The EU Nitrates Directive aims to prevent nitrates from agricultural sources polluting ground and surface waters and to promote the use of good farming practices. All the EU member states are committed to meet the Nitrates Directive, as one of the key instruments to protect European waters against agricultural pressures.

The EU Nitrates directive forces member states to develop action programmes, aimed to prevent, monitor, minimize and ameliorate the nitrates pollution in water.

The area to which action programmes apply constitutes about 47% of the total EU land area now. The member states have to monitor the water status, as well as to review the Nitrate Vulnerable Zones (NVZs) designation and the effectiveness of their action programs, reporting to the EU Commission every 4 years.

The agricultural “Good Practices” are compulsory in NVZs zones, according to the Common Agricultural Policy (CAP) “cross-compliance”. Furthermore, the agro-environmental measures in the EU Rural Development aids encourage pollution free practices. However, a recent report from the EU Court of Auditors pointed out several weakness in CAP regarding the Water Framework directive goals.
Actually, nitrates movement through the soil and the related water pollution is a very complex process, which hinders detection of the actual origin of pollution, verifying the fulfilment of the “Good Agricultural Practice” codes, as well as evaluating the reliability of the action programs and CAP measures.

Modelling tools in recent years provided a solution to regional administrations, to evaluate the performance of the measures taken to prevent nitrate pollution of waters, as well as to control and identify the pollution sources.

Simulating nitrates leaching – Procedure
This was just the goal of a LIFE proposal where Zeta Amaltea was involved. Although many models are available, we follow a physically based approach, combining the agrohydrological model SWAP with the hydrological model Modflow. This approach is scientifically sounder, has been implemented by the Dutch Hydrologic Instrument and can be easily extended to any soil, climate and agronomic conditions.

The SWAP simulations provide estimations of the amount of water and solutes that percolate to ground and surface waters. We used the CAP data to parameterize SWAP at all the agricultural areas of the target zone. The information retrieved comprise the land use, seeding and harvest date, water and fertilizer management, etc. The soil hydraulic properties were estimated from soil data, using Pedotransfer functions, as well as measured from undisturbed samples. We considered the Van Genuchten’ model for the soil hydraulic properties and SWAP simulations.

modflow-exampleThe three-dimensional hydrological model provided the water and nitrates movement, considering the vertical recharges simulated by SWAP at each plot. The hydrological model will consider other inputs, as urban waters or irrigation channels, as well as outputs from wells, pumping systems, etc.

The three-dimensional model pointed out water and solutes lateral movement, as well as interaction with surface waters as rivers and channels. The hydrological model was parameterized using international databases of dispersivity and other transport phenomena parameters, as well as field measurements. The piezometer network, as required by Nitrates Directive, was used to calibrate and validate the whole procedure.

The combined modelling approach has been used for several years and agronomic scenarios, providing indications of which combinations of soils, crops and agronomical practices mean the highest risks of nitrate pollution in the zone.