Nitrate leaching from agricultural lands is a worldwide concern particularly in intensively cropped areas which often are net sources of nitrate to surface water and groundwater. The Ferrara Province is a completely flat territory located in the North-eastern part of Italy, very suitable for intensive agriculture and recently declared vulnerable to nitrate from agricultural sources. This study focuses on factors affecting mineral nitrogen speciation in shallow aquifers below agricultural soils by means of marker species, witnessing the occurrence of denitrification. A grid of shallow piezometers, screened through the water table, was established in 58 agricultural plots throughout the FP. Inorganic nitrogen species were monitored together with conservative species, as chloride. In parallel, low molecular weight organic compounds (acetate, formate and oxalate) were analyzed and employed as tracers of labile dissolved organic carbon, potentially fuelling denitrification. Where, acetate formate and oxalate were continuously exposed to oxygen and more likely consumed within the unsaturated zone, the dissolved organic carbon is assumed to be low. Comparing acetate versus nitrate in all the groundwater samples an hyperbolic relationship is evident, indicating a stoichiometric control of dissolved nitrate concentration due to the presence of labile organic compounds. In addition the temporal variation of chloride, nitrate and acetate is used to discriminate between conservative and reactive transport; the disappearance of nitrate and acetate suggests that denitrification is taking place. This study shows that acetate can be used as a proxy for labile dissolved organic carbon which drives denitrification processes, while formate and oxalate cannot be used because of their low concentrations.
Nitrogen speciation and denitrification in a low land territory receiving synthetic fertilizers (Province of Ferrara, Northern Italy)
COLOMBANI, Nicolo';MASTROCICCO, Micol;VINCENZI, Fabio;CASTALDELLI, Giuseppe
2012
Abstract
Nitrate leaching from agricultural lands is a worldwide concern particularly in intensively cropped areas which often are net sources of nitrate to surface water and groundwater. The Ferrara Province is a completely flat territory located in the North-eastern part of Italy, very suitable for intensive agriculture and recently declared vulnerable to nitrate from agricultural sources. This study focuses on factors affecting mineral nitrogen speciation in shallow aquifers below agricultural soils by means of marker species, witnessing the occurrence of denitrification. A grid of shallow piezometers, screened through the water table, was established in 58 agricultural plots throughout the FP. Inorganic nitrogen species were monitored together with conservative species, as chloride. In parallel, low molecular weight organic compounds (acetate, formate and oxalate) were analyzed and employed as tracers of labile dissolved organic carbon, potentially fuelling denitrification. Where, acetate formate and oxalate were continuously exposed to oxygen and more likely consumed within the unsaturated zone, the dissolved organic carbon is assumed to be low. Comparing acetate versus nitrate in all the groundwater samples an hyperbolic relationship is evident, indicating a stoichiometric control of dissolved nitrate concentration due to the presence of labile organic compounds. In addition the temporal variation of chloride, nitrate and acetate is used to discriminate between conservative and reactive transport; the disappearance of nitrate and acetate suggests that denitrification is taking place. This study shows that acetate can be used as a proxy for labile dissolved organic carbon which drives denitrification processes, while formate and oxalate cannot be used because of their low concentrations.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
