Precipitation over coal fly ash surfaces raises concerns about potential downstream impacts of dissolved selenium (Se) on aquatic ecosystems. Detention ponds hold runoff until aqueous Se concentrations meet water quality regulations: within 10 days, 90% of runoff must be discharged and cannot exceed 11.8 μg Se L-1 (ppb). Constructed wetland (CW) phytoremediation is a potential treatment option to meet these regulations. This research was conducted to 1.) Assess the potential of native southeastern aquatic macrophytes for Se tolerance and removal efficiency compared to unplanted (UNP) detention ponds; 2.) Evaluate seasonal influence on Se removal in CWs over four, weekly flood-discharge cycles; and 3.) Determine the effect of temperature on aqueous Se removal. Monoculture CW microcosms (110 L) were flooded six days with 500 or 1000 ppb Se, as selenite (SeO32-) or selenate (SeO42-) evaluating five plant species for Se tolerance. Seasonal evaluations were conducted with cattail (Typha angustifolia L.; CAT) and duckweed (Lemna minor L.; DWD) over four weekly flood-discharge cycles at 16 or 32 ppb SeO42--Se. Cattail, DWD, or UNP volatilization chambers (VCs) flooded with a 3 L solution at 35 ppb SeO42--Se were evaluated under 12 h photoperiod at either 20 or 30°C. All experiments contained a zero Se control. Water, plant, and soil total Se concentrations were determined by inductively coupled plasma-mass spectroscopy (ICP-MS) and analyzed with PROC GLM (SAS EG 7.1) at α=0.05. Cattail and DWD were selected for further evaluation with SeO42--Se. The greatest aqueous Se removal was observed in the summer (73%), followed by the fall (42%) and spring (41%), compared to winter (18%). Temperature was strongly correlated with Se removal (0.65, P<0.0001). Except for summer, after two flood-discharge cycles, CAT and DWD improved aqueous Se removal compared to UNP controls. Volatilization chamber data indicated greater Se removal at 30 (69%) compared to 20°C (54%). At 30°C, DWD decreased aqueous Se concentrations below 11.8 ppb Se within 10 days. Given their efficacy and abundance, CAT and DWD are deemed suitable species for phytoremediation in CWs supplied with Se-impacted waters.

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Phosphorus (P) is one of the three major macronutrients that plants need to grow and survive. When P is scarce, plants utilize a network of characterized responses known as the Phosphate Starvation Response (PSR) to remobilize internal stores of P as well as external P from soil. Emerging evidence shows the PSR is regulated by a specialized group of secondary messenger molecules, inositol pyrophosphates (PP-InsP). PP-InsPs and their precursors, inositol phosphates (InsPs), are important for plant abiotic stress responses, hormone signaling, and other stress responses. While PP-InsPs are critical for plant survival, much about the roles of PP-InsPs and how they are regulated remains to be understood. Further, the enzymes responsible for the synthesis of PP-InsPs in plants have been recently discovered; however, not much is known about the enzymes that degrade PP-InsPs in plants. The goal of the work presented herein is to understand critical aspects of the PP-InsP signaling in plants and leverage this information into a P phytoremediation strategy. To achieve this, I have investigated a group of PP-InsP phosphatases and assessed long-term impacts of depleting PP-InsPs in two plant species, Arabidopsis thaliana (Arabidopsis) and Thlaspi arvense (Pennycress). Exploring the impact of plant PP-InsP phosphatases has allowed me to explore critical aspects of PP-InsP sensing that show great promise for informing P remediation strategies. / Doctor of Philosophy / The Phosphorus (P) crisis presents a major challenge to food security. While Phosphorus (P) is critical for crop growth, P is a nonrenewable and increasingly limited resource. Our global population is fed at the expense of the remaining mineable P reserve, which may be depleted in as early as 30 years. Further, fertilizer runoff from farmland and urban areas poses a dangerous problem as increased nutrients in watersheds toxifies our water supply and aquatic ecosystems. Time is running out to preserve our P supply. New and innovative strategies that reduce fertilizer inputs and watershed pollution are key to securing the global food supply and protecting the environment. Emerging evidence shows plants sense and respond to P using signaling molecules known as inositol pyrophosphates (PP-InsPs). My work and that of others are key in showing that alteration of the levels of PP-InsPs can decrease plant P dependency or cause plants to hyperaccumulate P. Understanding how plants are able to sense, respond, and acquire P is crucial to inform future P phytoremediation strategies to secure global food security.

