High-resolution electrospray ionization mass spectrometry for molecular level characterization of dissolved natural organic matter in the Lake Superior watershed.

Abstract

Recent studies have begun to explore the molecular-level link between terrestrial and aquatic dissolved organic matter (DOM) in rivers and estuaries and their receiving oceans or lakes. This is of interest because of DOM‟s roles in carbon, nitrogen and phosphorus cycles and its reactivity with trace metals and anthropogenic organic molecules. These recent studies, primarily in brackish or salt-water systems, have shown that allochthonous components of DOM contain more aromatic compounds, while autochthonous components contain more aliphatic compounds. Here we extend these techniques to a temperate oligotrophic large lake (Lake Superior). Samples from the lake and watershed, including swamp, creek, river, near-shore lake, and offshore lake sites are compared using Fourier transform ion cyclotron resonance mass spectroscopy. In addition, replicate analyses on the instrument allow us to study reproducibility of the instrument method. Results are analyzed using cluster analysis, non-metric multidimensional scaling, Van Krevelen diagrams, and carbon versus mass diagrams. We find interesting similarities and differences between sites based on hydrological proximity of sites, storm events, and terrestrial impact.