A preliminary groundwater field and incubation study to test isotope methods for distinction of various N transformation processes in a contaminated aquifer

Incubation 1

Groundwater samples were collected from selected piezometers with high nitrate concentrations and incubated under two conditions: anoxic (flushed with N₂ gas for 15 minutes) and oxic (flushed with synthetic air). pH was left unaltered. Samples were divided into four replicates per treatment and incubated in the dark at 16 °C and agitated at 100 rpm for 3 weeks. Glucose was added after one week to stimulate microbial denitrification. Inorganic nitrogen species (NO₃⁻, NO₂⁻, NH₄⁺) were analyzed using colorimetric methods throughout the incubation i.e. before the start of incubation, before addition of glucose and at the end of the experiment to study N transformation processes under controlled conditions. Further, isotopic analysis were conducted using the bacterial denitrification method: Pseudomonas aureofaciens for NO₃⁻ and Stenotrophomonas nitritireducens for NO₂⁻ isotopes.