Date of Award

2019

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering (PhD)

Administrative Home Department

Department of Civil and Environmental Engineering

Advisor 1

Alex Mayer

Advisor 2

David Watkins

Committee Member 1

Joseph Wagenbrenner

Committee Member 2

Robert Handler

Abstract

A simulation-based framework for studying hydrologic impacts and associated tradeoffs for existing and proposed biofuel projects in the US (poplar), Argentina (eucalyptus) and Mexico (oil palm) is developed. For each case study, a representative watershed is selected and a SWAT model is set up and calibrated for an improved simulation of hydrologic processes and plant growth cycles. Potential bioenergy scenarios are developed that represent various planting densities, harvest cycles, fertilization and irrigation rates, land cover types being converted, slope, and locations across the watershed.

Simulations indicate that growth and biomass production are significantly dependent on nitrogen availability, making fertilization a necessary management practice. However, there is a threshold beyond which further fertilization has no impact on yield and only increases the potential for non-point source pollution from contaminated runoff and leaching of nutrients. In contrast to fertilization, irrigation is not an impactful parameter due to the high average annual precipitation amounts in the case study watersheds.

All the studies show significantly higher water use (evapotranspiration, ET) by the bioenergy feedstock due to fertilization, high planting density and/or morphology of the trees compared to the land cover that they replace. Simulation results indicate that average annual ET rates are 24%, 24% and 45% higher for poplar, eucalyptus and oil palm, respectively.

The higher water use leads to a decrease in streamflow, especially during the low-flow months and dry years. The timing and degree of change in the streamflow is dependent on the crop, area of the plantation, and climate. On a watershed scale, the average annual decreases in streamflow as a result of planting poplar (on 70% of the watershed), eucalyptus (63% of the watershed) and oil palm (62% of the watershed) are found to be 21%, 28% and 9%, respectively.

In all case studies, management practices are demonstrated to be significantly sensitive parameters for improving yield and mitigating negative environmental impacts. Water-energy tradeoff curves are plotted for each case to evaluate the most efficient management practices in terms of water and fertilizer use. The most productive scenarios can produce up to 6.5, 12.8 and 12.9 ton/ha/year biomass for poplar, eucalyptus and oil palm, respectively.

Farm gate-level water footprints to produce bioenergy are estimated for all the case studies, indicating a lower water requirement for biodiesel production from eucalyptus compared to other case studies and reported values in literature. The green water footprint estimates indicate 98, 57 and 87 m3 water/GJ for poplar, eucalyptus and oil palm, respectively.

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