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Water pollution is a major global problem that requires ongoing evaluation and revision of water resource policy at all levels (from international down to individual aquifers and wells). It has been suggested that it is the leading worldwide cause of deaths and diseases, and that it accounts for the deaths of more than 14,000 people daily. In addition to the acute problems of water pollution in developing countries, industrialized countries continue to struggle with pollution problems as well. Water is typically referred to as polluted when it is impaired by anthropogenic contaminants and either does not support a human use, such as drinking water, and/or undergoes a marked shift in its ability to support its constituent biotic communities, such as fish. Natural phenomena such as volcanoes, algae blooms, storms, and earthquakes also cause major changes in water quality and the ecological status of water. Most water pollutants are eventually carried by rivers into the oceans.

Hydrologic cycle. --- Cycle, Hydrologic --- Hydrological cycle --- Water cycle --- Cycles --- Hydrology --- Hydrology & the hydrosphere

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Climate change stirs up more and more citizens’ interest and concern, and the role of greenhouse gases (GHG)
in climate change has now been widely discussed. The agricultural sector is pointed as one of the main causes of
climate change, mostly for its emissions of biogenic GHG. However, the impact of ecosystems environment and management
practices on these emissions is yet not fully understood, and the response of agroecosystems to a changing
environment is still questioned. This context highlights the necessity of studying and understanding ecosystem
dynamics in order to design climate change mitigation strategies. To do so, mechanistic models reproducing the
carbon, nitrogen and water cycles of ecosystems can be developed.
This thesis aims at modifying the ASPECTS model, developed by Rasse et al. (2001) to simulate the evolution
of forest stands, into a cropland and grassland model. The main dissimilarities between forests and croplands
or grasslands were identified, and the required modifications were implemented in a new version of ASPECTS,
called the Terrestrial Agroecosystems Dynamics Analysis (TADA) model. This new model was then calibrated
against data acquired in two cropland and grassland sites, both equipped with eddy covariance (EC) systems and
meteorological stations.
In this work, the attention is paid to the water cycle. Soil evaporation and canopy transpiration were calibrated
against evapotranspiration fluxes (ET) measurements, and the dynamics of water infiltration and percolation within
the soil profile was compared to measures of soil water content (SWC). Soil evaporation was calibrated during bare
soil conditions and resulted in a calibration RMSE of 1.37 and 2.57 mm day-1 and a validation RMSE of 1.82 and
2.75 mm day-1 for, respectively, the cropland and the grassland sites. These results could not be transferred to soils
covered with vegetation, making plant transpiration impossible to calibrate. Canopy aerodynamic resistance was
identified as a possible cause of this problem and a new methodology is proposed to calibrate these two processes
with a wide and diverse dataset in terms of environmental conditions.
In addition to this calibration, the new grazing module was tested by comparing measured and modelled grass
height. The discrepancies are mainly due to the partitioning of assimilated carbon between the shoot and root
compartments and to uncertainties in the estimation of cattle intake capacity. Paths of improvement are provided
for a future calibration of this grazing module, considering both available data and potentially measurable variables.

Water cycle --- Evapotranspiration --- Grazing --- Ecosystem model --- GHG fluxes --- Sciences du vivant > Agriculture & agronomie

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alternative water sources --- sanitation --- water infrastructure --- water cycle --- water sensitive cities --- water catchment management --- Hydrology --- Water --- Hydrologie --- Eau --- Hydrology. --- Research --- Recherche --- Research. --- Aquatic sciences --- Earth sciences --- Hydrography

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Hydrologic cycle --- Hydrology --- -Hydrologic cycle --- -Cycle, Hydrologic --- Hydrological cycle --- Water cycle --- Cycles --- Aquatic sciences --- Earth sciences --- Hydrography --- Water --- -Hydrology --- Cycle, Hydrologic --- Hydrologic cycle - Iceland - Jökulsá á Fjöllum Watershed --- Hydrology - Iceland - Jökulsá á Fjöllum Watershed

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Hydrologic cycle. --- 556.1 --- 631.432 --- Cycle, Hydrologic --- Hydrological cycle --- Water cycle --- Cycles --- Hydrology --- Hydrologic cycle. Properties. Conditions. Global water balance --- Groundwater. Agricultural hydrology --- 631.432 Groundwater. Agricultural hydrology --- 556.1 Hydrologic cycle. Properties. Conditions. Global water balance --- Hydrologic cycle