Earth and Atmospheric Sciences, Department of


First Advisor

Dr. Vitaly Zlotnik

Date of this Version



Adane, Z. A. (2017). Evaluating the impacts of grassland conversions to experimental forest on groundwater recharge in the Nebraska Sand Hills. Doctoral dissertation. University of Nebraska-Lincoln.


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Earth and Atmospheric Sciences (Hydrogeology), Under the Supervision of Professor Vitaly A. Zlotnik. Lincoln, Nebraska: April, 2017

Copyright (c) 2017 Zablon A. Adane

Chapter 2 and Chapter 3 of this dissertation are published in Hydrogeology Journal and in Forest Science, respectively. Chapter 4 is ready to be submitted to Journal of Hydrology.


The Nebraska Sand Hills grasslands provide the greatest groundwater recharge rates in the High Plains Aquifer. However, the grasslands and their ecological services have become vulnerable to land use change and degradation. This study used a series of field data to investigate the effects of grassland conversions to forest on recharge rates in a century-old experimental forest in the Sand Hills. The results show that the impact of grassland conversion on recharge was dependent on the species and plantation density. Estimated recharge rates beneath the dense plantations represent reductions of 86–94% relative to the native grassland. Results of 1H Nuclear Magnetic Resonance spectral analysis suggested that the surface soil organic carbon beneath pine plantations also contain up to 3 times the ratio of hydrophobic components than the native grasslands and may alter the soil hydraulic properties. This investigation further uncovered a previously overlooked feedback between the effect of soil organic carbon chemical shift generated by the ponderosa pine needle litter decomposition; namely that the alteration may have a link to reduced groundwater recharge rates. Thus, a global optimizer algorithm was used to estimate the effective soil hydraulic parameters from monthly soil moisture contents and recharge rates were then estimated through HYDRUS 1-D numerical modeling for grassland and pine forest soils. The impact of grassland conversion to pine was an overall reduction of groundwater recharge by nearly 100%. These outcomes highlight the significance of the grasslands for recharge, in the Sand Hills and the sustainability of the High Plains Aquifer.