## Results
### Seasonal and Interannual Variabilities of Modeled and Observed Carbon Dioxide and Water Fluxes
#### 3.2.1 Day-to-Day and Seasonal CO\({}_{2}\) and Water Fluxes Variability
For the grazed paddock, model/data differences were even more important with annual EC-derived and modeled ER varying from 14.3 to 19.0 tC ha\({}^{-1}\) yr\({}^{-1}\) (five-year average: 16.3 tC ha\({}^{-1}\) yr\({}^{-1}\)) and from 15.2 to 19.9 tC ha\({}^{-1}\) yr\({}^{-1}\) (five-year average: 18.3 tC ha\({}^{-1}\) yr\({}^{-1}\)), respectively. There is a good agreement between modeled and observed annual amounts of harvested C. Generally, the modeled and observed annual NEE agreed reasonably well for the moved grassland sites but large differences were retrieved for the grazed paddock and might result from the miss or only partial capture of grazing animals' respiratory losses by the EC system. Five-year averages of observed NEE for the mowed and grazed grassland sites were \(-\)4.2 (\(-\)3.0 to \(-\)4.9) and \(-\)1.8 (\(-\)0.9 to \(-\)3.2) tC ha\({}^{-1}\) yr\({}^{-1}\), respectively. CenW modeled NEE, averaged over 5 years, were \(-\)4.4 (\(-\)3.1 to \(-\)6.6) tC ha\({}^{-1}\) yr\({}^{-1}\) for the mowed paddock and 0.1 (\(-\)0.4 to 0.4) tC ha\({}^{-1}\) yr\({}^{-1}\) for the grazed pasture. Modeled annual net CO\({}_{2}\) fluxes, for the grazed paddock, were significantly lower than observed ones because, as we have seen, part of C harvested (grazed) is taken into account in observed NEE, while it is fully accounted for in the modeled NEE. Apparently, the mowed paddock fixed more CO\({}_{2}\) than the grazed paddock however, when harvested C is taken into account (Figure 11a) the mowed grassland C sink activity is drastically reduced. Modeled and observed daily evapotranspiration rates generally agreed very well as we have seen in Section 3.1.2 with EF of 0.82 and 0.80 for the mowed and grazed paddocks, respectively. Both modeled and observed summer half-year evapotranspiration rates were higher for the grazed paddock because of the differences management practices (harvests and grazing) that affected vegetation dynamics. Even if there were fewer harvests than grazing events, the dramatic reduction of live foliage following grass cuttings affected water fluxes and reduced the annual amounts of evapotranspiration. Modeled summer half-year ET were also systematically lower than the observed results, which could result from (1) differences in modeled and observed roots dynamics (growth and senescence) affecting soil water extraction by plants and (2) the water returned directly to the field by cattle urinations which is not accounted for in the model. Observed five-year average annual ET were 521 and 544 mm yr\({}^{-1}\) while modeled values were 503 to 527 mm yr\({}^{-1}\) for the mowed and grazed paddocks, respectively. It also as to be noted that the conventional gap-filling and partitioning tool [69] was not designed to deal neither with heterogeneities in ecosystems as it the case in intensively managed grasslands, like our study site, nor to take into account the varying magnitude of respiratory CO\({}_{2}\) losses from rotationally grazing animals that not depend of meteorological conditions. These conditions would add uncertainties in gap filled NEE fluxes and on their partitioning into GPP and ER [79].