The Use of a Simple Sustainability Index to Protect Groundwater Quality Under Changing Agricultural Land Uses. A Case Study

Modern intensive agriculture justified by the need to support the food requirement of an always growing population, because of the heavy use of agrochemicals, has revealed in many cases to be responsible for surface and groundwater pollution. In this paper, the problems of water and, in particular of groundwater pollution from agricultural nitrates are dealt, with reference to a sub-basin, located in southern Portugal, of river Guadiana, where olive groves and winter wheat are the most common crops. The study area suffers problems related to water availability from one year to another and, for this reason many reservoirs were recently built in the area. In the last few years the resulting greater water availability is causing a shift towards modern intensive agricultural production methods with a consequent, possible water quality deterioration. This is the reason why some BMP scenarios, aimed at reducing the impacts of agriculture on groundwater have been adjusted and their effect in terms of kg/ha of leached NO3 have been estimated using the simulation model GLEAMS. The irrigation water consumption referred to each scenario was also calculated. The load of leached nitrates and the water consumption from the whole area, with reference to each scenario were then merged within a unique synthetic index that summarizes in one number the suitability of that scenario at reducing both nitrate leaching and water consumption. Among the most interesting conclusions is the fact that, in the hypothesis of optimal agricultural management, modern intensive olive grove not always results to be responsible for a higher NO3 leaching in comparison to the traditional ones and could, for this reason, be considered in itself a way to perform a sustainable agriculture.