Nitrogen isotope ratios in pine bark as an indicator of n emissions from anthropogenic sources

The article describes the use of Scots pine bark to identify nitrogen sourc es in eastern Germany, as well as background areas in Russia and Bulgaria, by using natural isotope ratios of total nitrogen (N-t) and individual N co mpounds such as ammonium (NH4+), nitrate (NO3-) and amid nitrogen (amide-N) . The samples collected were analysed using an elemental analyser in connec tion with a gas isotope mass spectrometer (EA-IRMS). Natural N-15 abundance s in pine bark from impact areas suggest that the ammonium accumulated on t he surface of the bark is released from livestock management. Bark of Scots pines growing near agricultural land had highly depleted delta N-15(t) val ues (between -8 and -12 parts per thousand), while bark from background are as (unpolluted areas) displayed slightly negative delta N-15(t) values (mea n N-15(t) = -3.8 parts per thousand). It is assumed that part of the N adso rbed on the bark surface is mainly derived from ammonia (mean N-15(t) = -40 .3 parts per thousand) escaping from livestock housing and during the appli cation of manure. This assumption is confirmed by experiments under control led conditions in which manure samples were spread on soil. In addition, te mporal and spatial variations of N-15(t) abundances in pine bark from vario us locations in eastern Germany as well as pine stands in Nature Park Duben er Heath are discussed.