Managed Aquifer recharge (MAR) is an increasingly worldwide important water management strategy to mainatin, enhance and secure stressed groundwater systems and to improve water quality.

FIA is a MAR technique consisting in the distribution of surface water on areas specially equipped with a network of drainage trenches and forested with trees and/or shrub species. The forest area maximizes the infiltration rate whereas the “active layer” generated in the rhizosphere has an effective action to promote nitrate attenuation, due to the occurrence of anoxic conditions, abundant organic matter provided by the woody plants and denitrifying bacteria living in symbiosis with the roots.

In collaboration with the Arborea Farmers’ Cooperative and the Oristanese Land Reclamation Consortium, a pilot site has been identified in the southern part of the Arborea plain, where high nitrate concentrations in groundwater, even over 250 mg L^-1, have been detected. 

The FIA System consists of 6 parallel recharge trenches with a depth of 1 m which are supplied with drainage water, pumped from an existing dewatering pumping station. Water infiltrates into the sandy soil through the trenches towards the aquifer. An incoming sediment control system (a mesh filter) has been installed upstream to the system. 

In the recharge trenches, rows of poplar (white and Luisa Avanza species) and euchalyptus trees have been planted thanks to the support of students from the Agricultural Technical Institute of Bosa. In such forest areas, the water that infiltrates into the soil meets an effective filter made up of tree roots. 

While waiting for the full development of the forested area that, in the medium-long term, will ensure the denitrification process, the depurative action, in the short term, is ensured by an innovative Passive Treatment installed on the bottom of the recharge trenches. The system consists of a mixture of inert and organic materials, to attenuate organic and inorganic contamintation and to prevent clogging processes.     

The effectiveness of the FIA technique in reducing nitrate concentrations is evaluated through a complex monitoring network  by monitoring several chemical and hydrological parameters, by laboratory analytical methods and field instrumentation. The monitoring has started in June 2023 and is still ongoing under the new project “NATMed - Nature-based Solutions on existing infrastructures for resilient Water Management in the Mediterranean” (🔗link) funded by the PRIMA Programme, of which NRD-UNISS is a partner (2023-2026).

Preliminary results of hydrogeochemical monitoring show up to an 80% reduction in nitrates in infiltration water due to the positive action of the Passive Treatment System, as well as a significant decrease in nitrate concentrations in groundwater. This indicates that the FIA technique can be an effective Nature-Based Solution for the decontamination of nitrate-polluted waters.