Comparison of Two PARAFAC Models of Dissolved Organic Matter Fluorescence for a Mid-Atlantic Forested Watershed in the USA

The composition of dissolved organic matter (DOM) in a mid-Atlantic forested watershed was evaluated using two fluorescence models—one based on previously validated model (Cory and McKnight, 2005) and the other developed specifically for our study site. DOM samples for the models were collected from multiple watershed sources over a two-year period. The previously validated parallel factor analysis (PARAFAC) model had 13 DOM components whereas our site-specific model yielded six distinct components including two terrestrial humic-like, two microbial-derived humic-like, and two protein-like components. The humic-like components were highest in surficial watershed sources and decreased from soil water to groundwater whereas the protein-like components were highest for groundwater sources. Discriminant analyses indicated that our site-specific model was more sensitive to subtle differences in DOM and the sum of the humic- and protein-like constituents yielded more pronounced differences among watershed sources as opposed to the prevalidated model. Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations and selected DOM metrics were also more strongly correlated with the site-specific model components. These results suggest that while the pre-validated model may capture broader trends in DOM composition and allow comparisons with other study sites, a site-specific model will be more sensitive for characterizing within-site differences in DOM. 1. Introduction Dissolved organic matter (typically <0.45？μm) is a heterogeneous mixture of aromatic and aliphatic organic compounds, ranging from proteins, carbohydrates, polysaccharides, and lipids to humic and fulvic acids [1]. In terrestrial and aquatic ecosystems, DOM does not only influence the geochemical and photochemical reactions by participating in carbon (C) and nutrient (N, P, and S) cycles, but also control microbially mediated reactions by serving as potential substrate. It also plays a key role in transport and transformation of major contaminants and/or pollutants and their reactivity with the environment [2, 3]. Additionally, DOM exerts a strong control in the formation of disinfection byproducts (DBPs), for example, trihalomethanes (THMs) and haloacetic acids (HAAs), during the drinking water supply treatments with disinfectants [4]. The amount and quality of DOM in terrestrial and aquatic environments influence biological processes such as microbial degradation [5, 6]. It is also a key player in altering the depth of the photic zone in aquatic ecosystems by controlling the