Dissertation Abstract

Dissolved organic matter (DOM) is ubiquitous to all natural waters and characterization of its chemical properties elucidates biogeochemical processes taking place in a water body. DOM sources can be autochthonous (microbial) or allochtonous (terrestrial) and impart very distinct chemical signatures. Through the study and characterization of DOM in two different Antarctic lake ecosystems the chemical composition and in situ processing of microbial DOM has been advanced. Pony Lake, the focus of the first chapter of this thesis, is a hypereutrophic, saline, coastal pond in Antarctica which thaws seasonally allowing for prolific algal growth. In contrast, the other Antarctic lake, Lake Vida, is a hypersaline, ice-covered lake that has an ecosystem based largely on chemoautotrophy with some heterotrophic bacteria also present. This thesis also presents the characterization of DOM changes in laboratory cultures of A. fundyense, an algal species responsible for annual harmful algal blooms (HABs) in the Gulf of Maine. This thesis shows that DOM character as measured by 13C NMR, fluorescence excitation emission matrices (EEMs), and UV-Vis spectroscopy influenced the bioavailability of DOM to algal cultures. Terrestrial DOM from the Suwannee River enhanced A. fundyense growth while microbial DOM from Pony Lake did not. Lastly, this thesis presents a study of the mixing of riverine and marine DOM in the Gulf of Maine system using parallel factor analysis (PARAFAC) to analyze field samples collected over a 4-year period. A new fluorescent component was found in the Gulf of Maine samples collected in 2004 and 2005.