only shifted the problem to new and
unknown substances for which we have not yet identified the environmental effects.
Improving water quality and reducing impacts are new challenges involving limiting
and banning the use of these new substances. This requires a deep change in
agricultural practices and systems. Organic agriculture is a typical agriculture system
which bans chemical molecules of pesticides as well as mineral fertilisation. However, this agriculture accounts for only 2% of the agricultural land use in the Paris
basin [82].
Even if this solution would be preferable for the environment and human health,
buffer zones and grass strips can be used over the short term to reduce pesticide
transfer [83–85]. In the case of the Seine catchment, about 20% of arable soils are
drained, depending on soil waterlogging characteristics. Sub-surface drained areas
are mainly covered with redoxic or reductic degraded luvisol. In this context, the
management of sub-surface drained water is important to reducing the impact of
agriculture’s activities on water quality. An experiment conducted since 2012 near
the Orgeval basin led to co-constructing, with local stakeholders, a set of four
artificial wetlands implemented between the outlet of sub-surface buried pipes and
the receiving waterbody. The ratio between the area of what the farmers accepted to
convert into artificial wetland and the total cultivated areas (355 ha) was established
at 0.20%. A 3-year evaluation of the removal rate of pesticides from surface water
showed a reduction of about 30% of pesticides from agricultural plots and surface
waterbodies by artificial wetlands, with, however, a high variability depending on
(1) the pesticides’ properties, (2) temperature dependency and (3) the hydraulic
residence time. By extension of this in situ monitoring, the recommended ratio to
adequately design artificial wetlands was evaluated at 1% for an objective of 70%
pesticide removal from drained water. However, even if artificial wetlands are
constructed at the recommended ratio on the Seine basin, it would not be able to
solve pesticide contamination, because a large proportion of pesticides are directly
transferred from fields to groundwater.
A mechanic modelling approach would help assess the risk of pesticide transfer in
a watershed and explore scenarios of changing agriculture. However, several difficulties have been noted: (1) correctly representing past uses, (2) documenting the
long-term behaviour of an active ingredient in a large watershed and (3) identifying
the effect of changes in agricultural practices on pesticide transfer.
In that case, other parameters must be taken into account such as trajectories of
pesticide uses and landscape changes regarding agricultural activities. The new
national BNV-D database indicating sales of pesticides, available since 2008
How Should Agricultural Practices Be Integrated to Understand and. . .
157