Impacts of agriculture and dairy farming on groundwater quality: An optimization problem

A decision model for groundwater quality preservation in areas affected by intensive agriculture and dairy farming, with specific reference to the Azores islands, is presented. In these islands, the exigency to find appropriate instruments to support decisions in Integrated Water Management (IWM) is particularly felt because the increase of tourism and the dairy farming have increased water demands and depletion of water quality. An optimization problem, in terms of decision variables, objectives, and constraints is formalized. The physical/chemical/ecological models are embedded as constraints in the decision model. Specifically, four types of models (hydraulic model, chemical model, agricultural model, and dairy farming model) are integrated and defined. Hydrological data are used to build the hydraulic model that influences the transport and the dilution of pollutants in the groundwater. The chemical model is influenced by the amount of fertilizers and waste from animals used for yield production in the fields (agricultural model). Finally, the dairy farming model influences the agricultural model because of the presence of animals and at the same time is influenced by the available quantity of food produced in the area. The objective function is the maximization of milk production. The other objectives to be taken into account are transformed into constraints: limits on pollutant concentration in the aquifer, on minimum water demand requirements, on the quantity of used fertilizers. The optimisation problem is non linear with non-linear constraints and continuous decision variables. The decision model has been applied to a case study of Terceira Island.