Nitrous oxide emissions from Amazonian ecosystems

Nitrous oxide (N{dollar}sb2{dollar}O) is a long-lived greenhouse gas and the chief source of nitric oxide (NO) in the stratosphere, an important catalyst in deletion of the ozone shield. The humid tropics are the largest known source, natural or anthropogenic, contributing to increasing levels of atmospheric nitrous oxide (N{dollar}sb2{dollar}O). This research evaluated N{dollar}sb2{dollar}O emissions from different ecosystems in the Central Amazon Basin. Field studies over two years near Manaus, Brazil (1) developed methodologies for monitoring N{dollar}sb2{dollar}O emissions from humid tropical environments, (2) compared N{dollar}sb2{dollar}O emissions from terra firme forest and abandoned pasture ecosystems over an annual cycle, (3) characterized spatial and temporal patterns of N{dollar}sb2{dollar}O emissions from the terra firme forest and abandoned pasture sites, and (4) identified the soil physical and chemical properties affecting N{dollar}sb2{dollar}O emissions from these humid tropical ecosystems.; A double injection valve process was used for the chromatographic analysis of ambient levels of N{dollar}sb2{dollar}O which eliminated the need for sample preparation and backflushing. A closed, vented soil cover with a minimum surface area of 300 cm{dollar}sp2{dollar} and volume of 3 liters gave the highest flux estimates from an abandoned pasture site. Nitrous oxide samples (330, 915 and 1376 ppbv) stored in glass serum bottles retained 95% of their original concentration after 450 hours of storage.; Mean N{dollar}sb2{dollar}O emissions were slightly higher at the abandoned pasture site (1.75 kg N{dollar}sb2{dollar}O-N ha{dollar}sp{lcub}-1{rcub}{dollar} y{dollar}sp{lcub}-1{rcub}{dollar}) than at the terra firme forest (1.36 kg N{dollar}sb2{dollar}O-N ha{dollar}sp{lcub}-1{rcub}{dollar} y{dollar}sp{lcub}-1{rcub}{dollar}). Seasonal N{dollar}sb2{dollar}O flux patterns were directly correlated with soil moisture patterns when water filled pore space was below 75% at both ecosystems. During the dry season the abandoned pasture site had consistently higher soil moisture levels resulting in higher N{dollar}sb2{dollar}O emissions. At the height of the rainy season N{dollar}sb2{dollar}O emissions at the abandoned pasture declined when water filled pore space exceeded 75% resulting in higher N{dollar}sb2{dollar}O flux from the terra firme forest for a two month period.; Temporal patterns of N{dollar}sb2{dollar}O flux reflected increases or decreases in emissions from a majority of the permanently located sampling points at each site. Nitrous oxide emissions from the terra firme forest and abandoned pasture sites showed remarkable spatial stability over the sampling period. High and low flux sampling points remained relatively high and low throughout the experiment. Spatial variability increased in both ecosystems as the distance between sampling points increased. Monitoring of tropical ecosystems will require distributing sampling points over large areas to make accurate emission estimates.; Multiple regression analysis of N{dollar}sb2{dollar}O emissions indicated that soil surface properties affected N{dollar}sb2{dollar}O loss. Nitrous oxide emissions tended to increase with increased total nitrogen, water filled pore space, phosphorous, aluminum saturation and volumetric water content in both the terra firme forest and abandoned pasture. Reduced emissions were associated with increases in sand content. These soil physical and chemical properties predicted 35% and 17% of N{dollar}sb2{dollar}O emissions from the abandoned pasture and terra firme forest ecosystems, respectively. Information on vegetation type, soil properties, and climatic conditions may be used to better estimate N{dollar}sb2{dollar}O release from the Central Amazon Basin.