Mosses and lichens are important components of arctic ecosystems as well as being an internationally important component of the biodiversity of the British Isles and Scandinavia. They are typically associated with nutrient poor ecosystems and are often eliminated with increased supplies of nitrogen. This study is part of a programme examining the impact of elevated nitrogen in nutrient poor ecosystems on mosses and lichens. This particular study will examine the contribution of airborne nitrogen in the form of ammonia to the growth of mosses in the arctic tundra in Kongsfjord. Breeding colonies of seabirds deposit large quantities of guano, which can be major sources of nitrogen as well as heavy metals (Headley 19xx) and other contaminants in the marine ecosystems. The nitrogen in fish and other organisms high up in the marine food chains have higher concentrations of the heavier stable isotope of nitrogen called 15N. The ratio of this isotope to the usual isotope of nitrogen (14N) can be used as a marker as to the relative contributions of different forms of nitrogen that are being utilised by an organism. By taking samples of moss at different distances from seabird colonies and analysing these and the soil and guano for the concentrations of the two stable isotopes of nitrogen (15N:14N ratio) the relative contributions of nitrogen from the soil and atmosphere can be determined. This can then be utilised along with details of the relative abundance of the mosses along transects away from seabird colonies to ascertain how important atmospheric ammonia is in altering the species composition of moss communities.