Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains viii, 129 p.; also includes graphics. Includes abstract and vita. Advisor: D. Lynn Forster, Dept. of Agricultural, Environmental, and Development Economics. Includes bibliographical references (p. 124-129).

Thesis (Ph.D.)--The University of Regina (Canada), 2005. / Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Stevens Point, 2007. / Includes bibliographical references (leaves 105-112).

Thesis (M.S. - Department of Soil, Water and Environmental Science) - University of Arizona. / Includes bibliographical references (leaves 80-81

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains ix, 169 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 122-132).

Thesis (Ph. D.)--Duke University, 2007. / Includes bibliographical references.

This study investigated the pollutant removal performance of a constructed wetland treating stormwater runoff from a residential townhome complex in Manassas, Virginia. The facility was constructed by retrofitting a dry detention basin to retain a permanent shallow pool and included additional temporary storage to detain roughly the first half inch of rainfall for approximately 24 hours. Vegetation was allowed to establish itself through volunteer colonization, rather than active planting of selected wetland species. Flow measurements showed substantially greater volume passing through the outlet than entering through the single gaged inlet. The extra volume (about 41% of the total) was attributed to ungaged overland flow which drained a wooded/grassy area adjacent to the site. Mass balance calculations employing the rational method with a runoff coefficient of 0.2 to estimate the flow from this area showed good agreement between long-term total estimated inflow and measured outflow. However, this method was not effective in accounting for the discrepancies between inlet and outlet volumes of individual storms. Thirty-three runoff events were monitored between April, 1996 and May, 1997. Because of greater flow volumes passing through the outlet, constituent mass calculations which ignored the overland contribution generally exhibited higher loads exiting than entering the facility. With the results from a limited number of grab samples representing concentrations in overland input, estimated efficiencies improved substantially, showing overall net removal for most constituents. Less than one year after being retrofitted, the basin showed signs of beginning to develop a diverse wetland flora. / Master of Science

Thesis (Ph. D.)--Dept. of Geosciences and School of Computing and Engineering. University of Missouri--Kansas City, 2004. / "A dissertation in geosciences and computer networking." Advisor: Wei Ji. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed Feb. 28, 2006. Includes bibliographical references (leaves 226-236). Online version of the print edition.

A probabilistic risk assessment (PRA) for the discharge of excessive nitrogen from nonpoint sources (NPSs) to a stream was performed for a small agricultural watershed in northern Virginia. Risk, by definition, is the product of the frequency of occurrence of an event and the consequences of that event. The purpose of this research was to determine the probability of occurrence of a nitrogen discharge event (i.e., frequency). The consequences of such a discharge event were not explicitly determined but were implicitly assumed to be negative in nature. An event tree was developed to show the basic hydrologic processes at work in a small watershed. However, the event tree could not be used to discover the causes for nitrogen loss from the watershed. Therefore, a fault tree was developed for excessive nitrogen discharge in surface runoff on any day from agricultural sources. The development of the fault tree was found to be a useful exercise in understanding the intricate cause and effect relationships between agricultural practices and NPS pollution. Based on the results, the fault tree methodology might be used as an effective teaching or communication tool. The fault tree was also evaluated quantitatively to determine a probability of occurrence for excessive nitrogen discharge to the stream on any day. Land use, fertilization, monitoring, and long-term weather records were used in conjunction with scientific judgment and expert opinion to establish the probabilities within the fault tree and to calculate the overall probability of nitrogen discharge to the stream on any day. The results obtained from the fault tree calculations tend to underestimate the importance of cropland best management practices (BMPs) over the long term, because the fault tree was developed on a daily basis (i.e., every day in a year has the same probability of a discharge event occurring). A more accurate depiction of the NPS pollution control problem was achieved by assuming the occurrence of a runoff event. A second fault tree was presented for the discharge of excessive nitrogen to the stream during a runoff event. The quantitative assessment of the new fault tree showed more clearly the impact of BMPs on reducing the likelihood of nitrogen discharge. A 0.15 decrease in the probability of nitrogen discharge during a runoff event was calculated for the Owl Run watershed from 1987 to 1993 due to the effects of BMPs installed during that time period. A 0.20 decrease was calculated for an Owl Run subwatershed for the same time period. This subwatershed isolated two major dairy operations and the effects of the BMPs installed for those dairies. Despite the success of the fault tree in mirroring changes within the watershed, the amount of data and time required to perform the quantitative assessment may limit its use in the NPS pollution control field. The basic nature of the fault tree technique also limits its usefulness in the field. One such limitation is that degrees of events cannot be expressed. For example, a BMP is either present or not present on a fault tree. There can be no indication of how effective the BMP is in preventing NPS pollution without substantially increasing the level of detail displayed by the tree. Another limitation is that the ultimate result of the fault tree calculations is a probability of occurrence. This value is not as easily understood as the output of NPS pollution computer models, for example, where the output has specific meaning and units (e.g., milligrams of nitrogen per liter of runoff). The qualitative fault tree, however, has the advantage over computer models when it comes to understanding the concepts behind the technique and being able to see the cause and effect relationships at work in the watershed. Laypersons can understand the fault tree more easily than the complex computer code and intricate equations of models. / Master of Science

A dynamic, compartmental, continuously stirred tank reactor, simulation model (SET-WET) was developed for design and evaluation of constructed wetlands in order to optimize non-point source (NPS) pollution control measures. The model simulates the hydrologic, nitrogen, carbon, dissolved oxygen, bacteria, vegetative, phosphorous and sediment cycles of a wetland system. Written in Fortran 77, SET-WET models both free water surface (FWS) and sub-surface flow (SSF) wetlands and is designed in a modular manner which gives the user the flexibility to decide which cycles and processes to model. SET-WET differs from many existing wetland models in that it uses a system's approach, and limits the assumptions made concerning the interactions of the various nutrient cycles in a wetland system. It accounts for carbon and nitrogen interactions, as well as effect of oxygen levels upon microbial growth. It also directly links microbial growth and death to the consumption and transformations of nutrients in the wetland system. Many previous models have accounted for these interactions with zero and first order rate equations that assume rates are dependent only on initial concentrations. The SET-WET model is intended to be utilized with an existing NPS hydrologic simulation model, such as ANSWERS or BASINS, but may also be used in situations where measured input data to the wetland are available. The model was calibrated and validated using limited data collected at Benton, Kentucky. A non-parametric statistical analysis of the model's output indicated eight out of nine examined outflow predictions were not statistically different from the measured observations. Linear regression analysis showed that six out of nine examined parameters were statistically similar, and that within the expected operating range, all of the examined outflow parameters (9) were within the 95% confidence intervals of the regression lines. A sensitivity analysis showed the most significant input parameters to the model were those which directly affect bacterial growth and oxygen uptake and movement. The model was applied to a subwatershed in the Nomini Creek watershed located in Virginia. Two year simulations were completed for five separate wetland designs, with reductions in percentage of BOD5 (4%-45%), TSS (85%-100%), total nitrogen (42%-56%), and total phosphorous (38%-57%) comparable to levels reported by previous research. / Master of Science