| Summary: | Inland aquatic systems such as lakes, rivers, and wetlands are pivotal in cycling carbon between the landscape and the atmosphere. However, as global air temperatures increase and precipitation patterns continue to change, their roles as net carbon sources or sinks will become uncertain. New carbon sources will become available to aquatic systems in regions such as the permafrost zone in the northern high latitudes or in temperate forested wetlands where increased precipitation connects waterbodies to upland catchments. In dryer regions, the water residence time of aquatic systems will increase, restricting the inputs of organic carbon from the surrounding landscape, but also amplifying its internal production and degradation. This dissertation aims to investigate the sources and molecular properties of dissolved organic matter (DOM) across northern high-latitude lakes and temperate North American wetlands and to consider its potential role in the carbon cycle as these regions continue to experience changes in temperature and precipitation. Using a combined approach of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), optical and fluorescence spectroscopy, and mediated electrochemical oxidation and reduction, molecular-level DOM composition was revealed and related to large-scale climate and physiographic variables. Specifically, the goals of this dissertation were to characterize DOM in lakes spanning the Western North American Arctic with respect to differences in seasonality and climate (Chapter 2) as well as hydrology and landscape characteristics (Chapter 3). Using these findings, a quantitative relationship between molecular level-composition and bulk electrochemical DOM properties was also assessed (Chapter 4). Finally, DOM properties were surveyed across various wetland types across temperate North American regions and further examined between surface waters and porewaters as well as during different annual hydroperiods (Chapter 5). DOM composition and dissolved organic carbon ...
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