Denitrification is a key microbial-mediated reaction buffering the impact of agriculturally-derived nitrate loads. Groundwater denitrification capacity is often assessed by measuring the magnitude and patterns of dinitrogen excess, although this method can be biased by dissolved gasses exsolution and ebullition. To address this issue, shallow groundwater was sampled in two field sites via nested mini-wells on a monthly basis over an entire hydrological year and analysed for dissolved gasses, nitrate and physical parameters. Both sites are located in lowland areas of the Po River basin (Italy) and are characterized by intensive agriculture. The GUA site, a freshwater paleo-river environment, with a low content of organic matter (SOM) and oxic sub-oxic groundwater. The BAN site, a reclaimed brackish swamp environment, with abundant SOM and sulphidic-methanogenic groundwater. Groundwater samples evidenced a general deficit of dinitrogen and Argon concentrations, because of ebullition induced by a total dissolved gasses pressure exceeding the hydrostatic pressure. Ebullition was recorded only during winter at the reclaimed brackish soil and was triggered by methane exsolution. While in summer both sites were affected by ebullition because of the water table drawdown. Denitrification evaluated using dinitrogen excess via dinitrogen-Argon ratio technique, was not only affected by gas exsolution, but also by groundwater temperature fluctuations. In fact, the latter induced large biases in the calculated N2 excess even in the freshwater paleo-river environment. For these reasons, dinitrogen excess estimate with standard methods resulted to be unreliable in both lowland environments and a modified method is here presented to overcome this issue.

Effect of ebullition and groundwater temperature on estimated dinitrogen excess in contrasting agricultural environments

Soana, Elisa
Secondo
;
Vincenzi, Fabio;Castaldelli, Giuseppe
Ultimo
2019

Abstract

Denitrification is a key microbial-mediated reaction buffering the impact of agriculturally-derived nitrate loads. Groundwater denitrification capacity is often assessed by measuring the magnitude and patterns of dinitrogen excess, although this method can be biased by dissolved gasses exsolution and ebullition. To address this issue, shallow groundwater was sampled in two field sites via nested mini-wells on a monthly basis over an entire hydrological year and analysed for dissolved gasses, nitrate and physical parameters. Both sites are located in lowland areas of the Po River basin (Italy) and are characterized by intensive agriculture. The GUA site, a freshwater paleo-river environment, with a low content of organic matter (SOM) and oxic sub-oxic groundwater. The BAN site, a reclaimed brackish swamp environment, with abundant SOM and sulphidic-methanogenic groundwater. Groundwater samples evidenced a general deficit of dinitrogen and Argon concentrations, because of ebullition induced by a total dissolved gasses pressure exceeding the hydrostatic pressure. Ebullition was recorded only during winter at the reclaimed brackish soil and was triggered by methane exsolution. While in summer both sites were affected by ebullition because of the water table drawdown. Denitrification evaluated using dinitrogen excess via dinitrogen-Argon ratio technique, was not only affected by gas exsolution, but also by groundwater temperature fluctuations. In fact, the latter induced large biases in the calculated N2 excess even in the freshwater paleo-river environment. For these reasons, dinitrogen excess estimate with standard methods resulted to be unreliable in both lowland environments and a modified method is here presented to overcome this issue.
2019
Mastrocicco, Micòl; Soana, Elisa; Colombani, Nicolò; Vincenzi, Fabio; Castaldi, Simona; Castaldelli, Giuseppe
File in questo prodotto:
File Dimensione Formato  
1-s2.0-S0048969719335636-main.pdf

solo gestori archivio

Descrizione: versione editoriale
Tipologia: Full text (versione editoriale)
Licenza: NON PUBBLICO - Accesso privato/ristretto
Dimensione 3.25 MB
Formato Adobe PDF
3.25 MB Adobe PDF   Visualizza/Apri   Richiedi una copia
ManuscriptR1clean.pdf

accesso aperto

Descrizione: versione preprint
Tipologia: Pre-print
Licenza: PUBBLICO - Pubblico con Copyright
Dimensione 1.75 MB
Formato Adobe PDF
1.75 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2406658
Citazioni
  • ???jsp.display-item.citation.pmc??? 0
  • Scopus 4
  • ???jsp.display-item.citation.isi??? 4
social impact