wAbstract
@The SWAT model was used to model the impacts of climate, soils
and agricultural practices on nitrate flows in a 1310 km2
catchment in western France. Spatialized data were used for natural
features (climate, soil, topography), while agricultural activities,
finely represented by crop sequences over 3 years, and their associated
cultural practices were mapped by remote sensing. The model was
calibrated and validated for discharge and nitrate flows at a
gauging station. Results are analyzed with respect to leaching
for each crop sequence and for each soil type, as nitrate leaching
is highly sensitive to the soil and the crop sequence. The lowest
risks were found in clayey soils and the highest in sandy soils
and/or in sequences including maize. In collaboration with local
stakeholders, five scenarios of alternative practices were simulated
to evaluate their consequences for nitrogen flows: reduced fertilization,
catch crops, shallow cultivation, no-till with catch crops and
filter strips. The impacts of the conversion of a pasture into
wheat and rapeseed were also assessed. At the catchment gauging
station, our 9-year simulations showed a reduction in nitrate
flow of 8% with filters strips, 11% with catch crops, 12% with
no-till with catch crops, and 15% with reduced fertilization.
Shallow cultivation had no impact on nitrate flow. Inversely,
the conversion of temporary pastures, which accounts for 32% of
the catchment area, to cereals and rapeseed increased nitrate
flow by 18%. The impacts of each scenario varied in a accordance
with leaching at the parcel scale and with the proportion of area
affected by the practice. The results show that modelling can
improve our understanding of the impacts of agricultural practices
on water quality at different scales.
Keywords: Best management practices; Crop sequences; Soil; Nitrate;
Modelling; SWATx
1. Introduction
2. Materials and methods
@2.1. Study area
@2.2. Description of the SWAT model
@2.3. Model inputs
@@2.3.1. Meteorological data
@@2.3.2. Soil mapping
@@2.3.3. Crop sequence map
@@2.3.4. Cultural practices
@2.4. Model calibration and assessment
@2.5. Scenarios of alternative cultural practices
3. Results and discussion
@3.1. Model efficiency
@3.2. Hydrological processes and nitrate loads
@3.3. Simulations of alternative practices
4. Conclusions
Acknowledgments
References