Groundwater assimilative capacity: Evidence for and quantification of denitrification

Abstract

It has become evident in recent years that many groundwater systems exhibit some degree of assimilative capacity for nitrate. Denitrification is the key component of this assimilative capacity, as it is the only process that permanently removes reactive nitrate from the groundwater by converting it under oxygen-depleted conditions into gaseous N (predominantly N₂). To be able to ‘Manage within Limits’, as stipulated in developing land and water resource policy, we need to ascertain the maximum nitrate leaching losses that can be accepted in a catchment without violation of the water quality standard agreed for a given monitoring site. Being able to quantify any denitrification that may occur along the groundwater flow paths to the monitoring site is crucial for the establishment of such catchment-scale cause/effect relationships, as denitrification can represent a significant buffer in these relationships.