Departments: Biomedical | Civil & Environmental | Electrical & Computer | Mechanical

2008-2009

Matthew Grunstra PhD Thesis

Title: Investigation of Juniperus Woodland Replacement Dynamics

Supervisor: Dr. Oscar Van Auken

Abstract: Juniperus encroachment is occurring in many northern hemisphere grasslands.  However, there have been few studies of mature Juniperus communities or community replacement especially considering predicted increases in atmospheric CO2 and temperature.  In central Texas woodlands, Juniperus ashei and Quercus virginiana were the major canopy species but varied in relative density and basal area depending on the site.  Markov models suggest that when there is a species in greater numbers in the understory, J. ashei will become a lesser component of the canopy.  Gas exchange measurements for ten species (J. ashei, Ungnadia speciosa, Diospyros texana, Ulmus crassifolia, Q. virginiana, Garrya lindheimeri, Sophora secundiflora, Celtis laevigata, Juglans microcarpa and Sapindus saponaria) indicate a variety of shade and drought tolerances.  Juniperus ashei was identified as a shade intolerant species and therefore less likely to sustain growth and replacement in a closed canopy, and elevated CO2 would have little effect on its shade tolerance. The ambient CO2 SORTIE models indicated that J. ashei woodlands will be replaced with a mixed deciduous canopy composed of Q. virginiana, C. laevigata and U. crassifolia trees.  But the elevated CO2 SORTIE model showed J. ashei will be maintained as a major component of the canopy in a denser woodland.  From this study, the majority of the Markov models, the photosynthetic data and the SORTIE models suggest that J. ashei woodlands that are currently established are not the final climax community, but changes will continue into the future. 

 

Syam Sundar Andra PhD Thesis

Title: Phytoremediation of Lead Contaiminated Soils

Supervisor: Dr. Rupali Datta

Abstract: Despite considerable national public health efforts to reduce lead (Pb) exposure, Pb poisoning remains the most common environmental health problem affecting the children in the U.S. Phytoremediation is emerging as an attractive option for cleanup of Pb paint-contaminated soils in housing facilities built prior to 1978. The objective of this study was to investigate the use of a high biomass, metal tolerant grass, Vetiveria zizanioides (vetiver grass), to remediate Pb paint-contaminated residential soils of variable physico-chemical properties. Developing a successful phytoremediation model requires a good understanding of the role of soil properties governing Pb availability for plant uptake, biochemical mechanisms involved in Pb tolerance, and changes in Pb bioaccessibility. Therefore, a comprehensive greenhouse-based study was conducted to evaluate the effectiveness of vetiver in Pb uptake and reducing soil Pb concentrations. Chelation of Pb is an important factor in enhancing its solubility and therefore availability to vetiver to promote phytoremediation. We compared the effects of two chelating agents – namely ethylenediaminetetracetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS) – at 4 different concentrations such as 0, 5, 10 and 15 mmol kg-1 soils. Our studies indicate that (1) soil properties determine the extent of soluble Pb; (2) EDTA is more effective than EDDS in mobilizing bound soil Pb; (3) unlike EDTA, EDDS reduced the leachable Pb fraction in soils; (4) activities of antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase were elevated in vetiver under Pb stress; (5) lead-binding phytochelatins were induced as a Pb tolerance mechanism; and (6) Pb bioaccessibility in soils decreased with an increase in Pb uptake by vetiver. This study demonstrated that EDDS could be regarded as a good chelant candidate for the environmentally safe phytoextraction of Pb using vetiver grass in Pb paint-contaminated residential soils.

Rachana Nagar PhD Thesis

Title: Effectiveness of Al- and Fe-based Drinking Water Treatment Residuals in Remediating Soil Arsenic: Mechanisms and Implication

