Physical-Chemical Dynamics of Dissolved Gases in Wetland Soils: Implications for the Water Quality and Carbon Sequestration Functions of Wetlands

Abstract

Gas transfer phenomena are fundamental to the water quality and biogeochemical functions of wetlands. Characterizing the physical-chemical controls on wetland dissolved gas dynamics, and distinguishing those processes from the confounding influences of biochemical production and/or consumption, has been a challenge for wetland science. In this thesis I describe a set of laboratory, field, and modeling studies intended to resolve the eects of transport and gas exchange on the biogeochemistry

of complex soil - plant systems. Results are discussed in the context of the

water quality and carbon sequestration services provided by wetland ecosystems.

Gas tracers are used in push-pull measurements in well-controlled laboratory

experiments and in natural wetland environments to quantify the kinetics of root-mediated gas exchange in situ and to account for the effects of trapped gas bubbles on rate determinations. Root uptake of volatile chemicals from wetland soils is partitioned into different biophysical mechanisms, and an empirical relationship is developed to scale root-mediated gas exchange kinetics between different chemical compounds. The controls on tidal marsh methane dynamics are explored in a year-long field study, and a complementary set of observations reveals how spatially varying gas exchange pathways influence spatiotemporal patterns of subsurface

methane pools and contribute to seasonal lags in emissions. In the nal chapter, I shift my focus to a separate topic linking water resources and biogeochemistry, and develop a model for quantifying methane emissions from decomposing organic matter in pit latrines. A global water table model is used to determine aerobic versus anaerobic conditions in pit latrines, and is coupled with spatial sociodemographic data to estimate global emissions and to inform a discussion of mitigation opportunities and costs.