Environmental Science & Technology Theses and Dissertations

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NATIVE PLANTING IN TIDAL WETLANDS FOR PHRAGMITES AUSTRALIS MANAGEMENT: FIELD AND MESOCOSM EXPERIMENTS
(2022) Jacobson, Sylvia Rebecca; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Efforts have been made in U.S. wetlands to eradicate the invasive grass Phragmites australis. But eradication of Phragmites does not always lead to the return of native plants. This research investigated native vegetation recolonization across 12 tidal wetland study sites in the Chesapeake Bay watershed and tested the potential of planting perennial native wetland species to accelerate site recovery following Phragmites removal. Our study found that site salinity was a dominant driver of plant recolonization rate: low salinity sites (0.5-3 ppt) had, on average, 4.3x greater aboveground biomass and 2.5x higher vegetation cover than brackish sites (5-9 ppt) two or more growing seasons after Phragmites removal. The composition of returning plant species also differed by salinity, with a higher abundance of annuals and fewer graminoids at low-salinity sites. Site hydrology also influenced native plant recolonization—more frequently flooded sites had lower aboveground biomass of native vegetation two or more years following Phragmites removal. Experimental planting had variable results, with high die-off at several sites, but showed potential to accelerate vegetation recovery at brackish sites in the first years after Phragmites removal—plots with transplants at brackish sites had 17.5x, 2.4x, and 1.5x higher plant cover than unplanted plots in years one, two, and three, respectively, after planting. All sites had some amount of native vegetation recovery within three to four years following Phragmites removal, suggesting that native planting may not be necessary for many tidal wetland sites. Sites with especially high salinities and flooding frequencies may benefit the most from plantings, as larger plants may be able to survive in conditions that are not favorable for seedling emergence. In a mesocosm experiment, we planted six different clonal wetland species in a sand-vermiculite mixture at three different elevations in a tidal creek on the Rhode River in Maryland, USA. We found that peak plant biomass in the sandy substrate occurred at lower elevations and higher flooding frequencies than is typical in marsh environments and than was observed in other mesocosm experiments with organic soils. In well-drained, sandy substrates, wetland plants may benefit from more frequent tidal pulses, likely due to increased water supply and nutrient flux. This has implications for wetland-restoration practitioners using dredged sand to create or elevate tidal wetlands, as wetland species may grow at different elevations and flooding frequencies in these conditions than in a typical tidal marsh with organic soils.
DISTRIBUTION AND VARIABILITY OF CARBON STOCKS IN MID-ATLANTIC TIDAL MARSH SOILS
(2022) Kim, Jordan; Rabenhorst, Martin C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Tidal marsh wetlands have the capacity to store disproportionately large quantities of Cdespite their small areal extent. Good estimations of this “blue C” are now more critical than ever due to implications for the global C cycle and climate change, especially since C storage in tidal marshes has historically been understudied. In this study, we set out to measure, more accurately estimate, and conceptually model the C stocks in representative tidal marshes of the Mid-Atlantic region. We found that C storage differs significantly in marshes formed among various pedogeomorphic settings due to differences in pedogenic processes and soil morphology. Further, we have demonstrated that the mean C densities of particular soil materials can be used in conjunction with soil morphological descriptions to reliably estimate the C stocks in the absence of laboratory data. Finally, we augmented existing concepts of tidal marshes in the region by incorporating newly gained understandings of the spatial changes in morphology and C stocks across marshes within different pedogeomorphic settings.
SUSTAINABLE WATER RESOURCES MANAGEMENT THROUGH AGRICULTURAL WATER REUSE: APPLICATION OF A DECISION SUPPORT SYSTEM
(2022) SHOUSHTARIAN, FARSHID; NEGAHBAN-AZAR, MASOUD; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The water crisis caused by climate change, population growth, high urbanization rate, lifestyle changes, and industrialization has decreased global access to safe freshwater resources. As the primary food-producing and the largest water-consuming sector, agriculture heavily depends on water availability. Incorporating alternative water supplies (e.g., water reuse) can reduce freshwater demands, addressing water crisis consequences. Water reuse generally includes recycling treated effluent (known as recycled water) from wastewater treatment plants for different applications (e.g., agricultural irrigation). This alternative water resource can reliably and sustainably increase the resiliency of agriculture to water shortage. However, the complexities inherent in water resources management and the challenges associated with water reuse make planning and managing agricultural water reuse practices demanding. Agricultural water reuse projects include many interrelated/ interconnected components, including the human (e.g., farmers) and technical (e.g., engineering and natural infrastructures) components. The abilities of existing models are limited in simulating these components’ complex and adaptive behaviors. It is necessary to utilize tools capable of capturing these complexities and adaptations to plan and manage agricultural water reuse practices sustainably.The main research question of this dissertation was: How to capture the complex and adaptive dynamics of socio-hydrological systems inherent in sustainable water resources management when alternative water sources are introduced in the water supply system? The primary focus of the dissertation was to develop a dynamic decision support system that can successfully simulate the complexities and adaptations inherent in agricultural water reuse practices. It aims at increasing the existing knowledge regarding agricultural water reuse planning and management and help water resource decision-makers make sustainable and better-informed decisions in agricultural water reuse practices. To accomplish this goal, first, the literature was thoroughly reviewed to identify, collect, and analyze the data related to