Ashby Pond in the City of Fairfax, Virginia was retrofitted to treat runoff from 54.7 hectares of urban land of mixed use. The pond discharges into Accotink Creek, a highly urbanized tributary of the Potomac River and Chesapeake Bay that is listed on the State of Virginia 303(d) list for multiple impairments. The entire multi-state Chesapeake Bay Watershed is subject to Total Maximum Daily Load (TMDL) restrictions on sediment, phosphorus and nitrogen. Virginia and local municipalities assign pollutant reduction credits to retention ponds that meet certain design requirements. However, to actually meet existing and future water quality goals set by TMDLs, it must be proven that such ponds truly provide the water quality benefits for which they have been credited. The inflow and outflow water quality of Ashby Pond was examined over 7 months from fall 2012 to spring 2013. During that period, the pond provided statistically significant reductions of phosphorus, nitrogen and suspended sediment, but not organic carbon or oxygen demand. Ashby Pond had non-significant export of sodium, chloride and calcium. The pond underperformed when compared to state reduction credits for phosphorus load and concentration, but met and exceeded the credits for nitrogen load and concentration, respectively. The pond was under-sized compared to state design standards, and some underperformance should be expected. / Master of Science

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 220-229). / Also available by subscription via World Wide Web / vi, 229 leaves, bound 29 cm

Thesis (Ph.D.)--George Mason University, 2009. / Vita: p. 152. Thesis director: Thomas E. Jordan. Thesis director: Donald P. Kelso. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Science and Public Policy. Title from PDF t.p. (viewed June 10, 2009). Includes bibliographical references (p. 140-151). Also issued in print.

The nitrogen reduction goals for the Chesapeake Bay are proving particularly difficult achieve. One of the contributing sources of N loading to the Bay is legacy N from groundwater springs. Denitrifying spring bioreactors are a best management practice that offers an opportunity to abate N from groundwater springs. The objective of this research is to estimate the regional abatement costs to remove legacy N using bioreactors. We identified 196 candidate springs for bioreactor installation that had a median spring flow of greater or equal to 100 m3 d-1 and greater or equal to 3 mg L-1. Under assumptions that 25% of the spring flow can be diverted to the bioreactor and a bioreactor N removal efficiency of 20%, we estimate that it would cost $3,325,400 yr-1 to abate 106,911 kg N yr-1. The driving factor of driving the unit costs of N removal is the amount of spring flow treated by the bioreactor. Further research is needed to understand how to optimize bioreactor performance and the benefits of increasing the percentage of spring flow treated given the impact these two factors on the cost-effectiveness of spring bioreactors in removing N. / Master of Science / There is a Chesapeake Bay Watershed total maximum daily load (TMDL) to reduce pollutants from going into the Bay. The reduction measures to achieve the TMDL goals must be in place by 2025. The nitrogen reduction goal for the Bay is proving particularly difficult to achieve. One of the contributing sources of N loading to the Bay is legacy N from groundwater springs. Denitrifying spring bioreactors are a best management practice that offers an opportunity to abate N from groundwater springs. One form of a denitrifying bioreactor is a hole in the ground filled with carbon substrate (i.e. woodchips) that is used to treat N rich water. Due to the conditions created in the spring bioreactor, the process of denitrification occurs, and N is removed from the water treated. The objective of this research is to estimate the regional abatement costs to remove legacy N using bioreactors. We identified 196 candidate springs for bioreactor installation that had a median spring flow of greater or equal to 100 m3 d-1 and greater or equal to 3 mg L-1. Under assumptions that 25% of the spring flow can be diverted to the bioreactor and a bioreactor N removal efficiency of 20%, we estimate that it would cost $3,325,400 yr-1 to abate 106,911 kg N yr-1. The driving factor of driving the unit costs of N removal is the amount of spring flow treated by the bioreactor. Further research is needed to understand how to optimize bioreactor performance and the benefits of increasing the percentage of spring flow treated given the impact these two factors on the cost-effectiveness of spring bioreactors in removing N.

