Water pollution induced by rainfed and irrigated agriculture in Mediterranean environment at basin scale

The study area is a small basin (190 ha), located in centre of the Portugal, and the agricultural activity is developed in the winter and irrigation season. The nitrates and the total dissolved solids load depends, all time, on the availability in the soil and the runoff volume, due to its solubility. The ammonium shows a different dynamic; when it is present in large amount in the soil, its load depends on the sediments load and the extremes peak flow. The total daily load of sediments does not show a direct relation with de runoff volume, except when it has a sufficient energy to detach and carry out, as during extreme events.