BIRD EFFECTS ON ORGANIC PROCESSES IN SOILS FROM 5 MICROHABITATS ON A NUNATAK WITH AND WITHOUT BREEDING SNOW PETRELS IN DRONNING-MAUD-LAND, ANTARCTICA

Five microhabitat types with varying degrees of bird influence were ex amined. Soils were collected from open polygons, under mosses and bird nests on a nunatak with breeding snow petrels (Pagodroma nivea) and f rom open polygons and under mosses on a non-bird nunatak. Nutrient lev els (total N and P, nitrate, nitrite and ammonia), moisture levels and delta(15)N values were determined and the organic processes of nitrog en fixation (acetylene reduction) and soil respiration (CO2 flux) were examined. Nests represented the most favourable microhabitat type for soil respiration having the highest nutrient levels and most favourab le temperature and moisture regimes. The soils under mosses were also Favourable and appear to act as a nutrient sink for nutrients originat ing from the nests. The open polygons were the least favourable for bi ological activity. There was little nitrogen fixation in any of the so ils except for the soils under mosses from the non-bird nunatak. Fixat ion is possibly limited in favourable microhabitat types on the bird n unatak by high nitrogen levels. These results were confirmed by the de lta(15)N results, which had high values typical of a seabird signal in the soils from the bird nunatak and values near zero, typical of soil s containing fixed nitrogen, on the non-bird nunatak.