M. S.

M.S.

Nutrient loadings to the Chesapeake Bay are a source of concern for water quality agencies. In particular, excess nitrogen loadings from agricultural production activities threaten water quality in the Bay. Questions have been raised about how effectively traditional BMPs can control nitrogen loss from crop production. This study examines agricultural nitrogen pollution control from an input management perspective. Using an economic and physical model, seven production systems and nitrogen management strategies are compared in terms of input use, profitability, and nitrogen loss potential. Results suggest that several of the production systems will reduce residual nitrogen without reducing profits. However, it is recognized that factors in addition to profitability will influence producers' nitrogen management decisions. Therefore, using the results of a farmer survey, adoption models are estimated to examine the impact of production system characteristics and producer characteristics on the decision to use an alternative production system and nitrogen management strategy. Finally, a sensitivity analysis is conducted to examine the impact of alternative policy tools on adoption incentives. Both financial incentives and education and information programs are found to be important tools for influencing producers' decisions. Producers' interest in the alternative systems and desire for information on the systems suggest that agricultural research will contribute by assuring that producers have access to adequate information on the alternative systems. / Ph. D.

Lake Manassas is a 706-acre public water supply reservoir for the City of Manassas, formed by the impoundment of Broad Run. It is located in western Prince William County at the periphery of the metropolitan Washington, D. c. area. Its watershed drains approximately 46,500 acres of rural land that is expected to undergo rapid development in the next 25 years. The objective of this study was to provide a comprehensive report of the quality of water in Lake Manassas and its tributary streams, analyzing data that had been collected from October, 1984 through April, 1986, as part of a monitoring program funded by the City of Manassas. The capacity of Lake Manassas at full pool was determined to be 4.2 billion gallons (15.8 million cubic meters) and its mean depth 25 feet (7.7 meters). The calculated volume was considerably less than had been previously thought. Trophic state indices indicated that Lake Manassas is eutrophic, and water column chemistry suggested phosphorus to be the limiting nutrient. The Vollenweider model was applied to illucidate the relative impacts of South Run and Broad Run on the lake. While Broad Run contributed the vast majority of flow to the reservoir, higher concentrations of algal nutrients, nitrogen and phosphorus, were transported to the lake by South Run, which receives effluent from the treatment plant at Vint Hill Station, a U.S. Army reservation. Phosphorus loadings from South Run were higher than from Broad Run under baseflow conditions. On an annual basis, stormflow runoff contributed as much as twelve times the tributary baseflow loading of phosphorus. / M.S.

Allochthonous nutrients were monitored during three storm events on one of the major tributaries entering the shallow VPI&SU Duck Ponds. Autochthonous nutrients were monitored for a period of ten months. During these storms, the stormwater runoff contributed large amounts of organic matter and fertilizer nutrients that settled in the ponds and during anoxic conditions, recycled to stimulate algal blooms. Alum was applied to one pond to reduce internal cycling of nutrients. A 25 mg/L dose of alum produced an aluminum hydroxide floc that settled to the bottom and afterwards, lowered othophosphate-phosphorus concentrations below 10 µg/L in the water column. The longevity of the one-time treatment in reducing the sediment-phosphate release rate is unknown because the monitoring program was not continued beyond July of 1988. A pond-treatment program involving copper sulfate was initiated to control algal blooms consisting mainly of the green alga, Chlamydomonas. Based on the complexing properties of the water, such as alkalinity and humics, a copper sulfate dose of 13.6 kg was determined to be a safe and effective dose that reduced algal densities but did not result in any visible adverse effects upon other aquatic life. Both of the pond management schemes were designed to aid managers of small urban ponds who have low operating budgets and a lack of technical equipment. / Master of Science

A major goal of environmental monitoring is to determine whether the environment is improving or deteriorating. Questions about the health of the environment are usually questions about trends in environmental indicators, typically a number of chemical, physical, and biological variables. Because multiple indicators are required to characterize any but the most simple environment, the problem is statistically a multivariate problem. In this work, methods for analyzing multivariate environmental trends are presented and illustrated on 17 years of approximately monthly observations on 5 water quality variables from southwestern Virginia, USA. Multivariate methods can also be applied to analyze correlated univariate data collected on a seasonal or monthly basis. A variety of methods from the literature are discussed. A unified approach is described based on a general class of correlation measures to construct a general framework for the nonparametric analysis of multivariate trends. / Ph. D.

The objective of this study was to develop a comprehensive, basin-wide, water-quality-planning model using system dynamics methodology. Later, the model was to be interfaced with a more conventional system dynamics model: one simulating social, technological, economic, and political interactions. By doing so, it is envisioned that such management policies as zoning, abatement facilities, and best management practices may be simulated together. / Master of Science