The oxidation of dissolved organic matter (DOM) by microbial respiration and photo-mineralization contributes to the massive efflux of CO2 to the atmosphere from freshwaters with the potential to influence global climate change. Despite this important role for DOM, the chemistry of this complex mixture of thousands of molecules, and in particular, the nature of those molecules that are susceptible to oxidation is unknown. This proposal focuses on the microbial oxidation of DOM and scientists from three institutions will study stream networks from two different climatic regions with the objective of identifying what molecules within the DOM pool support high rates of CO2 evasion to the atmosphere from streams and rivers. The scientists suggest that to accomplish this objective, there is a need to obtain detailed molecular-level information with sufficient frequency to capture the temporal dynamics of the biologically reactive DOM in nature. This challenge represents a second objective, which is to connect sample high-through put capacity with detailed molecular information. Generating the data necessary to address their research questions and test their hypotheses requires that the scientists separate DOM from stream water into different bio-reactivity classes, quantitatively measure the amounts of DOM that are biologically oxidized, qualitatively characterize the molecular and optical properties of the DOM pools, and statistically relate the molecular and optical properties of DOM to each other. A proof of concept is provided that demonstrates the efficacy of the proposed collaboration and an ability to accomplish these steps with laboratory-scale biofilm reactors, Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS), UV-visible absorbance and fluorescence spectra, and advanced statistical analyses, including 2-D correlation analysis.