Phytoremediation is an attractive remediation technology due to its relative low cost and maintenance requirement. Acceptance of phytoremediation requires that the contaminant removal mechanisms are characterized and demonstrated in the field. Quantification of contributions from each mechanism to the overall remediation rate is crucial for optimization of phytoremediation systems, risk management and prediction of the total remediation time. The objective of this research was to characterize and quantify removal mechanisms for naphthalene at a creosote-contaminated site with poplar trees in Oneida, Tennessee. Groundwater monitoring for seven years in the surficial aquifer at this site demonstrated a reduction in polycyclic aromatic hydrocarbons (PAHs) with selective removal of naphthalene and three-ring compounds. Naphthalene mass loss mechanisms investigated at this site are biodegradation in the saturated zone, volatilization and biodegradation in the vadose zone and phytovolatilization. This is probably the most comprehensive field study of PAH phytoremediation mechanisms conducted to date. The significance of this research is to contribute to predictions of remediation time and end result for phytoremediation of PAHs. The understanding of in situ factors controlling each mechanism can facilitate future optimization of phytoremediation systems as well as improve risk assessment and monitoring strategies. Biodegradation rates were determined for different conditions at this site with in situ respiration tests, laboratory soil microcosms and laboratory soil columns. The combined remediation mechanisms of volatilization and biodegradation in the vadose zone were investigated in the field and in laboratory columns. Field measurements show that lower groundwater elevations in the summer and early fall lead to elevated groundwater concentrations of naphthalene and increased volatilization. The increase in the fraction of the porespace occupied by gas (gas saturation) in the unsaturated zone during the summer and fall further enhances the volatilization by increasing effective diffusion rates. Water consumption and interception by the phytoremediation system are believed to enhance mass transfer to the vadose zone. Column experiments and field measurements show that more than 90% of the naphthalene vapors are biodegraded within 5-10 cm above the groundwater table. The data indicate that biodegradation increases the overall volatilization flux out of the source by 10-300 times, when the source is exposed directly to the gas phase. In situ the naphthalene is generally dissolved from the source into the groundwater and then volatilezed from the groundwater to the gas phase. Under these conditions biodegradation in the vadose zone will still indirectly have an enhancing effect on the flux out of the source. This is the result of removal naphthalene from the soil gas by biodegrdation driving removal from the groundwater by volatilization, which in turn drives dissolution form the source into the groundwater. Phytovolatilization was quantified in flux chambers mounted on trees and calculated from transpiration rates. A laboratory uptake study and analysis of tree cores from the site provided supplementary evidence for naphthalene uptake by poplar trees. Phytovolatilization was detected throughout the year and was highest in the summer and fall when the groundwater concentrations were highest and transpiration was active. The role of biodegradation relative to physical removal mechanisms was compared for a year, for winter and summer conditions and with and without the impact of phytoremediation. Biodegradation of naphthalene in the saturated zone dominates by orders of magnitude over the removal by volatilization and phytovolatilization of naphthalene at this site. The removal of the total residual naphthalene mass was estimated to require up to 100 years with phytoremediation, but more than twice as long without phytoremediation. The estimated removal of naphthalene was three times larger in the summer than in the winter due to slower biodegradation in the saturated zone and smaller rates of volatilization to the vadose zone in the winter. The research shows that phytoremediation enhances the overall naphthalene removal, mainly by stimulating faster biodegradation in the rhizosphere and promoting mass transfer of naphthalene to the vadose zone followed by rapid vadose zone biodegradation. In the future, phytoremediation research focusing on the capillary zone is desirable. / Ph. D.

