Biological sources and sinks of methane in tropical habitats and tropical atmospheric chemistry

This dissertation describes investigations of the magnitudes and mechanisms of methane emission from tropical wetlands as well as the flux of methane from well-drained tropical soils. The impact of deforestation on regional and global atmospheric chemistry is reviewed and modeled.; Chamber techniques and a novel inverted funnel bubble trapping technique were developed to study wetland methane emissions. Where bubbling was the major route of methane emissions from wetland sediments to the atmosphere, the funnel technique measured emissions more efficiently and precisely than the chamber techniques.; Emission of methane by bubbling dominated methane emission to the atmosphere from Gatun Lake, Panama. Methane emission occurred episodically. Bubbling episodes were most common for several hours around noon. Wind triggered bubbling episodes. Average bubble methane concentrations ranged from 67 to 77%.; Methane emission from Gatun Lake measured by chamber and bubble trap techniques was strongly anticorrelated with water depth. Typical methane emissions were 10 to 200 mg m{dollar}sp{lcub}-2{rcub}{dollar} d{dollar}sp{lcub}-1{rcub}{dollar} for sites deeper than 7 meters and 300 to 2000 mg m{dollar}sp{lcub}-2{rcub}{dollar} d{dollar}sp{lcub}-1{rcub}{dollar} for shallow sites less than 2 meters.; Methane emission from swamp and marsh localities was strongly seasonal. Emissions dropped to near zero when soils dried in the dry season. Annual methane emissions from the swamp and marsh sites ranged from 100 to 500 mg m{dollar}sp{lcub}-2{rcub}{dollar} d{dollar}sp{lcub}-1{rcub}{dollar}.; Methane flux at rain forest and moist forest sites depended on soil moisture. During the dry season soils consumed methane at rates slightly less than 1 mg m{dollar}sp{lcub}-2{rcub}{dollar} d{dollar}sp{lcub}-1{rcub}{dollar}. During the wet season, moist forest fluxes were similar while rain forest soils emitted about 1 mg m{dollar}sp{lcub}-2{rcub}{dollar} d{dollar}sp{lcub}-1{rcub}{dollar}. The conversion of moist forest sites to pasture and agriculture diminished soil methane consumption by a factor of 4.; Conversion of tropical forest to agriculture and pasture will have global and regional atmospheric effects. Exports of odd-nitrogen compounds and greenhouse gases will increase after deforestation. Tropical forest regions could switch from being a global sink for tropospheric ozone to being a source. Regional episodes of high troposphreic ozone concentration and acid deposition are likely under current patterns of deforestation and development.