Doctoral Dissertations

Date of Award

5-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geography

Major Professor

Carol P. Harden

Committee Members

Sean M. Schaeffer, Liem Tran, Sally P. Horn

Abstract

A better understanding of soil-water interactions and associated feedbacks in carbon-cycle processes is necessary for addressing knowledge gaps in the global carbon budget. This doctoral dissertation research investigated soil carbon-cycle processes in two ecosystems, Ecuadorian páramos and constructed agricultural wetlands, which are understudied in terrestrial carbon research. These sites represent ecosystems where land-use induced changes in soil moisture were expected to play an important role in soil carbon processes.

Soil carbon dioxide (CO2) flux and extracellular enzyme (EE) activities were measured to assess changes in soil carbon processes in soil from four types of land use in Ecuadorian páramos. Soil CO2 flux was greater at sites with tree cover, which had lower soil moisture content, than at grass páramo sites, with higher soil moisture content. The results suggest that soil CO2 flux responds to biological soil moisture thresholds, but the relationship between CO2 flux and moisture in aerobic and anaerobic conditions is unclear. Carbon-acquisition EE activity indicated that soil carbon resources were in high demand for microbial utilization under non-native pine trees. Despite high soil carbon content at the grass páramo site, high carbon-acquisition EE activity there indicated high microbial demand for carbon resources, possibly due to the development of more stable forms of pyrogenic soil organic matter from a history of burning for grazing management.

Field-based data and a controlled laboratory experiment were used to investigate the relationship between soil moisture and soil CO2 flux in two constructed agricultural wetlands with different hydrologic regimes, perennial and intermittent, in East Tennessee. The results suggest that constructed wetland hydrology plays an important role in soil moisture variability and mean CO2 flux, and highlight the importance of the hydrologic design of constructed wetlands with respect to potential CO2 emissions.

Results of this research suggest that soil moisture change due to land-use change can influence soil carbon decomposition and loss through CO2 flux. The relationships between soil moisture, land-use change, and CO2 flux have implications for land management and constructed wetland design.

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