Dissolved organic matter (DOM) is ubiquitous in a wide range in aquatic environments and plays important ecological roles by fueling the microbial loop, acting as a factor determining light penetration, as the substrate for photoproducts, as a pH buffer, and as a medium for the complexation of trace metals. In addition, DOM fluxes from terrestrial to marine environments have been reported to steadily increase due to climate change and anthropogenic influences. Thus, the chemical characteristics of DOM have extensive implications in aquatic environments. Therefore, detailed chemical characterization in terms of quality of DOM is necessary for a better understanding of DOM dynamics in aquatic environments, and differences in DOM quality among different biomes have not been well documented.

We carried out an extensive chemical characterization exercise of ultrafiltered DOM (UDOM, > 1000 Da) from different biomes along a climatic gradient. The samples were collected from headstream waters at LTER sites from the arctic to the tropics, including the Arctic (ARC), Bonanza Creek (BNZ), Niwot Ridge (NWT), Konza Prairie (KNZ), Coweeta (CWT), and Luquillo (LUQ) LTER sites. Samples were characterized using stable carbon isotopic analysis, excitation-emission matrix with parallel factor analysis (EEM-PARAFAC), size exclusion chromatography (SEC), black carbon analysis, X-ray photoelectron spectroscopy (XPS), solid state 13C nuclear magnetic resonance (13C NMR), and Fourier Transform Ion Cyclotron Resonance Mass Spectroscopy (FT-ICR-MS). In addition, to clarifying the soil organic matter characteristics as a possible factor controlling the DOM quality, humic substances extracted from surface soils were characterized using EEM-PARAFAC. The application of a multi-analytical approach allowed us to determine differences and similarities in the DOM composition regarding with their chemical structure. Preliminary results show that KNZ had the highest microbial contributions to the DOM pool of all the studied sites, while the DOM composition ARC and BNZ and to a lesser degree the KNZ sites were affected by biomass burning contributions as indicated by the higher content in black carbon and associated elevated aromaticity of the dissolved organic nitrogen.