"Transparency- the ability to see into and understand the inner workings of a landscape- is an absolutely essential ingredient to sustainability" -Robert Thayer from "Green World, Green Heart" Current land filling practices that bury waste and debris below layers of earth and synthetic caps do not take into account the potential of reclamation of the site after the landfill debris has become stable. As development and consumerism increases, the need for land reclamation grows stronger, as earth will succumb to overabundance of human excessiveness. Can a space be created that not only reclaims land, but also exposes what is hidden- in order to educate the public on the importance of recycling and sustainability? Is it possible to design a space that addresses the issues and culture of the past, present and future, particular to a geographic site? Can landscape architects use landscape as an educational medium for self-discovery? / Master of Landscape Architecture

Floating treatment wetlands (FTWs) are an innovative best management practice that can enhance the performance of traditional retention ponds by increasing removal of the nutrients nitrogen (N) and phosphorous (P). FTWs consist of floating rafts on which wetland plants are planted, allowing the roots to be submerged below the water surface while the shoots remain above. A growing body of research has documented FTW performance with regard to urban runoff treatment, however evaluation of FTW effectiveness for treatment of agricultural runoff has received less attention. Due to high fertilization and irrigation rates, commercial nursery runoff contains much higher concentrations of N and P than runoff from urban areas. We conducted this study over two growing seasons (2015 and 2016) to assess the effectiveness of FTWs for use in commercial nursery retention ponds. In the first study we used two different nutrient concentrations, one to simulate nursery runoff (17.1 mg∙L-1 TN and 2.61 mg∙L-1 TP) and one to simulate concentrations that fall between urban and nursery runoff (5.22 mg∙L-1 TN and 0.52 mg∙L-1 TP). Four treatments were used: 1) Pontederia cordata planted in cups supported by a Beemat, 2) Juncus effusus planted in cups supported by a Beemat, 3) a Beemat with no plants, and 4) no treatment (open-water). Performance was evaluated based on a 7-day hydraulic retention time (HRT). Pontederia cordata removed between 90.3% and 92.4% of total phosphorus (TP) and 84.3% and 88.9% total nitrogen (TN), depending on initial loads. These reductions were significantly more than other treatments at both high and low nutrient loading rates. Juncus effusus performed better than the control treatments for TP removal at low nutrient concentrations, but did not perform any better than the control at higher nutrient loads. In the second study, conducted in 2016, we evaluated different plant species over two 8-week trials using simulated nursery runoff. We used five monoculture FTWs with the following species: Agrostis alba, Canna ×generalis, Carex stricta, Iris ensata, and Panicum virgatum. Additionally, two treatments were created from mixed species plantings and the final treatment consisted of an open water control mesocosm. Nutrient removal performance was evaluated over a 7-day HRT. P removal (phosphate-P) by FTW treatments ranged from 26.1% to 64.7% for trial 1 and 26.8% to 63.2% for trial 2. Trial 1 N removal (sum of ammonium-N, nitrate-N, and nitrite-N) efficiencies ranged from 38.9% to 82.4%, and trial 2 ranged from 12.9% to 59.6%. Panicum virgatum removed significantly more N and P than the control and any other FTW treatment in the second study. Both studies indicated, depending upon plant species, that FTWs can effectively remove nitrogen and phosphorous from urban and commercial nursery retention ponds. / Master of Science / Floating treatment wetlands (FTWs) are used to enhance the nutrient removal performance of stormwater retention ponds. FTWs consist of a buoyant raft on which wetland plants are planted, allowing the shoots to extend above the water surface while the roots stay submerged. The purpose of this research was to evaluate FTW nutrient removal performance in a commercial nursery environment where runoff has much higher concentrations of nitrogen and phosphorous than urban stormwater. The study spanned across two growing seasons (2015 and 2016), during which, different plant species and nutrient concentrations where evaluated. The first study evaluated Pontederia cordata and Juncus effuses as well as two control treatments at a high nutrient concentration and a low nutrient concentration. The Pontederia cordata performed better than the other treatments at both the high and low initial nutrient concentrations. In the second study, the following species were evaluated using a combination of mixed and monoculture plantings: Agrostis alba, Canna ×generalis, Carex stricta, Iris ensata, and Panicum virgatum. Panicum virgatum removed significantly more nitrogen and phosphorous than any other FTW treatment in the second study. Both studies indicated that FTWs can be effective technologies for nutrient removal from urban and commercial nursery retention ponds.