Bio-geological processes of nitrogen transport and transformation in the aeration zone and aquifer

Abstract

Nitrate contamination in groundwater originates mainly from excessive use of fertilizers and uncontrolled discharge to land of incompletely-treated wastewater associated with agricultural activities. A systematic field investigation was carried out in a sub-catchment of Dianchi Lake, Kunming, Yunnan, China, into the hydrological, biological and geological processes of nitrogen transport and transformation in the aeration zone and aquifer system. In situ experiments showed that the quantity of NO 3 -N recharged into groundwater was related to fertilization. Nitrification and denitrification behaved quite differently but were affected by moisture content and Eh value. The vertical infiltration rate was controlled by the groundwater table and hydraulic conductivity of the soil. The existence of a zero-flux plane reflected the dynamics of water fluxes in the soil profile and Eh was measured in the aeration zone. In response to these factors, the nitrification rate was greatest in the top soil and reduced with the depth of soil; it was 6.53 mg/(kg·h) in the vegetated plot and 0.2-0.3 mg/(kg·h) in the unvegetated one. The denitrification rate in the unvegetated plot was 6.36 mg/(kg·h), and it was 2.79 mg/(kg·h) in the vegetated one.Key words nitrogen; groundwater; nitrate; nitrification; denitrification Processus bio-géologiques du transport et de la transformation de l'azote en zone non saturée et au sein de l'aquifère Résumé La contamination des eaux souterraines par les nitrates provient essentiellement d'une utilisation excessive de fertilisants et d'un rejet incontrôlé vers le milieu d'eaux usées incomplètement traitées en lien avec les activités agricoles. Une étude de terrain systématique a été menée dans un sous-bassin du bassin versant du Lac Dianchi, Kunming, Yunnan, en Chine, afin de comprendre les processus hydrologiques, biologiques et géologiques déterminants dans le transport et la transformation de l'azote dans la zone non saturée et dans le système aquifère. Des expériences in situ ont montré que la quantité de NO 3 -N apportée par recharge des eaux souterraines est liée à la fertilisation. La nitrification et la dénitrification se comportent très différemment mais sont liées à la teneur en eau et à la valeur de Eh. Le taux d'infiltration verticale est contrôlé par le niveau de la nappe et par la conductivité hydraulique du sol. L'existence d'un plan de flux nul reflète la dynamique des flux hydriques dans le profil de sol et la distribution de Eh dans la zone non saturée, au niveau des sites de mesure. En réponse à ces facteurs, le taux de nitrification est plus fort dans les horizons superficiels et diminue avec la profondeur dans le sol; il s'élève à 6.53 mg/(kg·h) dans la zone végétalisée et à 0.2-0.3 mg/(kg·h) dans la zone non végétalisée. Le taux de dénitrification dans la zone non végétalisée s'élève à 6.36 mg/(kg·h), et à 2.79 mg/(kg·h) dans la zone végétalisée.

Total Nitrogen Concentrations in Surface Water of Typical Agro- and Forest Ecosystems in China, 2004-2009

“…The average annual application rate of N in China gradually increased to 130 kg·ha −1 in 1985, then rapidly increased to 236 kg·ha −1 in 1995 and then to 262 kg·ha −1 in 2001 [22]. However, less than half of the fertilizer N applied in China is taken up by crops [23].…”

“…Fertilizer consumption has grown rapidly in China since 1978, and China recently became the biggest producer and consumer of N fertilizer in the world. The average annual application rate of N in China gradually increased to 130 kg·ha −1 in 1985, then rapidly increased to 236 kg·ha −1 in 1995 and then to 262 kg·ha −1 in 2001 [22] . However, less than half of the fertilizer N applied in China is taken up by crops [23] .…”

Carbon release mechanism of synthetic and agricultural solid carbon sources

“…When N is in the range of 0.45–0.89, diffusion and disintegration are the main mechanism. When N is bigger than 0.89, framework disintegration is the main mechanism (Zhang et al ., 2009a).…”

Study of Groundwater Vulnerability to Contamination in Part of the Klaten District Area, Central Java-Indonesia

“…Low nitrate levels can be attributed to the dynamic movement of groundwater and the complex mechanisms with which nitrates enter the groundwater. The amount of nitrate that enters the aquifer zone is also influenced by several factors, including fertiliser application, nitrification, denitrification and transportation by rainwater [20].…”