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Diffuse reflectance (visible) and attenuated total internal reflection Fourier-transform infrared (ATR-FTIR) spectroscopies were used to examine a colloidal nontronite clay in the presence of Fe2+(aq). pH-dependent changes are observed in both types of spectra. In the visible region, a broad feature at approximately 750 nm appears as the pH is raised to circumneutral values. This absorbance band overlaps with a portion of the spectrum of the chemically reduced clay which is dominated by an intervalence charge-transfer transition between Fe2+ and Fe3+ within the mineral structure. The similarities between these spectra suggest that Fe2+(aq) adsorbs to the clay in such a way that it can undergo charge transfer with structural Fe3+ within the clay. ATR-FTIR spectra at pH 5-8 reveal a transformation in the Si-O stretching region between pH 6 and pH 7 with a shift of the component peaks to lower frequency. Taken together, these spectroscopic studies indicate that Fe2+ forms an inner-sphere complex with the clay at higher pH values. The pH threshold for these observed changes in physical and electronic structure is in good agreement with the point of zero charge (pzc) of the hydroxyl groups on the edge surfaces of the clay, suggesting that complexation of Fe2+ to deprotonated edge sites leads to the observed spectroscopic features.

Development of natural landscapes to support human activities impacts the capacity of the landscape to provide ecosystem services. Typically, several ecosystem services are impacted at a single development site and various footprint scenarios are possible, thus a multi-criteria analysis is needed. Restoration potential should also be considered for the area surrounding the permanent impact site. The primary objective of this research was to develop a heuristic approach to analyze multiple criteria (e.g. impacts to various ecosystem services) in a spatial configuration with many potential development sites. The approach was to: (1) quantify the magnitude of terrestrial ecosystem service (biodiversity, carbon sequestration, nutrient and sediment retention, and pollination) impacts associated with a suite of land use change scenarios using the InVEST model; (2) normalize results across categories of ecosystem services to allow cross-service comparison; (3) apply the multi-criteria heuristic algorithm to select sites with the least impact to ecosystem services, including a spatial criterion (separation between sites). As a case study, the multi-criteria impact minimization algorithm was applied to InVEST output to select 25 potential development sites out of 204 possible locations (selected by other criteria) within a 24,000 ha property. This study advanced a generally applicable spatial multi-criteria approach for 1) considering many land use footprint scenarios, 2) balancing impact decisions across a suite of ecosystem services, and 3) determining the restoration potential of ecosystem services after impacts.

This project investigates the energy-water usage efficiency of large scale civil infrastructure projects involving the artificial recharge of subsurface groundwater aquifers via the reuse of treated municipal wastewater. A modeling framework is introduced which explores the various ways in which spatially heterogeneous variables such as topography, landuse, and subsurface infiltration capacity combine to determine the physical layout of proposed reuse system components and their associated process energy-water demands. This framework is applied to the planning and evaluation of the energy-water usage efficiency of hypothetical reuse systems in five case study regions within the State of California. Findings from these case study analyses suggest that, in certain geographic contexts, the water requirements attributable to the process energy consumption of a reuse system can exceed the volume of water that it is able to recover by as much as an order of magnitude.

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