Nitrous oxide production and consumption in British limestone aquifers

Nitrous oxide and other nitrogen species were measured in groundwater from the most important limestone aquifers in the UK. Nitrous oxide levels were generally very high, with concentrations exceeding the concentration of air -equilibrated water by up to 320 limes. The correlations between N2O, NO3 a nd dissolved oxygen, as well as the spatial distribution of these chemical parameters, were used to identify nitrification as the main N2O production mechanism in the investigated aquifers. Most of the N2O in groundwater appe ars to be produced via nitrification in the unsaturated zone, which is prob ably strongly supplemented by nitrogenous compounds from anthropogenic land applications. Nitrous oxide production in the saturated zone is less subst antial and can also be denitrification mediated; denitrification under very reducing aquifer conditions can result in nitrous oxide consumption. The o bserved high N2O concentrations in groundwater, which are most likely cause d by agricultural aquifer pollution, can potentially lead to large N2O emis sions from aquifers to the atmosphere, which will contribute to the climati c forcing induced by higher atmospheric N2O concentrations. (C) 1998 Elsevi er Science B.V. All rights reserved.