Date of Graduation

2017

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Omar I Abdul-Aziz

Committee Co-Chair

Kakan Dey

Committee Member

Khandker S Ishtiaq

Abstract

Net ecosystem exchange (NEE) indicates the balance between photosynthetic uptake and respiration of CO2 in a biological system. A large set of climatic and ecohydrological variables drives the dynamics of NEE through complex, interacting biophysical processes. The relative climatic and ecohydrologic linkages of NEE were determined in this study for different temporal scales (i.e., 1-hour, 1-day, 8-day, 15-day, and 30-day) by utilizing a systematic data analytics methodology. Pearson correlation matrix and factor analysis were employed to identify the interrelations and grouping patterns among the biophysical variables. The climatic and ecohydrologic linkages of NEE were then estimated using bootstrapped (1000 iterations) partial least squares regression by appropriately resolving multicollinearity among the drivers. Four biophysical components of NEE were identified based on hourly datasets from 57 AmeriFlux sites, representing six diverse ecosystems (wetland, cropland, grassland, evergreen, deciduous, and mixed forests) across North America. The multi-temporal (1-day to 30-day) dataset for the Florida Everglades short-hydroperiod marsh also indicated similar groupings. In general, NEE was strongly linked with the 'radiation-energy' (RE) component, while having a moderate linkage with the 'temperature-hydrology' (TH) component across the temporal scales. The 'aerodynamic' (AD) component was weakly linked to NEE; however, a moderate AD control on NEE was observed in the short canopy ecosystems at the 1-hour scale. The 'atmospheric CO2' (AC) component exhibited moderate to weak linkages with NEE across the temporal scales. RE and TH had a decreasing trend with the increasing time-scales (1-30 day) at the Everglades short-hydroperiod site. In contrast, the linkages of AD and AC components increased from 1-day to 8-day scales, and then remained relatively unchanged at the longer scales of aggregation. The estimated linkages provided valuable insights into the biophysical process components and drivers of ecosystem carbon across variable spatial and temporal scales. The findings would also help to develop robust, low-dimensional models to reliably predict ecosystem CO2 fluxes at variable times and space scales.

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