The purpose of this study was to analyze the cost implications of various provisions of the Virginia Nutrient Credit Exchange Act. The first objective was to estimate the cost implications of point source trading provisions of the Act. An integer programming cost minimization model was constructed to estimate the cost of achieving four point source trading policy scenarios. The model estimated the annual cost of meeting two different nutrient cap levels, each with and without a limits-of-technology concentration standard requirement for new and expanding point sources. The limits-of-technology concentration standard requirement was found to significantly affect cost while providing little apparent benefit to water quality. The second objective was to develop a screening procedure for municipalities to estimate the cost of generating waste load allocation from nonpoint source offsets under their jurisdictional control. A spreadsheet based cost screening procedure was developed for municipalities to estimate the cost of implementing of nitrogen offsets from stormwater practices, septic retirement, and land conversion. One of the important findings from developing the screening procedure is that the cost of generating WLA from non-point sources under the control of local governments was much higher than the cost of removing nitrogen at wastewater treatment plants. / Master of Science

The first civilizations we have ever heard of were along the banks of mighty rivers like Nile, Euphrates, Indus and Huang. These civilizations developed along rivers as riverfronts provided opportunities for tradeand transportation, fertile land to grow crops, water for drinking, washing, livestock and other domestic uses and food in the form of fish. Gradually, they came to define cities, became a part of identities of people, such as "India" from "Indus," while, providing a sense of place and connecting the populace to nature. Yet rivers have often ended up being abused and neglected in our course towards urbanization. It is this "neglect" that needs to be shunned. The relationship with the rivers needs to be re-forged. To develop a strategy for this shift in attitude, this research has chosen the case of Chesapeake Bay. Chesapeake Bay is an estuary lying inland from the Atlantic Ocean. It has mainland North America to its west and Delmarva Peninsula on the east. It is the largest Estuary in the United States. More than 150 major rivers and streams flow into the Chesapeake Bay. The estuary provides habitat to several species of wildlife and aquatic life. Today, this bay faces many issues such as nutrient and sediment pollution, Storm water runoff, lowering of shellfish species etc. One of the major causes of the polluted bay is storm water runoff. Storm water washes pollution off the roads and other surfaces and takes them to the water. Stormwater is generally more polluted in urban areas than rural areas. This thesis, attempts to demonstrate what can be done with a typical pixel in the whole mosaic of the bay . The Maine Avenue Fish Market, sitting just upstream to the now being developed Southwest Waterfront, seems a perfect choice for this endeavor. This market, a small urban waterfront space, is ideal for exploring ideas and solutions to avoid water pollution by stormwater, cleaning the quality of water and also, in the process, develop the area in relation to the city and its surroundings. This thesis aims to establish an ecological and social relationship between the natural resource and the urban life. / Master of Science

Excess nutrient pollution and eutrophication are widespread problems that must be solved at watershed scales, and stream restoration is increasingly implemented as a solution. Yet few studies evaluate the cumulative effects of multiple individual restoration projects on watershed-scale nutrient loading. We constructed a HEC-RAS model of stream restoration implemented throughout a generic 4th order watershed typical of the Piedmont physiographic province of the eastern USA. We simulated restoration of hyporheic exchange as one increasingly popular technique that receives dissolved nitrate-nitrogen (NO3--N) mitigation credit under the Chesapeake Bay TMDL. We populated the model with hyporheic exchange (0.3% of surface flow per hyporheic-exchange inducing in-stream restoration structure) and NO3--N removal (supply-limited denitrification removes all NO3--N that enters the hyporheic zone) values from prior literature on in-stream structures and related restoration techniques. We then varied the percentage of stream channels in the watershed in which restoration occurred. For watersheds with less than 100% of stream channels restored, we also varied where in the watershed (i.e. stream order) that restoration occurred. We found that hyporheic restoration in our 4th order watersheds has the potential to reduce NO3--N loading to downstream waterbodies by up to 83%, but that a maximum of <100% reduction exists given certain watershed characteristics. Model results revealed a nonlinear relationship between percent of stream channels restored and percent NO3--N loading reduction that occurred at the watershed outlet. This indicates that the effects of individual projects are not linearly additive, and must be evaluated in the context of how much of the watershed has already been restored. We also found that restoration was more effective at reducing NO3--N loading when it occurred in higher order streams (e.g., 3rd and 4th order), yielding load reductions upward of 30% compared to < 10% in lower order streams (e.g., 1st and 2nd order). Thus, the location of an individual restoration project within a watershed is important in determining its effect on NO3--N. Overall, our results indicate that hyporheic restoration can have significant effects on watershed NO3--N loading to downstream waterbodies, yet the watershed must be viewed as a whole to understand the potential impacts of any particular project under consideration. / Master of Science / Nutrient pollution and harmful algal blooms are widespread problems that must be solved at watershed scales, and stream restoration is increasingly implemented as a solution. Yet few studies evaluate the cumulative effects of multiple individual restoration projects on watershed-scale nutrient loading. We constructed a HEC-RAS model of stream restoration implemented throughout a generic watershed typical of the mid-Atlantic USA. We simulated restoration of nutrient-reducing groundwater flow cells along a stream corridor (hyporheic exchange) as one increasingly popular technique that is emphasized under the Chesapeake Bay TMDL. We populated the model with hyporheic exchange and nitrate-nitrogen (NO3--N) removal values from prior literature on in-stream structures and related restoration techniques. We then varied the percentage of stream channels in the watershed in which restoration occurred. For watersheds with less than 100% of stream channels restored, we also varied where in the watershed (i.e. stream order) that restoration occurred. We found that hyporheic restoration in our watershed has the potential to reduce NO3--N loading to downstream waterbodies by up to 83%, but that a maximum of less than 100% reduction exists given certain watershed characteristics. Model results revealed a nonlinear relationship between percent of stream channels restored and percent NO3--N load reduction that occurred at the watershed outlet. This indicates that the effects of individual projects are not linearly additive, and must be evaluated in the context of how much of the watershed has already been restored. We also found that restoration was more effective at reducing NO3--N loading when it occurred in larger streams, yielding load reductions upward of 30% compared to less than 10% in smaller streams. Thus, the location of an individual restoration project within a watershed is important in determining its effect on NO3--N. Understanding the maximum possible degree of NO3--N reducing hyporheic exchange is an important step for practitioners and policy-makers in choosing the most effective location for a stream restoration based on a project's goals, and cannot be done without analyzing the watershed as a whole. With more watershed-scale planning and a better understanding of certain physical characteristics, we can choose restoration locations and strategies that will ultimately work more efficiently toward reaching a nutrient reduction goal.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 220-229).

