『Abstract
Nitrogen fertilizers used in agriculture often cause nitrate
leaching towards shallow groundwater, especially in lowland areas
where the flat topography minimize the surface run off. In order
to introduce good agricultural practices that reduce the amount
of nitrate entering the groundwater system, it is important to
quantify the kinetic control on nitrate attenuation capacity.
With this aim, a series of anaerobic batch experiments, consisting
of loamy soils and nitrate-contaminated groundwater, were carried
out using acetate and natural dissolved organic matter as electron
donors. Acetate was chosen because it is the main intermediate
species in many biodegradation pathways of organic compounds,
and it is a suitable carbon source for denitrification. Sorption
of acetate was also determined, fitting a Langmuir isotherm in
both natural and artificially depleted organic matter soils. Experiments
were performed in quadruplicate to account for the spatial variability
of soil parameters. The geochemical code PHREEQC (version 2) was
used to simulate kinetic denitrification using Monod equation,
equilibrium Langmuir sorption of acetate, and equilibrium reactions
of gas and mineral phases (calcite). The reactive modeling results
highlighted a rapid acetate and nitrate mineralization rate, suggesting
that the main pathway of nitrate attenuation is through denitrification
while calcite acted as a buffer for pH. However, in the absence
of acetate, the natural content of organic matter did not allow
to complete the denitrification process leading to nitrite accumulation.
Reactive modeling is thought to be an efficient and robust tool
to quantify the complex biogeochemical reactions which can take
place in underground environments
Keywords: Denitrification; Soil; Organic matter; Acetate; Reactive
modeling』
1. Introduction
2. Materials and methods
2.1. Soil and groundwater characterization
2.2. Batch experiments set up
2.3. Analytical methods
2.4. Acetate adsorption isotherm determination
2.5. Reactive modeling
3. Results and discussion
3.1. Acetate adsorption experiments
3.2. Reactive modeling
3.3. Transient nitrite accumulation
4. Conclusions
Acknowledgments
References