Application of the SWAT model to assess the impact of changes in agricultural management practices on water quality

An excessive use of nitrogen in agricultural regions leads to nitrate pollution of surface and groundwater systems. The Alegria River watershed (Basque Country, northern Spain) is an agricultural area dominated by a Quaternary shallow aquifer that has suffered nitrate-related problems since the 1990s. Our objective was to use the SWAT hydrological water quality model for long-term backward simulation (1990–2011) considering main changes in management practices to determine their impact on water quality. Hydrology, crop yield, nitrogen losses and soil nitrogen budgets were simulated satisfactorily. Nitrogen budgets indicated that annual N inputs exceed outputs (which consider main N loss pathways), resulting in mean N surpluses of 114 and 65 kg ha ⁻¹ year ⁻¹ in the periods 1990–1999 and 2000–2011, respectively. In the long-term, trends in N surplus generally follow those of fertilization input, which directly affect groundwater nitrate concentration. The characteristics of the aquifer and non-point source pollution have enabled us to properly simulate the historical trends in N concentration in the Vitoria-Gasteiz aquifer. Editor Z.W. Kundzewicz; Guest editor V. Krysanova