Agricultural practices—particularly those involving poorly managed irrigation, synthetic fertilizer use, and livestock manure application—are key drivers of soil and groundwater contamination, mainly through nitrate (NO₃). In response, the European Union adopted the Nitrates Directive (91/676/EEC) in 1991, requiring systematic monitoring, the designation of Nitrate Vulnerable Zones (NVZs), and the implementation of good agricultural practices and action programmes to prevent and reduce non-point source (NPS) nitrate pollution. However, despite these regulations, nitrate concentrations in shallow groundwater remain elevated in the Arborea area on the west coast of Sardinia, Italy, with monitoring records indicating a continuing increase. The NVZ located in the sandy Arborea Plain is particularly affected due to excessive nitrogen inputs linked to intensive livestock farming and agriculture. This study seeks to reduce agricultural NPS nitrate contamination by combining Site-Specific Best Management Practices (SSBMPs) with low-cost, field-scale bioreactors (BRs) designed to intercept and attenuate nitrate loads. Three pilot fields were selected in Arborea, where detailed data on soils, vegetation, groundwater, irrigation, and fertilization were collected. The physically based agro-hydrological model FLOWS was applied to (1) assess and quantify water and nitrate leaching under current farming practices and (2) optimize irrigation strategies to limit nitrate losses to groundwater. In each pilot field, an artificial subsurface drainage system was installed to capture percolation flows and convey them to a dedicated bioreactor. The bioreactors were designed to treat drainage water under anoxic conditions for nitrate removal through a porous medium created by filling an excavated trench (25 × 4 × 1.2 m) with eucalyptus woodchips. Each system included inlet and outlet structures and monitoring equipment to measure water quality, collect samples, and regulate hydraulic gradients to maintain an average residence time of 4–6 hours. Laboratory results demonstrated strong bioreactor efficiency, achieving nitrate removal rates of 100% in two pilot systems and 89% in the third. Over a four-month monitoring period (June 1 to September 30, 2025), the three bioreactors treated approximately 1,222 kg, 2,929 kg and 1,830 kg of nitrate, respectively. The collected field data were then used to calibrate and run the FLOWS model, which indicated that optimizing irrigation—by aligning water supply with daily evapotranspiration demand—could substantially reduce both water percolation and nitrate fluxes reaching groundwater.
Integrated Modelling and Technological Tools to prevent Agricultural Non-Point Source Nitrate Pollution of Shallow Groundwater in Arborea Area, Sardinia, Italy
Da Pelo S.;Lobina F.;Sessini A. M.;Vacca A.;Coppola A.Ultimo
2026-01-01
Abstract
Agricultural practices—particularly those involving poorly managed irrigation, synthetic fertilizer use, and livestock manure application—are key drivers of soil and groundwater contamination, mainly through nitrate (NO₃). In response, the European Union adopted the Nitrates Directive (91/676/EEC) in 1991, requiring systematic monitoring, the designation of Nitrate Vulnerable Zones (NVZs), and the implementation of good agricultural practices and action programmes to prevent and reduce non-point source (NPS) nitrate pollution. However, despite these regulations, nitrate concentrations in shallow groundwater remain elevated in the Arborea area on the west coast of Sardinia, Italy, with monitoring records indicating a continuing increase. The NVZ located in the sandy Arborea Plain is particularly affected due to excessive nitrogen inputs linked to intensive livestock farming and agriculture. This study seeks to reduce agricultural NPS nitrate contamination by combining Site-Specific Best Management Practices (SSBMPs) with low-cost, field-scale bioreactors (BRs) designed to intercept and attenuate nitrate loads. Three pilot fields were selected in Arborea, where detailed data on soils, vegetation, groundwater, irrigation, and fertilization were collected. The physically based agro-hydrological model FLOWS was applied to (1) assess and quantify water and nitrate leaching under current farming practices and (2) optimize irrigation strategies to limit nitrate losses to groundwater. In each pilot field, an artificial subsurface drainage system was installed to capture percolation flows and convey them to a dedicated bioreactor. The bioreactors were designed to treat drainage water under anoxic conditions for nitrate removal through a porous medium created by filling an excavated trench (25 × 4 × 1.2 m) with eucalyptus woodchips. Each system included inlet and outlet structures and monitoring equipment to measure water quality, collect samples, and regulate hydraulic gradients to maintain an average residence time of 4–6 hours. Laboratory results demonstrated strong bioreactor efficiency, achieving nitrate removal rates of 100% in two pilot systems and 89% in the third. Over a four-month monitoring period (June 1 to September 30, 2025), the three bioreactors treated approximately 1,222 kg, 2,929 kg and 1,830 kg of nitrate, respectively. The collected field data were then used to calibrate and run the FLOWS model, which indicated that optimizing irrigation—by aligning water supply with daily evapotranspiration demand—could substantially reduce both water percolation and nitrate fluxes reaching groundwater.
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