Ecology

The availability of carbon (C), nitrogen (N) and sulfur (S) for the vegetation has increased in many ecosystems on earth since beginning of the industrial revolution. The change in availability of these essential nutrients has affected ecosystem functions in a complex manner. Stable isotopes on natural abundance level have turned out to be among other techniques a suitable tool to study the fate of C, N and S inputs to ecosystems due to the frequently distinct isotope signature of the C, N and S sources of anthropogenic origin. n , i s contribution summarises in its fist part present knowledge on the stable isotope signature of C, N and S compounds of anthropogenic origin, which are already known to play a major role as inputs to ecosystems, like COz, SOz and NO, from fossil fuel combustion, NH3 from livestock farming and nitrate and ammonium either originating from NO, or NH3 and deposited in wet or dry form or originating from mineral fertilizer applications to agricultural ecosystems. The second part presents case studies, which have already successfully used natural isotope abundances in various ecosystem compounds to trace C, N and S inputs of anthropogenic origin to terrestrial ecosystems. These studies are mostly based on two source mixing models (natural source versus anthropogenic source) and on different isotope signature of these two sources. From the literature are, however, also case studies available, which indicate that simplistic two source mixing models are not always suitable to quantify anthropogenic nutrient inputs to ecosystems. The latter case studies are mainly dealing with the rather complex nitrogen cycle. Vegetation and soils of ecosystems exposed to high N inputs tend to become enriched in "N despite of I5N depleted N inputs. This phenomenon is explained by losses of "N depleted N compounds ( N 2 0 emission, N H 3 volatilisation, nitrate leaching) due to ecosystem N saturation.