IMPACT ON HYDROLOGY AND NUTRIENT MOVEMENTS OF DEVELOPMENTS IN RIVER BASINS DRAINING INTO RESERVOIRS

One of the main causes of lack of potability in a water supply is eutrophication. This is caused by the natural or anthropogenic contributions of nitrogen and phosphorus. The dumping of domestic sewage, Leaching from urban waste dumps, farm purine and even habitual agricultural and forestry practices contribute these elements to water. Whatever the use of a territory, it involves a greater or lesser degree of movement of nitrogen and phosphorus and the consequent eutrophication of water to different degrees. The central theme of this work is an evaluation of the relative impact that different degrees of development have had on the production of nitrogen and phosphorus in relation to the specific use of land in three river basins draining into reservoirs in the Madrid Community (Valmayor, Santillana and Pinilla). The data corresponding to the three reservoirs were studied over a period of two years (October 1988 to October 1990) during which hydrological entries into the reservoir by different means were determined (runoff from the main entries into the reservoir, direct precipitation on the reservoir and subterranean supplies). To do this we have started with a Model Basin-unaffected-having in common with the three river basins studied the use of the land that represents the natural geochemical source of nutrients. Using this Basic Model of a basin we can also establish a series of recommendations to achieve the reversal of environmental impacts that may have arisen and starting with this an estimate has been made of the increase in the production of nutrients due to anthropication in the whole area of study, considering all the hydrological contributions as well as nutrients contributed in relation to the characteristics of the river basins, mainly in that which refers to the use of the surrounding land. We can conclude that the greater the development of the basin the farther the characteristic hydraulic contribution from its original, unaltered state, and that the contribution of nutrients is very closely related to the specific hydrology of each supplying river basin.