Measures required to reach the nitrate objectives in groundwater based on a long-term nitrate model for large river basins (Júcar, Spain)

Abstract

Nitrate pollution, primarily in groundwater (GW), has been one of major water pollution problems in Europe over the last 30years. Specially, Mediterranean areas (semi-arid zones) are more vulnerable to nitrate pollution, as in these areas a small excess of nitrogen produce higher nitrate concentrations than in more humid countries because the aquifer recharge is minor. A large number of GW bodies in the Júcar River Basin District (RBD) (43.000km2), located in Spain, has nitrate concentrations above 50mg/L. The Water Framework Directive (WFD) sets out the goal of good status for the water bodies of the European Union, which also implies compliance with the Nitrates Directive.The River Basin Authorities (RBAs) must define the measures needed to reach the environmental objectives in the River Basin Management Plans (RBMPs), considering the long time-lag of aquifers is decisive in the measures effectiveness. By means of nitrogen cycle simulation in the river basin district and with the help of the monthly distributed PATRICAL model, the Júcar RBA has defined the measures to be applied and the exemptions to reach the objectives in GW in relation to nitrate pollution. Both, model and methodology are useful for other river basins to define measures.The total nitrogen inputs in the Júcar RBD amounts to 180,000tN/year, which represents a nitrogen surplus of 80,000tN/year and a pressure of 58.5kgN/year/ha-crop. Around 3/4 of GW bodies have currently the good status while the remaining of GW bodies could reach the good status during following hydrological planning cycles through the implementation of modernized irrigation systems that include fertigation -the use of fertilizers in the water for irrigation. The implementation of this scenario involves increasing efficiency in fertilizer application, in order to reduce nitrogen losses from slightly under a half to <1/3.