Thesis (M.A.)--State University of New York at Binghamton, Department of Geological Sciences and Environmental Studies, 2005. / Includes bibliographical references.

While research has shown that riparian forests are effective in reducing shallow groundwater nitrogen levels, the relative importance of the mechanisms responsible for this reduction have not been adequately addressed. This project focused on the microbial mediated process denitrification, which has been hypothesized to be a major factor responsible for decreased groundwater nitrate levels observed in forested regions. The study site was located on Virginia’s Eastern Shore and incorporated a transect extending from a field under agricultural use through a mesic forest to a distance of 91.4 meters. Groundwater flowed from a well drained agricultural field of Bojac sandy loam (coarse-loamy, mixed, thermic Typic Hapludults) and Munden sandy loam (coarse-loamy, mixed, thermic Aquic Hapludults) to a poorly drained forest soil, Nimmo sandy loam (coarse-loamy, mixed, Typic Ochraquults). Previous work along this transect reported mean nitrate (NO₃-N) levels of 1,161 ± 393 μmol·liter⁻¹ for shallow groundwater underlying the agricultural field, whereas shallow groundwater 91.4 meters into the forest had a mean concentration of 2.2 ± 2.6 μmol·liter⁻¹. Groundwater nitrate (NO₃-N) levels below ~3 meters of the water table 91.4 meters into the forest 559.5 ± 101.9 increased to approximately 250 μmol·liter⁻¹. In addition to nitrate levels, other water quality parameters and soil characteristics suggested that vertical variations of soil environments existed and therefore, must be incorporated into experimental design. Denitrification activiy was measured at various depth increments in the agricultural field and forest using an acetylene blockage technique. In addition, denitrification activity was measured after subjecting the soils to carbon and nitrate amendments. Denitrification activity from the forest was limited by nitrate at the water table and were carbon limited as vertical depth increased. Denitrification activity measured with nitrate amendments at the water table in the forest were two orders of magnitude higher than those in the field (7.37 nmol·g⁻¹·hr⁻¹ vs 0.074 nmol·g⁻¹·hr⁻¹). Dentrification activity measured with nitrate ± glucose amendments were higher at the water table in the forest, 6.88 nmol·g⁻¹·hr⁻¹, as compared to the field, 0.15 nmol·g⁻¹·hr⁻¹. Denitrifier microbial densities were measured at various vertical depths in the forest and agricultural field. Results demonstrated that denitrifiers densities at the water table in the forest were greater than those at the water table in the field. The number of denitrifying organisms per cubic centimeter of soil at the water table in the field averaged 2850 ± 1553(SD) as compared to 14,350 ± 13,369(SD) at the water table in the forest. At 0.91 meters below the water table in the field and in the forest the number of denitrifying organisms per cubic centimeter of soil were 1343 ± 1086(SD) and 3922 ± 3919(SD), respectively. The differences in denitrification measurements were due to location of the water table. The water table in the forest was located in the A horizon as compared to the water table in the field which was located in the C horizon. Results demonstrated that denitrification was an active mechanism that affected nitrate reduction in shallow groundwater in this system. Thus, riparian vegetation can be quite beneficial in reducing shallow groundwater nitrogen levels through microbially mediated processes such as denitrification. As a result nonpoint source nitrogen loadings from groundwater discharge can be reduced. / Master of Science