In situ methane and nitrous oxide fluxes in soil from a transect in Hennequin Point, King George Island, Antarctic.

The study aimed at to determine the magnitude of the methane (CH(4)) and nitrous oxide (N(2)O) flux rates in soils at Hennequin Point, King George Island, Antarctic, under different slope positions, vegetal covers and presence of skuas, as well as to evaluate the main soil and climate factors that are involved with the flux of such gases. In situ gas sampling (closed chamber method) was performed in four sites along a transect involving a skua nesting field in a moraine with 5% and 100% of surface covered by vegetal, and two poor-drained soils in the toeslope (a bare alluvium soil and a poor-drained moss field with 100% soil cover). Flux rates ranged from -0.86±0.45 to 2.75±1.52 μg N(2)O-N m(-2) h(-1) and -12.26±3.05 to 1.42±1.31 μg CH(4)-C m(-2) h(-1). The soil totally covered by vegetal in the skua field had the largest CH(4) influx rates. However, this benefic effect was counterbalanced by the greatest N(2)O efflux rates from this soil, resulting in the largest contribution to the global warming potential among the soils evaluated. Flux rates were closely related to soil temperature, but no significant relation was observed with mineral N contents and water-filled pore space. In turn, accumulated CH(4) and N(2)O emissions were closely related to the total N and total organic C stocks in the soil. Net CH(4) influx predominated even in the poor-drained soils, suggesting that the coarse soil texture avoided critical anaerobic conditions. No significant changes in flux rates were observed for sampling time along the day.