Sunlight, Iron, and the Environmental Fate of Dissolved Organic Matter in Freshwater Systems

Abstract

Dissolved Organic Matter (DOM) makes up a significant part of the global carbon cycle, is a source of energy and nutrients in aquatic ecosystems, and can affect the way pollutants are stored and transported across large environments. The composition of DOM, which can affect the mechanisms responsible for all of the previously mentioned processes, is constantly undergoing both inter- and intramolecular changes driven by a variety of natural conditions, such as exposure to sunlight and interactions with inorganic components of natural waters, like aqueous Fe. However, little is known about the details of how these forces, and especially the way that they interact, change specific chemical and physical qualities of DOM. In this paper, I aim to contribute to this area of ongoing research by reporting the results of an investigation into how the concentration and speciation of Fe affect the photochemical reactions that transform and degrade DOM. In order to do this, I analyzed Excitation-Emission Matrix fluorescence spectroscopy data with Parallel-Factor analysis, a method of mathematically deconstructing a sample set into a small number of fluorescent components, especially suited for describing extremely heterogeneous mixtures of complex molecules, in addition to X-ray Absorbance spectroscopy. The results of a series of irradiation experiments with variable additions of aqueous Fe demonstrated a number of trends in DOM composition related to the concentration and speciation of Fe.