agricultural water reuse (e.g., current agricultural water reuse regulations and guidelines). Second, two models were developed using a “bottom-up” approach to study two agricultural water reuse practices in the Southwest (CA) and Mid-Atlantic (MD-DE) regions. These two models were used to further study the dynamics of agricultural water reuse adoption by farmers and their impacts on local water resources. The results showed that the regulations and guidelines were mainly human health centered, insufficient regarding some potentially dangerous pollutants such as emerging constituents, and with large discrepancies when compared with each other. In addition, some important water quality parameters, such as pathogens, heavy metals, and salinity, were only included in a few of the regulations and guidelines investigated in this study. Finally, specific treatment processes were only mentioned in some of the regulations and guidelines, with high levels of discrepancy. Moreover, results showed that agricultural water reuse adoption by farmers is a gradual and time-consuming process. In addition, results also showed that agricultural water reuse could significantly decrease the water shortage (by 57.7%) and groundwater withdrawal (by 74.1%) in CA. The results also showed that climate change and recycled water storage capacity and unit price were among the top factors with significant influence on agricultural water reuse practice studied in this dissertation. This study demonstrated the importance of conducting time-varying sensitivity analysis for complex simulation models. Furthermore, results demonstrated that implementing agricultural water reuse could decrease farmers' water shortage, groundwater consumption, and surface water consumption (by almost 19.5 %) in MD. This dissertation’s results can help decision-makers effectively take advantage of agricultural water reuse projects and other alternative water resources to plan and manage water resources sustainably.
Decentralizing Stormwater Management: Shifting Infrastructure and Evolving Hydrosocial Relationships
(2022) Wilfong, Matthew Tyler; Pavao-Zuckerman, Mitchell; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Stormwater management has historically remained in the technocratic realm of engineers and scientists disconnecting society from stormwater to protect public and environmental health. Despite incremental improvements, state and local governments are beginning to change their management practices and techniques in response to climatic changes, increased urbanization, and intensifying regulatory pressures. Scholars and practitioners have argued that this paradigm shift in stormwater management is required to continue to protect public and environmental health and reach regulatory goals. Despite the need for this paradigm shift, there continues to be slow progress towards decentralization. Thisshift is characterized by two key developments: the increased implementation of decentralized green infrastructure and increased involvement of individuals in managing stormwater. Broadly, this dissertation sets out to investigate two key aspects of this paradigm shift: (1) the hydrologic performance of these decentralized practices and (2) the social, political, cultural, and economic dynamics that are currently underpinning this paradigm shift. This dissertation begins with a chapter investigating the hydrologic performance ofdecentralized, green infrastructure treatment trains in Clarksburg, MD. Using stormwater monitoring methodology, we analyze how effectively treatment trains can hydrologically manage stormwater and the effects of precipitation dynamics on the ability of these treatment trains to manage stormwater. This research suggests that these treatment trains are generally highly effective at managing stormwater volumes across a host of storm events with an average of 93% of discharge abated throughout the monitoring period. We also demonstrate that precipitation intensity was the most influential precipitation dynamic on the performance of each treatment train suggesting that designing these treatment trains with the potential higher prevalence of higher intensity storm events due to climate change. To begin the social science portions of the dissertation research, we utilize an alternative framework, the hydrosocial cycle, to analyze how stormwater and society have and continue to shape each other over time. Building upon this work, we investigate the political, social, and cultural dynamics influencing and arising within this paradigm shift occurring within stormwater management. Through semi-structured interviews and Q-methodology within two urban watersheds in Maryland and Washington DC, we assess changes in the hydrosocial relationships between stakeholders and stormwater. Using these insights, we discuss the potential for alignment and cooperation among these diverging hydrosocial relationships and continuing the shift towards decentralizing stormwater management. Arising from this holistic and critical analysis, we seek to provide actionable recommendations focused on how, where, and who manages stormwater to reach more sustainable, resilient, and equitable outcomes. Additionally, we aim to demonstrate the effectiveness of theseframeworks and methodologies to better attend to political and power dynamics involved in water governance and management, more broadly
Biosolids and Compost For Urban Soil Restoration and Forestry
(2022) Keener, Emily Cathryn; Pavao-Zuckerman, Mitchell A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Elements of urban soil quality such as compaction and low organic matter are underexamined, important challenges to urban afforestation. In this Beltsville, Maryland field experiment, I examined biosolids and compost as amendments to improve soil quality and planted tree survival in a degraded urban proxy soil and identified correlations between soil properties and tree survival. Organic amendments increased organic matter content, decreased bulk density, and had no effect on tree survivorship compared to controls. Effects on soil were more profound and lasting with compost than with biosolids. Soil organic matter and bulk density were correlated with tree survival early in the study and microbial respiration was correlated with tree survival throughout the study. High tree mortality was driven by transplant shock, limiting insights from tree response data. This study highlights the importance of soil quality and good planting practices in future research.

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