Thesis (Ph. D.)--University of Delaware, 2006. / Principal faculty advisor: David L. Kirchman, College of Marine and Earth Studies. Includes bibliographical references.

The study investigated seasonal and spatial distributions and biogeochemical processes of dissolved and particulate organic matter in the upper layer of northern South China Sea (SCS). Concentrations of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) in the euphotic zone of northern SCS were in the range of 55-147 £gM, 2.4-9.9 £gM and 0.13-0.38£gM, respectively. A maximum concentration of DOC, DON and DOP, was found in the station close to the Pearl River due to freshwater input. The concentration of DOC decreased generally with distance away from the continent, but the ratio of DOC/TOC increased with distance primarily due to trophic dynamics. Concentrations of DOM were generally the highest in the surface layer and decreased with depth, but their C/N/P ratios increased with depth, indicating that both nitrogen and phosphorus were preferentially decomposed over carbon. Below the mixed layer, DOC degradation contributed only about 16% of AOU (apparent oxygen utilization). Inverse correlation between DOM and density was significant in the upper layer suggesting that the distributions of DOC, DON and DOP were largely controlled by vertical mixing. Inverse correlation was also significant between DOM and AOU, showing the effect of microbial decomposition on DOM in deep water. Concentrations of POC, PON and POP in the euphotic zone were in the range of 1.8-17.7£gM, 0.18-2.45£gM and 10-163 nM, respectively. Relatively high concentrations of POC, PON and POP in the surface water of inner shelf were also likely attributed to the input of the freshwater. Significant correlation between POC abundance and Chl-a suggested that phytoplankton abundance may control the distribution of POC. The ratio of ¡µPOC/¡µPON in the euphotic zone ranged from 4.57 to 7.3, implying various effects of bacteria and planktons on POM. A simple one-dimensional vertical eddy diffusion model was applied to estimate downward fluxes of DOC and POC and upward fluxes of nutrients across the boundary of euphotic layer and/or thermocline base. Total downward fluxes of organic carbon (OC) were compared with total upward nutrient-derived OC fluxes. The results suggested that additional nutrient sources in the euphotic layer were required to balance OC budgets. The ratios of DIN/DIP were much smaller than the Redifield N/P Ratio of 16:1, suggesting a status of N-limitation in the euphotic zone. The DOC/DON ratio, however, was much higher than the Redfield ratio. These results implied that DOM must play an important role in modulating nutrient cycling and food web dynamics in the euphotic layer.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

The geochemical, biogeochemical, and hydrologic controls on the stream chemical composition of alpine watersheds were investigated using the Alpine Hydrochemical Model (AHM). This model was successfully applied to the Emerald Lake watershed and two nearby watersheds as well as two watersheds in the Rocky Mountains, Andrews Creek and the Green Lakes Valley. The results reveal that snowmelt in alpine watersheds must come into contact with either soil, sub-talus, or reactive bedrock surfaces to explain the geochemistry observed in alpine lakes and streams. These materials do not differ geochemically but they do differ in their influence on the amount of mineral nitrogen observed in alpine lakes and streams. Improvements to the carbon-nitrogen dynamics portion of the ARM indicate that the Emerald Lake watershed is nearing nitrogen saturation. A robust multi-criteria sensitivity analysis technique was used to determine what processes were important for simulating the observed stream chemical composition. This sensitivity analysis revealed that concentration and mass flux representations of stream chemical composition contain different information about the watershed. The sensitivity analysis results were used to guide a multi-criteria parameter estimation algorithm. The results showed that stream chemical data is useful in discerning the importance of different processes and the role they play in determining stream chemical composition.

No description available.

No description available.

Significant species differences in foliar litter quality have been well-documented but differences within species, as a function of variation in genotype or environment, have not been directly addressed and, thus, remain poorly understood. We studied the significance of genetics, the environment, and their interaction in regulating forest nutrient dynamics and productivity using trees from four full-sib black spruce (Picea mariana (Mill.) B.S.P.) families of a complete 7 x 7 diallel cross experiment at the Petawawa National Forestry Institute (Chalk River, Ontario). Foliar litter composites from each family-plot on two sites of contrasting water availability were collected in October, 1993, and sub-samples were analyzed for initial N, P, K, Ca, Mg, cellulose and lignin concentrations. Inherent decomposition rates and nutrient dynamics of the litter composites were followed for one year. Samples of forest floor and mineral soil collected from within each plot were used to determine organic matter accumulation, pH, total nutrient contents in the forest floor and extractable nutrient concentrations in the mineral soil. Height, dbh, and total tree cubic volume, were used to characterize tree productivity. (Abstract shortened by UMI.)

Thesis (M.S.) in Plant, Soil and Environmental Sciences--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 72-83).

Thesis (Ph.D.). / Written for the Dept. of Earth and Planetary Sciences. Title from title page of PDF (viewed 2008/01/12). Includes bibliographical references.

Thesis (M.S.)--University of California, Santa Cruz, 1997. / Typescript. Includes bibliographical references.