a standardised method for measuring in situ denitrification in shallow aquifers: numerical validation and measurements in riparian wetlands

Abstract

A tracer test to examine in situ denitrification in shallow groundwater by a piezometer with a packer system used bromide as a tracer of dilution and acetylene (10%) to block the denitrification process at the nitrous oxide stage. During the test, dissolved oxygen, nitrate (NO₃^‾), bromide (Br^‾), nitrous oxide (N₂O) and dissolved organic carbon (DOC) were measured. To calibrate the experimental method, comparison with numerical simulations of the groundwater transfer were carried out, taking into account the environmental characteristics. The method was tested by measurements undertaken in different environmental conditions (geology, land use and hydrology) in two riparian wetlands. Denitrification rates measured by this method ranged from 5.7 10^-6 g N-NO₃^‾L^-1 h^-1 to 1.97 10^-3 g N-NO₃^‾L^-1 h^-1 The method is applicable in shallow aquifers with a permeability from 10^-2 to 10^-4m s^-1.

Keywords: denitrification, shallowaquifer, groundwater modelling, wetlands, nitrate-nitrogen, packer system