Nonpoint source pollution in an agricultural catchment and the quality of return flows, under Mediterranean conditions.

Land-use, especially agricultural activities, change the natural functions of a watershed and affects both water quantity and quality through point and nonpoint sources, and impair aquatic ecosystems. The intensification of the agricultural activity, in particular the irrigated agriculture, increases the use of the agrochemical products, and the problems in the soil and water bodies. The study watershed is located within the Idanha Irrigation Scheme, Idanhaa-Nova, Portugal, and it covers an area of 189 ha. Climate is typically Mediterranean; the topography is slightly sloppy; the area of the catchment is well drained (12.2 m ha-1); the predominant soil classes are Cambisols and Luvisols. The agricultural activity is developed in two different seasons; the winter season where the farmers produce especially winter cereals, and the irrigation season where they produce typical crops in this region (corn, sorghum, tobacco and pasture). A hydrological station was installed at the outlet of the watershed. At the beginning of this study, the water samples were collected almost once a day; now, we have a multiparameter probe to collect data continually. Computer simulation models provide an efficient and effective alternative for evaluating the effects of agricultural practices on soil and water quality at basin level, and provide alternatives to avoid or reduce the degradation of the environment. AnnAGNPS model was selected as the simulation tool to be used in this study. Some conclusions were possible to take from this study, by analyzing the collected data and the results of simulation output: the water derived to the basin study to be used in irrigation has a good quality, and also the water returned to the natural drainage meets largely the quality standards (nitrogen, salinity and sediments) not compromising its use downstream; the nitrate load depends, all time, on the availability in the soil and the runoff volume, due to its solubility; the total daily load of sediments not shows a direct relation with the runoff volume, except when it has a sufficient energy to detach and carry out, as in the extreme events.

info:eu-repo/semantics/publishedVersion