Nitrate leaching from agricultural sources is a worldwide concern and in Europe a large part of farmed areas are affected by nitrate pollution since decades. In Italy, the Po River valley is the largest and more intensively farmed alluvial plain, heavily impacted by agricultural pollution and especially by NO3- groundwater contamination and surface water eutrophication. With the enactment of the European Directive for water protection (2000/60 CE), a large portion of the Po river valley has been declared vulnerable to nitrate from agricultural sources and limitations to the use of N fertilizers have been applied. However, in agricultural practices, the types of soils and soil tillage, different crops and irrigation techniques and different nitrogen fertilizers, which may be synthetic, as ammonium nitrate and urea, or natural, as manures and sludge from different animal farming, form a variety of terms emphasizing site specificity of WFD application and results. Moreover, the general knowledge of key factors governing patterns and processes of N transport and transformations through the vadose zone to the water table are not fully clarified. Within this multidisciplinary framework, for any applied research finalised to reduce nitrogen losses , it is essential to fix a benchmark to star from, which in our view is aquifer recharge assessment, i.e. to quantify water resources and flux toward aquifers. Presently, the most effective tool to quantify recharge flux is to model the unsaturated soil water dynamics, although this process faces many challenges in field conditions. In order to identify the dominant processes affecting nitrate leaching in the Po River Delta area, a series of tracer tests were performed to determine conservative mass transfer and the fate and transport of nitrogen species. Results highlight the reliability of the use of conservative tracers and numerical modeling jointly, to understand nitrate mass transfer rate and mass balance. For the practical interest of WFD application, this approach has evidenced that in the sandy soil, more permeable and intrinsically more vulnerable, the relatively low amount of organic matter lasting from manure use in the previous year, was sufficient to prevent nitrate leaking, by removing the excess via denitrification. This result highlights the need to pay attention to the kind of manure used and to the relative degradation kinetics which may also be heavily affected by farming type, organic or industrial. This last term, in fact, other than impacting water quality for the presence of hormones and other undesired chemicals, may influence organic matter and nitrogen mineralization rates, interfering with bacterial activities due to the presence of antibiotics.
The role of the unsaturated zone in determining nitrate leaching to groundwater
MASTROCICCO, Micol;COLOMBANI, Nicolo';CASTALDELLI, Giuseppe;SALEMI, Enzo;VINCENZI, Fabio
2010
Abstract
Nitrate leaching from agricultural sources is a worldwide concern and in Europe a large part of farmed areas are affected by nitrate pollution since decades. In Italy, the Po River valley is the largest and more intensively farmed alluvial plain, heavily impacted by agricultural pollution and especially by NO3- groundwater contamination and surface water eutrophication. With the enactment of the European Directive for water protection (2000/60 CE), a large portion of the Po river valley has been declared vulnerable to nitrate from agricultural sources and limitations to the use of N fertilizers have been applied. However, in agricultural practices, the types of soils and soil tillage, different crops and irrigation techniques and different nitrogen fertilizers, which may be synthetic, as ammonium nitrate and urea, or natural, as manures and sludge from different animal farming, form a variety of terms emphasizing site specificity of WFD application and results. Moreover, the general knowledge of key factors governing patterns and processes of N transport and transformations through the vadose zone to the water table are not fully clarified. Within this multidisciplinary framework, for any applied research finalised to reduce nitrogen losses , it is essential to fix a benchmark to star from, which in our view is aquifer recharge assessment, i.e. to quantify water resources and flux toward aquifers. Presently, the most effective tool to quantify recharge flux is to model the unsaturated soil water dynamics, although this process faces many challenges in field conditions. In order to identify the dominant processes affecting nitrate leaching in the Po River Delta area, a series of tracer tests were performed to determine conservative mass transfer and the fate and transport of nitrogen species. Results highlight the reliability of the use of conservative tracers and numerical modeling jointly, to understand nitrate mass transfer rate and mass balance. For the practical interest of WFD application, this approach has evidenced that in the sandy soil, more permeable and intrinsically more vulnerable, the relatively low amount of organic matter lasting from manure use in the previous year, was sufficient to prevent nitrate leaking, by removing the excess via denitrification. This result highlights the need to pay attention to the kind of manure used and to the relative degradation kinetics which may also be heavily affected by farming type, organic or industrial. This last term, in fact, other than impacting water quality for the presence of hormones and other undesired chemicals, may influence organic matter and nitrogen mineralization rates, interfering with bacterial activities due to the presence of antibiotics.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
