CORRELATING THE SPATIAL DISTRIBUTION OF ATMOSPHERIC AMMONIA WITH δ 15 N VALUES AT AN AMMONIA RELEASE SITE R. SKINNER 1∗ , P. INESON 1 , W. K. HICKS 1 , H. E. JONES 2 , D. SLEEP 2 , I. D. LEITH 3 and L. J. SHEPPARD 3 1 Stockholm Environment Institute, University of York, Heslington, York, YO10 5YW, UK; 2 Centre for Ecology and Hydrology, Merlewood, Grange over sands, Cumbria, LA11 6JU, UK; 3 Centre for Ecology and Hydrology, Edinburgh, Bush Estate, Penicuik, EH26 0QB, UK, ( ∗ author for correspondence, e-mail: ras108@york.ac.uk) Abstract. A field ammonia (NH 3 ) release experiment and open top chambers containing moorland monoliths continuously fumigated with NH 3 or sprayed with NH 4 Cl were used to assess the potential for using δ 15 N values in determining the area of influence around a point NH 3 emission source. δ 15 N values are being increasingly used as environmental tracers and we tested the hypothesis that the δ 15 N signal from an NH 3 emission source is observable in nearby vegetation. Using modified monitoring devices, atmospheric NH 3 concentrations were found to decrease with distance from source, with δ 15 N values also reflecting this trend, producing a signal shift with changing concentration. Open top chamber studies of δ 15 N values of Calluna vulgaris (L.) Hull indicated a correlation with deposition treatments in current year shoots. Analysis of Calluna shoots from the NH 3 release showed a similar trend of δ 15 N enrichment. Significant linear correlations between δ 15 N and percent N in plant material were found, both in the controlled conditions of the open top chambers and at the NH 3 release site, illustrating the possible use of this technique in N deposition biomonitoring. Keywords: ammonia, deposition, δ 15 N, isotopes, Calluna 1. Introduction The majority of NH 3 emissions arise from agricultural practices (Buijsman et al., 1987; Sutton et al., 1995) and because of the chemically reactive nature of gaseous NH 3 , the atmospheric residency time is comparatively short (Moller and Schieferdecker, 1985). Therefore, emissions can have significant localised ef- fects, with NH 3 concentrations decreasing exponentially with distance from source (Asman et al., 1989). Several detrimental effects of deposition have been doc- umented on semi-natural ecosystems including, for example, eutrophication and acidification of soils (Fangmeier et al., 1994). Increased N deposition can cause a significant shift in the N status of an ecosystem and lead to oligotrophic plant species being replaced by more nitrophilous varieties, resulting in a loss of biodi- versity (Bobbink and Roelofs, 1995). In order to protect ecosystems sensitive to increased N deposition, the distance travelled by, and concentrations of, NH 3 need to be accurately quantified. Passive NH 3 monitors have been used to assess the range of deposition (Fowler et al., 1998), but identifying the precise source can frequently be difficult (Sutton et al., 1998). However, to legislate for NH 3 abatement measures, the concentration and Water, Air, and Soil Pollution: Focus 4: 219–228, 2004. C  2004 Kluwer Academic Publishers. Printed in the Netherlands.