Stormwater detention basins are commonly used in the Eastern United States to temporarily store and attenuate stormwater runoff, and also serve as habitats for native and exotic plants. However, during winter, these basins receive saline runoff from road salt application, which contributes to Freshwater Salinization Syndrome (FSS). Since limited research has connected direct measurement of soil and stormwater salinities to biodiversity and phytoremediation potential of salt-tolerant plant species, this thesis aimed to fill this gap. We selected a set of detention basins draining mostly pervious areas, parking lots, or roads in Northern Virginia and measured temporal variations in stormwater and soil salinities, depth profiles of soil salinities, plant community composition, and plant tissue ion concentration. The results indicated elevated levels of sodium, chloride, electrical conductivity (EC), and exchangeable sodium percentage (ESP)/sodium adsorption ratio (SAR) in soil and stormwater after road salt application during winter, followed by a decrease during the growing season for basins draining parking lots and roads. A subsequent increase at the end of the season was observed for all site types. While some stormwater samples exceeded toxicity thresholds, most soil samples did not exceed their respective thresholds nor reach saline or sodic conditions, and native and exotic plant species of both salt-sensitive and salt-tolerant classifications were observed at almost all sites, although proportions of each varied by site type. Tissue analysis of select plants revealed ionic concentrations that generally coincided with observed soil and stormwater concentrations at each major site type. These findings have implications for future detention basin planting regimes to mitigate FSS, and the thesis discusses native plants found to provide the most benefit for phytoremediation. / Master of Science / Stormwater detention basins are commonly used in the Eastern United States. They slowly release stormwater runoff and serve as habitats for native and exotic plants. However, during winter, these basins receive saline runoff from road salt application. This contributes to Freshwater Salinization Syndrome (FSS). Limited research has connected direct measurement of soil and stormwater salinities to biodiversity and plants' ability to uptake salts, so this thesis aimed to fill this gap. A set of detention basins draining mostly pervious areas, parking lots, or roads in Northern Virginia were selected. Next, stormwater and soil salinities over time, depth profiles of soil salinities, plant community composition, and plant tissue ion concentration were measured. The results showed higher levels of standard salinity benchmarks in soil and stormwater after road salt application during winter, followed by a decrease during the growing season for parking lot and road sites. A final increase in the fall was observed for all site types. While some stormwater samples were toxic to plants, most soil samples were not toxic, saline, or sodic. Also, native and exotic plant species of both salt-sensitive and salt-tolerant classifications were observed at almost all sites, but proportions of each varied by site type. Plant tissues contained ionic concentrations that reflected observed soil and stormwater concentrations at each site type. These findings can inform future detention basin planting regimes to mitigate FSS. The thesis also discusses native plants that provide benefits for phytoremediation.

Increased salinity in freshwater systems – also called the Freshwater Salinization Syndrome (FSS) – can have far-ranging implications for the natural and built environment, agriculture, and public health at large. Such risks are clearly on display in the Occoquan Reservoir – a drinking water source for roughly one million people in the northern Virginia/ National Capital Region. Sodium concentrations in the Occoquan Reservoir are approaching levels that can affect taste and health. The Reservoir is also noteworthy as a flagship example of indirect potable reuse, which further adds complexity to understanding the sources of rising levels of sodium and other types of salinity. To help understand the role residential discharges might play in salinization of the Occoquan Reservoir, a suite of laundry detergent products was identified based upon survey data collected in the northern Virginia region. The ionic compositions of these products were then characterized using ion chromatography and inductively coupled plasma-mass spectrometry to quantify select ionic and elemental analytes. Sodium, chloride, and sulfate were consistently found in appreciable amounts. To comparatively characterize the laundry detergents, principal component analysis was employed to identify clusters of similar products. The physical formulation of the products was identified as a marker for their content, with dry formulations (free-flowing and encapsulated powders) being more enriched in sodium and sulfate. This result was corroborated by comparing nonparametric bootstrap intervals for individual analytes. The study's findings suggest an opportunity wherein consumer choice can play a role in mediating residential salt inputs in receiving bodies such as the Occoquan Reservoir. / Master of Science / Many streams, rivers, and other freshwater systems have become increasingly salty in recent decades. A rise in salinity can be problematic, stressing aquatic life, corroding pipes, and even enhancing the release of more pollutants into the water. This phenomenon, called Freshwater Salinization Syndrome, can threaten such systems' ability to serve as sources of drinking water, as is the case for the Occoquan Reservoir in northern Virginia. Serving roughly one million people, the Reservoir is notable for being one of the first in the country to purposely incorporate highly treated wastewater upstream of a drinking water supply. Despite the Reservoir's prominence, the reasons behind its rising salt levels are not well understood. This study sought to understand the role that individual residences could play when household products travel down the drain and are ultimately discharged into the watershed. Laundry detergents are potentially high-salt products. A survey of northern Virginian's laundry habits was conducted to understand local tastes and preferences. Informed by the survey, a suite of laundry detergents was chemically characterized to measure salt and element concentrations. The detergents were found to have notable amounts of sodium, chloride, and sulfate in particular, with sodium being the most abundant analyte in every detergent. However, not all detergents were equally salty; statistical tools revealed that dry formulations (such as powdered and powder-filled pak detergents) contributed more sodium and sulfate, among other things. This study's findings suggest that laundry detergents could be contributing to Freshwater Salinization Syndrome in the Occoquan Reservoir, and that local consumers' choice of detergents could make a difference.

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