Supervisor: Dr. Dibyendu Sarkar

Abstract: The phenomenon of urban sprawl around metropolitan areas has given rise to serious concerns regarding the risk of human contact with arsenic (As)-contaminated soils. The utilization of a drinking-water treatment residual (WTR) was proposed as a cost-effective technology for As remediation. WTR is a by-product of the drinking water purification process and contain sediment, organic matter, Al/Fe hydr (oxides), and activated carbon. WTRs are typically amorphous and have a high affinity for oxyanions due to high specific surface area. The ultimate goal of the present study was to evaluate the effectiveness of WTR (Al- and Fe-based) in lowering the human health risk from soil As exposure. We conducted: a) short-term laboratory studies to evaluate the detailed As adsorption mechanism of WTR and WTR-amended soils, because only a fraction of soil As is available that is not retained or adsorbed; and b) long-term (3 years) greenhouse studies to examine the effectiveness of WTR on geochemical speciation, in-vitro (simulated human gastrointestinal conditions), and in-vivo (animal study) As bioavailability in inorganic and organic As pesticide-amended soils. Results indicated that As adsorption by WTRs was a function of solution properties. Adsorption of As onto the Al-WTRs were stronger than onto Fe-WTRs. Arsenic bioaccessibility (in-vitro) significantly decreased by ~60% in WTR-treated soils compared to WTR-unamended controls over a 3-year time period. In-vivo (relative bioavailability) results confirmed the trend observed in in-vitro tests. Results showed that WTR amendment has the potential to develop into an effective remediation technology for As-contaminated soils.

 

Blake Weissling PhD Thesis

Title:Watershed Streamflow Estimation Utilizing Remote Sensing time-series proxies of landscape moisture state and radar precipitation.

Supervisor: Dr. Hongjie Xie

This research conjectures that streamflow in large (> 250 km2) semi-arid watersheds, in south central Texas, can be reasonably estimated with statistical regression methods based on a model solely parameterized by remote-sensing derived proxies for landscape moisture state and radar (NEXRAD) precipitation estimates.  The utility of such an approach is obvious:  estimating streamflow in watersheds for which no other flow records exist.  The structure of the research methodology is based on three stages, 1) test the initial hypothesis that remote-sensing-derived biophysicals of the landscape (in a test watershed) are sensitive to land surface soil moisture state, and compare the resulting model against a benchmark model for streamflow estimation, 2) re-assess the significance of the previous model parameters (and evaluate new parameters) in the same test watershed for an extended calibration and validation period, and 3) test for the transferability of parameters to three regionally proximate watersheds of varying dimension and environmental condition. Chapter 2 reports on the development of the original model, including a discussion of the forward stepwise regression approach for the initial selection of model parameters.  Spatially distributed NEXRAD radar precipitation estimates are introduced as an improvement over local gauged estimates.  A benchmark comparison model, the Natural Resource Conservation Service curve number method, is built with multiple approaches for assessing antecedent moisture condition.  The curve number method model is compared to the remote sensing model, demonstrating that the remote sensing model performs at least as well as the benchmark model, as assessed with standard efficiency criteria.             Chapter 3 continues the basic line of research but significantly expands on the evaluation of other remote sensing derived parameters potentially sensitive to landscape moisture status.  The effects of deseasonalizing (removing long-term mean seasonal variation) the parameters are assessed.  A final parameter set consisting of the radar precipitation estimate and two biophysical parameters derived from MODIS/TERRA satellite imagery, a land surface temperature and a vegetation moisture stress index, are regressed against a 4-year streamflow gauge record in the test watershed.  The resultant calibrated streamflow estimation equation is applied to a 15 month follow-on period for model validation. Finally, Chapter 4 evaluates the validity of applying the test watershed regression equation to three regionally proximate watersheds for the generation of a 4-year modeled flow series for each watershed.  The efficiencies of these series are assessed against known gauged flow records.  The results indicate that the estimation equation performed reasonably well at predicting streamflow for the watershed most similar to the test watershed in environment and dimension, with an expected loss of efficiency in the watershed for which environment and climate were most dissimilar.  The estimation equation was recalibrated with parameter sets specific to each watershed with much improved results.  Chapter 5 represents a significant departure from the line of research presented in chapters 2 – 4, although it is also framed within the realm of remote sensing imagery analysis.  An imagery acquisition system was built and deployed (by the author) for the monitoring of sea ice during the Sea Ice Mass Balance in Antarctica (SIMBA) expedition of 2007.  A post-processing image analysis methodology was developed to accurately quantify sea ice state, such as ice concentration, floe size, and area of deformed ice.  The techniques developed represent ground-breaking research for sea ice monitoring and analysis.