In this study, a new analytical method for the simultaneous determination of total N, P and S using hydrogen peroxide oxidation has been developed for the analysis of water and sediment samples. The products of the oxidation reaction (nitrate, phosphate and sulphate) were determined by ion chromatography. A method for the simultaneous chemical speciation of arsenic, selenium and chromium was developed using ion chromatography coupled with ICP-MS. Reversed phase chromatography and ICP-MS was used for the simultaneous determination of mercury and selenium species. For the speciation of vanadium a new method using HPLC with reversed phase and ICP-MS detection was developed. The species arsenite, arsenate, selenite, selenate, chromate, methylmercury, inorganic mercury, selenocystine, selenomethionine, vanadium (IV) and vanadium (V) in samples of water, sediment, fish muscle tissue and mussel, were determined using the developed methods. Simultaneous determination of nutrients and metal species were applied to the study of pollution in Lake Maracaibo, Venezuela. The distribution of As, Se, Pb, Hg, Sn and V in sediment was studied using a sequential extraction scheme and related to the physicochemical parameters and nutrient content. The major concentrations of arsenic and lead found inside the lake were associated with the fraction associated with the Fe/Mn hydroxides phase, however, mercury and selenium were distributed at the main zone of the lake in the organic-sulphide fraction. In the strait and the gulf, metals were distributed mainly in the residual phase with the exception of tin. Conditions which favour mercury methylation in the lake are discussed. In the centre of the lake, with anaerobic conditions, methylmercury was the predominant species for mercury. The results found for vanadium and arsenic speciation showed that the predominant species in all the samples of Lake Maracaibo was vanadium (IV) and arsenite, respectively. Results were compared with those from lakes with similar pollution problems.

No description available.

No description available.

Lake Manassas is a man-made impoundment in the Northern Virginia suburbs of Washington, D.C. The lake currently supplies drinking water at an average rate of 10.5 million gallons per day to the City of Manassas, Virginia. The lake discharges, via the Broad Run, a tributary of the Occoquan Reservoir. The Occoquan Reservoir supplies potable water to over 750,000 people in the Northern Virginia area. This thesis presents the results of a limnological analysis of Lake Manassas. The techniques used are established limnological techniques to arrive at a profile which can be compared to accepted scales of ranking. One conclusion from the analysis is that Lake Manassas is eutrophic, which means that the production of biomass in the lake is at a higher than desired rate. The result of this eutrophic condition is that the water quality of the lake will decline rather rapidly. Another conclusion is that Broad Run is the major supplier of nutrients into Lake Manassas, but that conditions are also affected by a point source discharge from a sewage treatment plant. These conclusions are consistent with previous studies done on Lake Manassas. In summary, Lake Manassas is an important water resource in the Northern Virginia area, and it is important to continue to closely monitor and manage runoff practices in the watershed to ensure the lake does not degrade to unacceptable conditions. / Master of Science

No description available.

No description available.

Video summarizing Ph.D. dissertation for a non-specialist audience. / Civil and Environmental Engineering / College of Engineering

Ecologists have studied the responses of pelagic ecosystems to varying levels of nutrient loading and fish predation on many different scales ranging from small experimental enclosures to whole lake systems. There are recurring patterns of response to these two variables, which are generally predictable on the basis of biogeographic, behavioral, morphological, and physioenvironmental ecological principles applied to the life histories stategies of individual species. This study focused on the changes in pelagic trophic structure in response to varying levels of productivity (regulated by nutrient loading rates) and fish densities (determined by stocking densities). Zooplankton life history traits used to explain the community responses to these two variables included: body size at sexual maturity, generation time, reproductive potential, temperature dependant growth rates, morphological adaptions to vertebrate and invertebrate predation, and modes of food acquisition. A small naturally fishless lake in southeastern Alaska was the observational unit of this study conducted over a seven year period from 1980 through 1986. The objectives of this study were to 1) test whether additions of inorganic fertilizer to the lake would increase its capacity to produce coho (Oncorhyncus kisutch) smolts, and 2) describe the structural and functional changes in the pelagic ecosystem in response to varying rates of nutrient loading and zooplanktivore densities. The study design consisted of no treatments during four of the study years, and one year of each of the following treatments: 1) fertilization only, 2) no fertilization and low stocking densities (2,000 fry/ha), and 3) fertilization and high stocking densities (4,000 fry/ha). During nonfertilized years, rainfall was the driving force behind nutrient loading rates. Nutrient loading rates (exclusive of fertilizer additions) displayed a two to three fold magnitude in annual variation over the seven year study period. Changes in nutrient loading during nonfertilized years appeared to regulate pelagic productivity, but in a complex and counter intuitive manner. In contrast to the widely documented positive correlation between chlorophyll concentrations and nutrient loading rates, grazing pressure by zooplankton appeared to be the factor regulating standing crops of phytoplankton. During nonfertilized years, mean summer total chlorophyll was inversely correlated to total zooplankton biomass, and displayed a 2.5 fold magnitude in annual variation. Diaptomus kenia biomass (the primary component of total zooplankton biomass) was low in 1980 following a year with a low amount of summer rainfall (1979), then increased after each year (1980 and 1981) with relatively high amounts of summer rainfall. The positive response of D. kenia to conditions stimulated by high summer rainfall (and high nutrient loading rates) was delayed by their long generation time (one reproductive period per year). D. kenia and total zooplankton biomass peaked in 1982, the year that the least amount of summer rainfall was observed. In contrast to the intuitive perception that nutrient poor conditions are less productive, the highest zooplankton production occurred when nutrient loading rates and phytoplankton concentrations were at their lowest levels. Accelerated nutrient regeneration rates and phytoplankton turnover times were the most probable factors which allowed the high zooplankton production to be maintained under these nutrient poor conditions. Fertilizer treatments increased the mean summer total chlorophyll concentrations four to six fold over the maximum observation (1.03 μg/1) for nonfertilized years. At high nutrient loading rates, the relationship between total chlorophyll and zooplankton biomass switched to a positive correlation. Rapid egg production and short maturation times allowed the cladocerans to most efficiently exploit the food resources stimulated by fertilization. B. longirostris dominated zooplankton biomass during the fertilized stocking period, but was only preyed upon by a small percentage of the fish when larger zooplankters (Holopedium gibberum and Epischura nevadensis) were abundant. Fertilization treatments increased the the coho smolt producing capacity of the lake by about 60 %. / Graduation date: 1991

Thesis (M.A.)--York University, 2007. Graduate Programme in Geography. / Typescript. Includes bibliographical references (leaves 112-121). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR38799

Thesis--University of California, Davis. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.