Box 3
Coupling agrosystems and hydrosystems from headwater to estuary by a
model cascade for nitrogen, phosphorus and carbon circulations.
GRAFS model calculates N, P and C budgets in agricultural systems
[18]. From N surplus, it generates nitrate leaks into the unsaturated zone
[19] and into the atmosphere (N 2 O, a greenhouse gas; [20]). It operates from
the farm scale (e.g. crop rotation, nitrogen uptake by crops, imports/exports of
fertilizers, feed and food, recycling of organic residues). This diffuse nitrate is
addressed in the Riverstrahler model, a semi-spatialized model organized by
stream order that transfers the N products across the river continuum. Lateral
groundwater river inputs of nitrate and local denitrification in the riparian zone
are taken into account. In the river, the biogeochemical reactivity of C, N, P
and Si species is handled by the RIVE model.
Ten-day river fluxes to the Seine estuary and to small coastal rivers are then
used by the coastal zone biogeochemical model ECOMARS-3D, which was
developed by marine scientists [21, 22]. This model simulates estuary functioning, from Poses to Honfleur and the Bay of Seine (Fig. 4). After crossing
the estuarine filter, the impact at the coastal zone of the net nutrient fluxes can
be evaluated in terms of eutrophication and harmful algal proliferation. It took
almost three decades and millions of Euros for around a dozen scientists to
build and operationalize such a chain of models, which has been conceptualized by biogeochemists since the 1990s.
The challenge in terms of modelling the biogeochemical functioning of
aquatic environments is multiple: (1) to project at multiregional scales capable
of including all contributory hydrosystems from headwaters to coastal zones
by proposing a quantification of flows at sea and (2) to represent at various
scales the microscopic processes operating in the aquatic continua that ultimately determine basic water quality (dissolved oxygen, ammonia, phosphorus, organic carbon, etc.). The scales considered by these models range from
microscopic physiological processes (bacterial activity, algal uptake of nutrients, etc.) to large spatial scales from small catchments (100 km
2 ) to
multiregional river basins (inputs to the North East Atlantic coast,
1,000,000 km
2 ).
3.2 Models Are Used to Support Management Decisions
Primarily seen as research tools, models indeed allow for a better scientific understanding of the functioning of the Seine River basin while also supporting
392
C. Carré et al.
Coupling agrosystems and hydrosystems from headwater to estuary by a
model cascade for nitrogen, phosphorus and carbon circulations.
GRAFS model calculates N, P and C budgets in agricultural systems
[18]. From N surplus, it generates nitrate leaks into the unsaturated zone
[19] and into the atmosphere (N 2 O, a greenhouse gas; [20]). It operates from
the farm scale (e.g. crop rotation, nitrogen uptake by crops, imports/exports of
fertilizers, feed and food, recycling of organic residues). This diffuse nitrate is
addressed in the Riverstrahler model, a semi-spatialized model organized by
stream order that transfers the N products across the river continuum. Lateral
groundwater river inputs of nitrate and local denitrification in the riparian zone
are taken into account. In the river, the biogeochemical reactivity of C, N, P
and Si species is handled by the RIVE model.
Ten-day river fluxes to the Seine estuary and to small coastal rivers are then
used by the coastal zone biogeochemical model ECOMARS-3D, which was
developed by marine scientists [21, 22]. This model simulates estuary functioning, from Poses to Honfleur and the Bay of Seine (Fig. 4). After crossing
the estuarine filter, the impact at the coastal zone of the net nutrient fluxes can
be evaluated in terms of eutrophication and harmful algal proliferation. It took
almost three decades and millions of Euros for around a dozen scientists to
build and operationalize such a chain of models, which has been conceptualized by biogeochemists since the 1990s.
The challenge in terms of modelling the biogeochemical functioning of
aquatic environments is multiple: (1) to project at multiregional scales capable
of including all contributory hydrosystems from headwaters to coastal zones
by proposing a quantification of flows at sea and (2) to represent at various
scales the microscopic processes operating in the aquatic continua that ultimately determine basic water quality (dissolved oxygen, ammonia, phosphorus, organic carbon, etc.). The scales considered by these models range from
microscopic physiological processes (bacterial activity, algal uptake of nutrients, etc.) to large spatial scales from small catchments (100 km
2 ) to
multiregional river basins (inputs to the North East Atlantic coast,
1,000,000 km
2 ).
3.2 Models Are Used to Support Management Decisions
Primarily seen as research tools, models indeed allow for a better scientific understanding of the functioning of the Seine River basin while also supporting
392
C. Carré et al.